Economic Impacts of Desalination

## **Chapter 1**

## Perspective Chapter: Technical and Economic Analysis of Reverse Osmosis Desalination System

*Mehdi Sepahvand*

## **Abstract**

Economic thermodynamic analysis is a branch of engineering science that is derived from economic laws. The goal of economic thermodynamic analysis of systems is the lowest price. Price calculation in a system includes the following steps: Determining the actual price of products. Provide a reasonable way to price products. Providing information on which calculations are made. The overall investment cost of a project includes fixed investment costs, including the costs related to the purchase of land, the construction of the necessary facilities and equipment, and the purchase and installation of machinery, as well as the initial costs related to the investment, including a series of other side costs. It is possible that their relationships and the percentage of their allocated costs in the project are explained separately and finally the estimation equations of each part of the power plant cycle as well as the economic modeling of the RO system and the effective input parameters such as the input salt concentration, discharge Feeding and input water, ambient pressure, number and type of membrane, etc. are stated along with their relationships. Finally, a RO system design flowchart and how to solve its algorithm are explained in detail.

**Keywords:** desalination, reverse osmosis, economic, cost, power plant, MED system

## **1. Introduction**

The need for water all over the world has increased due to the growth of the population and also due to the growth of the industry, and the water resources are rapidly being depleted. Since 1990, more than 80 countries are facing the problem of water shortage, while more than 70% of the earth's surface is covered with water; But only one percent of these resources are suitable for use, and 97.5% of them are oceans. The only solution; The use of salt water desalination techniques can solve the problems of water shortage. The two main types of desalination techniques that are widely used are evaporation methods and membrane methods. Evaporation methods such as MSF and MED are common in regions such as the Middle East that have huge energy resources. In 2007, all over the world, 66% of sweetening was done with the MSF process, and only 22% was using reverse osmosis (RO) [1]. In 2011, this statistic changed to 60% for reverse osmosis and only 27% for MSF, which shows the

increasing importance of the reverse osmosis process [2]. Reverse osmosis is a separation process whose driving force is pressure, in which salt water is purified by pressure by passing through a semi-permeable membrane. This process depends on the resistance of the membrane and the concentration of water impurities. Reverse osmosis is a process that consumes a lot of energy. The costs of a reverse osmosis system, which includes investment and operating costs, are classified in the diagram "**Figure 1**". Due to the operation of reverse osmosis membranes at high pressure, the electric energy of feed pumps is an important part of the operating cost of these systems. However, the pressure drop in reverse osmosis systems is low and the concentrated water flow leaves the last membrane with a pressure equal to 80 to 90% of the supply pressure. If the concentrated water of the system is directed to the surface water, this excess pressure must be dissipated before discharge. The pressure that is lost in the flow of concentrated water through the control valve is wasted energy, because it does not do any useful work in the purification system. Due to the high level of pressure and flow rate of condensed water, the amount of wasted energy is significant.

## **2. Estimation of total capital investment (TCI)**

In order to estimate the total investment cost of a project, the costs related to the purchase of land, the construction of necessary facilities and equipment, and the purchase and installation of special machinery and equipment that are used to make the system work should be calculated. These costs are Fixed Capital investment (FCI); But the initial costs related to the investment of a project, in addition to these fixed costs, also include a series of other side costs, the sum of these costs and fixed costs is called total investment costs (TCI).

## **2.1 Cost estimate of purchased equipment (PEC)**

Estimating the cost of purchasing equipment is the first and most important step in estimating the costs of a project. It is clear that the accuracy of estimating these costs

#### **Figure 1.**

*Classification of seawater reverse osmosis costs for fresh water production (produced water flow rate 125 m3 /h, system recovery 40%, one pass and with a life of 10 years) [2].*

#### *Perspective Chapter: Technical and Economic Analysis of Reverse Osmosis Desalination… DOI: http://dx.doi.org/10.5772/intechopen.110002*

depends on the amount of information available to engineers. Of course, in addition to the amount of available information, the time and the budget given to the relevant engineers for price estimation will also affect the accuracy of cost estimation. The best way to estimate the cost of purchasing equipment is to refer to the sellers of these items and use their information in this regard. It should be noted that the costs related to the transportation and installation of the equipment should be added separately to the cost of purchasing the equipment. Another way to estimate the cost of purchasing equipment is to refer to previous purchases and use the information in them. In such a case, by referring to professional and experienced people whose job is to estimate the price, or by using the information that engineering companies often make available to users, the cost of purchasing equipment can be estimated. In addition to these methods, software packages designed for this purpose can also be used, although it should be noted that the costs estimated by these softwares may be higher than which are calculated through different charts, do not have more accuracy and advantage.

#### *2.1.1 Use of price estimation charts*

In cases where referring to equipment sellers is not very useful or the time and budget required for price estimation is insignificant, in such cases, by referring to various brochures that are mostly presented in the form of price estimation charts. Can be estimated the cost of purchasing equipment. Such charts are obtained experimentally and are provided to users by different manufacturers.

#### *2.1.2 The effect of the size of parts on the price of equipment*

In all price estimation charts, the purchase cost of equipment is shown in a logarithmic chart according to their size changes. The lines drawn in such diagrams have a slope of α. The value of α plays a very important role in estimating the cost of purchasing equipment; Therefore, you should be careful in choosing it. The relationship that relates the cost of purchasing equipment to α is [3];

$$\text{PEC}\_{\text{y}} = \text{PEC}\_{\text{w}} \left( \frac{\text{X}\_{\text{y}}}{\text{X}\_{\text{w}}} \right)^{a} \tag{1}$$

By using this relationship, the cost of purchasing equipment *(*PECy) for a desired capacity or size *(*Xy) can be calculated by having the cost of purchasing equipment (PECw) for a known capacity or size (Xw) achieved.

For processes that deal with heat, α is usually smaller than 1; This means that the percentage increase (or decrease) in the purchase cost of equipment is less than the percentage increase (or decrease) in their size or capacity. If there is no information about the desired design, α = 0.6 is used. This work is known as the sixteenth law.

#### *2.1.3 Cost indices*

All the prices that are examined in the economic analysis must be stated relative to the same year in which those prices were estimated; That is, if we want to use the data related to a specific year for the present, we must also consider the price index and the inflation rate. For this purpose, the following relationship can be used [3];

Current time in price equipment ¼ The price of the equipment in the desired year �ðPrice index for the presentÞ*=*ðPrice index for the desired yearÞ

(2)

#### **2.2 Purchased equipment installation**

The cost of installing the equipment actually includes the cost of transporting the goods from the factory, workers' wages, the cost of emptying the cargo at the place of installation of the equipment, the insurance of the workers and related goods, the foundation of the intended place for the installation of the equipment, and in general, it includes all the costs that have been purchased for the installation of the equipment. They find communication [3].

#### *2.2.1 Piping cost*

The cost related to piping includes the cost of the pipe used and also the wages of the workers during the period when the piping of the system is completed [3].

#### *2.2.2 The cost of instrumentation and control*

The multiplier value that is considered for these costs depends on the degree of automation of the devices. The more advanced the regulating and controlling devices are, the higher the cost of using them will certainly be. Of course, in cases where the use of advanced computers and complex control systems is more common, this coefficient will have a higher value [3].

#### *2.2.3 The cost of electrical equipment and materials*

These costs include the cost of parts used in power distribution lines, current replacement levers, control centers, emergency power stations, etc. [3].

#### *2.2.4 The cost of purchasing or renting land*

The cost of purchasing or renting land is significantly dependent on the geographical location of the place in question, and unlike other costs that have been studied before, this cost is likely to increase over time. But it never decreases [3].

#### *2.2.5 The cost of civil, structural and architectural work*

This category of costs includes the general costs of construction as well as other services such as the construction of streets, sidewalks and fences in the desired location and the development of green spaces. As seen in **Table 1**, the costs related to this part are variable depending on whether the construction is related to the construction of a new system inside the site, or a new unit inside the site, or the development of a site.

#### **2.3 Costs related to auxiliary equipment**

The costs related to auxiliary equipment include all the costs that must be spent so that the main equipment can perform optimally. These costs are often spent on fuel,

*Perspective Chapter: Technical and Economic Analysis of Reverse Osmosis Desalination… DOI: http://dx.doi.org/10.5772/intechopen.110002*

**Table 1.**

*Costs related to civil, construction and architectural affairs as a percentage of the cost of purchasing equipment [3].*

water, steam, electricity, cooling and sewage management. Eliminating garbage, controlling environmental pollution, providing firefighting equipment, first aid, and building dining halls are among the other uses of these expenses [3].

#### **2.4 Costs related to engineering and supervision and supervision**

This category of costs includes costs such as development and construction, preparation of appropriate maps and plans of the desired location, and other costs that are related to engineering matters; Such as the cost of purchasing engineering equipment, the cost of supervision and supervision, the implementation of construction plans, and the wages of consulting engineers [3].

For a better understanding of the issue, the costs and the ratio of each percentage to the cost of purchasing equipment are shown separately in **Tables 1** and **2**.

#### **2.5 The cost of constructing a building including the contractor's wages**

These costs include the cost of all temporary equipment and facilities. Among the examples of these equipments, we can mention the living place of the workers, which is temporarily built inside the site, the insurance fee and the wages of the construction workers. It should be noted that these costs are in addition to the construction costs that were mentioned in the previous sections. It should be noted that in the costs related to this part, the contractor's profit and wages are also calculated. The experimental estimate of these costs is equivalent to 15% of direct cost (DC) [3].

#### **2.6 The cost of possible accidents**

Sometimes, unpredictable events such as weather changes, sudden stoppage of work, sudden changes in market prices and problems caused by the transportation of goods may have some effect on the estimated costs. For this purpose, a cost is usually included as a cost caused by possible incidents [3].

#### **2.7 Startup costs**

The Startup Costs (SUC) of system includes workers' wages, the cost of materials and equipment, and other additional costs that must be spent during the setting up of

#### **Table 2.**

*Costs related to a percentage of the cost of purchasing equipment [3].*

the system. Of course, to these costs, the costs resulting from the decrease in income due to the system being shut down or its operation under partial load should also be added [3].

*Perspective Chapter: Technical and Economic Analysis of Reverse Osmosis Desalination… DOI: http://dx.doi.org/10.5772/intechopen.110002*

#### **2.8 Working capital cost**

The Working capital (WC) cost of the system depends on the average period of time required to produce the product and reach the customer; The meaning of products reaching the customer is when money is received from the customer for the sale of the products [3].

For a better understanding of the issue, the costs and the ratio of each percentage to the fixed investment cost (FCI) and the total investment cost (TCI) are shown separately in **Table 3**.

#### **2.9 The cost of obtaining a licensing, research and development department**

If there is a desire to use franchise to obtain a work permit, in this case, the cost of obtaining a licensing, research and development (LRD) department are directly dependent on the process that is carried out inside the system. In fact, for any type of industrial activity and according to the extent of the activity, these costs have a specific range, so we should add these amounts to the total investment cost. Therefore, there is no standard or conventional amount for these costs.

