*Article* **Mental Health Well-Being and Attitudes on Mental Health Disorders among Family Physicians during COVID-19 Pandemic: A Connection with Resilience and Healthy Lifestyle**

**Tina Vilovic 1,2, Josko Bozic 3, Sanja Zuzic Furlan 1,2, Marino Vilovic 3, Marko Kumric 3, Dinko Martinovic 3, Doris Rusic 4, Marko Rada 1,2 and Marion Tomicic 1,2,\***

**Abstract:** Family physicians (FPs) are exposed to high amounts of stress, and could be susceptible to the development of mental health disorders (MHD), especially after the emergence of the COVID-19 pandemic. The aim of the current study was to assess MHD history, attitudes toward MHDs and stress-coping strategies in FPs. An additional goal was to estimate their comprehensive well-being and investigate connections with resilience and a healthy lifestyle. A total of 483 FPs submitted their responses via online survey. MHD attitudes were assessed with the according questionnaires, while burnout levels, healthy lifestyle, resilience, job and life satisfaction were estimated with validated scales. Results have shown that 32.5% of FPs disclosed positive MHD history, while 68.7% used professional help. Resilience and healthy lifestyle levels were significantly higher in MHD negative FPs (*p* < 0.001), while burnout levels were lower (*p* < 0.001). Moreover, healthy lifestyle (β = 0.03, *p* < 0.001) was an independent correlate of resilience, while healthy lifestyle (β = −0.35, *p* < 0.001, and resilience (β = −1.82, *p* < 0.001) were of burnout levels. Finally, resilience (OR = 0.387, *p* < 0.001) and healthy lifestyle (OR = 0.970, *p* = 0.021) were shown as independent predictors of positive MHD history status. Strong promotion and education of FP population regarding resilience and healthy lifestyle should be utilized in practice in order to alleviate the possibility of mental health disturbances and the according consequences.

**Keywords:** COVID-19; mental health; help-seeking; family physician; primary care; resilience; healthy lifestyle


**2. Glycerine conversion**

methanol, organic and inorganic salts, water, unreacted triglycerides, soap, fatty acid, etc. Hence, for large-scale biodiesel manufacturers, the plants are normally equipped with crude glycerol refining facilities to produce glycerol with purities up

value-added chemicals via catalytic conversion such as hydrogenolysis to

value addition of producing diglycerol.

**Figure 1.**

**118**

*General process flow of glycerine refining.*

propanediol and ethylene glycol, dehydration to acrolein, fermentation to propane-1,3-diol, thermal reduction into syngas, etherification to fuel oxygenates, conversion into glycerol carbonate, and synthesis of epichlorohydrin [6]. Among these, the etherification of glycerol into polyglycerols particularly diglycerol (DG) and triglycerol (TG) is gaining more interest in the recent research due to their possibility in controlling the hydrophilic–lipophilic balance (HLB) which is highly important as additive to food and pharmaceutical industries, lubricants, stabilizers, dispersants, plasticizers, etc. [6]. According to Grand View Research in polyglycerol market size, the demand for diglycerol and triglycerol is expected to grow by 50% from 2012 to 2022. The global diglycerol demand is expected to grow at a CAGR of 5.3% due its extensive use in various industries, thus validating the importance and

Due to the volatility of refined glycerine market price and increasing demand of polyglycerol especially the shortest chain oligomer which is diglycerol, research has been conducted to upgrade glycerol via various processes such as pyrolysis, epichlorohydrin, and catalytic etherification to produce polyglycerols. Etherification is a single-step process of catalytic conversion of glycerol into polyglycerols, involving the condensation of two glycerol molecules to form the simplest oligomer which is diglycerol with linear, branched, or cyclic isomers. Further reaction yields tri-, tetra-, and higher oligomers. Short-chain oligomers are preferred. Therefore, the

Generally, there are three types of glycerol, namely, crude glycerine, technical grade glycerine, and refined glycerine. The process of refining glycerine is a complex process which involves distillation, bleaching, acidification, and several intermediate steps. In the distillation step, refined glycerine is obtained from the side draw of the distillation column and then subsequently bleached and deodorized to achieve the refined grade. Technical grade glycerine, also called yellow glycerine, is obtained from the top of the column with some impurities such as water, fatty acids, soap, etc. [2]. **Figure** 1 shows the general process flow of glycerine refining. According to MarketWatch 2018, the global glycerine market is expected to reach approximately 6200 metric tons by 2024 from 3550 metric tons in 2016, resulted from the growth in bio-renewable chemicals, biodiesel production, and wide range of applications. However, with regard to the market price, technical grade glycerine is cheaper than the refined glycerine which are approximately RM4400 and RM5400 per metric ton, respectively, as reported by Oleoline (2017). Furthermore, glycerol can be used as a starting material for the synthesis of

to 95.5 and 99% [3].

*Apolipoproteins,Triglycerides and Cholesterol*

### **2.1 Existing diglycerol synthesis method**

#### *2.1.1 Laboratory-scale routes*

On small scale, pure diglycerol is produced via direct synthesis methods in which diallyl ether is used as a primary reactant [1]. Diallyl ether is accessible by the reaction between allyl chloride and allyl alcohol in inert solvents under hydrogen chloride release. Direct hydroxylation of this product can be performed with peroxyformic acid, CH2O3, or permanganate at 40°C under safety precautions for 4.5 hours. However, several additional steps are needed for neutralization, filtration, derivatization, and fractional distillation which are required for the isolation of diglycerol and triglycerol. The isolation of diglycerol can be done using neutralization with barium hydroxide solution, centrifugation to separate the solid, digestion of the product in absolute ethanol, and fractional distillation under reduced pressure.

#### *2.1.2 Thermal conversion of glycerol*

The thermal reaction for glycerol oligomerization is conducted at a certain temperature under inert protecting reactor condition [1]. For selective reaction, pure glycerol up to 99% purity should be used. Commonly, before the use of the oligomeric products for further reactions, a distillation is needed to remove unconverted glycerol. Reaction temperature, basicity, and organic impurities would affect the glycerol oligomerization. For pure thermal conversion of glycerol without the addition of catalyst, temperature is normally set above 200°C. However, at reaction temperature higher than 290°C, side products with strong smelling are formed. At 180°C (low temperature) with the addition of alkali catalyst, the formation of diglycerol from glycerol is observed but at low conversion of glycerol.

#### *2.1.3 Epichlorohydrin method*

The epichlorohydrin method of producing polyglycerol is commonly applied. It involves basic hydrolysis by sodium hydroxide, led to the formation of intermediate product, namely, glycidol and glycerol, and it will react with unconverted epichlorohydrin or glycerol to diglycerol [6]. Further separation and purification of

products are required. Residue glycerol will be separated, and then water has to be removed from the raw diglycerol, and, finally, the product has to be subjected to a fine distillation. The reaction of glycidol or epichlorohydrin with glycerol has in common that the coupling OH groups are not confined to the terminal positions but also the middle OH groups of glycerol can be involved as well. This leads to the formation of primary or secondary dimer of glycerol.


**5. Conclusions**

It is important for the Republic of Croatia to consider the possibilities of reducing their emissions by making use of CCS technology. This is the only way to achieve the Paris agreement targets in time, simply because the existing large stationary industrial sources from the energy and other industrial sectors can be cost-effectively, safely and quickly decarbonised, before the uptake of renewable technologies really starts "kicking in." Timely preparation of this will positively influence energy prices and save many jobs, not to mention that every nation should take care of its contribution to the global effort to reduce GHG emissions. Croatia is at present, still far from phasing out its fossil fuel energy sources and has a comparably high proportion of industrial emissions that will not just disappear in the near future. This can all be dealt with by evaluating the new "geological storage resource" to make use of the deep subsurface rock formations by the building of carbon capture and storage (CCS) systems.

There are favourable conditions for geological storage of CO2 in Croatia, both in the southern part of the Pannonian basin and the Adriatic offshore [7]. The capacity declared for hydrocarbon fields is better defined than estimates for aquifer formations which still need detailed exploration in order to define the structures for storage. Regarding the Adriatic offshore, it is far less explored than Pannonian Basin, but it has a considerable dataset, enough for screening in terms of the basic characteristics of subsurface geology.

Since almost half of emissions occur in the coastal areas, the Adriatic offshore's CO2 storage potential gains importance now that even exceeds petroleum exploration. That is simply because one can import oil or natural gas, but one cannot export CO2. There is still the significant professional knowledge and technical potential from the otherwise declining upstream part of national petroleum industry. It simply must be put into use while the window of opportunity still exists.

The most prospective CO2 storage objects are the small gas fields in the Northern Adriatic. Total storage potential in their reservoirs is not large (32 Mt) but it is available, and there are installations on exploitation sites which would significantly reduce investments. Another group of objects are deep saline aquifers. They offer much larger potential but with large uncertainty; that is why this is called "theoretical storage capacity". We think we have demonstrated the two most important "CO2 storage plays" based on the regional geological data—Miocene sandstones in the Dugi otok basin (as a regional deep saline aquifer, DSA Dugi otok) and Triassic to Eocene carbonate rock formations, whose paleotopography is covered by thick impermeable layers of Miocene to Early Pliocene age, so five structurally defined aquifers were delineated, each of them representing a site where CO2 storage capacity could be investigated on a local scale. They are all distant from sources of carbon dioxide and maybe the two of them will eventually prove to be too small to be economical, but the other three show significant potential that should not be overlooked.

