Assaying coliform removal in waste stabilisation ponds system through the dispersed flow regime

Abstract

This study aims to investigate total coliform (TC) and thermotolerant coliform (TTC) removal efficiency of the waste stabilisation ponds (WSPs) system in Central India through the dispersed flow regime. To accomplish this, coliform (TC and TTC) die-off coefficient (Kb) was estimated for each pond (anaerobic, facultative and maturation) by the dispersed flow regime. Maximum Kb value was observed for the maturation pond (Kb, 5.8) in comparison to the facultative (Kb, 5.6) and anaerobic ponds (Kb, 1.8) and satisfactory correlate with the pond's depth (R2, 0.99) and hydraulic detention time (HDT) (R2, 0.73). On comparing coliform (TC and TTC) removal efficiency of different ponds in different seasons (viz; post monsoon, winter and summer), it was observed that total and thermotolerant coliform load increased in the post monsoon season. This was attributed to differences in the prevalence of infection and fecal excretion levels and due to the mixing of runaway water with raw sewage during the monsoon, which increased the bacterial load. Applying the dispersed flow model to assay coliform removal efficiency of WSPs system, we concluded that shallow ponds with a higher hydraulic detention time have good removal efficiency compared to deep ponds with lower hydraulic detention time.