### *2.9.1 The cost due to the lack of budget estimated during the construction*

The time it takes for a project from the initial design stage to be put into operation and its equipment is launched is between 1 and 5 years. During this period, some of the investment costs should be spent on providing the salaries of the system design engineers and civil engineers, as well as the purchase and installation of system equipment and things like this. In the same way, a large amount of initial capital is spent without obtaining any income. This money may be withdrawn from the company's fund, or taken as a loan from a bank or institution, or a combination of these two cases. In any case, some of the money intended for investment will be spent on things that will not bring any profit or income to the company. In fact, the costs of this section are applied due to the change in the value of money during the construction period; That is, the longer the project takes, the higher the costs of this part will be.

#### **Table 3.**

*Costs related to a percentage of the cost of fixed capital investment (FCI) and the Total investment cost (TCI) [3].*

## **3. Simplified relationships related to the initial investment of the project**

The purpose of stating the contents mentioned so far is to provide simple methods for estimating the initial investment cost of a new plan or expansion of old plans. After examining the various factors that are effective in estimating the cost of a reverse osmosis system and a multi-stage distillation system, in this part, by creating a mathematical relationship between these factors, we will arrive at simple relationships to estimate the cost of these systems.

As seen, total capital investment (TCI), Fixed Capital investment (FCI), Startup Costs (SUC), Working capital cost (WC), licensing, research and development department cost (LRD) and the estimated cost of underfunding during construction (AFUDC) also direct costs (DC) of the project are calculated, which includes onsite cost (ONSC) and offsite cost (OFSC) [4].

$$\text{TCI} = \text{FCI} + \text{SUC} + \text{WC} + \text{LRD} + \text{AFUDC} \tag{3}$$

$$\text{DC} = \text{ONSC} + \text{OFSC} \tag{4}$$

$$\text{OFSC} = \begin{cases} 1.2 \text{ ONSC} & \text{new system} \\ 0.45 \text{ ONSC} & \text{expansion} \end{cases} \tag{5}$$

$$\text{WC} = \mathbf{0.15TCI} \tag{6}$$

$$\text{SUC} = \mathbf{0.1FCI} \tag{7}$$

If it is assumed:

$$\text{LRD} = \text{AFUDC} + \text{0.15FCI} \tag{8}$$

In this case, by combining relations (3),(8) and (6), (7) the following relation is obtained:

$$\text{TCI} = \mathbf{1.47} \text{FCI} \tag{9}$$

It follows from relations (4), (5), (9):

$$\text{TCI} = \mathbf{1.84DC} = \mathbf{1.84(ONSC + OFSC)} \tag{10}$$

By combining relations (6) and (10), the following relation is obtained:

$$\text{TCI} = \begin{cases} 4.05 \text{ ONSC} & \text{new system} \\ 2.67 \text{ ONSC} & \text{expansion} \end{cases} \tag{11}$$

Experience has shown that the cost of fixed investment in a new system is between 2.8 and 5.5 times the cost of purchasing equipment [4]. Therefore:

$$\text{FCI} = \begin{cases} \text{2.8} \sim \text{5.5PEC} & \text{new system} \\ \text{2.83 PEC} & \text{expansion} \end{cases} \tag{12}$$

By combining the above relations and relations (12), the following general relation is obtained:

$$\text{TCI} = \begin{cases} 4.12 \sim 8.09 \text{ PEC} & \text{new system} \\ 4.16 \text{PEC} & \text{expansion} \end{cases} \tag{13}$$

*Perspective Chapter: Technical and Economic Analysis of Reverse Osmosis Desalination… DOI: http://dx.doi.org/10.5772/intechopen.110002*

As it is clear from relations (12) and (13), by having equipment purchase cost (PEC) and internal site costs (ONSC), the total investment cost (TCI) can be estimated. Therefore, you should be as accurate as possible in estimating the cost of purchasing equipment and the internal costs of the site; Because the more accurately the costs are estimated, the more accurate the overall investment cost will be.

Several methods to express the cost of purchasing equipment in terms of design parameters are stated in the equation, but here by using the cost functions for multistage distillation and reverse osmosis and other components extracted from references [3–5] respectively has been used.

Zk is the purchase cost for the k-th component, N is the number of operating hours per year, φ is the maintenance factor, if there is no comprehensive information, the value of 1.06 can be used, and the investment return factor (CRF) which depends on the rn percentage of inflation and the estimated life It is the equipment that is determined from the following relationship:

$$\mathbf{Z\_{K}} = \frac{\mathbf{TCI} \times \mathbf{CRF} \times \boldsymbol{\varrho}}{\mathbf{N} \times \mathbf{3600}} \tag{14}$$

$$\text{CRF} = \frac{r\_n (\mathbf{1} + r\_n)^{\text{year}}}{(\mathbf{1} + r\_n)^{\text{year}} - \mathbf{1}} \tag{15}$$

where year is the useful life of the power plant. With the purchase cost of equipment (Zk) and the internal costs of the site, the total investment cost can be estimated. The operating cost of multi-stage distillation and reverse osmosis system will be explained in the form of the relationships presented below.

## **4. Economic modeling of RO and MED system**

With the equipment purchase cost (CC) and internal site costs (ONSC), the total investment cost (TCI) can be estimated. Equations for estimating the price of each component of the reverse osmosis and MED system are shown in **Tables 3** and **4**, respectively, and the cost of other available equipment such as steam turbine and condenser are described below. It is worth mentioning that the fixed parameters of the economic analysis are shown in **Tables 5** and **6**.

#### **Table 4.**

*To estimate the cost of purchasing equipment, the functions related to the price estimation of the mentioned system can be extracted from Table 5.*

#### **Table 5.**

*Price of RO cycle components [6, 7].*

#### **Table 6.** *MED price [5].*

which in these relations AE&C is the total area of condenser and effects.

According to the model stated in the previous part, the maintenance cost can also be determined by calculating the cost of each component.

The operating cost of the reverse osmosis system is calculated as follows:

$$\text{OCm} = \text{0.2} \times \text{CCm} \tag{16}$$

$$\text{OCinsu} = \text{0.005} \times \text{TCI} \tag{17}$$

$$\text{OClaor} = \text{Qp} \times 24 \times \text{365} \times \text{fc} \times 0.01 \tag{18}$$

$$\text{OCO\&M,RO} = \text{OCinsurance} + \text{OClaro} + \text{OCmain} + \text{OCch} \tag{21}$$

$$\text{AOCRO} = \text{OCm} + \text{OCO\&M,RO} \tag{22}$$

*Perspective Chapter: Technical and Economic Analysis of Reverse Osmosis Desalination… DOI: http://dx.doi.org/10.5772/intechopen.110002*

which in these equations OCm is the replacement cost. OCO& M is the total cost of operation, which includes OClaor, OCmain, OCch, OCinsurance, which are the annual cost of the laboratory, the annual cost of repairs, the annual cost of chemicals and the insurance cost, respectively.

The operating cost of the MED system is calculated as follows [4];

$$\mathbf{C\_{el}} = \mathbf{c\_{el}} \times \mathbf{P} \times \mathbf{f\_c} \times \mathbf{Q\_p} \times \mathbf{365} \tag{23}$$

$$\mathbf{C\_1 = 0.1 \times f\_c \times Q\_p \times \mathbf{365}} \tag{24}$$

$$\mathbf{C\_{ch}} = \mathbf{0.04} \times \mathbf{f\_c} \times \mathbf{Q\_p} \times \mathbf{365} \tag{25}$$

$$\mathbf{C\_{in}} = \mathbf{0.005} \times \mathbf{C\_{A}} \tag{26}$$

$$\text{AOC}\_{\text{MED}} = \text{C}\_{\text{th}} + \text{C}\_{\text{el}} + \text{C}\_{\text{l}} + \text{C}\_{\text{ch}} + \text{C}\_{\text{in}} \tag{27}$$

which Cel is the cost of electricity, Cl is laboratory costs, Cch is chemical costs, Cin is insurance costs, and finally AOCMED is the annual operating cost. In relations (23) to (25), Qp is equal to the flow rate of permeate water and P represents the power of the pumps. The operating cost of other components have also been calculated according to reference [3, 4]. Finally, the annual total of exploitation is calculated as follows:

$$\text{AOC}\_{\text{Total}} = \text{AOC}\_{\text{Other}} + \text{AOC}\_{\text{RO}\&\text{MED}} \tag{28}$$

The normalized total cost is also determined from the eq. (29):

$$\text{TAC} = (\text{TCI}/\text{CRF}) + \text{AOC}\_{\text{Total}} \tag{29}$$

Finally, the unit cost of fresh water production is calculated as follows.

$$\text{UPC} = \frac{\text{TAC}}{\text{Qp} \times 24 \times 365} \tag{30}$$

where in:

UPC: production cost of one m3 of produced water (\$/m3 ).

TCC: Investment Cost (\$).

AOC: annual operating cost (\$/year).

OC: Operating Cost (\$).

ΔPhpp: High pressure pump pressure drop (MPa).

ΔPTb: Turbine pressure drop (Francis, Pelton) (MPa).

Ew energy consumption (KW).

Also, regarding the costs of other components of the cycle, we can refer to the suggested formulas of the reference which is stated below.

#### **4.1 Gas turbine cycle cost**

The gas turbine is made up of various components, the relationships related to the cost estimation of compressor (AC), combustion chamber (CC) and gas turbine (GT) can be expressed in the **Table 7**.

**Table 7.** *Gas turbine cycle costs.*

#### **4.2 Steam turbine cycle cost**

The Steam turbine is made up of various components, the relationships related to the cost estimation of Steam turbine (ST), Pump (P) and Condenser (CON) can be expressed in the **Table 8**.

## **5. Input parameters for RO system modeling**

In a practical process, several stages are used for the RO system, each stage includes several parallel Pressure Vessel (PV) that work with the same conditions. Each PV consists of several membrane elements connected in series. The feed water enters the first element and after purification, the condensed water (water coming out of the membrane) enters the second element and continues in the same way until the last element. The output of the products of all the elements are connected to each other and finally the water output of the final product is collected. The number of elements of the numerical series is between 2 and 8.

