Biogas production as affected by heavy metals in the anaerobic digestion of sludge

Biogas production can be generated by sludge digestion process in the form of methane which in some plants is collected and used as a source of energy. Sewage which is collected from mixed industrial and domestic population may be contaminated with metals and industrial chemicals. The aim of the present study is to investigate the effect of heavy metals on the biogas production in the anaerobic digestion process for the treatment of sewage sludge. The selected metals are Hg, Cd and Cr III. The toxic effect and the inhibitory impact of the digestion process are among the objective of the study. The fate and toxic effects of heavy metals on the biogas production was determined. The sewage sludge samples were separated from the sewage water of the pilot plant at the National Research Centre, TDC site. The effect of heavy metals on the biogas production of the anaerobic digester was studied. The inhibitory effect on the biogas production and toxic level of metals was determined in this study. The general ranking of heavy metal toxicity appears to be Hg > Cd > Cr (III). The present investigation reveals that heavy metals in addition to the anaerobic digester decreased the biogas production as an indication of efficiency of the process. A significant decrease in gas production and volatile organic matter removal was obtained. It was also noted that an accumulation of organic acid intermediates was obtained as a result of methanogenic bacterial inhibition. This accumulation was limited during the pulse feed of metals. This is due to the rapid poisoning of the active bacterial forms in the digester.