Study On The Pretreatment Of Landfill Leachate By Calcium-Silicon Material

There are above80%of municipal solid wastes are treated by sanitary landfill in China. Landfill leachate will be produced by some complex factors during landfill process, such as organics decomposition and rain shower. The landfill leachate is a kind of complex wastewater which with strong pollution property and high toxicity. It will cause serious damage to the environment once the landfill leachate is directly discharged to the environment.Adsorption is a physical pretreatment method which can effectively remove various organic pollutants and some heavy metals in leachate, as well as provide favorable conditions for biological treatment. This paper used the calcium-silicon material, an industrial semi-finished product, as an adsorbent to pre-treat landfill leachate.By single factor experiment, the optimum conditions for CODCr removal of leachate by the treatment of calcium-silicon material were determined at first. At the same time, the adsorption kinetic model was studied. Combining with the hydrolysis character of calcium silicon material, the heavy metals and the organics and water quality treatment effects of landfill leachate were analysed under optimum conditions. The feasibility of improving CODcr removal by adding flocculant as an auxiliary agent was investigated at last. The conclusions of this study are summarized as follows.(1) When calcium-silicon mineral dosage was100g/L, it can reach the optimal removal efficiency of CODCr by means of swing oscillation for24h at room temperature. Under28℃centigrade, the adsorption process of CODCr from landfill leachate with calcium-silicon mineral conformed to the pseudo second-order kinetic model.(2) By the treatment of calcium-silicon material, Mn、Pb、Zn、Ni、As、 Fe of leachate could be removed effectively under the optimum experimental conditions. And the results revealed that the removal rates of total phosphorus, color, ammonia nitrogen, CODCr, TOC, UV254, and BOD5could be increased to99%,97%,30%,59%,60%,57%and69%, respectively. The effluent concentration of Pb, As, color and total phosphorus all reached the corresponding discharge standards which is noted in the State Standard for Municipal Solid Waste Sanitary Landfill Pollution Control (Standard No GB16889-2008). Moreover, there was the certain effect that the calcium-silicon material could adsorb some organic matters in leachate, such as long chain alkenes, ester, anhydride and some alcohols. Some toxic organic pollutants of leachate, such as N-[4-bromo-n-butyl]-2-Piperidinone and N-(2-trifluoromethylphenyl)-Pyridine-3-carboxamide oxime, also could be removed with the treatment of calcium-silicon material. (3) The removal rate of pollutants in landfill leachate was enhanced when the calcium-silicon material compositing cationic organic flocculants or low molecular inorganic flocculant, especially aluminum sulfate led to satisfactory results, the optimum mass ratio was10:1, and the improvement of CODCr removal efficiency was about7%.(4) Early in the oscillation process, pollutants could be removed mainly depended on surface absorption function of calcium-silicon material. During the middle and late stages of oscillation process, a large number of hydrate silicate calcium and Ca(OH)2, as well as a small quantity of Al(OH)3and Fe(OH)3were formed by the hydrolysis of calcium-silicon material. Hydrate silicate calcium had stronger adsorption. There existed bridge and net-capture effect due to the polymer which was respectively produced from Al(OH)3, Fe(OH)3and Ca(OH)2. Therefore, during this hydrolysis process, pollutants were removed mainly depended on adsorption and flocculation from the hydrolysis of calcium-silicon material.