RO system modeling is done according to the entries in **Table 9**. The assumptions used in this modeling are expressed as follows:

#### **5.1 Relevant equations for modeling an RO system.**

At first, we should determine the average current intensity of the membrane (f) according to the type of water entering the membrane, then the total number of

*Perspective Chapter: Technical and Economic Analysis of Reverse Osmosis Desalination… DOI: http://dx.doi.org/10.5772/intechopen.110002*

**Table 8.** *Steam turbine cycle costs.*

required elements of the NE system is calculated by eq. (31) and the number of PVs is calculated from eq. (32) is determined. Using the tables in the DOW catalogs and the number of elements, we can determine the number of steps needed to achieve the desired recovery. By determining the number of stages using the stage ratio eq. (33), the number of pressure pipes in each stage is obtained eq. (34, 35) [4].

$$\mathbf{N}\_{\rm E} = \frac{\left(\mathbf{Q}\_{\rm p}\right)}{\mathbf{f} \times \mathbf{S}\_{\rm m}} \tag{31}$$

In this equation, Qp is the permeate flow rate (m3 /h) and Sm is the membrane area (m2 ).

$$\mathbf{N}\_{\rm V} = \frac{\mathbf{N}\_{\rm E}}{\mathbf{N}\_{\rm E \, pv}} \tag{32}$$

#### **Table 9.**

*Input parameters for RO system design.*

Nv is the total number of pressure pipes and NEpv is the number of series elements in each pressure pipe.

$$\text{RR} = \left[\frac{\mathbf{1}}{\mathbf{1} - R}\right]^{\frac{1}{n}} \tag{33}$$

RR is the step ratio, R is the system recovery and n is the number of steps.

$$\mathbf{N}\_{\mathbf{V}(1)} = \frac{\mathbf{N}\_{\mathbf{v}}}{\mathbf{1} + RR^{-1}} \tag{34}$$

$$\mathbf{N}\_{\mathbf{V}(2)} = \frac{\mathbf{N}\_{\mathbf{V}}(\mathbf{1})}{\mathbf{1} + RR} \tag{35}$$

Nv(i) is the number of pressure tubes in the i-th stage.

According to the mass transfer relations, it can be seen that the flow rate of water and salt through the membrane will be in the form of eqs. (36) and (37) and also the average velocity in each element of the membrane in relation (38) will be determined [6–8]. The amount of salt concentration in produced water is determined from the eq. (39) [6]. Also, according to the concentration polarization phenomenon of the mass transfer process, the salt concentration near the wall is calculated based on the film theory in the form of eq. (40) [6]. According to the continuity equation, eqs. (41) and (42) can be used for water, and eq. (43) can be used for salt.

$$\mathbf{J}\_{\mathbf{w}} = \mathbf{A} \times \text{TCF} \left[ \left( P\_f - P\_p - \frac{\Delta P\_f}{2} \right) - \left( \pi\_w - \pi\_p \right) \right] \times \mathbf{10}^6 \tag{36}$$

*Perspective Chapter: Technical and Economic Analysis of Reverse Osmosis Desalination… DOI: http://dx.doi.org/10.5772/intechopen.110002*

$$\mathbf{J}\_s = \mathbf{B} \left( \mathbf{C}\_\mathbf{w} - \mathbf{C}\_\mathbf{p} \right) \tag{37}$$

$$\mathbf{V\_w} = \frac{\mathbf{Jw} + \mathbf{Js}}{\rho\_p} \tag{38}$$

$$\mathbf{C\_{p}} = \frac{\text{Js}}{\text{Vw}} \times \mathbf{1000} \tag{39}$$

$$\mathbf{C\_w} = \mathbf{C\_p} \times \left[ \left( P\_f - P\_p - \frac{\Delta P\_f}{2} \right) - \left( \pi\_w - \pi\_p \right) \right] \times 10^6 \tag{40}$$

$$\mathbf{Q\_p} = \mathbf{V\_w S\_m} \tag{41}$$

$$\mathbf{Q\_B} = \mathbf{Q\_F} - \mathbf{Q\_P} \tag{42}$$

$$\mathbf{C}\_{B} = \frac{\mathbf{Q}\_{\rm F}\mathbf{C}\_{\rm F} - \mathbf{Q}\_{\rm P}\mathbf{C}\_{\rm P}}{\mathbf{Q}\_{\rm B}} \tag{43}$$

In the above equations, A and B and Sm is the permeability coefficient of water and salt in the membrane and its area, respectively. Permeation coefficients for different membranes are fixed and considered based on the Dow catalog. The relationships that can be used to reduce the number of adjectives are as follows [7–9];

$$\mathbf{k} = \mathbf{0}.04 \times \text{Re}^{0.75} \times \mathbf{S} \mathbf{c}^{0.33} \times \frac{\mathbf{D}\_{\mathbf{s}}}{\mathbf{d}} \tag{44}$$

$$
\Delta \mathbf{P}\_{\mathbf{f}} = \frac{\mathbf{0}.0033 \mathbf{Q}\_{\mathbf{a}} \mathbf{L}\_{\text{PV}} \mu}{\mathbf{W} \mathbf{d}^3} \tag{45}
$$

$$\mathbf{Q\_a} = \frac{\mathbf{Q\_b} + \mathbf{Q\_f}}{2} \tag{46}$$

$$\pi = \frac{\textbf{0.2641} \times \textbf{C} (\textbf{T} + 273)}{\textbf{1.0} \times 10^6 - \textbf{C}} \tag{47}$$

and in these relationships Re is Reynolds Number, Ds is the salt permeability (m2 /S), d is the distance of the feeds from each other, and Qa is the average flow rate, which is calculated from the eq. (45). LPV=m. Lm where Lm is the length of the

**Table 10.** *Adjectives in RO system modeling equations.*

#### *Desalination – Ecological Consequences*

*Perspective Chapter: Technical and Economic Analysis of Reverse Osmosis Desalination… DOI: http://dx.doi.org/10.5772/intechopen.110002*

membrane Δ*Pf* ≤ 0*:*35 *MPa*. π is Osmotic pressure and C in this relationship is salt concentration.

In order to estimate the average pressure drop, the Hagen-Poisey equation is used. Sherrod's number is calculated according to the eq. (44) and (45); by which concentration polarization can be calculated.

For a spiral membrane element, each of the feed and product water flows can be considered as a flow between two parallel planes with length L, width W and distance d; and based on that, he calculated the pressure drop on the supply side. For the spiral element, the width of the membrane W can be calculated with the following relationship based on the area of the membrane and the number of sheets (Nl) Sm ¼ W � l � Nl [6]. According to the above equations from (36) to (43), the number of adjectives for each equation can be determined in the following **Table 10**. In some equations, the adjectives are repeated, we have tried to mention the adjectives that are expressed for the first time in the table in order to determine the number of variables completely.

As can be seen, there are 8 equations with 9 variables, which can solve 8 equations and 8 nonlinear adjectives by assuming the input pressure and correcting it.

#### **5.2 RO system design flowchart**

In some references, to solve these equations, the rate of salt rejection (for example, in Ref. [6]) or in some other references, the recovery of any RO system is assumed (reference [10]) and the equations are solved based on that. Nader et al. [8] presented another solution that solves equations with the same number of adjectives, which is based on the trial and error method. Here, due to the fact that an accurate and comprehensive modeling is used, the minimum assumptions of the method presented by Nader et al. [8], have been used, whose values can be seen in **Table 8**. But in the following, according to the determination of the inlet water pressure and the requirement to solve the equations by repetition method, the duration increases, and as a result, the equations are solved according to the solution of nonlinear equations by Newton's method. Finally, according to the repetition method, the amount of feed water inlet pressure has been determined by trial and error; According to the explanations given, the problem solving flowchart is presented in "**Figure 2**".

In the solution process, to increase the accuracy, each element is divided into smaller components, and the output from one component will be the input to another

#### **Figure 3.**

*Schematic of each element for RO system modeling [4].*

component. "**Figure 3**" shows the method of dividing an element into smaller components to increase accuracy, which is chosen based on the method proposed by Nader et al. [8].

## **6. Conclusions**

In this chapter, the technical and economic analysis of the reverse osmosis desalination system was discussed. Relationships and parameters that are important in discussing the cost of produced water in reverse osmosis desalination systems as well as different parts of the power plant were explained in detail. Also, relationships, parameters, and mathematical models used to simulate reverse osmosis water desalination were also explained.

## **Author details**

Mehdi Sepahvand Kashan University, Kashan, Iran

\*Address all correspondence to<EMAIL_ADDRESS>
© 2023 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Perspective Chapter: Technical and Economic Analysis of Reverse Osmosis Desalination… DOI: http://dx.doi.org/10.5772/intechopen.110002*

## **References**

[1] Haghparast HAM, Kabir K. Reducing the operating cost of reverse osmosis systems using hydro turbine energy recovery systems. In: The First International Conference of Power Plants; 15 April;. Iran; 2010

[2] Osmosis R. 2012. Available from: http://www.lenntech.com

[3] Bejan A, Tsatsaronis G, Moran M. Thermal Design and Optimization. Michigan: John Wiley and Sons; 1996

[4] Mokhtari H, Ahmadisedigh H, Ebrahimi I. Comparative 4E analysis for solar desalinated water production by utilizing organic fluid and water. Desalination. 2016;**377**:108-122. DOI: 10.1016/j.desal.2015.09.014

[5] Esfahani IJ, Ataei A, Shetty V, Oh T, Park JH, Yoo C. Modeling and genetic algorithm-based multi-objective optimization of the MED-TVC desalination system. Desalination. 2012; **292**:87-104. DOI: 10.1016/j. desal.2012.02.012

[6] Lu Y, Liao A, Hu Y. The design of reverse osmosis systems with multiplefeed and multiple-product. Desalination. 2012;**307**:42-50. DOI: 10.1016/j. desal.2012.08.025

[7] Du Y, Xie L, Liu J, Wang Y, Xu Y, Wang S. Multi-objective optimization of reverse osmosis networks by lexicographic optimization and augmented epsilon constraint method. Desalination. 2014;**333**(1):66-81. DOI: 10.1016/j.desal.2013.10.028

[8] Al-Bastaki NM, Abbas A. Predicting the performance of RO membranes. Desalination. 2000; **132**(1–3):181-187. DOI: 10.1016/ S0011-9164(00)00147-8

[9] El-Halwagi MM. Synthesis of reverseosmosis networks for waste reduction. AIChE Journal. 1992;**38**(8):1185-1198. DOI: 10.1002/aic.690380806

[10] Maskan F, Wiley DE, Johnston LP, Clements DJ. Optimal design of reverse osmosis module networks. AIChE Journal. 2000;**46**(5):946-954. DOI: 10.1002/aic.690460509

## **Chapter 2** Household Water Treatment Practice

*Dejen Tsegaye*

## **Abstract**

Improvements in water quality and a decrease in the prevalence of diarrheal disease in poor nations have been linked to household water treatment and safe storage practices. The objective of this study was to assess knowledge and practice of household water treatment and associated factors in rural kebeles of Dega Damot Woreda, North West Ethiopia, 2021. In Dega Damot Woreda, North West Ethiopia, in 2020, a community-based cross-sectional study was carried out. To choose 845 households in the study area, a multistage sampling procedure was used. Pretested questionnaires were used to collect the data, which was then entered into Epi-data for cleaning and analysis before being exported to SPSS, and multivariable logistic regression analysis was used to identify factors. Only 14% of participants in this research were actively treating their home's water, whereas 71.8% knew about the technique. The following variables were significantly associated with household water treatment practice: educational status, income earning >600ETB per month, number of children under five in the household, and methods of fetching water. In Dega Damot Woreda, there was severe lack of household water treatment practices. The Woreda health office needs to raise community awareness and knowledge of domestic water treatment techniques.

