Ecology, Environment and Conservation Paper

CASCADE AERATION: A PROMISING POST TREATMENT OF EFFLUENT FROM UASB REACTOR

Rinku Walia, Pradeep Kumar, Amit Handa and Indu Mehrotra

Abstract

Effluents from (i) bench scale 56 L upflow anaerobic sludge blanket (UASB) reactor and (ii) four UASB based sewage treatment plants (STPs) of capacities ranging from 27 to 70 ML/d stored in containers were pumped to flow over inclined plane at a rate of 200 mL/min. The objective of the project is to evaluate the performance of inclined plane and to find correlation between oxidation reduction potential (ORP), dissolved oxygen (DO), chemical oxygen demand (COD) and biochemical oxygen demand (BOD). The DO after fall was dependent on initial COD whereas increase in ORP was dependent on DO increase after fall. The cascade was designed for increase in DO to 4-5 mg/L. However in N-34 and G-70 DO increase was 0.5-2 mg/L. The increase in DO has been shown to be dependent on wastewater characteristics. Oxygen transfer efficiency was found to be independent of DO influent. But it showed positive correlation with DO after fall. E20 of 50% was attained when DO after fall was 5.7 mg/L (63 % of DOs). Overall reduction of COD ranged between 20-40 %. The decay rate of COD and ORP ranged between 0.1-0.2 h-1 and 0.6-1.2 h-1 respectively. The empirical equation of SW2 predicted the temporal variation of fraction of COD in four STPs.