Investigation of constructed wetlands, lagoons and other treatment systems for reducing Salmonella and enteric microbial indicators in swine waste

The presence and control of human pathogens in waste from commercial swine farms has emerged as a public health and policy issue that impacts management practices for swine waste treatment. This research focused on quantifying the reductions of enteric microbes in anaerobic swine waste lagoon systems and alternative treatment systems (e.g., constructed wetlands, anaerobic digestion, aerobic biofiltration, UV irradiation). Swine waste samples were analyzed for a suite of six microbial indicators of fecal contamination (fecal coliforms, Escherichia coli, enterococci, Clostridium perfringens spores, somatic coliphages and F-specific coliphages) and the bacterial pathogen Salmonella. Salmonella were consistently found in untreated flushed swine waste and anaerobic swine lagoon liquid at high concentrations. In general, Salmonella and enteric microbial indicators were substantially reduced (90–99%) in anaerobic swine lagoons, but high concentrations of these microbes remained in lagoon liquid. Additional enteric microbe reductions of 90–99% were achieved if a second lagoon was used in series with a primary anaerobic lagoon (resulting in overall reductions of 98–99.97%). An ambient temperature in-ground anaerobic digester was found to achieve similar or greater enteric microbial reductions compared to single-stage anaerobic lagoon systems. Two alternative aerated biological treatment systems were found to achieve similar or greater enteric microbial reductions compared to single-stage anaerobic lagoon systems. In addition, UV irradiation was found to be effective for reducing vegetative bacteria and somatic coliphages in swine wastewater from one of the biological treatment systems. Substantial reductions (90–99%) of Salmonella and enteric microbial indicators were measured for a surface flow (SF) constructed wetland treating lagoon liquid at a commercial swine nursery. Experiments using laboratory-scale SF and subsurface flow wetland reactors to treat swine lagoon liquid determined that temperature, loading rate and hydraulic residence time were important variables affecting the performance of the reactors for reducing concentrations of enteric indicators, S. typhimurium, chemical oxygen demand, total Kjeldahl nitrogen and ammonium-N. First-order and multiple regression equations were developed to quantify the effects of independent variables on observed enteric microbe and nutrient reductions.