REMOVAL AND FATE OF SPECIFIC MICROBIAL PATHOGENS WITHIN ON-SITE WASTEWATER TREATMENT SYSTEMS
Untreated or improperly treated wastewater has often been cited as the primary contamination source of groundwater. Decentralized wastewater treatment systems have applicability around the world since it obviates the need for extensive infrastructure development and expenditures. The use of a sand filter, a submerged flow constructed wetland and an aerobic treatment unit to remove bacterial and viral pathogens from wastewater streams was evaluated in this study. Salmonella sp. and a bacteriophages tracer were used in conjunction with the conservative bromide tracer to understand the fate and transport of these organisms in these treatment systems. Viral transport patterns in the sand filter and constructed wetland had a correlation of 0.8 (P< 0.05). In the constructed wetland, the virus exhibited almost a 3-log reduction, while in the sand-filter, the viruses exhibited a 2-log reduction. The bacterial tracers, however, did not exhibit similar reductions. Low numbers of bacteria and viruses were still detectable in the effluent streams suggesting that disinfection of the effluent is critical. The survival of the tracer bacteria and viruses were as expected dependant on the biotic and abiotic conditions existing within the wastewater. The results suggest that the microbial removal characteristics of decentralized wastewater treatment systems can vary and depend on factors such as adsorption, desorption and inactivation which in turn depend on the design specifics such as filter media characteristics and local climatic conditions.