Virus Removal in Primary Settling of Raw Sewage

Abstract
Previously published data indicate only minor removal of viruses during primary sedimentation of raw sewage. A reassessment based on quantitative estimates of viruses in temporally matched raw sewage and primary effluent samples was made. In the present study, both full-scale and pilot settling tanks were monitored for their virus removal efficiency, the latter under varying operational conditions. In the full-scale plant, the average percent reduction of viruses in fall, winter and summer was 63% with values ranging from 41% to 83%. However, during the monsoon months of June and July, the average percent removal was 29%. In the pilot plant study, suspended solids (SS) concentration in the influent raw sewage affected the density and degree of flocculation which in turn influenced the extent of virus removal. Percent removal of SS also affected the degree of virus removal.

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