Assessment of virus removal by a multi-stage activated sludge process

Viruses seeded into a 50,000 gal day⁻¹ three-stage activated sludge pilot plant were effectively reduced in the treatment process. Reduction was highest in the system's denitrification and high-rate activated sludge modules, both averaging more than 95% virus removal. Combining the removal capacity of each unit process resulted in a calculated virus reduction of 99.97% for the total treatment system.A study of the indigenous viruses present after primary settling illustrated the wide diversions that can occur in wastewaters during a 24 h period. It illustrated as well the necessity of collecting temporally related samples within the treatment system. No direct relationship was evident between the numbers of coliphages and enteroviruses present in the primary effluent.