Virus removal by the domestic wastewater treatment system named Johkasou

Virus removal by a treatment plant for domestic wastewater (Johkasou), was investigated using a small model of the plant. Under standard BOD loading of 0.076 BOD kg/m³/day, 97% of E. coli phage T2, 98% of poliovirus 1 and 93% of coxsackievirus B3 were removed from inlet wastewater by the system. About 80% of the viruses in the influent were removed in the first and second anaerobic zones under the standard conditions. When the loading was increased to double the standard loading (0.152 kg BOD/m³/day) the removal rate decreased to 64%. Poliovirus 1 and coxsackievirus B3 were removed more easily than T2 phage. Assuming the stream in each zone was completely mixed, the virus reducing activity of microorganisms was estimated by the rate constant of the first order reduction equation. It was found that the higher the BOD loading rates, the lower the values of the constant.