Assessment of Cu(II) impact on aerobic sludge biomass and its post-exposure self-recovery potential

Abstract

Heavy metals are released from various sources, including metal plating, potentially at a small-scale industrial level, and from automobile service and repair workshops, paint works, etc., spread across the city. Being part and parcel of the city, the wastewater from these metallic sources finds its way into the sewage system and can potentially disrupt biological sewage treatment plants. Therefore, conducting health and quality assessments of the sludge biomass becomes crucial to ensure the effective operation of these treatment plants and to maintain environmental and public health standards. In this study, impacts of Cu(II) (10, 20, 40, and 80 mg/L) exposure on sludge biomass have been investigated, and the potential of self-recovery of sludge biomass was explored when Cu(II) exposure is stopped. Reactors have been operated for 0–25 d with Cu(II) (termed as stressed phase) and then another 29 d without Cu(II) (termed as recovery phase) in the feed. During stressed phase operation, Cu(II) stressed reactors have shown 39–75 % chemical oxygen demand (COD) removal, compared to 91 % for control. Biomass activity and ECatalase activity have been inhibited under Cu(II) stress with changes in microbial community structure. During the recovery phase, Cu(II) stressed reactors have shown 41–82 % COD removal, whereas the control reactor has shown 91 % COD removal. A low sludge volume index (SVI) and high biomass interface settling velocity (ISV) with increased biomass activity have been obtained for biomass exposed to 10 and 20 mg/L of Cu(II). Lower Cu(II) doses have led to partial recovery of enzyme activity and microbial community structure, but higher doses have shown incomplete recovery. The study shows the impact caused by Cu(II) metal in a biological wastewater treatment reactor. Through comprehensive analysis of basic and advanced physico-chemical and biological parameters, the study recommends preliminary and confirmatory tests to know metallic ingress through wastewater influent in a treatment system. Advanced knowledge about metallic ingress will be useful for operators to take necessary steps for the sustainable operation of wastewater treatment systems.