Experimental Study On Treatment Of Landfill Leachate With Effective Microorganisms

Landfill leachate is produced by fermentation, rainwater leaching and scouring, surface water and groundwater immersion when waste is piling up. This kind of wastewater may cause serious pollution, which can last for a long time and cause secondary pollution easily, to surrounding area and soil layer of landfill. Landfill leachate, which composition is quite complicated, is a kind of high concentration of organic wastewater and has different characteristics in water quality and quantity in different locations and hours. Therefore, treatment of leachate is difficult. Effective microorganisms (EM) technology which is an emerging technology in wastewater treatment has broad applications in leachate treatment as a result of its unique advantages which are much better than traditional methods.In this dissertation, landfill leachate of Chongqing Changsheng Bridge Municipality Sanitary Landfill was chosen to be treated with Fenton process and Magnesium Ammonium Phosphate Precipitation (MAP). Then exploratory experiments were carried out by using the biological diversity and combined effect of EM to treat leachate. Through the combination of bio-augmentation technology and traditional biological treatment technology with EM as biological enhancer, technical conditions and methods of landfill leachate advanced treatment were explored to improve landfill leachate treatment efficiency.Fenton process and MAP were combined to study the effect of landfill leachate pretreatment. It was showed that Fenton process was very effective for the degradation of organic matter, but ammonia removal was unsatisfactory, and chemical precipitation was not effective for organic removal. The method of leachate pretreatment by combination of Fenton process and MAP was able to make up their deficiencies and get good results. The optimum operation conditions of Fenton process were as follows: leachate pH (5), Fe2+ addition (0.05mol·L-1), reaction time (3h), nH2O2: nFe2+=1: 1. The molar ratio of Mg: N: P=1: 1: 0.7 was better for treatment effect when other factors of MAP were as follows: agents (MgO+Na2HPO4·12H2O), pH (8.5), reaction time (1h). Under the optimum operating conditions, COD of the leachate pretreated decreased from 6455mg/L to1300mg/L with removal efficiency of 79.86%, NH3-N decreased from 1119 mg/L to 251mg/L with removal efficiency of 77.57%, and TP decreased from 20.55 mg/L to 2.1mg/L with removal efficiency of 89.78%. At the same time, BOD₅/COD ratio was improved from 0.2 to 0.5 as well. Through this method, biodegradability of leachate was significantly improved and it was helpful for the follow-up biological treatment. Fenton process was easy to operate and magnesium ammonium phosphate produced in MAP can be used as slow-release fertilizers or fire-retardants of structural products. Instead of causing secondary pollution, this way could realize waste resource recovery.The study on the influencing factors of EM technology in landfill leachate treatment indicated that effective microorganisms in EM as biological enhancer played a strong role and promoted pollutant degradation obviously. The removal efficiencies of COD, NH₃-N and TP were significant. Orthogonal experiment and single factor analysis were carried out to determine the optimum operating conditions. The results were as follows: reaction time(48h～96h), aeration time(12h～36h), low-flow intermittent aeration, EM addition (VEM: Vwater, 1/5000～1/1000) and leachate pH(7～8.5). The optimum operating conditions of EM technology were as follows: reaction time (48h), EM addition (VEM: Vwater, 1/2000), aeration time (12h) and leachate pH (8.5).The study on the combination of EM technology and biofilm process to treat landfill leachate indicated that under the optimum operating conditions, the biofilm system with ceramic granules as filler was able to provide good environment for EM to grow and reproduce, and the system start up time which was greatly shortened was only 8～9d. The removal efficiency of COD, NH3-N and TP was respectively over 80%. During the formal operational stage of EM biofilm system, COD removal efficiency reached the maximum of 84.65% after 48h which was up to "Tier 2" Emission Standards of MSW Landfill Pollution Control (GB16889-1997), NH3-N removal efficiency reached the maximum of 81.09% after 72h which was up to "Tier 2" Integrated Wastewater Discharge Standard (GB8978-1996), and TP removal efficiency reached the maximum of 78.85% after 48h which was up to "Tier 1" Integrated Wastewater Discharge Standard (GB8978-1996). Compared with the method of using EM to treat leachate alone, this way significantly improved the removal efficiencies of COD, NH₃-N and TP. This technology conquered the disadvantage of traditional landfill leachate treatments which had horrible smell in the treating process, and also had some other advantages such as less amount of sludge which could avoid the problems of economic consumption and secondary pollution in sludge treatment, better removal effect of water color, elimination of the blockage of the filler, low operating costs, and easy operation.