**Author Contributions:** Conceptualization, B.S. and I.K.M.; methodology, B.S., I.K.M., M.C. and D.V.; software, I.K.M., M.C. and D.V.; validation of regional geology, J.V. and B.T.; formal analysis, I.K.M. and D.V.; investigation, B.S., I.K.M. and M.C.; resources, B.S. and M.C.; data curation, I.K.M. and M.C.; writing—original draft preparation, B.S., I.K.M. and M.C.; writing—review and editing, J.V. and B.T.; visualization, I.K.M. and M.C.; supervision, B.S.; project administration, B.S. and M.C.; funding acquisition, B.S.

**Funding:** The publication process was supported by the Development Fund of the Faculty of Mining, Geology and Petroleum Engineering, University of Zagreb. The authors would like to acknowledge that they have had support from European Commission (in a number of FP6, FP7 and Horizon 2020 projects), from the Croatian Environmental Protection and an Energy Efficiency Fund, from HEP (Croatian power utility who once ordered a professional study) and from the University of Zagreb with which they are affiliated.

**Conflicts of Interest:** The authors declare no conflict of interest.


**2. QOL of patients with muscular dystrophy**

Muscular dystrophy has an early onset, and thereafter body functions decrease progressively beginning with a decrease in motor functions that require the use of a wheelchair to maintain mobility and a decrease in the breathing function that require a ventilator to maintain breathing, which makes the patients bedridden. As a result, the patients' behavior repertoire becomes severely restricted, and they require considerable assistance. Netterlund et al. investigated activities of daily living (ADL) and the QOL of 45 people (mean age 44 years) with muscular

dystrophy [2] and reported that all the sampled patients were living at home. The QOL was assessed by the Sickness Impact Scale (SIP) and the Psychosocial Well-Being Questionnaire, which indicated that their disability and dependence on others increased, whereas ADL decreased during the previous 5 years. Moreover, the patients' QOL and life satisfaction also decreased. Boström and Ahlström investigated 46 people with muscular dystrophy through interviews using a qualitative research approach for 10 years [3]. They reported that nearly all muscular dystrophy patients had decreasing functions such as limited mobility, increasing fatigue, and feebleness, accompanied by psychological distress. Moreover, if there is a difficulty in securing assistance for patients to continue living in their homes, they must live in recuperation wards.

Ueda et al. [4] investigated the QOL of 50 inpatients with muscular dystrophy. The QOL was assessed by the World Health Organization-Quality of Life 26 (WHO-26). Results indicated that the mean QOL score (SD) of patients with muscular dystrophy was 2.96 (0.34), which was significantly lower than the general Japanese population (mean 3.75) or patients with cancer (mean 3.3). The results of the comparison between patients' conditions indicated that those who could move by using a wheelchair had higher QOL scores than those who were bedridden. The QOL score of patients that had throat surgery was higher than those who had no surgery. The comparison between clinical types indicated that the QOL in myotonic dystrophy was significantly lower than limb girdle-type muscular dystrophy or Fukuyama-type congenital muscular dystrophy. They also investigated factors that could affect the QOL of patients with muscular dystrophy, including age, gender, clinical type, duration of the diseases, throat surgery, duration from throat surgery, functional independence (Barthel Index), use of a ventilator, use of a wheelchair, use of a computer, the frequency of family visits, and participation in activities. The results of categorical regression analysis (R2 = 0.671, R2 = 0.400, F = 2.479, P < 0.05) showed that only the use of a computer influenced the QOL (β = 0.598). These results suggest that using a computer could be an effective method of maintaining or improving the QOL of muscular dystrophy inpatients, with deteriorated body functions and limited activities due to the progression of the disease.


**2.1 Approaches**

The data collection and analysis of the same in this study has taken several months starting sometime in February 2020 to date. This was the time when the first case of COVID-19 had just been reported in Kenya.

## *2.1.1 University class engagement and discussions*

The researcher, who is an instructor at the university, engaged other scholars at universities on this subject. The scholars were sampled from two public universities, one private university and a TVET. Some of the respondents were not available for face-to-face interview and had to be contacted using other channels. Their responses were captured and analysed to give an insight in the subject under study.

Sampling was systematically done for purposive reasons on desired outcomes as indicted in **Table 1**.

### **2.2 Analysis of information from stakeholder organizations**

Analysis of information from stakeholder organizations such as WIPO-PRV Training, KIPI, KECOBO, KeNIA, NACOSTI.

These organizations are the major stakeholders in matters of innovation, creativity and intellectual property management. The information concerning creativity was obtained from their publications and Websites. The information related to training, regulation and registration, funding among others. The sought data obtained was analysed, and important conclusions were drawn from the same.

### *2.2.1 A meeting and interviews with industry players*

A meeting and interviews with industry players who included representatives from commercial banks, The Kenya Seed Company Ltd., Knowledge Transfer Network (KTN), Eldo Bub, and County Government of Nandi. These organizations were represented by high-ranking officials who gave their views on creativity and the possible industry and university collaborations on the subject at hand.

The officials were purposively invited on the account that they represented their organizations on this important topic. This is shown in **Table 2**.

### *2.2.2 Input from experts*

Expert opinion was sought from among others, Technology Transfer Manager [Moi University], intellectual property [IP] official from the University of Eldoret

#### **Table 1.**

*Respondents who completed the questionnaires on creativity.*

#### **Table 2.**

*Respondents who were interviewed during the meeting.*

[U.o.E.] and Eldo-Hub Head. These three individuals who are experts in the area of innovation, research and intellectual property were extensively interviewed on the subject of creativity. They also made suggestions on the way forward of fostering creativity. From those interview schedules and proceedings, very essential information was obtained, and critical insights and conclusions were made in connection with creativity. This became the basis for making findings of this study for the purposes of disseminating the results.

#### *2.2.3 Output from innovation workshops: Public lectures*

As a way of creating awareness on innovation, the university arranged innovation week in the year 2021 and 2022.Other than the exhibitions that were displayed, there were engagements among the innovators and participants, and the culmination of this was public lectures that were given by scholars such as Dr. Jesper Vasell, the Deputy Director of NACOSTI in Kenya, the C.E.O of KeNIA among others. In this endeavor, the then Director of Innovation & Research at the University of Eldoret, Prof. Vincent Sudoi was very instrumental. The proceedings from these sessions of the Innovation week illuminated so much on the subject of creativity and greatly assisted in extracting some of the issues that had been identified as challenges.

#### **2.3 Impediments to creativity**

One of the ways of eliminating barriers to creativity is removing things that clutter the mindset. Impediments, barriers and gap are terms that were interchangeably used. In this case, mindset issues that contributed to barriers or impediments included the thinking state, which is the concern for certainty, and formed opinions about a certain aspect of concept. This limits creative thinking. Another issue is security hunting—it is the concern for risk. It makes one become risk averse. We also have stereotyping which is a case that keeps abstracting reality. The probability thinking, on the other hand, seeks predictable results, which ultimately impedes creativity.

#### *2.3.1 Fear*

Fear is one of the biggest reasons that make organizations as well as individuals not to achieve their full potential in creativity. They have the fear of failure in their endeavors. The fact that there is no assurance that the new idea will work makes the creative people and firms to develop fear. Fear consequently slows the creative thinking process. As it is, creative thinking process is a psychological or intuitional one. When fear is recorded, it hampers or inhibits thinking. However, coming to terms with the fact that failing is an important part of learning; when handled well, it can lead to development and progress [1].

#### *2.3.2 Leadership issues*

Studies show and scholars agree that issues of innovation and creativity can be well spearheaded from the top leadership of organizations. The top executives and directors of various firms are yet to strongly come out and support the strategic importance of innovation and creativity as key elements of corporate performance. It would appear that currently corporates are yet to take leadership on this subject in

#### *Creativity Impediments and Solutions DOI: http://dx.doi.org/10.5772/intechopen.110693*

order to foster performance and development. It is thought that if top leadership of organizations changes its attitude and approach to creativity, then the performance of various firms can also change. But it means the top managers must now change and lead innovation and creativity from the front in their respective entities. They also need to start nurturing upcoming innovators and creative thinkers [12].

#### *2.3.3 Deficient resources and capacity*

Investing in creative activities and in innovations can be a very expensive affair, and the same requires massive finances and human capital. Equally needed are systems, training infrastructure and the experts. All these require huge amounts of funding which is insufficient. This is a big impediment for this creativity which is a necessary endeavor. However, firms, institutions and countries must take deliberate decisions and set budgetary provisions for this purpose. They can also employ strategies such as networking and collaborations in a bid to foster the creativity task.

## *2.3.4 Lack of necessary alliances*

Internal budgeting and structures may not assist alliances between teams. It is reported that many years later, organizations do not appear to have embraced the required collaborations to have things changed. It also seems that various barriers are still existing. These barriers could be similar across organizations and among individuals. They still impede creativity significantly. Lacks of strategic alliances among other factors still inhibit the ability to think creatively and hence innovate. Alliances must be encouraged to foster creativity and help in the achievement of the desired results. Creative collaborations are also about bringing people together, viewing challenges from different viewpoints and then linking that knowledge and understanding together, to create a solution. This must be a solution that can then be strategically planned and implemented effectively [13].

### **2.4 How to enhance creativity**

Various scholars in their studies have attempted to find solutions to some of the impediments that have been identified so far. Although the impediments identified earlier are weighty, they are only a representation of the myriad of other challenges. Therefore, the suggestions here are just a few ways of enhancing creativity. It means a lot more can still be done through initiating further research [14].

## *2.4.1 The creative process*

According to Corazza and Agnoli [13], whether one calls it creativity, creative thinking or just creative ideas, there must be a process involved in it. This process needs to be meticulous and can also be learned because it involves individuals, firms and systems. Above all, it must be supported financially, morally and by establishing the right systems.

What is fascinating is that creative thinking process is largely a subconscious process. Due to this fact, the individuals must be targeted because this process takes place intuitively.

