The Degradation Study Of Old Landfill Leachate By Enhanced UASB-catalytic Ozonation-MBR Combination Processes

Sanitary landfill has become the main waste disposal method depending on the low technology process,convenient operation and low investment.A large amount of old landfill leachate is produced over landfill time.Old leachate can be represented by a large fraction of toxic and refractory organic pollutants and a low biochemical oxygen demand:chemical oxygen demand?BOD₅/COD?ratio.Biological treatment technology-membrane technology integrated process is often adopted in most landfills to meet the standard of discharge.However,there are many problems,such as high energy consumption,high requirements on the effluent of the pretreatment system,and serious membrane fouling in the reverse osmosis membrane treatment process.Therefore,it is particularly important to conduct deep research on the aged landfill leachate process owing to the water quality characteristics of the aged landfill leachate and the problems in its actual operation.The present work investigated the performance of enhanced UASB-catalytic ozonation-member combined process dealing with aged landfill leachate and certain scientific achievements were abtained.The performance of catalytic ozonation on the degradation of synthetic phenolic antioxidants and the mechanisms involved in the degradation process were also evaluated.The influence of aged landfill leachate loading on the UASB performance was discussed.The reactor was operated stably with an influent COD loading rate0.15 kg/?m³?d?.The results showed that the nitrite nitrogen accumulates,while the nitrate nitrogen concentration decreases in the reactor.The COD and the total nitrogen?TN?removal reached to 19.4%and 12.2%.The treatment efficiency of aged landfill leachate with the enhanced anaerobic process of glucose co-substrate was discussed.The results showed that the COD removal and total nitrogen?TN?removal increased by 56.4%and 64%under the condition of the addition of glucose co-substrate?300mg COD/L?.Further characterization of sludge morphology and microbial community in traditional anaerobic process and enhanced anaerobic process of glucose co-substrate was analyzed.The obtained results indicated that the corresponding most dominant phylum in the two samples were analogous.However,the proportion of the methanogenic Euryarchaeota bacterium,Chloroflexi,Armatimonadetes,and Firmicutes in enhanced anaerobic process of glucose co-substrate was larger than that of traditional anaerobic process.Further treatment of the effluent of enhanced UASB process was carried out by advanced oxidation technology.The Fe₃O₄ particles decorated Zr pillared bentonite and Fe₃O₄ nanoparticles loading cow-dung ash were synthetized as catalysts during the Fenton-like process and catalytic ozonation,respectively.The performance and influence factor of biologically pretreated aged landfill leachate treatment by the advanced oxidation technology were discussed.Under the conditions of catalyst dosage of 1.0mg/L,initial pH of 2,peroxide concentration of 0.1mmol/L and reaction time 4h,the COD removal increased to 68%and the BOD₅/COD was improved from0.036 to 0.27 through Fenton-like process.Under the optimal conditions of nano-Fe₃O₄@CDA dosage 0.8 g/L,input ozone 3.0 g/L and reaction time 2h,the COD and color number?CN?removal reached to 53%and 89%,and the BOD₅/COD increased from 0.05 to 0.32 during the catalytic ozonation.Based on the comparison analysis of the two advanced oxidation methods,from this perspective the improved biodegradability facilitates its further treatment by a low-cost bioprocess.Catalytic ozonation was more suitable than Fenton-like process for treatment of biologically pretreated aged landfill leachate because of its efficiency on degradation of humic-like and fulvic-like substances and improvement of biodegradability.The effect of catalytic ozonation on the removal efficiencies of two synthetic phenolic antioxidants in aged landfill leachate was studied,namely bisphenol A?BPA?,2,2?-Methylenebis?6-tert-butyl-4-methylphenol??AO2246?.Underthe conditions of initial pH of 7.0,the temperature of 25?,BPA concentration of 50mg/L,catalyst dosage of 0.10g/L,ozone concentration of 5 mg/L,the BPA removal reached to 78%.Coexisting substances,such as Cl^-,CO₃^2-,and HA reduced the degradation efficiency of BPA.Nine intermediates of BPA,such as oxalic acid and malonic acid,were detected by GC-MS and LC-MS in the degradation process.The possible degradation pathways were described.The results confirmed that hydroxyl radical was the main free radical in the degradation of BPA.Under the conditions of initial pH of 7.0,the temperature of 25?,AO2246 concentration of 10 mg/L,catalyst dosage of 0.20g/L,ozone concentration of 10 mg/L,the AO2246 removal reached to47.6%.Eleven intermediates,such as 3,5-bis?1,1-dimethylethyl?-Phenol,4-?1,1-dimethylethyl?-Benzoic acid,were detected by GC-MS and LC-MS in the degradation process.The possible degradation pathways were elucidated.Hydroxyl radical played a major role in degradation process of AO2246.The drainage from catalytic ozonation system then entered into MBR reactors.Under the conditions of HRT of 28h,the COD removal,the ammonia removal and the UV₂₅₄54 removal reached to 25.2%,45.2%and 20.1%,respectively.The refractory compounds with large molecular weight,e.g.humic-like and fulvic-like substances were degraded to the intermediates with low molecular weight.Furthermore,the types of organic compounds were identified in effluent from MBR system by GC-MS.The results showed that the proportion of biodegradable alkanes was significantly reduced,while the proportion of simple alcohols,olefins and esters was significantly increased.Further characterization of sludge morphology and microbial community in MBR reactor was analyzed.The results showed that the proportion of Gemmatimonadetes and Deinococcus-Thermus was higher in the Initial operation compared with the stable operation.During the operation period?HRT=28h?,the sludge in the reactor was fully adapted,the relative proportion of Nitrospirae increased from 0.49%to 5.98%.This thesis confirmed that the enhanced UASB-catalytic ozonation-member combined process has significant advantages in reducing toxicity,improving biodegradability and removing organic pollutants of old landfill leachate.The environmental behavior of SPAs in landfill leachate was studied,and the degradation efficiency and mechanism of catalytic ozonation were analyzed.The SPAs degradation by catalytic ozonation was explored in practical leachate treatment.