Technique And Mechanism Of Bioreactor Landfill For Rapid Degradation And In-situ Nitrogen Removal Of Refuse

The ammonia still remained a challenge in the leachate recirculation,phase separation and sequencing batch bioreactor landfills where the degradation of refuse could be accelerated.The objective of the dissertation was to develop the bioreactor landfill which could stabilize the refuse quickly and in-situ remove nitrogen effectively. From the viewpoint of theory and manipulation supply,the investigation was significant for increasing the volume recovery and eliminating nitrogen pollution of landfill.In the thesis,the bioreactor filled with aged-refuse was constructed after the aged refuse was characterized by physico-chemical properties and microbial distribution.The efficiencies and mechanisms which the bioreactor filled with aged-refuse reduced organic matter,nitrified ammonia and denitrified nitrate were also studied.Subsequently,the in-situ nitrogen removal bioreactor landfill(NBL),consisted of fresh-refuse filled(NBLF),methanogenic(NBLM)and nitrification(NBLN) reactors,was constructed and then operated.In the experiment,the sequencing batch bioreactor landfill(BL)which only comprised of fresh-refuse filled(BLF)and methanogenic(BLM)reactors,was used as control.The methanogenic and nitrification reactors were all loaded with aged refuse and the nitrification reactor was in situ aerated.The performances of refuse decomposition and in situ nitrogen removal were observed,and the mechanism of in situ nitrogen removal was further explored in the NBL.Furthermore,those behaviors and mechanisms were discussed sequentially during the optimal operation of NBL.With the help of traditional microbiological methods and molecular biological technologies,the distribution of ammonia-oxidizers on different carriers in the bioreactor landfill was observed,ammonia-oxidizers existed in the bioreactor were separated,purified and identified,the succession of ammonia-oxidizer population with the operation of the bioreactor landfill was explored deeply.The main results were summarized as follows:(1)The aged refuse has got stabilization and contains a wide spectrum and large number of microorganisms which can amount to 10¹²CFU g^-1after six to seven years' deposit.Thus,it was the favorable microorganism medium.(2)The efficiency of organic matter removal was excellent and could reach to 98.9%in the bioreactor loaded with aged refuse.However,its efficiency of reducing nitrate depended on the organic matter content in influent.The removal efficiency of NO₃^--N was only 36.2%when the concentration of COD and NO₃^--N was respectively zero and 317.1 mg L^-1,while the removal efficiency of NO₃^--N and COD increased to 99%and 90%when their concentrations in influent were 3400 mg L^-1and 491.1 mg L^-1),respectively.(3)The nitrification bioreactor loaded with aged refuse was high-effective in ammonia removal,nitrifying ammonia,oxygen utility and organic matter removal.Its nitrifiation efficiency kept above 50%and the NH₄⁺-N,TN and organic matter removal efficiencies could reached to 100%,50%and 98%when the NH₄⁺-N load of aged refuse was 89.1 mg N(kg d)^-1,the oxygen supply was 8.5 mg O₂(mg N d)^-1,and the COD concentration was 3000 mg L^-1,respectively.(4)The NH₄⁺-N was.mainly removed by adsorption on aged refuse in the bioreactor at the initial operational stage.The adsorption of ammonia on aged refuse was promptly,which could get to equilibrium during 0.5h,and the adsorption behavior met the Frendlich adsorption isotherm.The adsorption content was mainly affected by solid to liquid ratio and concentration of NH₄⁺-N in the liquid.(5)The in situ nitrogen removal efficiency of the NBL was better than the BL during the 200 days operation.The nitrogen removal of the NBL was 1.6 times as much as that of the BL.However,the methane production was reduced.The methane production of the NBLM was only 0.58 times as much as that of the BLM. Furthermore,the decomposition of refuse in NBL would be delayed if the NBL was operated for a long time.The sedimentation and mass decrease of the NBL was only 0.85 and 0.76 times as much as of the BL,respectively.(6)After the BL and the NBL were operated optimally,the in-situ aeration in top layer promoted the degradation/stabilization and in situ nitrogen removal of "old refuse" further.The optimal operation stage of the BL and the NBL lasted for 110 days. At the end of the experiment,the BDM,NH₄⁺-N,TN of the top layer refuse from the BLF decreased to 11.47%,26.79 mg kg^-1and 2159 mg kg^-1,while those of the NBLF still remained at 14.67%,181.1 mg kg^-1and 4213 mg kg^-1,respectively.(7)The BL which was carried out the combination of sequentially anaerobic/anoxic and aerobic operation was effective at in-situ nitrogen removal, energy recovery and refuse degradation.At the end of experiment,the leachate COD contributed by organic matter in the BL and the NBL were 114.6 mg L^-1and 244.1 mg L^-1,respectively.The concentration of NH₄⁺-N and TN in leachate from the BL reduced to 20.60 mg L^-1and 25.33 mg L^-1,which had met the level of current discharge standards in China(GB16889-2008),while those of the NBL still kept at the level of 49.70 mg L^-1and 53.00 mg L^-1,respectively.(8)The ammonia,nitrite oxidizers and denitrifying bacteria co-existed in the BLF and the NBLF during the 200 days of operation in the bioreactor landfill.The ammonia-oxidizer could survive from the high-organic and low oxygen condition because they could do on the inorganic carriers firstly.The nitrogen removal was ascribed to nitrification and denitrification simultaneously.Moreover,ammonia oxidizer population in the NBLF was more stable than that in the BLF,which enhanced the efficiency of in situ nitrogen removal in the BLF.(9)In the optimal operation of the bioreactor landfill,the aeration in top layer of BLF promoted the growth of ammonia-oxidizer in "old" refuse,and hence enhanced the efficiency of in situ nitrogen removal in the BLF.(10)Heterotrophic nitrifier might be the main contributor of nitrogen transformation in the bioreactor landfill.Two strains of heterotrophic nitrifiers(named as HN1 and HN2)were separated from the NBLF,BLF and NBLN.The HN1 and HN2 were identified to be Alcaligenes sp.and Acinetobacter sp.respectively.The most favorite growing condition of HN1 was pH 7.0,temperature 40℃,C/N 20, acetic 2000 mg L^-1and NH₄⁺-N 100 mg L^-1.Furthermore,the HN1 has the function of nitrification and denitrification simultaneously,and hence its ecological function for nitrogen transformation can't be evaluated only with the accumulation of nitrite during the process of pure culture.