Leaching and Eco Toxicity Studies Ofmetals in Sewage Sludge and Fly Ash Mixtures

Abstract

Leaching is the process of release of certain materials from a carrier into a liquid. Leaching and eco-toxic studies in different sewage sludge and fly ash mixtures were carried out. The 5 g mixture of FA/SS of three different ratios (1:1, 1:4 and 4:1) were taken and mixed with 100 mL of deionised water. The samples were then place on the rotatroy shaker at 120 rpm for 10 h at controlled temperature conditions of 26° ± 1C. The samples were then allowed to settle down and the supernantant was vaccum filtered with the help of 0.45 and#956;m. The leachate was tested for Pb, Cd, Ni, Cu and Co using atomic absorption spectrophotometer (ECIL, India, Model AAS 4129). The leachate was also tested for different water quality parameters such as electrical conductivity, sulphate, chloride, total hardness, permanent hardness, chemical oxygen demand, total kjeldahl nitrogen (TKN), total solids, total dissolved solids, turbidity etc. It was observed that the leachate from the mixture with higher amounts of sewage sludge showed more metal contents and higher contaminants of different water quality parameters, whereas the leachate samples from the mixtures with lesser content of sewage sludge and higher content of fly ash (samples with FA/SS 4:1 ratio) showed very less or no leaching. Experiments were performed with different fly ash and sewage sludge mixtures (1:1, 4:1 and 1:4) to achieve the optimised conditions for leaching of metals. It was observed that with the fly ash-sewage sludge mixture (1:4) leaching of metal ions was the maximum for copper metal (1.5 ppm), and minimum for the Pb (0.2 ppm). For other metals it was 0.0 ppm for Cd and 1.0 ppm for Ni. A decrease in leaching of metals was observed with increase in fly ash content in FA/SS mixture (1:1) which was 0.1 ppm for Pb, 0.0 ppm for Cd, 0.1 ppm for Ni, and 0.3 ppm for Cu, respectively. A decreasing trend in leaching of metal ions was observed with increased fly ash content in the fly ash-sewage sludge mixture.