Study On Physicochemical And Biological Pretreatment And Combined Techniques For Landfill Leachate Treatment

With the rapid development of Chinese economic construction, expansion of urban-scale and improvement of living standards, the amount of municipal solid waste is increasing. As the main technology of municipal solid waste treatment in China, landfill also brought new secondary pollution problems: leachate generated by landfill is high concentration organic wastewater which has a great harm, contains amounts of refractory organic matters, ammonia nitrogen and heavy metals, if not properly handled it will cause serious pollution to the surrounding environment and groundwater. Because of the complexity of leachate, a certain kind of process technology cannot fully solve this problem. With the promulgation and implementation of new standards, the upgrading of existing leachate treatment facility and optimization combination of process on new landfill leachate treatment facilities, finding efficient, economic and energy-efficient combination of physico-chemical and biochemical processes, meeting the new emissions standards, they have been the hot and difficult points in leachate treatment research in recent years.This paper summarizes the characteristics, research results and the problems of landfill leachate treatment technology of the domestic and overseas. Combination of characteristics of leachate quality and the operational and economic of processing technology requirements identified several physico-chemical and biochemical processing technology, and analysis the remove pollutants and effect of processing technology, study the dynamic model, process parameter optimization,organic matter degradation mechanism and other aspects; And based on the processing technolagy characteristics form on three effective conbination processes, and study the removal efficiency, optimization of operating parameters, etc. of combine process.In the aspect of physico-chemical treatment technology, establishing the empirical model of the magnesium ammonium phosphate ammonia-nitrogen removal rate and influencing factors by response surface method, optimizing the process parameters at the same time, found that at the situation of molar ratio of n(Mg):n(N),n(P):n(N) respectively is 1.40,1.20, and if not adjust pH(Reaction pH stables at around 9.5), be able to obtain a higher ammonia-nitrogen removal rate(average up to 92.2% ),and the average the amount of residual phosphorus in the water is 17.92mg/L, not show a significant increase. And then through the XRD and electrolytic-scan of the sediment we can see that the majority of Sediment is magnesium ammonium phosphate precipitation.Through testing the impacts of electrolysis and electro-fenton treatment of landfill lechate and comparative analysis, we found that the most appropriate pH of electrolysis treatment is about 8.3, but as to electro-fenton treatment, it is about 4; the appropriate spacing between two plates is 15mm; there is no need to add chlorine ions, 1mmol/L chlorine ions is enough to support the system of Fenton Reaction when electrolyzing Fenton. In the base of maintaining these above conditions, we electrolyze landfill lechate for 4h when the current density is 5A/dm2. Removal of COD, ammonia-nitrogen in electrolysis treatment are 50%,68% separately; removal of COD, ammonia-nitrogen in electrolyzing Fenton treatment are 62%,42% separately, electrolyzing Fenton treatment can strengthen the ability of electrolysis method to remove organic matters in landfill leachate, and further we analyze GC-MS, biodegradability of these organic matters which are produced in the process of electrolyzing Fenton degradation. In this paper, we establish the empirical model of the degradation kinetics of CODCr, ammonia-nitrogen by using linear and nonlinear regression methods.In the biochemical treatment technology, optimization of process parameters at the room temperature for hydrolysis acidification/the first-order/the second-order is 2.25d/6d/3d, adjust concentration of the first-order/the second-order SBBR for 2.0/2.5mg/L, sequencing batch cycle is 6.0h, removal rates of CODCr, ammonium, TN, TP is 89.64%,87.99%,63.64%,69.02%.The optimized process parameters at low temperatures is that HRT is 3d/4d/8d, adjust concentration of the first-order/the second-order SBBR for 2.5/3.0mg/L, sequencing batch cycle is 8.0h, removal rates of CODCr, ammonium, TN, TP is separately 77.86%, 80.61%, 54.22%, 65.69%.In the aspect of combined process: MAP + hydrolytic acidification + SBBR, hydrolytic acidification + SBBR + electro-fenton, MAP + electro-fenton, through the contrast and analysis to above three combined process of landfill leachate treatment, found that, hydrolytic acidification + SBBR + electro-fenton process has advantages in effluent water quality and running cost. Hydrolytic acidification + SBBR operated in accordance with optimization of process parameters, on the basis of Response Surface Method and according to empirical formula, during electro-fenton we determined the appropriate current density and electrolysis time, CODCr, BOD5, ammonia nitrogen, TN, SS, colourity, and they is separately in 22~98mg/L,<10 mg/L,<5 mg/L,<30 mg/L,<5 mg/L,<30, and heavy metals are able to meet the new promulgation of the standards "Pollution control standard of living solid waste landfill"(GB16889-2008). TP in effluent water fluctuates in1.8~3.10 mg/L, and needs to occasionally use of pharmaceutical for phosphorus removal.