The Removal of Faecal Coliforms in Waste Stabilization Pond Systems and Eutrophic Lakes

The reuse of domestic wastewater presents many challenges, including the risk of pathogen infection and algae is known to play a crucial role in the process of bacteria removal by raising the pH and dissolved oxygen concentration. However the role of algae is still not fully understood. The importance of faecal coliform (FC) attachment to algae in a hybrid pond system of algae and duckweed treating raw domestic wastewater, the effect of varying algal concentration on FC removal in wastewater and a eutrophic lake were investigated. Algae helped in sedimenting FC to the bottom of reactors. It was shown by experimentation that an optimum algal density exists at which maximum FC removal is achieved. FC numbers in duckweed ponds correlated strongly with ostracod numbers in ponds. FC attachment to suspended matter was important only in the first two ponds of the hybrid pond system and system performed well in FC (4.3 log units) and BOD (89%) removal, making it ideal for integration with aquaculture in developing countries. Algae achieved significant reduction in Escherichia coli contamination in the eutrophic lake. At algal density <=0.08mgL-1, decay rate of E. coli was directly proportional to the chlorophyll a concentration of the lake.