**Keywords:** household water treatment, knowledge and practice, factors, Dega Damot, Ethiopia

## **1. Introduction**

A sufficient supply of clean water is one of the most fundamental human requirements and must be provided for as they are two of the most significant factors affecting public health [1]. Water that poses no major risk to health over the course of a lifetime is considered to be safe for drinking. The United Nations (UN) formally recognized the human right to access safe water without restriction in 2010. To sustain a population's excellent health, safe water is essential [2, 3]. It is common knowledge that having access to clean water and sanitary facilities helps to stop the spread of disease. Only having access to clean water does not greatly lessen diarrheal illnesses. Even if the source is clean, feces can contaminate water during collection, transportation, storage, and home drawing [4–6].

Prior to usage, drinking water is subjected to household water treatment (HWT), which enhances its microbiologic purity. Due to the possibility of recontamination during the process of transport, storage, and consumption, it is thought to be superior to treatment at other levels (such as the source). It has been demonstrated to be among the most efficient and economical methods of preventing waterborne illnesses. Therefore, vulnerable groups take charge of their water security by treating and storing household water safely [7–9].

HWT can enhance the quality of drinking water at the point of use and lower the risk of diarrhea in the millions of people who rely on improved and unimproved water sources. HWT includes boiling, chlorination, filtration, and solar disinfection. When populations at risk of waterborne disease adopt efficient HWT procedures appropriately and consistently, the risk of diarrheal disease can be reduced by as much as 61% [10–12].

The majority of the world's 1.8 billion users of fecally contaminated water sources are in low- and middle-income nations. The largest health concern associated with water consumption is microorganisms found in water that has been feces-contaminated [13].

Nowadays, simple, low-cost, and acceptable household water treatment technologies are available. However, in many communities, there is limited knowledge and poor practice for water treatment [14]. Limited knowledge, misinformation, and lack of experience in best practices of alternative water treatment technologies are among the leading challenges [15]. People are not always aware of the risk related to transportation practices, storage, and handling of drinking water.

Nearly 90% of Ethiopia's rural residents do not use alternate water treatment techniques, putting them at significant risk for disease unless quick action is taken, such as alternative HWT techniques with safe water storage [16]. Furthermore, there are few studies on HWT knowledge, behaviors, and related factors in Ethiopia. Therefore, the purpose of this study is to evaluate household water treatment knowledge and practice in rural kebeles in Dega Damot Woreda, North West Ethiopia. The town/urban areas of eastern Ethiopia were where the majority of studies were conducted. The purpose of the current study is to evaluate home water treatment knowledge and practice in the study area.

## **2. Methods**

#### **2.1 Study area and period**

The West Gojjam Zone's Dega Damot Woreda is where this study was carried out. The distance between Bahir Dar City, the seat of the Amhara Regional State, and Addis Ababa, the capital city of Ethiopia, is 275 kilometers. The district has a 41% highland climate, a 37% temperate climate, and a 22% lowland climate. In 2019, it will have an expected 184,369 residents (91,263 men and 93,106 women), who will be split among 42,877 houses. More than 99% of followers are orthodox. There are two urban and thirty-two rural Kebeles, seven health centers, one general hospital, two private clinics, and one private pharmacy [17]. There are 779 functional and 20 nonfunctional hand-dug wells, 68 functional and four nonfunctional protected springs, and two functional and one nonfunctional borehole. The rural population who use protected water sources is 138,740 (82.4%) [17]. The study was conducted from March 20/2021–April 20/2021.

**Study design:** Community-based cross-sectional study was employed. **Source population:** All households in rural kebeles of Dega Damot Woreda.

**Study populations:** All households in the selected rural kebeles of Dega Damot Woreda.

**Study subjects:** Mothers who live in selected rural kebeles of Dega Damot Woreda.

**Inclusion criteria:** Mothers in the household were included in the selected kebeles.

**Exclusive criteria:** Mothers in the household who resided for less than 6 months were excluded from the study.

**Dependent variables:** Knowledge and practice of HWT.

#### **Independent variables.**

**Sociodemographic characteristics:** Sex, age, educational status, family size, marital status, occupation, religion, household income, and ethnicity were dependent variables that are found under sociodemographic character.

**Knowledge about HWT:** Knowledge of HWT methods, knowledge of purpose HWT, knowledge of water born disease, knowledge of negative outcome of drinking dirty water, and knowledge of causes and prevention of diarrhea.

**Water source and handling status:** Source of drinking water, type of container to fetch water, distance to fetch water, type of container to store water, and way of fetching water from container.

#### **Operational definition.**

**Knowledge:** Respondents are able to identify methods of HWT, recognize the importance of treating drinking water, and identify diseases that can result from drinking unclean water. Variables in the questionnaire were given a total score ranging from 0 to n where n is the number of knowledge questions. Using frequency distribution, a score of <50% of the total knowledge questions was considered as poor knowledge, whereas a score of ≥50% of the total knowledge questionswas labeled as good knowledge [15].

**Household water treatment practice:** Households who used at least one alternative method of HWT within the last 24 hrs were considered as good practices, which will be scored as one, while poor practices were considered as households who were not using any alternative method of HWT and scored as 0 [15].

## **Sample size determination and procedure.**

Single population proportion formula was used to determine sample size with assumptions of 5% margin of error (d) 95% CI (Z = 1.96), design effect (d) of 2 and 10% nonresponse rate and taking prevalence of practice 44.8% from the study done in Burie, Northwest Ethiopia [18]. Thus, the final sample size was 845. A multistage sampling technique was used. Twenty percent of kebeles in Dega Damot Woreda were selected by simple random sampling method. The samples were distributed proportionally by the number of households for each selected kebeles. Study participants were selected by systematic random sampling from HHs in the selected kebeles. The sampling interval (k) was determined by study population (5218 HHS in the selected kebeles) divided by sample size (845) =6. Then, the data were collected at every six HH intervals. Lottery method was used to select the first study subject. Respondents were mothers of the households. In case, if there were more than one mother in the household, one of them was selected by lottery method.

## **2.2 Data collection tools and procedures**

Socio-demographic characteristics were collected through face-to-face interviews and observation with mothers. The questionnaire and observation checklist were

developed in English and were translated into local language (Amharic) and were translated back to English to keep the consistency prior to the actual data collection. Data were collected by ten students who completed grade 12 and were supervised by two public health officers.

## **2.3 Data quality control**

The questionnaire was pretested on 5% of the sample size to check understandability and reliability of the questionnaires. One-day training was given to data collectors and supervisors on the study instrument, data collection procedure, and the ethical principles of confidentiality. The collected data were reviewed and checked for completeness and relevance by the supervisors and principal investigator each day.

## **2.4 Data processing and analysis**

The questionnaire was manually reviewed for accuracy. It was afterward coded, inputted into Epi-Data version 4.2, and exported to SPSS version 25 for additional analysis. The population was explained using descriptive statistics in relation to the pertinent variables. Chi-square testing was conducted. The multivariable logistic regression was fitted to the variables with fewer than 0.25 p-values from the bivariate analysis using the binary logistic regression technique. In the multivariable logistic regression, odd ratios with 95% confidence intervals (CI) were generated, and statistical significance was assessed at p-values 0.05. Hosmer and Lemeshow tests were used to assess the fitness of the models. Text, tables, and graphs were utilized to present the data.

## **2.5 Ethical consideration**

Ethical clearance was obtained from the ethical committee of BDU College of Medicine and Health Sciences and a letter of cooperation was delivered to the Dega Damot Woreda administration bureau in order to get letter of permission for kebeles. Anyone who has no willingness to participate in the study was not forced to participate. Informed (verbal) consent was obtained from each study participant. The study participants were also provided with information about the objectives and expected outcomes of the study. Information obtained from individual participants was kept secure and confidential.

## **3. Results**

#### **3.1 Sociodemographic characteristics of participants**

This study included 845 mothers in all, with a 100% response rate. The respondents' mean (+SD) age was 40.46 (+12.16) years, and 64.9% of them were illiterate. Respondents had a mean (+SD) family size of 4.88 (+1.2). Nearly all of the interviewees were farmers and Christians, and most (87.2%) were married. More than half of the households made monthly incomes of over 600 ETB, (**Table 1**), (**Figure 1**).

## **3.2 Practice of respondents on HWT**

Only 14.1% of the 845 participants were using HWT. For storing drinking water, nearly half of the respondents (51.7%) had two containers; the remaining respondents had three (27.7%), one (15.4%), and four or more (5.2%), respectively. Nearly all (98.8%) of the responders possessed a container large enough to hold more than 25 liters. Total of 43.6% of respondents reported fetching drinking water three times daily, while the rest of respondents did so only twice, three times, or more, once, or only once. The majority (96.9) of the household's drinking water storage containers were plastic containers (rotto). Others utilized iron containers (0.4%) and clay pots (2.72%). Similarly, they used jerican (96.8%) and clay pots for the remaining portion of water retrieval. Nearly all families (98.7%) had clean household water containers, and of those, little under half (53.8) were cleaned once a week. The others were cleaned every day (11.5%) and within three days (34.7%) (**Table 2**), (**Figures 2** and **3**).

## **3.3 Knowledge of participants on HWT**

About 28.2% of households have adequate knowledge of HWT, which is close to one-third. Only 24.4% of the respondents acknowledged knowing at least one HWT method, with the remainder not having done so. And of those, 84.4% had mentioned boiling, while the rest were familiar with chlorine. Only 34.8% of homes answered "yes" to the question "is it advisable to treat water for promoting child health" since the majority (84%) of households had little knowledge of diseases that are transmitted by water (**Table 3**), (**Figures 4–6**).

#### **Table 1.**

*Sociodemographic characteristics of participants in Dega Damot Woreda, North West Ethiopia, 2021 (n = 845).*

#### **Figure 1.**

*Age of respondents in Dega Damot Woreda selective kebeles, North West Ethiopia, 2020 (n = 845).*

#### **Table 2.**

*Practice of respondents on HWT in Dega Damot Woreda selective kebeles, Amhara, Ethiopia, 2021 (N = 845).*

## *Household Water Treatment Practice DOI:http://dx.doi.org/10.5772/intechopen.110484*

#### **Figure 2.**

*Main source of drinking water for respondents in Dega Damot Woreda selective kebeles, North West Ethiopia, 2021 (n = 845).*

#### **Figure 3.**

*Materials used for washing household containers for respondents in Dega Damot Woreda selective kebeles, Amhara, Ethiopia, 2021 (n = 845).*

## **3.4 Bivariate and multivariate analysis of factors associated with practices on HWT**

Age, educational level, family size, income, the number of children under the age of five, the method used to obtain drinking water, the type of container used to store

#### **Table 3.**

*Knowledge level of the respondents on HWT in Dega Damot selective Woreda, Amhara, Ethiopia, 2021 (N = 845).*

drinking water, the location where drinking water handling utensils were handled, and knowledge of HWT all had an association with HWT practice. Using the backward likelihood ratio approach, all factors with associations to the outcome variables in bivariate logistic regression analyses (p-value 0.25) were added to the multivariate logistic regression analysis models. Then, in multivariate logistic regression analysis, parameters such as educational status, income, the number of children under the age of five, the methods used to obtain drinking water, and HWT knowledge were found to be substantially associated with the practice of HWT.

