WERF Phase 2: The Impact of Shear during Biosolids Dewatering on Reactivation and Regrowth of Non-Culturable Indicator Bacteria
Recent reports have indicated that biosolids pathogen indicator exhibit reactivation and regrowth after dewatering, which has drawn concerns from the wastewater treatment industry. Studies have also shown that the observed reactivation and regrowth are usually associated with centrifuge dewatering and shearing to biosolids was suspected to be the key factor. A field trail collecting centrifuge dewatered biosolids subjecting to various shearing stresses indicated that the more shears the biosolids are subjected to, the higher indicator reactivation it is to occur. Laboratory simulation of centrifuge dewatering also showed that shearing stimulates indicator regrowth, while the no-shear control did not encourage regrowth. However, laboratory simulation was unable to recreate reactivation. Pathogen indictors can grow up to similar density of the undigested raw sludge (10E9), but also die off to below Class A or Class B limits. Results also suggest that food release and oxygen exposure resulting from centrifuge shearing are the two key factors to regrowth. Overall, biosolids shearing increases the chance of reactivation and regrowth, but well digested sludge can still prevent them from happening.