Treatment appraisal and fate of HMs in up-flow anaerobic sludge blanket and trickling filter-based sewage treatment process: The case of a kaliti Centralized Wastewater Treatment Plant, Addis Ababa, Ethiopia.

Heavy metals (HMs) in wastewater could pose a significant challenge to biological treatment systems such as in an Up-flow Anaerobic Sludge Blanket Reactor (UASBr) as well as Trickling Filter (TF) performances. These HMs are associated with retention and accumulation of solid precipitates, limitting solid-liquid separation, disrupting biochemical processes, which ultimately brings environmental risks, such as soil contamination and public health issues, dominantly due to the inhibited activities of degrading microorganisms. A cross-sectional study was applied to investigate the levels of HMs in sewage using composite and grab sampling taken from Kaliti Wastewater Treatment Plant and the samples were analyzed using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). The HMs concentrations in mean±(SD) were, Ag ranges from below detection level (BDL) to 63.5 (13.5) mg/kg; Ba 60 (4.47) μg/l to 1291(58.5) mg/kg; Al, BDL to 2358.5(662.5) mg/kg; Cd 0 μg/l to 0.35(0.15) mg/kg; Cr 0 μg/l to 10.5(0.7) mg/kg; Cu 0 μg/l to 23.9(1.2) mg/kg; Zn 5.45 (12.3) to 165(5.4) mg/kg, and Mn 165 (49.5) μg/l to 92.5(3.8) mg/kg. Results indicated that Kaliti Wastewater Treatment Plant was effective in removing pollutants and thereby meeting local and international discharge limits. The plant was also found to be effective in removing Al, Cd, Cu, and Cr, but not in removing Ba and Zn. However, a real time data collection and monitoring of seasonal physicochemical parameters and HM levels in the wastewater treatment plant is suggested useful.