Significance of Algae in eliminating and deactivating pathological index Organisms in Wastewater Stabilization Pond Systems

Abstract

Wastewater stabilization ponds (WSPs) are an economical alternative to conventional wastewater treatment technologies. They are commonly favored by small and rural communities. Due to long hydraulic retention time required by the treatment in these systems, algal activity is often expected during summer season. This study investigated the effects of algal growth on the removal and inactivation of pathogenic indicator organisms in WSP systems. Two predominant algae species (Mougeotia sp. and Nostochopsis sp) that were found in Iraq (Alkhademiyah sewage station in Baghdad) WSP were able to increase both pH and DO. The highest inactivation rates of both E. coli and total coliforms (TC) were observed at pH 10.6 compared to other pH (5.1, 8.2, 8.4, 10.6) investigated in the bench-scale experiments. Both high (20mg/L) and low DO (1 mg/L) levels can facilitate the removal and inactivation of both E. coli and TC. Enterococci were significantly reduced at both intermediate (8.6 mg/L) and high (20 mg/L) DO concentrations. Therefore, the presence of algae can potentially promote the removal of E. coli, TC and Enterococci. Much higher inactivation of E. coli, TC and Enterococci at a higher temperature (20°C) than at a lower temperature (4°C) indicates temperature is one the most important removal factor. Two potential/additional indicator organisms (Enterococci and Clostridium perfringens (C. perfringens)) exhibited different inactivation trends than the traditional indicators (E. coli and TC) under the same pH and DO conditions. C. perfringens were tolerant to all the tested pH, DO and temperature conditions. Their resistance to environmental stresses may pose potential health risk. Hence, both Enterococci and C. perfringens could be potentially used as indictor organisms to predict the overall level of pathogens in treatedwastewater.