The odds of practicing the HWT are more than seven times higher in homes with literacy than in households without literacy [AOR: 7.27, 95% CI: (4.36–12.11)]. When compared to households earning less than 600 ETB per month, households earning more than 600 ETB per month are almost three times more likely to practice HWT [AOR: 2.71 95% CI: (1.45–5.05)]. When compared to households with two or more under-five children, those without under-five children had an 83% lower likelihood of practicing HWT (AOR: 0.17, 95% CI: (.07–.41)). Similar to this, households that used pouring to obtain drinking water from the container are 0.42 times less likely to engage in HWT than households that utilized dipping [AOR: 0.42 95% CI: (.26–.67)].

## *Household Water Treatment Practice DOI:http://dx.doi.org/10.5772/intechopen.110484*

#### **Figure 4.**

*Thoughts of respondents about causes of childhood diarrhea in Degad Dmot Woreda selective kebeles, Amhara, Ethiopia, 2021 (n = 845).*

#### **Figure 5.**

*Source of knowledge for respondents in Dega Damot Woreda selective kebeles, Amhara, Ethiopia, 2020 (n = 845).*

Additionally, compared to their counterparts, those who had solid knowledge of HWT were approximately three times more likely to practice it [AOR: 3.03, 95% CI (1.84–5.01)] (**Table 4**).

## **3.5 Bivariate and multivariate analysis of factors associated with knowledge of HWT**

Binary logistic regression was used to find the variables connected to HWT knowledge. Age of respondents, educational level, marital status, income, source of water to fetch, quantity of containers to fetch, methods to fetch drinking water, type of

#### **Figure 6.**

*Knowledge about any disease caused by drinking dirty water of respondents in Dega Damot Woreda, North West Ethiopia, 2021.*

#### **Table 4.**

*Bivariate and multivariate analysis of factors associated with practice on HWT among respondents in Dega Damot selective kebeles, Amhara, Ethiopia, 2021 (n = 845).*

### *Household Water Treatment Practice DOI:http://dx.doi.org/10.5772/intechopen.110484*

container to store drinking water, and location of handling utensils for drinking water all had associations with knowledge of HWT practice in bivariate logistic regression analysis. Using the backward likelihood ratio approach, all factors from the bivariate logistic regression analyses that have a relationship with the outcome variables were incorporated into the multivariate logistic regression analysis models. The factors that were significantly associated with knowledge of HWT in the multivariable logistic regression analysis were educational level, marital status, source of drinking water, number of containers for drinking water (those who had two and three or more), and locations to handle drinking water utensils.

The odds of having knowledge of the HWT are 1.78 times greater in households with literacy than in households without literacy [AOR: 1.784, 95% CI: (1.237–2.572)]. Being single increases the likelihood of knowing about HWT compared to households with widows [AOR: 4.68, 95% CI: (1.68–13.05). Similar to this, families with protected drinking water sources have nearly three times the likelihood of knowing about HWT than those with unprotected sources [AOR: 2.73, 95% CI: (1.88–3.96)]. In this regard, the odds of having knowledge of HWT are nearly two times higher in households with two water storage containers than in households with only one container

#### **Table 5.**

*Bivariate and multivariate analysis of factors associated with knowledge of HWT among respondents in Dega Damot selective kebeles, Amhara, Ethiopia, 2021 (n = 845).*

[AOR: 2.22, 95% CI: (1.29–3.84)] and nearly eight times higher in households with three or more water storage containers than in households with only one container [AOR: 7.59, 95% CI: (1.29–3.84)]. Additionally, the likelihood that a family handles drinking utensils on a shelf as opposed to handling them randomly on the floor is nearly twice as high [AOR: 1.86, 95% CI: (1.34–2.56) (**Table 5**).

## **4. Discussion**

Water is the most significant factor affecting public health, and having access to enough clean water is crucial for lowering disease transmission. Access to clean water does not dramatically reduce disease rates even if the source is safe since it can become faecally polluted during collection, transit, storage, and drawing in the home [4–6]. Above all, it is crucial to be knowledgeable about household water treatment and to put that information into practice by using highly advised techniques.

According to this study, HWT practice was found to be 14.1% (CI 11.8–16.3). This self-reported study's prevalence of HWT practice (14.1%) was much lower than studies carried out in India (53%), Zambia (50%), Nigeria (54%), and Kenya (69%) [9, 19–21], respectively. The disparity may result from different coverage of clean water as well as different household-level water treatment options across the nation depending on people's knowledge of the availability and quality of water. Additionally, Ethiopian communities, particularly in rural regions, do not use this water purification procedure [16].

This study's results were lower than those of a study done in North West Ethiopia (23.1%), as well. The discrepancy is likely the result of a different study environment where the community in the prior study received information from many sources and, as a result, had greater awareness of the problem than the study site in the present [15]. The current finding, however, was slightly higher than a study carried out in a rural area of Haryana, India (10%) [22]. The difference could be the result of a time difference between now and seven years ago when the prior was completed. Additionally, the sample size used in the earlier study was less than half of the sample size employed in this investigation.

When examining the extent of HWT knowledge, it was discovered to be 28.2% CI (25.3–31.5). This result was consistent with a research carried out in Nigeria (26.1%) [9]. However, this was considerably less than research conducted in India (69%) [19]. The original study was carried out in a nation that is more developed than the current study area, where it would have been possible to provide information regarding HWT that was more easily accessible. Additionally, this was less than the research conducted in North West Ethiopia (49.3%) [15]. This discrepancy may be the result of the communities' varying socioeconomic conditions, which may have an impact on how they use source water for drinking. However, it exceeds a research conducted in Patan (16.7%) [23]. This is most likely a result of the use of a tiny sample size, which is almost one-fourth of the sample size used in the current study.

There were variables in this study that showed a strong correlation with HWT practice. The first one was the level of education in each household. Reading and writing-capable households performed HWT better than their counterparts. Two studies conducted in Ethiopia's Bure Zuria and Dabat districts backed up the conclusion [15, 18]. This is because literate people are better able to learn about HWT practice and comprehend procedures than their illiterate counterparts.

#### *Household Water Treatment Practice DOI:http://dx.doi.org/10.5772/intechopen.110484*

The second factor that was substantially linked to practicing the HWT was having a household income of more than 600 ETB per month, which was 2.71 times higher than that of their counterpart. This was corroborated by a study carried out in North West Ethiopia, which explained that the more money a household makes, the more they can afford to purchase the supplies required for therapy [15].

Thirdly, HWT was less common in homes with less than five kids compared to those with just one. Since this study indicated that most households (52.4%) are aware that untreated water causes juvenile diarrheal disease, it is probably because mothers who live in households with children practice HWT more to protect their children from water-borne illness. The fourth substantially linked variable was the likelihood of HWT practiced by households; these households were less likely to obtain their drinking water by pouring from the container. This might be because participants believed that pouring was a secure way to handle water.

Good knowledge of HWT practice is the final and fifth factor that is significantly related to HWT practice. Research conducted in Patan and North West Ethiopia supported this [15, 23]. The more information families have about HWT, the more likely they are to use it.

Knowledge of HWT was another dependent variable in this study. The first factor that was strongly linked to this variable was educational attainment. Reading and writing-capable households were more likely to be aware of HWT. A study conducted in Patan, Biye Kaduna state, Nigeria, and Dabat North West Ethiopia provided evidence in favor of this [9, 15, 23, 24]. It goes without saying that being able to read and write is crucial if one wants to increase their knowledge through various methods.

The second variable that was significantly linked to HWT knowledge was marital status. Single-person households knew more about HWT than widowed households did. This is supported by a study done in Patan [23]. Due to the lack of children or elderly people to carry out the practice, singletons are likely to have a lighter workload. Additionally, singles had higher levels of education than divorced people (88% vs. 12%).

Thirdly, factors related to understanding of HWT included sources of water that were protected. Families with improved/protected drinking water sources have higher levels of knowledge than their counterparts. This was corroborated by a study conducted in Northwestern Ethiopia [15]. This suggests that households take more precautions to avoid using unprotected drinking water the more they are aware of HWT. The knowledge of all the negative effects of unprotected water on health also made people aware of the need to use protected water sources.

The fourth and final variable was the number of water storage containers, and it was substantially correlated with understanding of HWT. Homes with two water storage containers for drinking water were more likely to be aware of HWT than homes with just one container. Similar to this, homes with three water storage containers were more likely to be familiar with HWT than those with just one container, and even they were more familiar with it than households with only two containers. Households on the HWT may already be aware of this, and its benefit may have forced them to have more water storage tanks. The number of water bottles a household has actually indicated how well-versed they are in using them individually for various functions. The others may be used for different purposes, while one may be used for dipping water that is obtained from containers by fixing it within.

Last but not least, the location where drinking utensils were handled was a factor that significantly correlated with HWT knowledge. Families who handled their utensils on a shelf or anywhere other than the floor were more likely to be familiar

with HWT than those whose utensils were handled on the floor. This suggests that handling their utensils while on the shelf, on the floor, or in a safe place may protect homes from many water-borne diseases. And they are acting in this way because they are aware of proper utensil handling. This is the fact that all water drinking supplies should be stored safely and away from any unclean items, such as on a shelf or somewhere else other than the ground.

## **5. Conclusion and recommendations**

## **5.1 Conclusion**

According to this study, there is a lack of HWT practice and knowledge in the Dega Damot Woreda. Factors substantially linked with HWT practice included educational status, income earning >600ETB, the number of children in the home under the age of five, the means of fetching water, and understanding of HWT. In contrast, characteristics such as educational level, marital status, drinking water source, quantity of water storage containers, and location of utensil handling exhibited a significant association with understanding of HWT.

## **5.2 Recommendations**

The author offers the recommendations below in light of the findings of this study: **Woreda government office:** The Woreda office, working with the Woreda health office, shall provide protected water for drinking in order to raise knowledge of the regional state.

**Dega Damot Woreda water office:** It is better to inform the community about HWT procedures and show them by kebeles/sub kebeles when the Woreda water office collaborates with the Woreda health office. Additionally, they must demonstrate how to obtain and use the chemicals used in water treatment.

**Nongovernmental organizations:** Nongovernmental organizations that are involved in the water supply are better to perform wonderful activities to enhance community knowledge and their practice. It is also preferable to adopt the supporting resources required for HWT practice as soon as the community approached to do so.

