The Underground Mitigation Process Of The Leakage Leachate From Landfill At Seawater Intrusion Region

Landfill is the main way of garbage disposal. In coastal cities, due to the demand of large space and the conspicuous impact on the environment, seaboard regions are usually chosen to build the Landfill for their cheap land price and few inhabitants. However, the safety protective measures are faultiness because of technical and historical shortages, which causes the leakage of leachate. The large quantity and long-term leakage does great harm to the underground environment. Taken Shanghai LaoGang landfill as the research object, this paper analyzed pollution manner, approach and extent caused by the leakage of leachate under the groundwater-leachate-salty water combined flow. Furthermore, the transformation of high concentration of ammonia nitrogen was investigated in REDOX zoning. The studies have important significance for leachate pollution control and rehabilitation of groundwater.This paper first studied the transformation of ammonia nitrogen along with the underground water through setting up a model to simulate the leakage of leachate. Then, the paper analyzed the formation, development and change of a series of REDOX. Incorporating the characteristics of ammonia nitrogen and each REDOX, the buffer capacity and variation were systematically analyzed when sea water intruded. In addition, the mechanism and efficiency of the decomposition were studied by using chemical methods to decompose ammonia nitrogen, respectively. Finally, one effective model was provided to investigate and confirm the transformation of ammonia nitrogen and REDOX.The experimental results show that:(1) The transformation process of the leachate has multi-zonings of oxidation and reduction in the underground salt water, and the zonings are the methanogenesis zone, sulfate-reducing zone, Fe and Mn deoxidation zone, nitrate reduction zone and oxygen deoxidation zone from the leakage point. These zonings play an important role in natural rehabilitation of pollutants. (2) Ammonia nitrogen in underground salt water is more easily spread along the flow in a horizontal direction. The diffusion speed along the flow decreases from 4cm/d to 3.2 cm/d. Meanwhile, the attenuation ratio increases along the saturated area, transitional area and adjust area. Ammonia nitrogen in underground salt water is hard to decompose by the microorganism. Thus, the degradation of ammonia nitrogen depends on the abiotic affect. Bits of ammonia nitrogen occurs nitrification and denitrification by microorganism, which can reduce the quantity of ammonia nitrogen. The sea water has high concentration of chloridion and great change of water flow in comparison with the fresh water. Therefore, the activity of microorganism is restricted and the removal of ammonia nitrogen is difficulty. (3) The high concentration of leachate can severely damage the underground environment beyond the repair capability of the environment. Therefore, the age-long landfill should pay more attention to the anti-seepage problem. (4) Seawater intrusion will expand the scope of leakage and increase the pollution area. Meanwhile, the flow direction is changed so that the pollution area can nearly double. (5) Artificially intensified experiments of ammonia nitrogen show that the attenuation ratio of TOC is different in each REDOX zone, and the sequence is oxygen reduction zone> methanogenesis zone> sulfate-reducing zone> nitrate reduction zone> iron deoxidation zone. The artificially intensified experiments of ammonia nitrogen have little influence.