On-line version ISSN 1816-7950
Water SA (Online) vol.35 no.2 Pretoria 2009
LC RietveldI, *; L MeijerII; PWMH SmeetsIII
On-line version ISSN 1816-7950
Water SA (Online) vol.35 no.2 Pretoria 2009
LC RietveldI, *; L MeijerII; PWMH SmeetsIII; JP van der HoekIV
IDelft University of Technology, Department of Water Management, PO Box 5048, 2600 GA Delft, The Netherlands
IIEvides, PO Box 4472, 3006 AL Rotterdam, The Netherlands
IIIKWR, Groningenhaven 7, 3422 PE Nieuwegein, The Netherlands
IVWaternet, PO Box 94370, 1090 GJ Amsterdam, The Netherlands
Wastewater reuse is becoming increasingly important for supplementing drinking water supply needs and/or to reduce costs in many communities around the world. However, wastewater reuse can result in a potential transmission route for infectious agents. Therefore, the occurrence of Cryptosporidium was assessed in a treatment plant geared for the production of drinking water from wastewater effluent and the results were compared to those on an existing typical drinking water treatment plant operated by Waternet, the water cycle company of Amsterdam, The Netherlands, and its surrounding areas. The assessment was done using Monte-Carlo simulation and probability density functions to determine the occurrence of Cryptosporidium in raw surface water and wastewater effluent and the removal in different treatment steps. From the research conducted, it was concluded that under normal conditions, drinking water that meets Dutch drinking water quality standards could also be produced from treated wastewater effluent. However, additional redundancy should be built in to meet the standards under extreme operating conditions.
Keywords: risk assessment, wastewater reuse, drinking water treatment
Wastewater reuse is increasingly becoming important for supplementing drinking water supply needs and/or to reduce costs in many communities around the world such as Windhoek-Namibia (Van der Merwe, 2006), Emahlaleni-South Africa (Gunther, 2006) and Wulpen-Belgium (Van Houtte and Verbauwhede, 2008). Wastewater reuse as an option becomes necessary and possible because of the increased environmental constraints, such as droughts and water scarcity, and the fact that wastewater discharge quality regulations have become stricter leading to a better water quality. Wastewater reuse practices have also become technically more feasible (Casani et al., 2005). However, wastewater reuse can result in a potential transmission route for infectious agents that are associated with human wastes and/or the presence of priority pollutants, endocrine disrupting compounds, pharmaceutically active compounds, or other unregulated trace compounds (Drewes et al., 2003). Reclamation plants must therefore be designed such that the desired effluent quality is consistently achieved. This should include built-in redundancy as a back-up when there is a problem (Cooper, 1991).
Drinking water should be free from substances with adverse health effects (e.g. organic micro-pollutants, pathogenic micro-organisms, disinfection by-products, salts, heavy metals and biofilm forming substances) and undesired substances (e.g. suspended particles). Therefore, drinking water treatment plants typically comprise several treatment steps - in a multi-barrier approach - to remove contaminants. In The Netherlands, artificial aquifer recharge is recognised as the most important barrier against pathogenic micro-organisms when producing drinking water from a surface water source. The infiltration areas for recharge are normally situated in coastal dune areas, which are relatively long transport distances away from the raw water source and the city, being a costly practice. Wastewater treatment plants are normally situated close to the city and could therefore provide an alternative raw water source for drinking water, thus avoiding the long transport distances between the dunes, raw water and the city. Treatment of wastewater in The Netherlands is continually improving, resulting in better treated effluent water quality similar to that of raw surface water. Therefore, combining wastewater and drinking water treatments could provide synergistic advantages. The question, however, is whether this alternative for drinking water production is a sustainable solution.
From recent studies it was concluded that current drinking water treatment practices in The Netherlands have a low environmental impact (Barrios et al., 2008; Tapia et al., 2008). Also, the costs of tap water are acceptable for the consumers. The most significant challenge for water utilities is to prevent consumers switching to bottled water. Bottled water is about 150 times more expensive than tap water and 30 times less environmentally friendly. In addition, wide variations in taste between tap water and bottled water are not detected by Dutch consumers (Consumentenbond, 2005), which means that the safety of drinking water consumption would prevail over cost reduction and environmental protection. It is therefore important to assess the health risk of different alternatives before deciding whether to switch to treated wastewater effluent as a source for drinking water production.
One of the emerging contaminants is Cryptosporidium. Cryptosporidium is a protozoan parasite that has been responsible for a number of negative public health outbreaks of diarrhoea in humans that have occurred through public water supply systems (Craun et al., 1998; Hrudey and Hrudey, 2004). This was due in part to the high infectivity of Cryptosporidium as well as to the resistance of the protozoan parasite to chemical disinfection. Subsequen