#### *2.4.2 Techniques for improving the creative process*

The findings indicate that there is the need of improving the creative process. If this process is improved, then the ideas that can be obtained as a consequence can go a long way in enhancing innovation. There will be a likelihood that those who become creative by the works of their minds may also benefit and feel valued to even improve in future. But they have to feel protected and also need to benefit from their creative minds. This is how intellectual property comes in play as an important component.

#### *2.4.3 Intellectual property: protecting the ideas*

Intellectual property protection plays a critical role in creative thinking and ultimately in supporting creativity. For instance, the generation of ideas that results in the improved efficiency or effectiveness of a system facilitates two important aspects of creativity. There is the existence of the process. Such a process is goal-oriented; it is designed to attain a solution to a problem. Then we have the people, they are the resources that determine the solution. These individuals must be assured that the works of their minds will be rewarded and also be protected from infringement.

#### *2.4.4 Embracing kaizen concept*

The Japanese term Kaizen which refers to improvement, or change for the better, can be embedded in the creativity process. This is because it can be taken to include efforts by all employees from the top most to the lowest in cadre in striving for improvement. It strives to ensure that there is improvement of all processes and systems—including coming up with creative ideas, innovation and entrepreneurship. This is intended for the functioning of a particular organization. The concept strives for long-term superior quality and ultimately customer satisfaction [8].In today's business world, an innovative organization can employ the Kaizen approach for evaluation of its core organizational procedures, operations and even in routine projects. Among the suggested principles of Kaizen that can address the paradigm shift include avoiding assumptions, being proactive in problem solving, creating an environment where everyone feels endowed to contribute and using creativity to find solutions to organization's needs among others**.**

#### *2.4.5 Creativity and trust*

Studies indicate that there is a correlation between creativity and trust. Scholars posit that as a way of nurturing creativity in order to have an innovative and supportive system in the organization, there must be provision for mistakes that might occur. In other words, there is need for crafting a safe space that provides allowance for failure. Some of the key attributes associated with firms that foster creativity and innovation are allowing individuals to acquire lessons from mistakes made. This needs some level of trust. It means the employer will have to develop patience in order to allow the employees take charge of tasks that risky enough that can lead to failure [15].

It is further argued that this may be one of the ways of getting the employees' very best ideas. For instance, it is said that those employees who are based and work in the field understand their area better than most of the other workers. What it therefore means is that by allowing them room to dip their hands in to become innovative is beneficial to them as well as to the organization.

*Creativity Impediments and Solutions DOI: http://dx.doi.org/10.5772/intechopen.110693*

Some firms have witnessed employee-driven creative ideas and innovative solutions that have enabled them to avoid costly mistakes thus save millions of dollars and hundreds of hours. Thus, if companies put its trust in the hands of the individuals who work hard for them daily, then the team and the firm is likely to reap benefits that far outweigh the risks and the occasional failures.


**4. Summary**

We have employed EMD simulations for the investigations of *S*(*k,ω*) over a wide range of Coulomb and Debye screening parameters (*κ*, Г). It has been shown that the presented EMD technique and previous numerical methods have equivalent performance for the wide range of plasma state points, both yielding satisfactory data for plasma *S*(*k,ω*). New simulations provide more consistent and inclusive results for the plasma *S*(*k,ω*) over a complete range of Г (1, 200) and *κ* (1.4, 4) than the previously known numerical results. Our investigations show that the dynamic of dust particles are exponentially decayed, sinusoidal form and crystalline form, respectively, in the gaseous, liquefy regime and crystalline states of SCCDPs. Moreover, the dynamical spectra of dusty plasma do not observe at very high values of Г and low values of *κ*. Moreover, our results indicate that the dynamical structure factor in SCCDPs depends on *κ*, Г and *k.* It has been shown that the presented simulation has comparable performance with the earlier simulation of *S*(*k,ω*) over the wide domain of plasma states. For future work, it is suggested that presented EMD technique based Ewald summation can be used to investigate and explore dynamical structure factor behaviors in other simple liquid, dipolar and ionic materials.


**5. Intracellular Consequences Associated with ABCC6 Transporter Activity in HepG2 Cells**

It is widely evident that changes in nuclear lamin expression are associated with cellular senescence and age-related diseases [36]. However, cells undergoing aging also adapt a phenomenon to proliferate inappropriately, migrate, and colonize, which are the hallmarks of cancer cells [37]. In both cases, changes in lamin expression traduce in morphological changes in nuclei, which are known as "nuclear atypia". Contrarily, induction of cellular senescence is recognized as an important tumor-suppressive mechanism [38].

In previous studies with *ABCC6* knockdown HepG2 cells, we have found decreased cell growth and lamin A/C expression [33]. Interestingly, in the recent study, pharmacological inhibition of ABCC6 by probenecid or its knockdown in HepG2 cells not only decreased the amount of extracellular ATP content but also decreased the expression of CD73 and lamin A/C proteins. Lamins are the most important structural component of the cytoskeleton and are required to maintain cells in a proper shape. In this context, we examined whether down-regulation of lamin expression affected the actin filaments, required for cytoskeleton rearrangement and cellular movement. In this study, a typical organization of actin filament in filopodia, which is a hallmark of moving cells, was absent in both probenecid-treated and *ABCC6* knockdown HepG2 cells (Figure 6). However, administration of adenosine or ATP restored the normal architecture of filopodia and migration rate (Figure 7). This finding indicates that ABCC6 can be a potential therapeutic target for anti-metastatic treatment and, with coordination of the purinergic system, also regulates the intracellular functions [32].

**Figure 6.** Representative confocal image of (**A**)—scrambled HepG2 cells; (**B**)—Abcc6-shRNA.HepG2 cells; (**C**)—Abcc6-shRNA HepG2 cells treated with 500 µM ATP; (**D**)—Abcc6-shRNA HepG2 cells treated with 100 µM adenosine. F-actin was stained with Texas Red-phalloidin. In the insets superposition of cytoskeleton (red) and EGFP (green) to monitor the infection efficiency. The scale bar in the inserts is 40 µm [32].

**Figure 7.** Effect of probenecid and ABCC6 silencing on the migration rate of HepG2 cells. Cells were treated with 250 µM probenecid for 48 h (gray plain bars, Probenecid+). DMSO-treated cells were used as the control (gray plain bars, Probenecid-). A total of 500 µM ATP was added to either the control cells (gray plain bars, Probenecid-, ATP+) or to probenecid-treated cells (gray plain bars, Probenecid+, ATP+). HepG2 cells were transduced with scrambled shRNA (grey-texturized bars, scr-shRNA) or with specific ABCC6-shRNA (black bars, ABCC6-shRNA). A sample of 500 µM ATP was added to either control cells (grey-texturized bars, scr-shRNA, ATP+) or to ABCC6 silenced cells (black bars, ABCC6-shRNA, ATP+). Data are expressed as mean ± standard error (SE) of three replicates from three independent experiments and were analyzed by one-way ANOVA followed by Dunnett's post hoc: \*\*\* *p* < 0.001 probenecid-treated cells vs. control cells in the absence of ATP and ABCC6-shRNA vs. scr-shRNA in the absence of ATP; ### *p* < 0.001 probenecid + ATP-treated cells vs. probenecid-treated cells and ABCC6-shRNA cells + ATP vs. ABCC6-shRNA cells without ATP. NS, not significant [32].


*Multifunctionality and Impacts of Organic and Conventional Agriculture*

infants, children, and adults, respectively. It was observed from the results that the dose ingestion to infants' testes exceeded the world acceptable limit of 1.0 mSv annually to the human-sensitive organs/tissues. The relatively higher dose to the testes and low-dose intake to the liver are justifiable from food nutrient absorption rate [15, 31]. The high radiological dose to the testes may justify the rampant rate of prostate cancer among young men which may be linked to accumulated effects of

*Economic Approach to Risk Analysis of Naturally Occurring Radioactive Materials (NORMs)…*

Cost-benefit analysis in radiation protection is the projection of radionuclide injection effects of consumption of food product versus the nutritional benefits derived from the intake of the food at low individual doses, below the dose limits. Applying the direct relationship between dose and effect, the health impairment is directly proportional to the effective dose-equivalent occasioned by the consumption of milk product. The proportionality element is termed the risk factors [35, 36].

The committed effective dose to an individual assessed for three age groups (0–1 yr infant, 1–7 yrs children, and >17 yrs age group for adults) over a typical

The calculated committed effective doses to the various age groups are presented in **Table 8**. The obtained doses to infants and children were futuristic and a forecast of the probable dose to be committed to the individuals in the period of 50 years. The obtained dose values for adult over an average lifetime of 50 years for powdered milk and liquid milk were 9.3 mS vy�1 and 9.1 mS vy�1 doses, respectively. The committed doses obtained for children were 48.1 mS vy�1 and 41.1 mS vy�1 for powdered and liquid milk, respectively, while for infants it is

that constant ingestion of the milk products may result to accumulation of radionuclides in some organs of the human, with more radionuclide dose intake in powdered milk than consuming liquid milk. Moreover, the values gotten are well

**Table 8** presents the summary of the result of the risk analysis and health detriment effect values that may arise from the consumption of milk product

**Table 9** presents the population of the three age groups under examination in this study, obtained from the National Population Commission report [37], and the computed two-thirds (2*=*3Þ of this population used for the evaluation of the collec-

It is insufficient that the risk to individuals is set at an adequately low level in radiation protection, but the total detriment to the public resulting from exposure to radiation should be kept as low as is reasonably achievable (ALARA) for health, economic, and social factors. The evaluation of the collective/total detriment to health for the public is the sum of detriments to the individuals making up the

CD ¼ 50 � ED (8)

, respectively. The result obtained points to the fact

the dose intake over time, which need further clinical investigation [34].

