Ensuring safe reuse of residential wastewater: reduction of microbes and genes using peat biofilter and batch chlorination in an on-site treatment system.

Abstract

A batch chlorination system was optimized for on-site wastewater treatment and reuse system (OWRS) and its efficiency was evaluated for reducing viruses, protozoa, bacteria and antimicrobial resistance in cold and warm seasons. The OWRS performance in reducing microbial contaminants was determined by assessing three different faecal indicators (Escherichia coli, F-specific coliphages and Clostridium perfringens for measuring the disinfection efficiency of bacteria, viruses and spore-formers and surrogate for protozoa, respectively) using culture-based methods. Quantitative PCR was used to quantify pathogenic bacteria (Shiga-toxin-producing E.coli (STEC), Campylobacter spp., and Arcobacter spp.), a human-associated faecal marker (gyrB), and tetracycline resistant bacteria (tetQ). The levels of E.coli, coliphages and Cl.perfringens showed 5·4, 2·3, 2·5 log reduction, respectively, upon disinfection. In the final effluents, coliphages (1·7×102 PFU 100ml-1 ) and Cl.perfringens (3·4CFU100ml-1 ) were detected in 80 and 100% of the samples, but E.coli was not found. The removal and inactivation of E.coli and Cl.perfringens were not significantly different across the seasons, however, efficacy of removal and inactivation of F-specific coliphage was significantly reduced during the winter/spring season compared to the summer/autumn season (P=0·009). The reduction of Arcobacter, gyrB and tetQ by 3·1, 2·3 and 2·3 log, respectively, was mostly due to peat biofiltration under the study conditions. This study demonstrated that peat biofiltration was the most important step of the OWRS to remove microbes and genes from wastewater before spray irrigation of the effluents. The irrigation system is not suitable for edible crops because of the potential presence of residual pathogens. On-site wastewater treatment systems are a practical option for reusing the wastewater for landscape, especially for those areas where geological and seasonal limitations impact the removal of microbial contaminants by soil infiltration.