Studies to determine the optimal coagulant dosage for the precipitation of landfill leachate pollutant

Abstract

The treatment of landfill leachate is a critical environmental, social and economic issue. This type of wastewater poses a threat to the environment and human health, so European standards (Council Directive 1999/31/EC on landfill, Water Framework Directive) require its mandatory treatment. Landfill leachate is composed of different toxins and complex chemicals due to the presence of different kinds of pollutants and trash. These toxins and pollutants include heavy metals, organic pollutants, ammonium nitrogen, and xenobiotic compounds. Due to this complexity and variation in the chemical composition, conventional treatment methods such as bio-logical treatment and membrane separation often face various challenges. To address these challenges, the combination of treatment methods such as coagulation/flocculation as pretreatment followed by adsorption techniques has shown promising results in removing all the toxins at a much lower price using natural materials. This combination ensures the removal of suspended solids and colloidal matter trapped in the leachate using coagulation; the remaining dissolved organic and inorganic matter are removed by the adsorption stage. The uncertainties lie in the fact that it is not known exactly which coagulants, and at what doses, would optimally reduce the amount of organic matter in the landfill filtrate. Experimental studies are being conducted to select suitable coagulants. In this study, Al2(SO4)3 and Fe2(SO4)3 metal salt coagulants were selected for the coagulation stage. At the optimal dosages of Al2(SO4)3, a maximum TC removal of 60% was achieved, whereas Fe2(SO4)3 achieved a slightly higher value of about 62%. On the other hand, low TN removal efficiencies were achieved for both coagulants after the coagulation process alone, not exceeding 11%, confirming that coagulation process alone is insufficient for effective nitrogen removal. Subsequent adsorption stage significantly improved the treatment performance using ZMT, as overall TN removal exceeded 90% for both coagulants at the optimal doses, while the overall TC removal remains slightly effected.