**4. Risk factors and cost-benefit analysis**

*DOI: http://dx.doi.org/10.5772/intechopen.92279*

**4.1 Committed effective dose (CD)**

80.4 mS vy�1 and 67.3 mS vy�1

within international standard.

tive effective dose equivalent.

**73**

**4.2 Collective effective dose equivalent**

samples investigated in this study.

lifetime of 50 years was computed using the formula:

#### **Table 7.**

*Average values of F for different organs or tissues [33].*

presents an optimized annual quantity of powdered milk to be consumed as 7 kg and 11 kg for children and infants, respectively, and 8 kg and 13 kg were recommended for children and infants, respectively, for liquid milk, while adult was not optimized because the value obtained was within the international permissible limit. Using the optimized quantity, the annual accrued values obtained for infants and children for powdered milk were 750.1 μSv and 755.9 μSv, respectively, while the accumulated values recorded for liquid milk were 717.6 μSv and 763.7 μSv for infants and children, respectively. The values recorded are well below the 800 μSv [26] yearly recommended permissible limit.

**Table 6** presents the result of calculated effective dose rate to the different human organs for consuming powdered and liquid milk.

**Table 7** presents the average values of F, for different organ or tissue uses in the computation of the effective dose rate of these organs.


**4. Immune response to** *L. (L.) mexicana*

The skin is the first immune barrier against *Leishmania* promastigotes inoculated by the sand fly vector. The immune response against *Leishmania* spp. is highly complex. Macrophages are the main host cells of *Leishmania* and also responsible for parasite elimination. The activation of the macrophage microbicidal mechanisms depends on the cell-mediated immune response [39]. Thus, the nature and intensity of cellular immune response and their mediators (i.e. cytokines and chemokines) in the lesions are of primary importance for the disease outcome.

Based on this rationale, the characterization of the cytokine expression profile was studied in 13 LCL lesions caused by *L. (L.) mexicana* from the Yucatan Peninsula [40]. Age of the patient ranged from 10 to 29 years and the lesion evolution time from 8 days to 18 months. Lesions were classified as of early (≤2-month duration) and late (≥4-month duration) evolution. Skin biopsies were taken from the border of the lesion to analyse cytokine gene expression by RT-PCR. *Leishmania* amastigotes were present in 8 of the 11 histological sections. Intra-lesional cellular infiltrate was made up of equal proportion of macrophages and plasma cells. Lymphocytes represented 50% of the cellular infiltrate in three of four of the early lesion evolution but only in one of seven of the late-lesion evolution. The analysis of the *in situ* cytokine gene expressions revealed a concomitant presence of Th1 (IL-1α, IFN-γ, TNF-α) and Th2 (IL-6, IL-10, TGF-β) cytokines in all biopsies. The high expression of IFN-γ, cytokine related with macrophage activation, in both early and late evolution suggested that the presence of this cytokine was not sufficient for parasite elimination and control of the disease. A significant increase in IL-1α, TNF-α, Il-10, and TGF-β expressions was observed in late-lesion evolution compared with that in early lesions suggesting the role of these cytokines in the chronicity of LCL caused by *L. (L.) mexicana*. Both IL-10 and TGF-β down-regulate macrophage functions [41, 42]. Thus, the intra-lesional expressions of these cytokines could promote the persistence of the intracellular parasites in the skin. On the other hand, the presence of TNF-α in cutaneous lesions caused by New World *Leishmania* species has been related with lesion formation and loss of integrity of the infected tissue [43]. Further studies to confirm the role of TNF-α in the immunopathogenesis of LCL caused by *L. (L.) mexicana* are needed.

for agriculture, hunting and gum collecting. Although the number of human cases of LCL reported each year has peaked from March to July, if the incubation period is considered, there is a strong correlation with the abundance, rates and timing of infection of both reservoirs and vectors (**Figure 2**). Based on these results, for the first time in the world, a seasonal transmission (from November to March) of LCL caused by *L. (L.) mexicana* in the sylvatic region of the state

**Figure 2.** Monthly percentage of patients and rodents infected by *Leishmania (Leishmania) mexicana*, and relative abun-

The skin is the first immune barrier against *Leishmania* promastigotes inoculated by the sand fly vector. The immune response against *Leishmania* spp. is highly complex. Macrophages are the main host cells of *Leishmania* and also responsible for parasite elimination. The activation of the macrophage microbicidal mechanisms depends on the cell-mediated immune response [39]. Thus, the nature and intensity of cellular immune response and their mediators (i.e. cytokines and chemokines) in the lesions are of primary importance for the disease outcome.

dance of *Lutzomyia cruciata* in a forest at 8 km from the village of La Libertad, Campeche, Mexico.

**4. Immune response to** *L. (L.) mexicana*

of Campeche was determined.

146 The Epidemiology and Ecology of Leishmaniasis

Another study of 20 LCL patients was carried out to analyse the role of IL-12 in the protective immune response to *L. (L.) mexicana* infection. The correlation of IL-12 with its counterregulatory cytokine, IL-10, was also evaluated [44]. The patients were 10–48 years old and their lesions ranged from 10 days to 20 months of evolution. Cytokine expressions were evaluated by RT-PCR. Intra-lesional expression of both IL-10 and IL-12 was present in most of the 20 patients. The more chronic, non-healing lesions had higher levels of IL-12 mRNA indicating that the expression of this cytokine alone was not sufficient to induce healing. The IL-10 expression correlated with both IL-12 and IFN-γ, suggesting that IL-10 promotes disease persistence by a direct inhibition of macrophage activation rather than by suppression of the Th1 response.

Epidemiological studies detected many individuals from the endemic area of LCL without suggestive signs of the disease but with a delayed hypersensitivity skin test (DHT) positive to *Leishmania* antigens. Asymptomatic infection is the most common outcome to the infection in the Yucatan Peninsula [10, 45]. From the immunological point of view, asymptomatic infection is explained as the elicitation of an appropriate immune response capable of controlling parasite replication and maintaining tissue integrity [46]. Therefore, the characterization of this protective immune response in asymptomatic individuals becomes imperative for vaccine designs. Thus, the *in situ* cytokine (IL-4, IL-10, IL-12, IFN-γ) and chemokine (MCP-1, MIP-1α) mRNA expressions were analysed in biopsies of the DHT area of asymptomatic individuals (*n* = 6) and subjects with healed lesions (*n* = 9) and compared with biopsies from active lesions (*n* = 11) [47]. The expression was highly variable. Neither IL-4 nor MIP-1 α was detected in any biopsy. IL-12 was detected in all three groups without significant differences in the median. MCP-1, chemokine that stimulates oxidative burst activity in macrophages thus killing intracellular amastigotes, was expressed in all three groups being significantly higher in active lesions. The most surprising finding was the absence of IFN-γ in both healed lesions and asymptomatic infection. Taken together, these results suggested that IL-12 and MCP-1 in the absence of IFN-γ might be playing a crucial role in the infection outcome at the skin level. Further studies are needed to identify the cytokine and chemokine network and their cell sources in asymptomatic infection. This knowledge is primordial to understand mechanisms involved in immune protection against *L. (L.) mexicana* and to develop better preventive and therapeutic strategies.


*4.1.3 Stability VAR model test*

The stability test of the VAR model was used to test IRF and VDC. The stability test for VAR estimation can be seen in **Table 4**.

36.79544, and 12.11161 and which are greater than the critical value of 0.05, namely, 29.79707, 15.49471, and 3.841466, respectively. In this regard, H0 is rejected and H1 is accepted. It implies that all variables have influence in the long term or are cointegrated with each other. Therefore, the next step is to carry out analysis with

**Hypothesized no. of CE(s) Trace static Prob Critical value Variable** None \* 80.84738 0.0000 29.79707 FDR At most 1 \* 36.79544 0.0000 15.49471 NPF At most 2 \* 12.11161 0.0005 3.841466 BOPO

Having tested the existence of VECM, the analysis is to estimate on how shortterm and long-term relationships affect each other. The variables of FDR, NPF, and

**Table 6** shows the influence of each variable to other variables, particularly the relationship between FDR with NPF and FDR with BOPO. The short-term estimation results show that the FDR variable is influenced by the NPF variable in lag 1, which has a positive effect of 1.36%. In lag 2, the relationship of the NPF negatively affects FDR for 0.37%. Furthermore, in lag 3, the NPF has a positive effect to FDR with a value of 0.34%. Then, the FDR variable is influenced negatively by the BOPO

**Table 6** shows the influence of BOPO and FDR to NPF. Results show that the NPF variable is influenced by the BOPO in the first lag which has a negative effect of 0.01% and the second lag also shows a negative effect of 0.02%. Then, the NPF variable is influenced by the BOPO in the third lag which has a positive effect that is 0.005%. Then, the NPF variable influenced by the FDR variable negatively affects

Furthermore, **Table 6** shows the relationship between BOPO with FDR and NPF. Empirically, BOPO is influenced positively by the FDR variable in the first and second lags for 0.12 and 0.11%, respectively, but in the third lag, the variables have a negative effect of 0.22%. On the contrary, the BOPO is influenced by the NPF,

and 0.60%, respectively, but in the third lag, it shows a positive effect on the

**Table 7** shows the summary of direction among variables. Results generally indicate that NPF has positive effects toward FDR and BOPO. It implies that NPF that is a proxy variable for financing risk could trigger other risk occurrence,

Based on **Table 8**, VECM estimation analyzes the influence of variables in the long term. The FDR variable is influenced by NPF and BOPO variables. In the first lag, the FDR variable was influenced negatively by 72.58%. However, in contrast to the first lag, the FDR variable was influenced positively by BOPO for 9.02%. The NPF variable is influenced by the BOPO variable and the FDR variable. In the first lag, both variables negatively affect the values of 0.12 and 0.01%. The BOPO variables are influenced by FDR and NPF variables. In the first lag, the BOPO variable is

which has a negative effect on the first lag and third lag, which is 0.95

namely, liquidity and operational risks, in the short run.

