SURVEY OF HEAVY METALS CONCENTRATION IN MUNICIPAL SOLID WASTES LEACHATE OF ISFAHAN CITY AND THEIR REDUCTION METHOD

Abstract

Introduction In duration steps of collection, transfer and disposal of solid wastes and also change of solid wastes to compost, produced leachate includes various pollutants such as heavy metals. The amounts of heavy metals don"t easily degrate in environment and would be concentrated in food chain and caused many problems for environment and human. Thus, the goal of present research is to investigation of heavy metals concentration in municipal solid wastes leachate of Isfahan city and reduction method for this case.
Methods. leachate from four transfer station and composting plant was sampled ten times and in the first stage, quality of samples was evaluated from pH, COD, total solids (TS), total volatile solids (TYS), total fixed solids (TFS) and heavy metals such as Cadmium, Chromium, Zinc, Copper and Nickel viewpoints. Chemical coagulants such as lime, alum and ferric chloride were applied using the Jar test to reduce heavy metals concentration.
Results. The results revealed that mean concentration of heavy metals Cd, Cr. Zn Cu and Ni in leachate was equal to 0.63, 1.22, 7.42, 2.15 and 2.22 mg/l respectively and also the results of statistical analysis (ANOVA) showed no significant difference between heavy metals concentration in various stations (P > 0.05). The results of Jar test revealed that optimum pH for chemical precipitation, and also optimum concentration of the three coagulants were 2400, 1400 and 1000 mg/l respectively.
Discussion. Under this study elements concentration of leachate as compared with effluent standard (Environmental Protection Agency) were exceeded the limits. Alum with 75-95 percent removal has the highest effciency as compared to other coagulants, lime with 70-88 percent removal and ferric chloride with 65-85 percent removal are in next order. Erom economical aspect, lime is cost benefit, ferric chloride and alum are in raked next respectively.