Mature Landfill Leachate Treatment By UIMF Process

The landfill leachate treatment was a worldwide problem and the current treatment processes were not perfect. In this paper, typical mature landfill leachate from Pingdi Landfill Plant in Shenzhen was used, with high NH4+-N and poor biodegradability. The water quality of this leachate was complicated and the COD, NH4+ and BOD5 concentration were 1800～2600mg/L, 400～750mg/L, 300～550mg/L, respectively. Combined process of Up-flow Anaerobic Sludge Bed(UASB),Immobilized Microorganism-biological Aerated Filter(IBAF) and Membrane Bioreactor(MBR) followed by Fenton process(UIMF process) were used to treat the leachate.The effect of pH and dissolved oxygen (DO) on treatment capacity was investigated in IBAF and MBR. The results indicated that, In IBAF, under condition of hydraulic retention time (HRT) =2d, DO=4mg/L, the best pH was 7.5～8.5, NH4+-N removal rate was about 95%; In MBR, removal rates of COD and NH4+-N were 62% and 55% under condition of HRT=10d, the range of influent pH was 7.5～8.5, the most suitable DO was 3mg/L.The running parameters of combined process of UASB-IBAF-MBR(UIM) were taken based on previous results. Treatment results in the stage of stability indicated that, average COD removal rate was 24.3% in UASB because of low influent COD and organic load; Average NH4+-N removal rate was up to about 95% in IBAF, which reflected the advantages of IBAF on high NH4+ treatment; Average COD removal rate was 30.8% in IBAF; NH4+-N concentration in the effluent of IBAF was low, so ,average removal rate was 89.2% in MBR; Average COD removal rate in MBR was 44.3% because of lower biodegradable organic compounds in IBAF effluent; Average total COD and NH4+-N removal rates were 70.8% and 99.6%. Average NH4+-N concentration was 1.9mg/L in leachate treated by combined process, but average COD concentration was 585mg/L.Fenton reagent is used to deal with residual refractory COD. Under condition of initial pH=4, H2O2/Fe2+=5:1, H2O2=0.05mol/L, feeding once, 2.5h reaction time with stirring, and 30min settlement time, more than 85% COD was removed. After Fenton treatment, total COD removal rate was about 95% and COD concentration of effluent was less than 100mg/L. The effluent agreed with the first degree discharge standard.