BOPO show the significant effect on lag 3 in monthly data.

the VECM estimation.

*Sources: Author's calculation. \*5% level of significance.*

*Risk Analyses on Islamic Banks in Indonesia DOI: http://dx.doi.org/10.5772/intechopen.92245*

**Table 5.** *Cointegration test.*

*4.1.5 VECM estimation*

in the first lag until the third.

the first lag until lag 3.

BOPO, namely, 1%.

**61**

Based on **Table 4**, it can be explained that the model used is stable in lags of 0–3. This can be seen from the range of modules with an average value of less than one. Therefore, the results of the IRF and VDC analyses are valid, so that the cointegration test can be done.

## *4.1.4 Cointegration test*

The fourth stage that must be passed in the VECM estimation is the cointegration test. Cointegration tests are conducted to determine whether there is a long-term relationship on each variable. If there is no cointegration relationship, the VECM estimation cannot be used. This study uses the Johansen cointegration test method available in EViews 7.2 software with a critical value of 0.05. The cointegration test results are shown in **Table 5** as follows.

Based on **Table 5**, at the 5% test level, there are three ranks of cointegration variables. This can be proven from the values of trace statistic, which are 80.84738,

*Sources: Author's calculation.*

*\*5% level of significance.*

#### **Table 3.**

*Lag length criteria.*

**Table 4.** *Test of VAR stability.*

#### **Table 5.**

on the sequential modified LR test statistical criteria. The lag length that was

in lag 3, that is, with the sequential modified LR test statistic 24.77971, PPE

Therefore, the results of the IRF and VDC analyses are valid, so that the

The fourth stage that must be passed in the VECM estimation is the

method available in EViews 7.2 software with a critical value of 0.05. The

cointegration test results are shown in **Table 5** as follows.

cointegration test. Cointegration tests are conducted to determine whether there is a long-term relationship on each variable. If there is no cointegration relationship, the VECM estimation cannot be used. This study uses the Johansen cointegration test

Based on **Table 5**, at the 5% test level, there are three ranks of cointegration variables. This can be proven from the values of trace statistic, which are 80.84738,

**Lag LogL LR FPE AIC** 502.5902 NA 4.943996 10.11180 491.1235 22.01603 4.706602 10.06247 479.1256 22.31603 4.435183 10.00251 465.3591 24.77971\* 4.037246\* 9.907182\*

**Root Modules** 0.165181–0.446285i 0.475873 0.165181 + 0.446285i 0.475873 0.239743–0.404530i 0.470235 0.239743 + 0.404530i 0.470235 0.239164–0.036076i 0.241869 0.239164 + 0.036076i 0.241869

Based on **Table 3**, the optimal lag on all variables from FDR, NPF, and BOPO is

The stability test of the VAR model was used to test IRF and VDC. The stability

Based on **Table 4**, it can be explained that the model used is stable in lags of 0–3. This can be seen from the range of modules with an average value of less than one.

4.037246, and AIC 9.907182. Therefore, the optimal lag has been statistically deter-

included in this study is from 0 to 3.

*4.1.3 Stability VAR model test*

*Banking and Finance*

cointegration test can be done.

*4.1.4 Cointegration test*

*Sources: Author's calculation. \*5% level of significance.*

*Sources: Author's calculation.*

*Test of VAR stability.*

**Table 3.** *Lag length criteria.*

**Table 4.**

**60**

mined and the VAR stability test is carried out.

test for VAR estimation can be seen in **Table 4**.

*Cointegration test.*

36.79544, and 12.11161 and which are greater than the critical value of 0.05, namely, 29.79707, 15.49471, and 3.841466, respectively. In this regard, H0 is rejected and H1 is accepted. It implies that all variables have influence in the long term or are cointegrated with each other. Therefore, the next step is to carry out analysis with the VECM estimation.


*2.5.2. Sample preparation and aflatoxin determination*

Aflatoxin analysis was carried out using immune-chromatographic assay Reveal Q+ mreader according to the manufacturer's recommendation. Prepared groundnut samples (500 g each) were ground finely using the Agri-Grind grinder until fine particles and homogeneity were obtained. Then, a subsample of 10 g was obtained from each of the composite samples. The subsample was aliquoting in 35 ml of 65% ethanol, and the contents were mixed gently by shaking the holding tube manually. After filtration of the blended subsample, 100 μl of the filtrate was mixed with 500 μl diluent solution in a dilution vial. After obtaining a fine mixture, a 100 μl extract of the aliquoted mixture was collected and added to a separate vial. Finally, a reveal Q+ test strip was placed in the vial containing the aliquoted mixture and was left to develop for 6 min. The test strip was later placed in the mreader holder, and the aflatoxin contamination levels of the sample were determined using the mreader based on the chromatographic characteristics of the sample in the strip. The data were statistically analyzed using GenStat Discovery 4. An independent Tukey's test was used to compare the means of the aflatoxin results. The tests for relationships were carried out using the Pearson Correlation Index, and the interpretation was performed at two-sided 95% confidence limit.


Opioids - From Analgesic Use to Addiction

*Edited by Pilar Almela Rojo*

Published in London, United Kingdom

### *Supporting open minds since 2005*

Opioids - From Analgesic Use to Addiction http://dx.doi.org/10.5772/intechopen.73905 Edited by Pilar Almela Rojo

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Pilar Almela Rojo, M. Luisa Laorden, Juan Antonio García-Carmona, Elena Martínez-Laorden, María Victoria Milanés, Javier Navarro-Zaragoza, M. Victoria Milanés, Marta Rodriguez-Arias, M Carmen Blanco-Gandia, Sandra Montagud-Romero, Shrenik Ostwal, Pamela Bolyanatz

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**Energy Efficient Cities of Today and Tomorrow**

Printed Edition of the Special Issue Published in *Energies* Jukka Heinonen, Sanna Ala-Mantila and Ortzi Akizu-Gardoki Edited by

www.mdpi.com/journal/energies


*Article* **Estimation of Energy Recovery Potential from Primary Residues of Four Municipal Wastewater Treatment Plants**

**Eleni P. Tsiakiri 1 , Aikaterini Mpougali 1 , Ioannis Lemonidis 1 , Christos A. Tzenos 2 , Sotirios D. Kalamaras 2 , Thomas A. Kotsopoulos 2 and Petros Samaras 1,\***

**Abstract:** Wastewater treatment plants have been traditionally developed for the aerobic degradation of effluent organic matter, and are associated with high energy consumption. The adoption of sustainable development targets favors the utilization of every available energy source, and the current work aims at the identification of biomethane potential from non-conventional sources derived from municipal wastewater treatment processes. Byproducts derived from the primary treatment process stage were collected from four sewage treatment plants in Greece with great variation in design capacity and servicing areas with wide human activities, affecting the quality of the influents and the corresponding primary wastes. The samples were characterized for the determination of their solids and fats content, as well as the concentration of leached organic matter and nutrients, and were subjected to anaerobic digestion treatment for the measurement of their biomethane production potential according to standardized procedures. All samples exhibited potential for biogas utilization, with screenings collected from a treatment plant receiving wastewater from an area with combined rural and agro-industrial activities presenting the highest potential. Nevertheless, these samples had a methanogens doubling time of around 1.3 days, while screenings from a high-capacity unit proved to have a methanogens doubling time of less than 1 day. On the other hand, floatings from grit chambers presented the smallest potential for energy utilization. Nevertheless, these wastes can be utilized for energy production, potentially in secondary sludge co-digestion units, converting a treatment plant from an energy demanding to a zero energy or even a power production process.

**Keywords:** screenings; fats; biogas potential; wastewater treatment plant; energy utilization; anaerobic digestion

### **1. Introduction**

The activated sludge process has been identified as an efficient method for the treatment of a wide range of wastewaters for a long time. The process is based on the aerobic degradation of organics, while pretreatment is required for the upstream removal of suspended solids contained in raw wastewaters. The design of a wastewater treatment plant is mainly carried out in order to satisfy the corresponding effluent quality regulations while less efforts are taken towards energy requirements. Effluent quality is achieved at the cost of significant energy consumption. Aerobic processes are highly energy-demanding techniques with an average energy input reported to range from 0.30 to 1.89 kWh/m3 depending on the treatment method used and the influent properties [1]. Secondary aeration accounts for about 50% of the total electricity demand and 25–40% of the plant operating costs [1–3]. Wastewater treatment plants are considered as the highest municipal

**Citation:** Tsiakiri, E.P.; Mpougali, A.; Lemonidis, I.; Tzenos, C.A.; Kalamaras, S.D.; Kotsopoulos, T.A.; Samaras, P. Estimation of Energy Recovery Potential from Primary Residues of Four Municipal Wastewater Treatment Plants. *Sustainability* **2021**, *13*, 7198. https:// doi.org/10.3390/su13137198

Academic Editor: Farooq Sher

Received: 1 June 2021 Accepted: 23 June 2021 Published: 27 June 2021

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

energy consumers [4]. This issue is becoming crucial since the overall energy demand by wastewater treatment plants in European countries is estimated at 27 TWh/yr [5].

The increase of electricity costs in combination with the awareness of climate change has given rise to efforts aiming at the development of energy conservation policies and the implementation of energy-efficient measures that can contribute to the international sustainability development goals. Anaerobic digestion of excess sewage sludge represents a common practice in activated sludge processes, developed rather as a method of stabilization of wasted sludge than focusing on its energy valorization. Dedicated methodologies have been applied including energy surveillance, benchmarking, and auditing tools adapted to wastewater treatment plants, resulting in 20–40% savings in energy consumption [6]. However, these methods ignore the inherent energy content of raw wastewaters.

