Impact of biofiltration on the UV-LED inactivation kinetics of E. coli, C. perfringens spores, and somatic coliphages in real secondary effluent

A slow sand biofilter was evaluated as a potential pretreatment stage for 265 nm UV-LED disinfection targeting three microbial indicators in a secondary wastewater effluent: E. coli , C. perfringens spores, and somatic coliphages. Disinfection efficacy and electrical energy per order were compared between the unfiltered raw effluent and the biofiltered water. The biofiltration step significantly improved the optical properties of the water matrix, increasing UV transmittance from 37.3% to 53.8% and reducing turbidity by 93.2%. This improved the physical clarification of the water sample prior to entering the UV disinfection stage. For E. coli , C. perfringens spores and somatic coliphages, the biofilter mechanically reduced the initial load by an average of 2.56-log, 2.75-log and 1.40-log. Overall, the integration of the biofilter contributed to reduce the electrical energy per order for E. coli (−76.9%) and C. perfringens spores (−72.3%).