Wastewater effluent in Israel was sampled in six reservoirs during different seasons. All the reservoirs were tested for biological oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), light transmission, temperature, pH, dissolved oxygen (DO), chlorophyll - a, phytoplankton, Zooplankton, as well as microbiological indicators (E.coli. enterococci, heterotrophic bacteria and F+ bacteriophages). The mean reduction of COD, BOD and TSS was 72%, 76% and 45%, respectively and the mean levels at the entrances to the reservoirs were 380 mg/l, 230 mg/l, and 265 mg/l, respectively. The percent reduction of the various microorganisms tested at the entrance to the reservoir and in the reservoir itself ranged between 83.2% and 99.98%. Significant correlation coefficients were found between the concentrations of the various microbiological indicators tested, as well as between the number of indicator microorganisms and pollution parameters (BOD, COD and TSS). A good correlation was found between BOD vs. COD, BOD vs. TSS, and TSS vs. COD. From this preliminary study it may be concluded that a) storage of wastewater in the reservoirs improves the quality of the effluent, and b) changes in physico-chemical parameters and the concentration of enteric microorganisms are significantly correlated.

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