The energy content of raw wastewater has been measured by bomb calorimetry at about 14.7 kJ/g COD, exceeding almost nine times the electricity demand for its aerobic treatment [7]. Taking into account a daily production of about 100 g COD/person, the energy content of wastewaters for a city with 1 million inhabitants is estimated at around 1470 MJ/d; these estimations are carried out without considering the energy content of industrial wastewaters, while recent calculations report an energy content chemically bound to influents exceeding 153 KWh/person equivalent-year [8,9]. Nevertheless, the benefits of energy utilization of the contents of raw influents have not been given much attention so far, due to the traditional concept of wastewater considered as a waste requiring energy for its safe disposal and not as a valuable resource. Energy harvesting from raw influents might support efforts towards self-energy efficiency of wastewater treatment plants, shifting them from energy consumers to zero-energy plants or even to power producers.

Traditionally, anaerobic digestion of excess sludge is the primary energy harvesting method often applied in wastewater treatment plants. However, an alternative potential energy source is represented by the primary screenings including papers, wood, plastics, stones, metal pieces, rag, etc., and byproducts such as fats, oils, and grease (FOG). These materials can be directly valorized since they are separated during the primary treatment stages in existing units, without the need for the installation of additional facilities. Screenings are currently disposed in sanitary landfills, representing an additional operation cost while contributing to GHG emissions during their biological degradation in landfills [10].

The energy utilization of these byproducts has received less interest mainly due to their small amount compared to the much larger amounts of excess sludge [11]. For example, about 1.5 kg/person-equivalent of screenings have been estimated for 2007 in Germany [12], while in another study in France, average production was estimated to range from 0.53 to 3.49 kg/person [11]. However, the amount of screenings and FOGs is expected to increase due to intense urbanization, the enforcement of more strict EU regulations related to primary treatment yields, and the application of measures to alleviate the pressure due to increased influent loadings bringing a wastewater treatment plant close to the design capacity [13]. Moreover, the utilization of every available energy resource has been recently re-examined for various reasons. These include the development of advanced technological innovations for fine screening (enhancing screening removal), which is a pre-requirement in advanced membrane bioreactor units, as well as the adoption of sustainability principles by EU countries, which are associated with less waste diverted to landfills and the utilization of non-conventional wastes for energy and resource recovery [14,15].

Anaerobic digestion represents a challenging method for the energy valorization of non-conventional wastes from wastewater treatment plants, which is favored since it is a process conventionally applied for excess sludge treatment. However, very few studies have been reported in the literature dealing with the examination of biogas production potential of screenings and FOGs, mainly due to the non-homogeneous character of these wastes and the utilization of FOGs for biodiesel production [11,16]. The concentration of volatiles solids in screenings may exceed 90% of total solids [13,17], resulting in biogas production as high as 0.62 L/kg vs. [18]. The application of fine screenings in a municipal wastewater treatment plant and the following anaerobic digestion demonstrated a 40% reduction of energy demand in the Netherlands [19]. On the other hand, the addition of FOGs collected from restaurants in a municipal sludge digester resulted in a 30 to 80% increase in biogas production [20].

Nevertheless, the biomethane production rate is greatly affected by the composition of screenings and FOGs. The characteristics of these wastes are related to a great number of factors such as the presence of a combined or separated sewer system, the number and the type of the sewer system pumping stations upstream to the treatment plant, the catchment area, and the primary stage installations. In addition, the properties of the wastes can be varied due to specific climatic conditions, consumers behavior, and time frameworks, including seasonal, weekly, or daily dimensions [11].

The objectives of this work include the examination of energy valorization of nonconventional wastes produced from municipal wastewater treatment plants, the determination of the corresponding biomethane potential during anaerobic digestion, and the identification of the relation to their composition and the type of primary treatment stage configuration. The primary target of the work is the justification of the beneficial role of screenings and FOGs towards energy utilization, as an alternative to currently used management methods of these side streams.

#### **2. Materials and Methods**

#### *2.1. Samples Collection*

Samples were collected from different areas of the primary treatment stage of four wastewater treatment plants (WWTP) located in Northern Greece, with various design capacities and servicing areas including a wide range of human activities. Samples identification and information on their origin are provided in Table 1.

**Table 1.** Identification of samples collected from the primary treatment stage of four wastewater treatment plants and their characteristics.

About 1 kg of each sample was collected, placed in plastic bottles, and transferred to the laboratory for further analysis. Samples were stored at 4 ◦C in a constant temperature refrigerator until the time of analysis. Prior to storage, samples were subjected to milling using a knife mill in order to receive particles of similar size of about 0.1 mm.

#### *2.2. Chemical Analysis*

The analysis of the samples took place for the determination of total and volatile solids, and fats using standard methods, i.e., drying at 105 ◦C for total solids; thermal treatment at 550 ◦C for volatile solids; and Soxhlet extraction for total fats [21]. Water-leached organic matter and nutrients concentrations were determined by the addition of 0.3 g of dry

solids in 20 mL of deionized water and stirring for 20 min, followed by centrifugation and determination of COD, N-NH4, and P-PO4 in the aqueous phase. Parameters were measured using a HACH-Dr Lange DR3900 spectrophotometer and the corresponding standard cuvette test kits, i.e., the LCK714 COD kit, the LCK303 ammonium kit, and the LCK049 orthophosphates test kit, respectively.

#### *2.3. Biochemical Methane Potential*

The biochemical methane potential (BMP) was determined by anaerobic digestion treatment performed in batch reactors. Glass reactors with a total volume of 322 mL and a working volume of 120 mL were used. In each reactor an amount of substrate containing 1 g of vs. was added followed by the inoculum to reach a working volume of 120 mL and achieve 202 mL headspace. Inoculum was collected from the anaerobic digester of the municipal wastewater treatment plant No. 4, with the highest design capacity operating for a long period. The glass reactors were sealed using rubber stoppers and aluminum caps suitable for retrieving gas samples. In addition, a blank sample was prepared, containing 120 mL of pure inoculum. The treatment for each of the 12 substrates along with the blank were carried out in triplicates. All reactors were initially flushed with pure nitrogen gas (N2), in order to ensure anaerobic conditions. The batch reactors were incubated at a temperature of 37 ± 1 ◦C for 80 days.

The production of methane (CH4) was determined by injecting gas samples from the reactors into a gas chromatographer (GC-2010plusAT, SHIMADZU, Kyoto, Japan) equipped with an appropriate detector and columns [22]. For each sample, 150 µL of gas were acquired from the headspace of the reactor with a gas-tight syringe outfitted with a pressure lock. During the first 10 days the reactors gas composition was monitored daily and after that on a bi-daily schedule. A standard gas mixture (60% CH4, 40% CO2) was utilized to determine the % concentration of CH4 of each gas sample. The obtained peak area was compared to that of a standard gas mixture (60% CH4, 40% CO2) injected at atmospheric pressure in the chromatographer. The calculation of the volume of the produced CH4 was carried out by the multiplication of the headspace volume of each reactor with the % concentration of CH4 of each gas sample [23].

For each substrate, the maximum specific growth rate of the methanogens (µmax) was derived from a graph of the natural logarithm of methane (CH4) production as a function of time, and calculation of the maximum value from the tangent's angle was conducted [24]. The methanogens' maximum doubling time (Tdoublemax) was calculated as the quotient of the natural logarithm of 2 (ln2) divided by the methanogens µmax [25].

#### **3. Results**

The content of primary samples in total and volatile solids and fats is shown in Figure 1. Efforts were taken to collect all samples at the same time period, in order to exclude potential seasonal variations. As shown, samples presented high total solids content, while volatile solids ranged from as low as 20% up to 90% of the total solids.

In addition to solid and fat content, a significant role in the energy valorization of samples through anaerobic fermentation is played by the composition of leachable organic matter, as well as the concentration of nutrients, i.e., nitrogen and phosphorous; these data are provided in Figure 2 for the various samples.

Biomethane production potential (BMP) represents a crucial parameter for the assessment of energy valorization of samples by anaerobic fermentation. BMP is illustrated in Figure 3 in mL of methane produced per g of vs. for the various samples as a function of fermentation time, while total net methane production in L/kg vs. is given in Table 2, excluding the corresponding methane produced by the inoculum, i.e., the blank sample.

*Sustainability* **2021**, *13*, x FOR PEER REVIEW 5 of 14

**Figure 1.** Total solids, volatile solids, and fats content in primary treatment samples from four WWTPs. **Figure 1.** Total solids, volatile solids, and fats content in primary treatment samples from four WWTPs. ganic matter, as well as the concentration of nutrients, i.e., nitrogen and phosphorous; these data are provided in Figure 2 for the various samples.

**Figure 2.** Leached COD, nitrogen, and phosphorous content in primary treatment samples from four WWTPs. **Figure 2.** Leached COD, nitrogen, and phosphorous content in primary treatment samples from four WWTPs.

**Figure 2.** Leached COD, nitrogen, and phosphorous content in primary treatment samples from

excluding the corresponding methane produced by the inoculum, i.e., the blank sample.

Biomethane production potential (BMP) represents a crucial parameter for the assessment of energy valorization of samples by anaerobic fermentation. BMP is illustrated

Biomethane production potential (BMP) represents a crucial parameter for the assessment of energy valorization of samples by anaerobic fermentation. BMP is illustrated in Figure 3 in mL of methane produced per g of vs. for the various samples as a function of fermentation time, while total net methane production in L/kg vs. is given in Table 2, excluding the corresponding methane produced by the inoculum, i.e., the blank sample.

four WWTPs.

