Improvement of virus removal by pilot-scale coagulation-ultrafiltration process for wastewater reclamation: effect of optimization of pH in secondary effluent.

Reclaimed water (i.e., reused advanced-treated wastewater)offers an alternative water resource. To reduce the health risks associated with its use, efficient virus removal such as with advanced wastewater treatment processes is important. Virus removal by coagulation followed by ultrafiltration (UF)for the treatment of drinking water has been well examined. But its efficacy in wastewater reclamation purpose using secondary treated effluent (SE)from wastewater treatment plant (WWTP)as feed water is unclear. Here, we optimized the virus removal efficiency of coagulation-UF in pilot-scale wastewater reclamation plants using SE as feed water, using the F-specific RNA bacteriophage MS2 as a model virus, at two wastewater treatment plants in Japan. We investigated how using coagulation as a pretreatment for UF improved virus removal efficiency. The efficiency varied greatly between SEs. To reveal the cause of the variation, we conducted laboratory-scale batch coagulation experiments. The efficiency of viral coagulation was negatively correlated with the concentration of dissolved organic matter in the feed water. The optimum pH for coagulation differed between SEs, and the efficiency of coagulation could be dramatically improved by optimizing the pH. We confirmed that the virus removal efficiency in the pilot-scale facility actually could be improved by adjusting the pH. In addition, we confirmed that coagulation-sedimentation-UF with pH adjustment could operate stably for more than 30 days at the pilot scale, with a high virus removal rate. Thus, the wastewater reclamation process described here offers promise in terms of reduced health risks and practical operation.