Physical-chemical and Electrochemical Methods for Landfill Leachate Treatment

Physical-chemical and Electrochemical Methods for Landfill Leachate Treatment

Landfill leachate contains various contaminants (i.e. organic and inorganic pollutants), of which the composition and content vary with geographic location, waste composition, age, pH, moisture content, and other landfill site characteristics.  Leachate requires pretreatment on-site to meet standards to discharge to wastewater treatment plants or directly into surface water.   
Due to the variable composition of landfill leachate, it contains recalcitrant organic matter and bio-toxic metals, the level of purification needed typically cannot be achieved using biological processes alone. Therefore, physical-chemical methods are more appropriate for the treatment of leachate.

Physical-chemical processes include coagulation-flocculation, activated carbon adsorption, ion exchange, membrane filtration, and advanced oxidation. Since conventional methods are not capable of dealing with increasingly strict discharge limits for the various multiple constituents found in landfill leachate, it has become imperative to evaluate newer technology.
Recently, electrochemical oxidation has been successfully used for treating wastewater from tanneries, textile mills,  coke plant wastewater, and wastewater containing cyanides.  
 
Electrochemical oxidation is an oxidation process that occurs through the application of external voltage. The process involves direct oxidation of pollutants at the anode as well as indirect oxidation by mixed oxidants including chlorine and hypochlorite ion, hydrogen peroxideand ozone. By direct anodic oxidation, pollutants absorbed on the anode surface may be destroyed to some extent. However, the removal of pollutants is primarily due to the indirect oxidation by chlorine/hypochlorite generated by the oxidation of chlorine (existed or added in the leachate) at the anode.

Researchers have studied the treatment of landfill leachate by electrochemical oxidation at different conditions. Factors affecting the efficiency of electrochemical oxidation include anode material, current density, time, pH, type and concentration of electrolytes, and pretreatment. Several other factors that may affect the treatment performance include flow rate, inter-electrode gap (the gap between anode and cathode), anode area to volume of effluent to be treated ratio (A/V), temperature, reactor geometry (two dimensional or three dimensional), cathode material, and pretreatment.