**Figure 3.** Biomethane production potential for the various samples collected from the four WWTPs of the study. **Figure 3.** Biomethane production potential for the various samples collected from the four WWTPs of the study.

**Table 2.** Total net methane production in L/kg vs. for each sample. **Table 2.** Total net methane production in L/kg vs. for each sample.

I 179.0224 3.8975 A crucial parameter in the efforts for the energy utilization of WWTPs residues is the time required to deliver an adequate amount of biogas, in relation to existing anaerobic fermenters of secondary sludge corresponding to sludge retention times of about 30 days. The kinetics of methane production for the various samples are shown in Figure 4, while A crucial parameter in the efforts for the energy utilization of WWTPs residues is the time required to deliver an adequate amount of biogas, in relation to existing anaerobic fermenters of secondary sludge corresponding to sludge retention times of about 30 days. The kinetics of methane production for the various samples are shown in Figure 4, while the calculated maximum specific growth rate µmax and methanogens doubling times are given in Figure 5.

the calculated maximum specific growth rate μmax and methanogens doubling times are

TPS 472.7396 48.0594

given in Figure 5.

**Figure 4.** *Cont.*

**Figure 4.** Time required for the production of 20, 40, 60, and 80% percentage vol. of total methane for the samples collected from WWTP No 1 (**a**), 2 (**b**), 3 (**c**), 4 (**d**). **Figure 4.** Time required for the production of 20, 40, 60, and 80% percentage vol. of total methane for the samples collected from WWTP No 1 (**a**), 2 (**b**), 3 (**c**), 4 (**d**).

(**d**)

**Figure 5.** Estimated μmax values and average methanogens doubling time as deduced from BMP curves of various samples. **Figure 5.** Estimated µmax values and average methanogens doubling time as deduced from BMP curves of various samples.

#### **4. Discussion 4. Discussion**

The aim of the study is the determination of the valorization potential of byproducts produced during the primary treatment of municipal wastewaters by the utilization of their energy content through anaerobic digestion. The BMP potential of the individual byproducts was utilized as an indication of their capacity for production of biogas; this parameter is commonly used for the estimation of the theoretical maximum potential of various wastes [26]. In addition, BMP represents a required preliminary step for the examination of the feasibility of anaerobic digestion of a wide range of wastes and products, and it has been applied in this study to elucidate the assessment of the properties of these unconventional energy sources. Such an approach will in addition reveal potential operation problems during the addition of screenings in sludge digestion, such as inhibition of the anaerobic biota resulting in negligible biogas production. On the other hand, successful results will enhance byproducts utilization, and expected potential benefits include the reduction of side streams amounts conventionally disposed in sanitary landfills, as well as suppression of aeration demands in the following activated sludge process in a wastewater treatment plant. Nevertheless, the amount of these byproducts favors their co-digestion in existing sewage sludge anaerobic digestion units rather than their treatment in individual reactors. Their co-digestion is expected to result in raising the biogas production rate compared to sludge treatment solely, accounting for about 300–400 mL/g vs. [27]. Additional effects on digestate quality should be encountered, as soon as the feasibility of the process will be justified through the estimation of BMP potential. Nevertheless, a study has been reported on the quality of digestate from anaerobically treated screenings which was similar to the corresponding one from sewage sludge, towards its valorization through phosphorous recovery [17]. The overall estimation of potential economic and energy revenues due to the introduction of these side streams in existing treatment plants requires an integrated assessment of all potential benefits expected, including The aim of the study is the determination of the valorization potential of byproducts produced during the primary treatment of municipal wastewaters by the utilization of their energy content through anaerobic digestion. The BMP potential of the individual byproducts was utilized as an indication of their capacity for production of biogas; this parameter is commonly used for the estimation of the theoretical maximum potential of various wastes [26]. In addition, BMP represents a required preliminary step for the examination of the feasibility of anaerobic digestion of a wide range of wastes and products, and it has been applied in this study to elucidate the assessment of the properties of these unconventional energy sources. Such an approach will in addition reveal potential operation problems during the addition of screenings in sludge digestion, such as inhibition of the anaerobic biota resulting in negligible biogas production. On the other hand, successful results will enhance byproducts utilization, and expected potential benefits include the reduction of side streams amounts conventionally disposed in sanitary landfills, as well as suppression of aeration demands in the following activated sludge process in a wastewater treatment plant. Nevertheless, the amount of these byproducts favors their co-digestion in existing sewage sludge anaerobic digestion units rather than their treatment in individual reactors. Their co-digestion is expected to result in raising the biogas production rate compared to sludge treatment solely, accounting for about 300–400 mL/g vs. [27]. Additional effects on digestate quality should be encountered, as soon as the feasibility of the process will be justified through the estimation of BMP potential. Nevertheless, a study has been reported on the quality of digestate from anaerobically treated screenings which was similar to the corresponding one from sewage sludge, towards its valorization through phosphorous recovery [17]. The overall estimation of potential economic and energy revenues due to the introduction of these side streams in existing treatment plants requires an integrated assessment of all potential benefits expected, including energy earnings from their utilization, reduction of landfilling costs, environmental costs revenues associated with fewer total GHG emissions, etc.

energy earnings from their utilization, reduction of landfilling costs, environmental costs revenues associated with fewer total GHG emissions, etc. According to the information provided in Table 1, samples were collected from four According to the information provided in Table 1, samples were collected from four WWTPs, with a wide range of design capacity, and servicing areas of different human activities. Selected WWTPs represented processes with a wide range of wastewater flowrates,

activities. Selected WWTPs represented processes with a wide range of wastewater

/d to values exceeding 155,000 m3

/d. In addition,

flowrates, ranging from as low as 8400 m3

ranging from as low as 8400 m3/d to values exceeding 155,000 m3/d. In addition, these units receive wastewaters from septic tanks reflecting, therefore, an additional contribution to screenings production. On the other hand, the composition of screenings was expected to vary due to the different origin of influents.

The lowest values of volatile solids were observed for the screenings collected during delivery of effluents from septic tanks transferred to one treatment plant by trucks and for the sewage screenings and the primary sludge screenings of the same WWTP. It seems that the volatile content of the samples can be attributed to their origin and the treatment stage: wastewater in septic tanks remains for a long time, subjected to anaerobic degradation of organic matter. Therefore, volatile solids in these effluents are expected to be lower than the corresponding solids removed in sewage treatment systems. On the other hand, the low volatile content of the screenings from the treatment plant with the highest capacity might be associated with the long sewage network system of the certain effluents, and their large transfer time from point of source to the treatment plant which might result in less organics content. Nevertheless, the fat content in the samples presented values reaching up to 30% of the total dry content, with great variation between the samples collected even from the same treatment plant. Similar values of volatile solids content have been reported in the literature ranging from 77 up to 95% of dry solids, depending on the screen size and the wastewater origin, with raw samples exhibiting considerably great variations in the moisture and the total solids content [11,17].

In addition to solids content, according to data given in Figure 2, high leached phosphorous and ammonia nitrogen contents were measured for the samples collected from the WWTP receiving effluents from an area with combined human activities, including extended agricultural areas and farming lands. Nevertheless, low leached organic matter values were observed in these samples, while the highest values of COD, up to 1000 mg/L, were measured for the other samples, without, however, an indication of potential trends due to the origin or wastewater characteristics. Limited studies related to the content of leached compounds from screenings have been reported, citing rather high COD values, ranging from 0.8 up to 1.6 g COD/g VS, close to theoretically estimated ones [28], while most studies include the elemental analysis of carbon, nitrogen, and phosphorous in screenings [13]. It must be underlined that biogas production potential is favored under certain ratios of organic matter: nitrogen:phosphorous and the presence of appropriate amounts of both carbon and nutrients sources is required for the efficient operation of anaerobic biocommunities. Although elemental nitrogen and phosphorous concentrations were not measured in this work, the corresponding leached contents of the nutrients were determined, as an indication of their presence in appropriate amounts and their availability towards the efficient operation of the anaerobes.

BMP results are given in Figure 3 as a function of reaction time, while the corresponding total net methane production is provided in Table 2. The methane potential is defined as the maximum produced methane of a specific substrate [29]; however, a methane production curve often presents an initial lag phase, and, therefore, the methane potential measurement for 80 days, as used in the study, provides valuable information about the requirement of a pretreatment step to speed up the whole process. As shown in Table 2, all samples exhibited methane production ranging from low values of around 90 L/kg vs. up to 740 L/kg vs. observed for fine screenings. Surprisingly, floatings from grit chambers had the lowest BMP of all samples from each wastewater treatment plant, although they were expected to deliver high biogas production potential due to their high content in fats (Figure 1) and the corresponding process stage where these samples are collected. As can be seen in Figure 1, fats represent a small fraction of the organic matter, and it is assumed that organic compounds other than fats in these samples were not easily assimilated by the anaerobes towards biogas production. In addition, it has been reported that the complicated composition of floatings containing low density materials such as cellulosic fibers can greatly affect the corresponding energy utilization available for anaerobic digestion [19], while methanogens can convert only a fraction of organics to

biogas ranging from 50 to 60% [10,30]. On the other hand, methane production has been reported to be inhibited due to the formation of long-chain fatty acids during fats anaerobic degradation [31]. Nevertheless, the low BMP potential of floatings from the other two treatment plants is in line with their low content of fats.

