Fecal Bacteria, Bacteriophage, and Nutrient Reductions in a Full-Scale Denitrifying Woodchip Bioreactor.

Denitrifying bioreactorsusing woodchipsor other slow-release carbon sources can be an effective method for removing nitrate (NO) from wastewater and tile drainage. However, the ability of these systems to remove fecal microbes from wastewater has been largely uninvestigated. In this study, reductionsin fecal indicator bacteria() and viruses (F-specific RNA bacteriophage [FRNA phage]) were analyzed by monthly sampling along a longitudinal transect within a full-scale denitrifying woodchip bioreactorreceiving secondary-treated septic tankeffluent. Nitrogen, phosphorus, 5-d carbonaceous biochemical oxygen demand(CBOD), and total suspended solids(TSS) reductionwere also assessed. The bioreactordemonstrated consistent and substantial reductionof (2.9 log reduction) and FRNA phage (3.9 log reduction) despite receiving highly fluctuating inflow concentrations [up to 3.5 × 10 MPN (100 mL) and 1.1 × 10 plaque-forming units(100 mL) , respectively]. Most of the removal of fecal microbial contaminants occurred within the first meter of the system (1.4 log reductionfor ; 1.8 log reductionfor FRNA phage). The system was also efficient at removing NO (>99.9% reduction) and TSS (89% reduction). There was no evidence of consistent removal of ammonium, organic nitrogen, or phosphorus. Leaching of CBOD occurred during initial operation but decreased and stabilized at lower values (14 g O m) after 9 mo. We present strong evidence for reliable microbial contaminant removal in denitrifying bioreactors, demonstrating their broader versatility for wastewater treatment. Research on the removal mechanisms of microbial contaminants in these systems, together with the assessment of longevity of removal, is warranted.