Treating landfill leachate by electrocoagulation

摘要

The determination of the optimal conditions for using electrocoagulation as a treatment for landfill leachate was carried out using surface response methodology. A central composite design was applied to investigate the effect of four control factors, namely current density, pH, time and fluid conductivity, as well as the interaction among (between) them to get an optimal turbidity removal. The independent variables were each coded at three levels and their values were selected on the basis of preliminary experimental results. The central composite design consisted of 29 experimental points with five replications at the centre point. A second order polynomial model was used for predicting the response. Regression analysis showed that more than 95% of the variation was explained by the model wherein current density with a 60.1% contribution turned out to be the factor with the most significant influence. Analysis of variance showed that time, pH, current density and the interaction time/current density had a significant influence on the turbidity removal, The optimal conditions obtained for the removal of turbidity were time 38.8 min, pH 7.6, current density 109.9 A m~(-2) and NaCl 2.9 g L~(-1). Experimental results showed that for a 96.9% turbidity removal, similar reduction in Al (97.0%) and Fe (99.5%) concentrations; as well as 66% total Kjeldahl nitrogen removal were obtained. Furthermore, the sludge formed exhibited a good floe size, which separated in less than 10 min by classical sedimentation. The results analysis provided evidence of reduction of chemical pollutants, although the electrocoagulated leachate could not satisfy regulations for the maximum Total Kjeldahl nitrogen leachate discharge level to public wastewater collection systems in the town of Freire, Chile.