*Household Water Treatment Practice DOI:http://dx.doi.org/10.5772/intechopen.110484*

## **Author details**

Dejen Tsegaye Department of Nursing, College of Health Nursing, Debre Markos University, Ethiopia

\*Address all correspondence to<EMAIL_ADDRESS>
© 2023 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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*Household Water Treatment Practice DOI:http://dx.doi.org/10.5772/intechopen.110484*

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[20] Ghislaine RP, Thomas C. Consistency of use and effectiveness of household water treatment practices among urban and rural populations claiming to treat their drinking water at home a case study in Zambia. Tropical Medicine and Hygiene. 2016;**94**(2):445-455

[21] Joseph OS, Wagura N, Jesper S. Risk perception, choice of drinking water, and water treatment evidence from Kenyan towns. Environment for Development. 2013;**2013**:1-24

[22] Mehta B, Malik M, Kumar V, Verma R, Chawla S, Sachdeva S. Knowledge attitude and practices regarding water handling and water quality assessment in a rural block of Haryana. Basic and Applied Medical Sciences. 2013;**2013**:2

[23] Nitinkumar SJ, Amaliyar. Study on knowledge, attitude and practice about purification of household water among 210 individuals of urban area of Patan District National Journal of. Community Medicine. 2019;**10**(7)

[24] Ibrahim J, Sufiyan M, Olorukooba A, Gobir A, Adam H, Amadu L. Knowledge, Attitudes, and Practices of Household Water Purification among Caregivers of Under-Five Children in Biye Community, Kaduna State. Wolters Kluwer - Medknow; 2017

## **Chapter 3**

## Reverse Osmosis in Industrial Wastewater Treatment Units

*Yehia A. Shebl*

## **Abstract**

The MENA region faces a severe water crisis, prompting governments to take action by improving irrigation methods, treating and reusing sewage and agricultural wastewater, and issuing restrictions regulating industrial wastewater discharge. As a result, many large factories have established industrial wastewater treatment plants to recycle water, reduce reliance on external sources, comply with environmental regulations, and implement MLD or ZLD principles. This chapter will focus on industrial wastewater treatment using reverse osmosis (RO) membranes. It will cover the treatment of various contaminants such as nitrogen, phosphorus, COD, BOD, TOC, and heavy metals. It will discuss different treatment methods and technologies to produce reusable water while achieving MLD and ZLD principles.

**Keywords:** RO, IWWTP, brine desalination, ZLD, MLD, effluent environmental impacts

## **1. Introduction**

*How is water recycled in your space?* Water reuse and recycling have become inevitable, especially in areas where water is scarce. Water scarcity is a global problem as most of the water on the surface of the planet is salty water, whether it is of high salinity, as in the seas, oceans, and salty lakes, or water of medium salinity, as in most of the wells waters, and that water represents about 97% of the total water present. While fresh water is mostly confined to snow in the north and south poles, which represents about 2% of the amount of water present, and the remaining 1% is divided between 0.6% fresh water in wells, and 0.3% represents moisture water in the atmosphere, and the remaining only about 0.1% of all available water resources is fresh surface water in rivers and freshwater lakes. Besides that, the easy-to-use surface freshwater is limited to about 0.1% of all water resources, and that represents a natural physical water scarcity; however, most of that water is exposed to different kinds of anthropogenic pollution, making it needs further treatment before using and leading to continued pressure on that limited water resources.

The massive industrial development in the last century and the spread of huge industrial complexes and their need for large quantities of water of different quality led to another kind of pressure on the limited water resources, in addition to the negative impact of the industrial wastewater of those industrial complexes in case it was discharged without treatment or with partial treatment to different water bodies, whether fresh or not fresh or seawater, so the safe disposal of these liquid wastes or recycling water and reusing it in various industrial processes has also become an indivisible necessity.

"*Save it before it is too late*", this slogan must have its meaning present in the minds of all those responsible for the industrial units and facilities that already exist or are under construction because one of the biggest reasons for the lack of proper and safe disposal of the industrial wastewater is the lack of interest or full knowledge of those responsible for the industry about the extent of the danger of these wastes on the environment and in the core of its water sources and its exposure to pollution. Furthermore, let us look from a narrow perspective and it will negatively affect the quality of the feed water for those factories themselves, which may lead to an increase in the cost of water treatment required for industry or affect the efficiency of the industrial process itself in an endless cycle of increasing pollution and additional treatments.

One of the best-applied methods to saving water is reusing or recycling it, where the most appropriate is to apply this at the industrial level, as the water required for industry varies in quality from one industry to another, as well as for various uses within the same industry, as (cooling water – manufacturing products – steam production – a carrier of raw materials or waste – or a solvent), and also as water reused at the industrial level that will not be affected by psychological and societal acceptance, as in the reuse of water for drinking purposes.

There are many water treatment technologies used in the treatment of industrial wastewater; probably the most prominent of them are; physical treatment like (screening, mixing, sedimentation, flotation, filtration, and gas transfer) and chemical treatment in which the removal or conversion of contaminants is carried by the addition of chemicals or by other chemical reactions like (precipitation, oxidation/ reduction, neutralization, adsorption, and disinfection), also biological treatment in which the removal of contaminants is carried by biological activity to remove the biodegradable organic substances whether colloidal or dissolved and nutrients like nitrogen and phosphorus from the industrial wastewater using one or all of aerobic, anaerobic, and anoxic biological treatment methods.

Industrial wastewater treatment is a general concept, and reuse is a particular case where after applying the recommended treatment method to remove different contaminates, the question remains, is this water suitable for the type of application that will be reused through it? Possibly one of the substantial and essential treatment methods is the removal of salts through reverse osmosis (RO) membrane technology.

Despite the wide use of reverse osmosis (RO) membrane technology in the treatment of industrial wastewater for reuse, this requires several critical challenges, one of which is; due to the higher sensitivity of these membranes; they require complex primary treatment, which is considered not only every industry has its industrial wastewater case or every factory, but every stream inside the factory is evaluated as a certain case study and needs unique treatment methods that achieve the bestneeded quality with the lowest costs. While the other is how to safely dispose of the resulting concentrated solution, whether by achieving the principle of minimum liquid discharge (MLD) using evaporation lakes, deep injection wells, or drainage on seawater after fulfilling the necessary environmental conditions, or thermal evaporation and crystallization achieving the principle of zero liquid discharge (ZLD), while the resulting desalinated water may not be suitable for use directly in some cases,

*Reverse Osmosis in Industrial Wastewater Treatment Units DOI: http://dx.doi.org/10.5772/intechopen.110680*

and it needs certain additions or additional treatments before using it, depending on the type of application. On the other hand, the selection of the RO unit's proper design recovery, membrane types, flux, and configuration is another one of the most important points for sustainable RO technology application in industrial wastewater treatment and reuse.

In this chapter, we will address some important points that must be taken into consideration when designing and implementing the various stages of the treatment and reuse of industrial wastewater.

## **2. Pretreatment of industrial wastewater**

The primary treatment of industrial wastewater is the cornerstone and depends on to what extent its efficiency could achieve the maximum benefit from that wastewater, whether by direct reuse, partially desalting using RO technology, or reaching demineralized water.

The first step is an accurate knowledge of the nature and sources of industrial wastewater based on a good knowledge of the industry processes, places of drainage, and the nature of its being continuous or patched (intermittent) streams of industrial wastewater, so you need to know the amount and frequency of each stream as well as their specifications, the next table help to know the nature of each stream flow (**Table 1**).

Also, it is essential to know the sources of raw feed water for the industry in which industrial waste treatment is to be done, as it gives an initial idea of the nature of wastewater composition, or at least the general tendency. For example, if the wastewater results from raw water from wells, it is necessary to analyze wastewater for elements such as silica, iron, manganese, calcium, magnesium, barium, and strontium. But if the raw water is surface fresh water, the the big focus will be on its organic load, silica, and so on. Also, kind of water treatment techniques used in the utility section of the industry where it is possible to maximize its recovery or rearrange it to make it more suitable and reduce the waste resulting from it, or parts of it can be used to treat wastewater or mix portion of the pretreated industrial wastewater with feed water for some of its units.

In the following, we will review some of the significant parameters of industrial wastewater, which must be closely monitored, and some of their effects on the treatment stages will be shown.

#### **Table 1.**

*Demonstrates a detailed approach to documenting different sources and quantities of industrial wastewater streams.*

### **2.1 Temperature**

The continuous follow-up of the change in the temperature of the industrial wastewater is a heightened concern because the shift in it may be unlike surface water or the well water is not always linked to the change in the ambient temperature during the different seasons, as there may be sources of industrial wastewater associated with a big rise in temperatures such as steam condensate drain which could be ranged from 50° C to 90° C, or some exothermic reactions which make the industrial waste stream temperature reaches 80° C. So identifying the temperature ranges of each industrial wastewater stream are very important because, based on the type of subsequent treatment of that water, the extent to which it needs to be cooled or not will be determined, and whether this stream (which may be small in quantity) can be separated and cooled separately before mixing it with the rest of the waste streams, to prevent the high temperature of the mixed (equalized) industrial wastewater above the recommended temperature for the subsequent treatment technologies like for ultrafiltration (UF) organic membrane (maximum temperature is 40° C) or RO membranes (maximum temperature is 45° C). Or there is a type of treatment that will be applied to this stream individually. Or on the contrary, blending it with the rest of the industrial wastewater sources may maintain an average temperature in different seasons, leading to improving some types of treatments that are greatly affected by the extreme drop in temperatures, such as biological treatment, coagulation processes, and also reverse osmosis, which requires certain precautions during the design phase to maintain the desired efficiency of these units.

#### **2.2 Organic content**

There are several ways to express the organic load of industrial wastewater, including the chemical oxygen diamond (COD), the biological oxygen diamond (BOD), and also the total organic carbon (TOC).

## *2.2.1 COD measurement*

COD represents the quantity of dissolved oxygen in the water that must be present to oxidize organic materials. As a pollution measuring tool, COD is used to measure the short-term influence that wastewater effluents will have on the receiving water bodies' oxygen levels. So, COD is an essential measurement that helps detect the organic pollutant amount and follows the efficiency of different treatment techniques to ultimately limit pollution in water.

COD measuring may be essential when treated wastewater is discharged into the environment. High levels of industrial wastewater COD indicate concentrations of organics that could deplete dissolved oxygen in the water, leading to adverse environmental and regulatory significances. But when using the pretreated wastewater as feed water for RO system, TOC measuring is the best way to get the total organic loads that may be above the RO membranes manufacturers recommendations.

COD measurement has many interferences which may be present on the industrial wastewater and cannot be dependent on measurement for assets the organic loads before the RO system as interference from chloride, florid, and bromide, chromium, nitrite, sulfite ions where mercuric sulfate that eliminates chloride interference up to 2000 mg/L and samples with higher chloride concentrations are typically diluted or may be removed by precipitation with silver ion and filtration before digestion. Some aromatic compounds like Pyridine and related compounds resist oxidation, and

#### *Reverse Osmosis in Industrial Wastewater Treatment Units DOI: http://dx.doi.org/10.5772/intechopen.110680*

volatile organic compounds will react in proportion to their contact with the oxidant; in contrast, straight-chain aliphatic compounds are oxidized more effectively in the presence of a silver sulfate catalyst. Also, some organic compounds are not oxidized completely with the COD method like urea compounds not properly appearing in the COD measurement, so using of COD only to measure the effectiveness of the pretreated wastewater is not accurate, and TOC measuring is a more accurate, faster, and more sharp method for the organic content [1].

