Sub-lethal effects of heavy metals on activated sludge microorganisms

The effects of heavy metals, at sub-lethal concentrations, on activated slu dge microbial ecosystem were investigated. Adsorption capacity and rate of copper, chromium, lead and zinc on microbial flocs were much faster than th at of organic matters. Metals affected not only the adsorption rate of orga nic matters but also the COD adsorption capacity of the activated sludge. E ffects of heavy metals, on wastewater treatment performance of a sequencing batch reactor were also studied. Metal-laden wastewater at sub-lethal leve ls affected the performance to different extents, depending on the hydrauli c retention time. Metal ions acted as a strong competitor against the organ ic compounds for active sites on the bioflocs instead of acting as a toxic microbial inhibitor, thus hampering organic adsorption and affecting the CO D removal efficiency under shorter HRTs. (C) 1999 Elsevier Science Ltd All rights reserved.