Effect of aeration and leachate recirculation on nitrogen and carbon removal from landfills

Abstract

The incorporation of MBT technologies in municipal solid waste (MSW) management has greatly changed the solid waste and landfill management. MBT not only significantly reduces the quantity of the output materials to be landfilled, but also reduces a considerable proportion of organic compounds and nutrients in the output materials, therefore, leading to a reductions of both gas and leachate emission potentials after the emplacement of such output materials on landfills. The main difference between leachates from MBT and MSW landfills is the low levels of organic carbon and ammonium in the MBT ones. Ammonium is regarded as the most problematic parameter in leachate from MSW landfills because it is normally present at high concentrations and persistent under anaerobic condition. Ammonium level in leachate from MBT landfills is much lower than that in leachate from MSW landfills, but is still relatively high compared to concentrations which are acceptable on the long term. Therefore, the treatment of leachate in the future is no longer or less focus on organic matter which has been dominant so far, rather on taking care of ammonium. A part of the study was about the effect of leachate recirculation on the characteristics of leachate from MBT residue and fresh MSW. The major part of the study focused on the effect of such recirculation combining with aeration on leachate quality of such waste materials. The lab-scale study results clearly showed that recirculation of leachate alone has little effect on the characteristics of leachates from both MBT residue and fresh MSW in the experimental duration. Meanwhile, such combination technique gives a remarkable influence on improving the quality of leachates from both types of investigated materials. Very high nitrogen removal efficiency (up to 99 %) was achieved by applying this combination technique to MBT residues, whereas organic carbon components were slightly affected. At the same time, the combination technique also has strong impacts on reduction of ammonium and organic carbon substances in the leachate from MSW. Though the combination technique results in considerable decreases of ammonium nitrogen in the leachates from both types of materials, the mechanism leading to such decreases is different. As for lab-scale lysimeters containing MBT residues, the study results indicated that nitrogen was lost via nitrification and denitrification processes by aeration. Meanwhile, the reduction of ammonium nitrogen in case of MSW was most likely due to the volatilisation of free ammonia. Despite such different mechanisms, the combination of in-situ aeration and leachate recirculation can be a simple and reliable measure to improve the quality of leachates from both MBT residue and MSW.