The total organic carbon (TOC) measurement is essential to assessing the pretreatment process capabilities before the RO membrane system in industrial wastewater treatment units. TOC is a measure of the total amount of organic compounds present in water and is used as an indicator of the quality and suitability of water and can provide valuable information about the efficiency of the pretreatment process and the potential for fouling of membranes in the RO system.

TOC limits before the RO membrane system will depend on the specific design consideration of the RO system, like; RO system recovery and choosing the type of RO membrane in terms of its fouling resistance capabilities. In general, it is recommended to keep the TOC levels as low as possible to minimize the risk of fouling the RO membranes. For industrial water treatment applications, the American Membrane Technology Association (AMTA) recommends a maximum TOC concentration of 5 mg/L [2].

The presence of nutrients in the pretreated wastewater can potentially impact the permissible limits of TOC before the RO membrane system. Nutrients, such as nitrogen and phosphorus, can stimulate the growth of microorganisms, even if it is less than 5 mg/l, so it is preferred to decrease TOC concentration to less than 2 ppm in case of the presence of residual nutrition in the pretreated wastewater, or it may be required to dose nonoxidizing biocide like 2,2-dibromo-3-nitrilopropionamide (DBNPA) whether continuous or intermittent shock doses to prevent or reduce RO membrane biofouling rates.

Both TOC and COD are commonly used to measure the concentration of organic matter in water. TOC measures the total amount of organic compounds present in water, while COD measures the oxygen-depleting capacity of organic compounds in water.

In general, TOC is considered a more comprehensive measure of organic matter in water because it includes a wider range of organic compounds, including both bio/ chemical degradable and nondegradable compounds. COD, on the other hand, only measures the oxygen-depleting capacity of biodegradable organic compounds.

TOC is generally considered to be more accurate than COD because it includes a wider range of organic compounds. Therefore, in terms of interferences, TOC is less subject to interference from various sources.

For this reason, TOC has generally been considered a more reliable indicator of the quality and suitability of water for various applications, including use in RO systems.

#### *2.2.2 Biodegradability of an industrial wastewater*

It is important to note that the biodegradability of industrial wastewater may vary depending on the specific contaminants present and the conditions in which the wastewater is treated. Therefore, it is important to conduct thorough testing in order to accurately determine the biodegradability of a particular industrial wastewater.

BOD5 is commonly used to measure the strength of wastewater and the effectiveness of the biological treatment processes.

There are several factors that can interfere with BOD measurements in industrial wastewater. These include:

#### *Desalination – Ecological Consequences*

Inorganic substances: Inorganic substances, such as sulfur, chlorine, and ammonia, can interfere with BOD measurements by reacting with the oxygen that is used in the test. This can lead to inaccurate results [1].

BOD20 [4, 5] is a similar measure, but the test is conducted for 20 days rather than 5 days. This can provide a more accurate measure of biodegradability, as some substances may take longer than 5 days to break down fully. However, the BOD20 test is not as widely used as the BOD5 test, as it takes longer to conduct and requires more resources.

In general, the BOD5 test is considered sufficient for most purposes, but the BOD20 test may be used in cases where a more accurate measure of biodegradability is required or if the substance being tested is known to take longer than 5 days to break down.

There are several factors that can hinder the biological treatment of industrial wastewater. Some of these factors include:

High levels of toxins or other contaminants: If the wastewater contains high levels of toxins or other contaminants, it may be more difficult for microorganisms to break down the organic matter in the wastewater.

There are many toxins or chemical types that can hinder the biological treatment of industrial wastewater. Some examples of toxins that have been shown to have negative impacts on the biological treatment process include:

• Cellulose is a type of organic matter that is resistant to decomposition, and it can interfere with the microorganisms that are used in the BOD test to measure the amount of oxygen required to break down the organic matter in the wastewater. This can result in an underestimation of the actual BOD of the wastewater, leading to false low readings. Cellulose compounds can be degraded by biological treatment of industrial wastewater, but it may be more challenging than other organic matter types. Cellulose is a complex carbohydrate that is found in plant cell walls and is resistant to decomposition due to its complex structure and the

fact that it is highly crystalline, which makes it difficult for microorganisms to access and break down. However, certain microorganisms, such as fungi and some bacteria, can break down cellulose or may need to reduce its concentrations using physical treatment methods like sedimentation, filtration, and centrifugation to remove cellulose from the source. Also, chemical treatment methods involve using chemicals to break down the cellulose, like the use of enzymes or chemicals like sodium hydroxide or hydrochloric acid [6, 7].

It is important to note that these are just a few examples of toxins that can hinder the biological treatment of industrial wastewater, and there are many other types of toxins that can have similar impacts.

Lack of nutrients: Some industrial wastewater may be deficient in essential nutrients, such as nitrogen and phosphorus, which are required for the growth and activity of microorganisms.

Overall, the success of a biological treatment process for industrial wastewater will depend on various factors, including the specific contaminants present in the wastewater and the conditions in which the treatment is carried out.

## **2.3 Oil and grease**

Oil and grease can be difficult to remove completely from industrial wastewater before the RO membranes system. It is necessary to effectively remove oil and grease from wastewater before it is treated using RO membranes to minimize their adverse impacts, where oil and grease can attach and accumulate on the surface of the RO membrane causing severe and may lead to irreversible organic fouling. RO Membrane manufacturers recommended that oil and grease concentrations should be less than 0.1 mg/l. Several techniques can be used to remove oil and grease from industrial wastewater, depending on the concentration of these contaminants. It may be necessary to use several successive methods to achieve the required quality and also according to the extent of the tendency and types of other pollutants associated with this industrial wastewater and the possibility of separating the sources of oils to treat them alone or not, especially if the concentration is high.

**Gravity separation (Skimming):** This involves using a floating device to physically remove oil and grease from the surface of the wastewater, where allowing the wastewater to sit in a settling tank, where the oil and grease float and can be separated by a skimmer [12].

**Coagulation and flocculation:** In this method, chemicals are added to the wastewater to cause the oil and grease to clump together, forming larger particles that can be more easily removed [13].

One of the important technologies that provide effective removal of many wastewaters contaminates is dissolved air flotation (DAF) is a wastewater treatment process that uses coagulation/flocculation combined with dissolved air to create tiny air bubbles that can attach to contaminants in the water, causing them to float to the surface and heavy suspended solids can sink down and then removed by a scrubber [14]. DAF is often used to remove oil and grease from industrial wastewater, as well as other suspended solids and some types of organic matter [15]. Here are a few reasons why DAF systems may be particularly important in the treatment of oil and grease in industrial wastewater:

However, DAF systems have some limitations that can affect their ability to effectively remove oil and grease from industrial wastewater. Some of these limitations include:

*Reverse Osmosis in Industrial Wastewater Treatment Units DOI: http://dx.doi.org/10.5772/intechopen.110680*

• The pH of the wastewater: The effectiveness of DAF systems can be affected by the pH of the wastewater. At high pH values (above 9), the air bubbles may not dissolve as effectively, which can reduce the overall effectiveness of the DAF system. At low pH values (below 6), the air bubbles may dissolve too quickly, which can also reduce the effectiveness of the DAF system.

**Biological treatment:** Certain types of bacteria can break down oil and grease into simpler, water-soluble compounds. This process can be done in a specialized bioreactor or as part of a broader wastewater treatment process. High concentrations of oil and grease can also interfere with the biological processes used to treat the wastewater, which can reduce the overall performance of the treatment plant [16].

**Absorption:** This involves using a solid material, such as clay or a synthetic polymer, to absorb the oil and grease from the wastewater.

Carbon filters can be used to treat industrial wastewater to remove residual traces of oil and grease, and other contaminants such as refractory organic compounds. Carbon filters work by adsorbing contaminants onto the surface of the carbon, then after accumulating on carbon media it can then be removed by backwashing and rinsing or either regenerating or replacing the carbon media. Carbon filters are typically used as a final step in the treatment of industrial wastewater to remove any remaining contaminants that other treatment methods may not have effectively removed or to reach out to a high-quality effluent. In addition, they are often used in combination with other treatment technologies, such as physical separation, chemical treatment, and biological treatment, to provide a high level of contaminant removal [17].

One of the main advantages of using carbon filters for oil and grease removal is their ability to effectively remove a wide range of contaminants. Carbon filters can also be effective at removing contaminants that have a low solubility in water, which can make them difficult to remove using other methods. However, carbon filters have some limitations that should be considered when using them for oil and grease removal. For example, carbon filters may become saturated with contaminants over time, which can reduce their effectiveness and increase the frequency of filter changes.

**Membrane filtration:** This method involves passing the wastewater through a membrane with small pores that can remove oil and grease by size exclusion. But also, it is important to effectively remove oil and grease from wastewater before it is treated using membranes like ultrafiltration (UF) to minimize these negative impacts, and it is considered a final removal step of only residual concentrations [18].

It is important to carefully consider the type and volume of oil and grease in the wastewater and the desired treatment level when selecting a treatment method.

One of the important contaminants that hurt the removal efficiency of oil and grease from industrial wastewater is the presence of emulsified agents in industrial wastewater which can make the removal of oil and grease more challenging and reduce the efficiency of treatment processes. Emulsified agents can cause oil and water to mix and form an emulsion, a stable mixture of oil droplets suspended in water [19].

Some common emulsified agents that may be present in industrial wastewater include surfactants, soaps, and detergents. These agents can interfere with the ability of physical separation methods, such as skimming, floating, and sedimentation, to effectively remove oil and grease from the wastewater. They can also make it more difficult to use chemical methods, such as coagulation and flocculation, to remove oil and grease by forming stable emulsions that are resistant to flocculation.

Biological methods, such as biodegradation, can also be affected by the presence of emulsified agents. Some microorganisms may be able to break down the emulsified agents, but this can also consume some of the oxygen in the wastewater, which can be detrimental to the overall treatment process.

Membrane filtration may be less affected by the presence of emulsified agents, as it relies on size exclusion rather than chemical or biological processes to remove contaminants. However, the efficiency of membrane filtration can still be reduced if the emulsified agents coat the membrane or if they form stable emulsions that are too small to be effectively removed by the membrane.