Screenings from the plants located in urban areas were similar or slightly higher than the corresponding BMP potential of floatings, while large differences were observed in BMP values of screenings collected from treatment plants receiving effluents from areas with combined activities. The highest methane potential values were measured for the fine and the coarse screening samples from the plant with agro-industrial activities. This may be attributed to various reasons, such as the short distance of the sewage network and the corresponding short time of effluents travelling to the treatment plant, which is allowing less washing and degradation of the compounds, or the presence of potential effluents from agricultural and farming lands in the municipal effluents with a high methane production capacity. Moreover, samples originating from the primary sludge screen presented a rather high methane potential, the highest of the samples obtained from the certain treatment plant. This is a valuable indication of the high energy content of that sludge which is currently disposed together with the secondary anaerobically treated sludge in composting units, with loss of the contained energy content. Efforts were taken to identify potential relations of BMP values shown in Figure 3 to the corresponding chemical composition of the samples in Figures 1 and 2, but no significant trends were observed.

It should be mentioned that substrates obtained from wastes and residues of municipal wastewater treatment plants may have considerable methane potential, depending on their origin and the wastewater treatment stage: anaerobic digestion of FOGs resulted in the production of 271 to 344 and from 325 to 681 mL of methane per g of vs. added, corresponding to samples with volatile solid content up to 30% and 60%, respectively [20]. Similar results regarding methane production capacity were observed by screenings fed to a continuous anaerobic bioreactor ranging from 197–512 mL of CH4/g vs. with 41.5% total and 29.4% volatile solids content [32]. Nevertheless, wastewaters from livestock production represent more efficient substrates, as they contain higher amounts of total solids and fatty compounds per m3 of raw material than municipal wastewater: The theoretical biomethane potential from fats is estimated to be about 990 mL/g, while that from proteins is about 640 mL/g vs. and from hydrocarbons is about 415 mL/g vs. [33]. Although residues from wastewater treatment plants may have lower biogas potential than wastes of livestock production, the benefits from the utilization of the energy content is profound, considering the current methods of handling, including either disposal in sanitary landfill or incineration in municipal facilities.

Data in Figure 4 indicate the time required to receive a certain volume percentage of the total methane production, i.e., 20, 40, 60, and 80%, for each sample. The wider a column, the longer the time required to produce the corresponding methane volume, while shorter columns and less wide bars represent samples producing methane in short times. Similar observations can be drawn from the results shown in Figure 5, where µmax and methanogens doubling time are reverse parameters, the latter corresponding to the time required for doubling the cells of the anaerobic micro-organisms. The lower the methanogens doubling time, the higher the maximum growth rate µmax.

As shown in Figure 4, more than 50% of gas volume is produced at short reaction times, while production of up to 80% of total gas required longer time, depending on the particular sample. Samples collected from the WWTPs with low design capacities required rather long times to reach up to 80% volume of methane, exceeding 70 days, while the shortest times were observed for the residues from the WWTP in the agricultural area, varying between 15 and 30 days (although floatings may require as long as 70 days). Moreover, 60% of total gas volume was already produced in a period of less than 10 days for these samples, and a similar behavior was observed for the corresponding samples from the high-capacity treatment plant. However, slow kinetics were obtained for the residues from the other plants.

These results are in line with the corresponding data on average methanogens doubling time given in Figure 5, where short times were calculated for the high design capacity unit, ranging from 0.8 to 1.13 days, followed by the agricultural area treatment plant with slightly higher methanogens doubling times from 1.34 to 1.53 days. The highest methanogens doubling times were measured for the low-capacity plant with semiindustrial characteristics, reaching up to 2.38 days, almost three times higher than the lowest value. The above observations are becoming important for the energy recovery of these substrates during co-digestion with secondary sludge in these units. The low methanogens doubling time is associated with short retention times for the treatment of these substrates, which could strongly affect the design of anaerobic reactors in a new WWTP by requiring smaller reactor volumes. In addition, the range of the µmax values and consequently of the doubling time is within that reported for a wide range of samples [22,34], and, therefore, the methanogens' growth rate was not differentiated due to the particular substrates used in this study.

Taking into account the BMP results presented in Table 2 and Figure 3 and the corresponding kinetic data in Figures 4 and 5, the beneficial role of the corresponding samples as potential energy sources could be identified. In general, all samples represent promising materials for energy recovery and the enhancement of energy production processes in the corresponding wastewater treatment plants. Nevertheless, efforts to identify the samples with the highest potential for biogas production should take into consideration both biogas cumulative volume and biota doubling time: under that framework, the fine and coarse screenings from the wastewater treatment plant receiving effluents from areas with mixed activities represent the best candidates for energy recovery through anaerobic digestion, followed by the primary sedimentation sludge screenings and the coarse screenings of the high flowrate municipal treatment plant. Both plants have already under operation an anaerobic digestion plant of secondary sludge, and the proposed energy utilization of their primary residues might represent an easy-to-apply process aiming at their energy self-efficiency.

**Author Contributions:** Conceptualization, P.S. and T.A.K.; methodology, A.M., I.L., C.A.T., and E.P.T.; validation, S.D.K., T.A.K., and P.S.; writing—original draft preparation, C.A.T. and S.D.K.; writing review and editing, S.D.K., T.A.K., and P.S.; supervision, T.A.K. and P.S.; project administration, P.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was co-financed by the European Regional Development Fund of the European Union and Greek national funds through the Operational Program Competitiveness, Entrepreneurship and Innovation, under the call RESEARCH—CREATE—INNOVATE (project code T1EDK-00284).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.

**Acknowledgments:** This research was co-financed by the European Regional Development Fund of the European Union and Greek national funds through the Operational Program Competitiveness, Entrepreneurship and Innovation, under the call RESEARCH—CREATE—INNOVATE (project code T1EDK-00284).

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

*Article*


*(a) Data Collection*

At this stage, the main inputs to the design process are gathered: topographic information, renewable resources (with special attention to wind resource, which is usually more difficult to evaluate), consumption characterization (crucial), and technical and economic information of the equipment. In projects of a certain size, it is a common practice to carry out field campaigns for both the wind resource and the consumption characterization [38].

In the case of performing a measuring campaign, in order to summarize the high quality requirements in wind measurement, international standards have been developed, such as the MEASNET guidelines. MEASNET is an international network of measurement institutes, which developed the guideline "Evaluation of site-specific wind conditions". This guideline describes the process of site assessment including data collection, evaluation, and interpretation. The MEASNET guideline refers to IEC 61400-12-1 and focuses on data quality, plausibility, and integrity [39].

Even for SWT there are some guidelines available for site assessment, such as [40], that covers most of the aspects that may apply when considering the inclusion of a SWT in a system. More detailed guidelines for site turbulence influence on the SWT estimated production can be found in dedicated guidelines, such as [15], for example.

However, one of the main limitations for taking into account wind generation in REDPS in the range that is being considered in this work is commonly the lack of reliable wind data necessary to evaluate its convenience. Nowadays, there are both global and local (usually at a national level) wind atlases. In this case, the no-data situation, which was not rare a few years ago, is almost extinguished. However, in order to perform a minimum performance evaluation of wind generation within a REDPS, it is not the case that any wind resource characterization will be valid: characterization needs to include spatial and temporal information in the most detailed possible manner. It should be remembered here that, of course, the best method to achieve this goal is an on-site wind measurement campaign, but it is precisely the case of not having this campaign that it is being covered at this point.

At least hourly average wind speed variation is needed to be able to assess the wind generation in a REDPS in order to evaluate its matching with load and other forms of generation profiles from an energy balance point of view. Other short-term phenomena (dynamics and/or transients) would require even higher time resolutions, but they are out of the scope of this particular application since there is long-term storage.

Global and local wind atlases may only bring information on the overall yearly wind regime [41] or even on the monthly average wind speed [42]. In the latter, some software (such as HOMER Pro) may generate hourly synthetic series from monthly average values of wind speed, so they might be a first approach. For the site assessment, wind direction estimation is also necessary. Global Wind Atlas [41] provides an overall wind rose.

The news on this topic is the availability of reanalysis data derived from satellite observations are described in Section 2.1.3 (a) in this paper, both globally and freely, and provides relatively sufficient time resolution (one hour) wind speed and wind direction data but with an insufficient spatial resolution of several square kilometers. However, there is a possibility to use these data as an input for downscaling (considering also the available information on roughness and DEM, Digital Elevation Models) by generating higher spatial resolutions down to several hundred meters. Although all these sources of information are freely available so that anyone could produce these results (these are good news for SWT), some commercial tools exist that allow performing it in an easier manner. As a reference, EMD in Europe and UL in the US offer different software solutions to obtain hourly wind resource estimation for any point (Windographer and WindNavigator, in the case of UL; WindPro, for EMD) with a reasonable spatial resolution: UL offers a Typical Year Time Series Short term data set using the AWST MASS model and scaled to 200 m resolution to represent a 365 day sample from a 15 year period [22], while with EMD's full windPRO modeling chain, it is possible to downscale the data from the global level to the mesoscale level and, further, to the microscale level (e.g., using the windPRO scaler options) to a 250 m resolution or even 100 m resolution with WAsP [21].

These two software groups also offer two particular applications that are especially suitable for the assessment of SWT in REDPS: myWindTurbine (EMD, [28]) was designed for the evaluation of the influence of obstacles in SWT production which, as it was mentioned in Section 2.1.3 (a), is a key issue for SWT; and HOMER Pro (recently acquired by UL, [29]), which is the reference for REDPS optimization, as it described in Section 2.1.3 (c). In its latest version of HOMER Pro 3.14.2 (10 August 2020), there is a link to WindNavigator ([43], UL software for wind resource estimation) that, while it is not yet available, opens the door to connect both applications.

One estimate of the cost to have a site modeled in the United States in 2016 was approximately \$500. The model utilizes static wind maps, which is a gross approximation using annual average site wind speed and micro-site adjustments [17]. A characterization using myWindTurbine software costs around 60 EUR/site [28]. However, care should be taken with respect to the temporal needs in REDPS previously described, which may not be covered by these solutions.