Performance of Anaerobic Sludge under Microcosm Experiments Treating Municipal Wastewater with Low Concentration of Heavy Metals

Low concentration of heavy metals in municipal wastewater comes from pipe sediments and domestic products including; Medicine, Caulking Products, Cleaners, Cosmetics and Auto Products. At certain concentrations, heavy metals showtoxicity and/or inhibition effect onto microorganisms in biological treatment systems. In this study, the effect of five heavy metals (Cr, Cu, Zn, Ni andPb) at low concentrations onto treating performance of anaerobic sludge were investigated using municipal wastewateras carbon source and electron donor in a batch experiments (serum bottle assays). The six concentrations of heavy metals were added to municipal wastewater; 0.35, 0.75, 1.25, 3, 5 and 10mg/l.The descending order of toxicity/inhibition activity of heavy metals were found Cr (most toxic), Cu, Ni, Zn and Pb (least toxic) respectively.In general, cumulative methane production (ml) decreased with increasing heavy metal concentrations above 1.25 mg/l. Inhibition effects of heavy metal values (0.35-1.25mg/l) were low on COD removal. Heavy metals in influent and effluent into serum bottles were also compared. Effluent heavy metal concentrations from low to high were found to be Pb, Cu, Zn,Ni and Cr. As a conclusion, heavy metals addition in municipal wastewater influent at low concentrations affected adversely performance of anaerobic sludge; although, did not cause complete inhibition to anaerobic microorganisms. The inhibition effects of heavy metal counted on type of metal, characteristics of sludge and hydraulic retention time.