REMOVAL OF CADMIUM, LEAD AND ORGANIC LOAD FROM WASTEWATER USING BIOGENIC SULFIDE UNDER ANAEROBIC CONDITIONS

Abstract

The influent of the wastewater treatment plant in Ismailia - Egypt loaded with many species of heavy metals, since no separation between industrial and municipal wastewaters because the plant was not designed to remove these metals. The objective of this study was to apply a method able to remove aforementioned metals with biomass concurrently and characterized to be cheap and effective. The removal of heavy metals such as lead, cadmium and minimize the volume of biomass simultaneously was achieved by using bench-scale biogas digester (vertical type) under anaerobic conditions and optimum temperature within the mesophilic condition 38 oC. The treatments of this work carried out on two phases; the first phase was conducted in the absence of gypsum adding (control treatments) and the second was performed with adding gypsum at a dose equal to 5gl-1 (gypsum treatments) with a fermentation time of 20 days. These treatments carried out on the slurry, which was the end residue in the treatment lagoons in Ismailia wastewater treatment plant. This slurry was supplemented with the studied metals. The objective behind adding gypsum was to reduce by native species of sulphate reducing bacteria (SRB) and then produce biogenic sulfide, which used in precipitation of these metals as sulfides and their loss with the wasted biomass. The results showed that the removal efficiency for both Cd and Pb metals increased with decrease the initial concentration of them. Since, the removal levels of both metals for gypsum treatments were >99% at Cd and Pb with initial concentrations not exceed over 120 and 150 mgl-1, respectively. By comparison with control treatments at initial concentrations of Cd and Pb not exceed over 60 and 75 mgl-1, respectively, the removal efficiency reached >99% for Cd and 98.9% for Pb. The pH values for all gypsum treatment were around pH 7. Furthermore, the removal of total solids for the gypsum treatments reached over 84% for the most treatments at the end of the fermentation time. The reaction of Cd and Pb belongs to the second-order kinetic model. It can be concluded that, the adding gypsum under previous conditions as a treatment process can be an effective approach to reuse this kind of wastewater safely in many purposes especially in irrigation.