The effect of reservoir operational features on recycled wastewater quality

Israel's wastewater recycling program is unprecedented internationally, with close to 80% of sewage treated and reused in agriculture. This article presents findings from a national survey of Israel's wastewater reservoir network. Israel's extensive reuse of wastewater is possible due to a national network of reservoirs that has been established in recent years. Sixty effluent reservoirs presently operating in all parts of Israel, were reviewed and evaluated for static data and sampled for water quality analysis during the intensive irrigation season of 2008. The measurement of 16 chemical, physical and biological parameters, along with 21 major and trace elements was carried out, revealing a wide range of concentrations that reflect reservoir physical and operational characteristics. Results indicate that 65% and 78% of the supplied wastewater volume met the old 20 mg/L BOD and 30 mg/L TSS regulations for unlimited irrigation. With reference to Israel's updated, more stringent, regulations, only 22% and 28% of the supplied wastewater volume met the new TSS and E.C. regulations for unlimited irrigation, respectively, and only 48%, 58%, 58% and 62% met the new BOD, fecal coliforms, chloride and sodium regulations for unlimited new irrigation, respectively. All measured major and trace elements were well under existing standards, although there were considerable regional variation. Both principal component analysis and redundancy analysis were used to examine how the wastewater quality relates to multiple static construction features and operational parameters of the studied reservoirs. Sewage treatment plant technology, along with the reservoir operational regime, were found to have the greatest influence on the organic, nutrient and suspended solids loads of the wastewater supplied. The geographic location of the reservoirs along with their designed area to volume ratio, were found to have the largest influence over salinity components loads. Careful consideration should be given to the aforementioned features in future the reservoir planning process.