There are some considerations that should be taken in the design and operations of the oil and grease removal process, and the following are the most common two of them;

#### **2.4 Heavy metals occurrence and treatment**

Heavy metals are naturally occurring elements with a high atomic weight and density at least five times greater than that of water. They are commonly found in industrial wastewater, and their presence can negatively impact the environment and human health. Also, have a negative impact on the performance of RO membranes, which are commonly used to treat and reuse industrial wastewater. When present in high concentrations, heavy metals can foul RO membranes. Fouling of RO membranes by heavy metals can occur through a variety of mechanisms, including adsorption of the metal ions onto the membrane surface, precipitation of the metal ions

*Reverse Osmosis in Industrial Wastewater Treatment Units DOI: http://dx.doi.org/10.5772/intechopen.110680*

within the membrane pores, and the formation of metal hydroxides or metal oxides or insoluble metal compounds on the membrane surface. In addition to fouling, heavy metals in the feed water can also lead to toxic disinfection byproducts, which can occur when the heavy metals react with disinfectants (such as chlorine) used to pretreat the wastewater, resulting in the formation of harmful compounds.

Heavy metals are commonly found in industrial wastewater due to their use in various industrial processes. Some examples of heavy metals that may be present in industrial wastewater include:

It is important to properly treat industrial wastewater containing heavy metals before it is processed using RO membranes (mostly should be less than 0.05 mg/l) to minimize the negative impact on the membrane's performance [20]. This may involve using physical, chemical, or biological treatment methods to remove or neutralize the heavy metals in the wastewater.

There are several important considerations to take into account when removing heavy metals from industrial wastewater:

There are a variety of treatments that can be used to remove heavy metals from water and other materials. These include physical, chemical, and biological treatments.

One example of a physical treatment for heavy metal removal is sedimentation, in which the heavy metals are separated from the wastewater by settling. Heavy metals can precipitate from wastewater by raising the pH to a level above their respective precipitation pH. Precipitation pH is the pH at which a particular metal ion will begin to precipitate out of the solution as a solid. Different metal ions have different precipitation pH values, so the specific pH required to precipitate a particular metal will depend on the type of metal. For example, if the wastewater contains lead ions and the pH is raised to 9.5, the lead ions may begin to precipitate out of the solution as a solid. It is important to note that simply raising the pH of the wastewater may not be sufficient to completely remove all heavy metals. Other treatment methods, such as chemical precipitation or ion exchange, may be necessary to effectively remove the heavy metals from the wastewater [21, 22].

Chemical treatments for heavy metal removal include the use of chelating agents, which can bind to the heavy metals and allow them to be removed from the water.

Biological treatments for heavy metal removal include the use of bacteria that can absorb and remove heavy metals from the water.

Once the heavy metals have been removed from the water, they can often be recovered and reused. This can be done through metal recovery, which involves separating the heavy metals from the material they were removed from and purifying them for reuse. By using this treatment process, the factory can reduce its environmental impact and recover valuable resources for reuse [23].

Several methods can be used to remove heavy metals from industrial wastewater. Here are some examples of treatment methods that can be used to remove specific heavy metals from wastewater:

## **2.5 Hardness removal**

Hardness in industrial wastewater is often caused by high concentrations of calcium, magnesium, carbonate, and sulfate ions, which can come from various industrial processes. These ions can cause various problems, including scale formation in pipes and equipment, and can interfere with the effectiveness of wastewater treatment and reuse in certain industrial processes. Softening industrial wastewater before it is treated with RO can help to increase the operated recovery of the RO unit with less dosage of antiscalant, so increasing the wastewater reused.

Hardness in industrial wastewater can come from a variety of sources, including:

Several methods can be used to remove hardness from industrial wastewater, including:

• Electrodialysis: This process uses an electric current to separate ions in the water based on their charge. It effectively removes hardness but is expensive and requires specialized equipment.

It is important to choose the most appropriate method for removing hardness from industrial wastewater based on the specific needs and constraints of the application.

Some important considerations that should be taken into account when deciding lime soda softening and caustic soda softening for the treatment of industrial wastewater:

Cooling tower blowdown water contains a dispersant and antiscalant that hindered or disturb the coagulation-precipitation process. Where dispersants are chemicals added to the cooling water to prevent the formation of scale and the precipitation of solids, they work by inhibiting the aggregation of particles and keeping them suspended in the water. This can make it difficult or impossible to remove contaminants through coagulation-precipitation. Also, antiscalants are chemicals added to the cooling water to prevent scale formation on surfaces. They work by inhibiting the precipitation of minerals such as calcium and magnesium. However, these chemicals can interfere with the coagulation-precipitation process by preventing the formation of the necessary flocs or aggregates of particles that are necessary for the process to be effective. So it is important to degrade this chemical and inhibit its functions by using a strong oxidizing agent like chlorine with a sufficient concentration and contact time to effectively inactivate those chemicals before the coagulation-precipitation process.

Ferric chloride and alum is a commonly used coagulants in the treatment of industrial wastewater. However, there is a negative impact that should be considered when using ferric chloride as a coagulant before the RO membrane system especially at softening clarifiers where pH is high enough to dissolve part of those minerals: membrane fouling: where ferric chloride can cause fouling of the RO membrane, which can reduce its efficiency and require more frequent cleaning.

It is important to consider these negative impacts carefully when deciding whether to use ferric chloride or alum as a coagulant before an RO system.

In the chemical softening process of wastewater treatment, the pH of the water is typically raised during the softening process and then lowered during the neutralization step. The alkalinity of the wastewater can play a role in the amount of chemicals (lime soda or caustic soda) required to raise the pH to the desired level for softening. Alkalinity is a measure of the water's ability to neutralize acids and is typically expressed in terms of the concentration of bicarbonate, carbonate, and hydroxide ions in the water.

If the alkalinity of the wastewater is high, it may take more chemicals to raise the pH to the desired level for softening. This is because the water's high alkalinity indicates the presence of a large amount of bicarbonate, carbonate, and hydroxide ions, which can neutralize the alkaline chemical added to raise the pH. As a result, more alkaline chemicals may be required to overcome the buffering effect of the alkalinity and achieve the desired pH.

On the other hand, if the alkalinity of the wastewater is low, it may take less chemicals to raise the pH to the desired level for softening. In this case, fewer bicarbonate, carbonate, and hydroxide ions are present to neutralize the alkaline chemical, so fewer chemicals are required to achieve the desired pH.

After the softening process, the pH of the wastewater is typically lowered during the neutralization step. To neutralize the excess lime or caustic soda, an acid such as

sulfuric acid or hydrochloric acid is added to the water. The acid reacts to effectively neutralize the pH of the water. It is important to carefully control the amount of acid added to the water, as adding too much acid can result in a pH that is too low, which can have negative effects on the environment or downstream processes.

The buffering effect in wastewater is a result of the presence of ions that can neutralize acids or bases, preventing significant changes in pH. High concentrations of ions such as ammonia/nitrate or bicarbonate can contribute to the buffering effect in wastewater.

Ammonia (NH3) and nitrate (NO3-) ions can act as weak bases in water, neutralizing acids and helping to maintain a relatively stable pH. Bicarbonate (HCO3-) ions can also act as a buffer in water, neutralizing both acids and bases and helping to maintain a relatively stable pH.

The buffering capacity of wastewater can have an impact on the effectiveness of pH adjustment or neutralization processes. If the wastewater has a high buffering capacity, it may take more acid or alkaline chemicals to achieve the desired pH change. Conversely, if the wastewater has a low buffering capacity, it may take less acid or alkaline chemical to achieve the desired pH change.

It is important to carefully monitor the pH and buffering capacity of wastewater during treatment processes and adjust the chemical dosage as needed to effectively adjust the pH or neutralize the water.

The addition of lime or caustic soda to wastewater during the softening process will typically result in an increase in the total dissolved solids (TDS) of the water. This is because the lime or caustic soda reacts with the hardness-causing ions in the water to form solid precipitates, which contribute to the TDS of the water. The neutralization step, in which acid is added to the water to neutralize the excess lime or caustic soda, will not typically result in a significant change in the TDS of the water.

It is important to note that the TDS of the water can also be affected by other factors, such as the presence of other dissolved solids in the water, the volume of water treated, and the efficiency of any downstream treatment processes. In general, it is desirable to keep the TDS of wastewater as low as possible, as high TDS can have negative effects on the environment and on any downstream processes.

### **2.6 Total dissolved solids**

It is important to accurately determine the final TDS and other component ions of pretreated wastewater before it is treated with a reverse osmosis (RO) system. This information is critical for properly designing the RO unit and optimizing its performance.

During the pretreatment process, various chemicals may be added to the wastewater to remove contaminants or adjust the water's properties. For example, chemical precipitation or softening may be used to remove hardness-causing ions, and pH neutralization may be used to adjust the pH of the water. However, these processes can increase the TDS of the wastewater, as the chemicals added can contribute to the dissolved solids content of the water.

Accurately measuring the TDS and other component ions of the pretreated wastewater is important because it allows the RO system to be properly sized and configured to meet the specific treatment needs of the water. It also helps to ensure that the RO system is operating at optimal efficiency and can effectively remove contaminants from the water.

It is generally recommended to measure the TDS and other component ions of the wastewater at various points throughout the treatment process, to gain a comprehensive understanding of the water's quality and to make any necessary adjustments to the treatment process.

Also, it is important to consider the potential for changes in the characteristics of the wastewater during the design and operation of a reverse osmosis (RO) system. For example, in situations where different streams of wastewater are combined and neutralized, there is a risk that changes in the flow or concentration of one of the streams could affect the final TDS and other ion concentrations of the RO feed water.

To address this risk, it is important to carefully design the RO system to be able to handle the worst-case scenario. This may involve selecting RO membranes that are resistant to fouling and able to handle a wide range of water qualities, selecting a highpressure pump that is capable of operating effectively under varying conditions, and specifying piping materials that are compatible with the wastewater being treated.

By designing the RO system to be able to handle the worst-case scenario, it is possible to ensure that the system is sustainable and durable and able to effectively treat the wastewater even if there are changes in the flow or concentration of the different streams. It is also important to regularly monitor the water quality and adjust the treatment process as needed to maintain the efficiency and effectiveness of the RO system.

## **3. Conclusions**

Industrial wastewater treatment and reuse are gaining high importance in many parts of the world. This chapter gives an overview of the considerations involved in the treatment and reuse of industrial wastewater, with a focus on the pretreatment of wastewater before the reverse osmosis (RO) treatment. It highlights the various factors that have contributed to the growing importance of industrial wastewater treatment and reuse, including environmental regulations, limited water resources, cost savings, and sustainability. The conclusion also describes the various pretreatment technologies and techniques that can be used to prepare industrial wastewater for RO treatment, such as chemical precipitation, softening, pH adjustment, oil and grease removal, biological processes, and filtration. It emphasizes the importance of properly designing and operating the pretreatment system, as well as accurately measuring the TDS and other component ions of the wastewater, to ensure the efficiency and effectiveness of the RO system. Finally, the conclusion notes that there is no one-size-fits-all treatment scheme for industrial wastewater and that the specific pretreatment steps required will depend on the characteristics of the wastewater and the specific requirements of the RO system being used.

*Reverse Osmosis in Industrial Wastewater Treatment Units DOI: http://dx.doi.org/10.5772/intechopen.110680*

## **Author details**

Yehia A. Shebl Chemistry Department, Faculty of Science, Cairo University, Giza, Egypt

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© 2023 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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