A Study On The Stabilization And Operation Strategies Based On The Anaerobic-semiaerobic Bioreactor Landfill

The sanitary landfill is playing a dominant role in the treatment and disposal of municipal solid waste (MSW) nowadays and is going to be a cardinal type in a long time in China. In order to overcome its deficiencies, including the high pollutants concentration in leachate. the slow stabilization of MSW. and the long and delaying aerogenesis and so on. the bioreactor landfill has become a hot research topic at present. Moreover the hybrid bioreactor landfill has been focused by more and more scholars for it can fully combine the advantages of different bioreactor landfills, such as the anaerobic bioreactor landfill, the aerobic bioreactor landfill, and the semi-aerobic bioreactor landfill. However, as the researches conduct intensively, the contradiction between the stable velocity and the costs for construction and operation of a bioreactor landfill become more and more obvious. Therefore, in this dissertation the anaerobic bioreactor landfill (ANBL) and the semi-aerobic aged refuse biofilter (SAARB) were combined to devise an anaerobic-semiaerobic bioreactor landfill (AN-SABL). Based on the laboratory scale experiments, I consistently discussed its treatment mechanisms, the evolution of leachate, landfill gas. and solid waste. Consequently, some operation strategies were provided. The results indicated that:Not only greatly different qualities of both fresh MSW and aged refuse in AN-SABL. but also alternating aerobic-anoxic-anaerobic zones in the space distribution of SAARB and the particle configuration of aged refuse. These would provide various growing environment for different microorganisms and greatly increase their populations and quantities. As a result, the AN-SABL made it possible to simultaneously remove nitrogen and organic carbon efficiently. Especially it was particularly effective in reducing the total nitrogen due to these different zones would allow a greater number of nitrogen transformations and removal processes, mainly including nitrification-denitrification. and anaerobic ammonia oxidation. Besides, dissimilatory nitrate reduction, ammonia oxidation, ammonia volatilization, adsorption, and some chemical reactions would be able to remove nitrogen in various degrees in different phases.After the 440-day experiment, the remove rates of chemical oxygen demand (COD), total carbon (TC), and total organic carbon (TOC) in the ANBL only were 22.85%,14.04%, and 14.29% respectively. While the remove rates of COD. TC. and TOC in the AN-SABL reached to 55.43%-57.84%,37.38%-37.73%, and 40.19%-49.57% respectively. Moreover, the reduction in total nitrogen (TN) and ammonia nitrogen (NH4--N) in the ANBL only attained 16.65% and 13.12%, while the reduction in the AN-SABL was 2-3 times that of the ANBL. In this experiment. the solid monitoring indexes of MSW fluctuated obviously during the evolution because of the non-uniform excavation and sampling, however, the differences of solid monitoring indexes among the simulated landfills were small. The organic matter in aged refuse remained stable on the whole but there was some accumulation of the TN. Furthermore, the aerogenesis in the ANBL cells of AN-SABL was restrained. And the cumulate gas volumes of the simulated landfills in descending order were the ANBL1#(5633L.52L/kg), the ANBL3# cell (5196L.49L/kg). and the ANBL2# cell (4237L, 39L/kg). whose highest contents of methane reached to 62.60%,62.67%. and 57.62% respectively. The results demonstrated that the AN-SABL could remarkably accelerate the stabilization of MSW compared with the ANBLThe settlement of MSW was obvious and the largest settlement reached up to 25.35% in the ANBL3# cell. However, the aged refuse was stable and its settlement was little. The water content of waste could be increased by recirculating leachate and there were remarkable reduction of leachate volume in the AN-SABL. In the initial stage, the low recirculation frequency (1 time per 3 days) could enhance the degradation of organic matter, but increasing recirculation frequency (1 time per 1 days) were better in the later stage, which could accelerate the aerogenesis and enhance the content of methane. Therefore the high recirculation frequency could reduce the restrain of gas production from the SAARB.The cumulate gas volume of the ANBL increased logarithmically in the initial aerobic phase:then increased linearly in the anaerobic acid phase; afterwards increased exponentially in the methane production of acid phase. The simulated values of carbon and nitrogen transformation models were well coincided with the experimental values, therefore the models could preferably reflect the evolution of pollutants. Furthermore, the degradation of organic matters was influenced by the environmental temperature obviously. Both the transformation coefficient from solid phase to liquid phase (KSL) and the maximal transformation coefficient from liquid phase to gaseous phase(KLGmax) arranged as AN-SABL3#>AN-SABL2#>ANBL1# in order. The concentration of nitrogen pollutants decreased exponentially. As a result. the AN-SABL could more markedly accelerate the degradation of carbon and nitrogen than the ANBL resulting in the landfill stabling faster.When arranging the ANBL and SAARB. there were 3 types of plane layout, such as the compact type. the separate type. and the combined type. The liner system of AN-SABL needed to be strengthened:the collection and removal system of leachate and landfill gas should be enlarged. The effective height of aged refuse in a SAARB was enough to be 900mm. The best treatment efficiency in the SAARB could be achieved at 30℃. with a leachate recirculation period of once every 3 days. hydraulic loading of 8 L/(m(?)·d). and COD of 40000 mg/L (COD loading of 320g/(m(?)·d)). The removal rates of COD, TN, and NH3-N could reached up to 99.40%,94.05%, and 99.52% respectively running in the optimal condition. However, the SAARB needed be kept warm in winter. When the AN-SABL running, it was suggested that the period of leachate recirculation was suitable to be once every 3 days and increased properly in the later phase; and the further advanced treatment of leachate was better to use the acticarbon.These results indicate that the AN-SABL not only accelerates the degradation of MSW faster than the ANBL. but also makes full use of the advantages of SAARB. including the high efficiency of nitrogen remove and the low initial construction costs and operating costs. Therefore, the AN-SABL can provide a novel way to deal with the contradiction between stable velocity and construction and operating costs of a bioreactor landfill. and it can boost the exploitation and the recycle of MSW after a landfill maturing.