| Mature landfill leachate always contains high concentration of ammonium and organic matter,and is characterized by low C/N ratio.How to achieve efficient and economical nitrogen removal from mature landfill leachate is still a huge challenge.Compared with conventional nitrification and denitrification process,partial nitritation and ANAMMOX?PN-ANAMMOX?process has advantages of low oxygen requirement,no organic carbon source consumption and less sludge production,which ensures it a bright prospect in application in treating mature landfill leachate and other wastewater characterized by high concentration of ammonium and low C/N ratio.In this study,a combined process of pre-denitrification,partial nitritation based on zeolite biological aerated filter?ZBAF?and ANAMMOX?PN-ANAMMOX?was used to remove nitrogen from mature landfill leachate,to support theoretical basis for the application of this combined process to remove nitrogen from mature landfill leachate with high efficiency and low cost.Before treating mature landfill leachate,the upflow sludge blanket?USB?,ZBAF and ANAMMOX reactors were started up with synthetic wastewater for 30 d.The USB,ZBAF and ANAMMOX reactor were started up successfully on day 6,14 and 10,respectively.And the nitrogen removal rate?NRR?of USB,nitrite production rate?NPR?of ZBAF and NRR of the Anammox reactor values of 0.961,0.621 and 0.434 kg N/?m3·d?,respectively,were obtained on day 30.When treating mature landfill leachate,effects of reflux ratio,external carbon source and influent nitrogen loading rate?NLR?on nitrogen removal performance of the combined process were investigated.Results showed that optimum nitrogen removal performance was obtained under reflux ratio of 2.0.Average ammonium removal efficiency?ARE?of 96.6%,total nitrogen removal efficiency?NRE?of 86.1%,and NRR of 0.266 kg N/?m3·d?were obtained,respectively.In addition,it was found that nitrogen removal performance of the USB and the combined process were significantly improved with addiction of 700 mg/L glucose into raw landfill leachate.Average ARE of 97.3%and NRE of 90.0%,and the highest NRR of 0.617 kgn N/?m3·d?were obtained in this phase.Moreover,nitrogen removal performance of combined process was not destroyed by the increase of NLR.The ARE and NRE remained at approximately 98.4%and 90.1%,respectively.When influent NLR was0.517 kg N/?m3·d?,NRR reached 0.471 kg N/?m3·d?.Additionally,operation characteristics of each reactor were analyzed.Results showed that fully utilized of biodegradable organic matters in USB reduced the risk of inhibition to the subsequent PN-Anammox process.Besides,due to the combined inhibition of free ammonia?FA?and free nitrous acid?FNA?on nitrite oxidizing bacteria?NOB?,ZBAF successfully achieved high-efficiency and stable partial nitritation for mature landfill leachate with an average nitrite accumulation rate?NAR?of 95.2%and a NPR of 1.659kg NO2--N/?m3·d?.In Anammox process,optimum nitrogen removal performance was observed under influent NO2--N/NH4+-N of 1.1?1.3.Effluent NH4+-N and NO2--N were stable within 50.0 and 30.0 mg/L,respectively.When NLR increased to 1.608 kg N/?m3·d?,NRRANAof 1.391 kg N/?m3·d?was obtained.Furthermore,TN removal efficiency in each reactor was discussed.It was found that TN in mature landfill leachate was mainly removed by USB and ANAMMOX reactor.The lower C/N ratio was,the lower TN removal efficiency of USB was,while the higher TN removal efficiency of ANAMMOX reactor was.When C/N ratio was 2.2,1.7 and 1.1,TN removal efficiency of USB was about 49.6%,34.5%and 27.4%,separatively,and that of ANAMMOX reactor was 40.3%,42.5%and 62.7%,respectively.High-throughput sequencing analysis further revealed that the dominant bacteria genera Paracoccus and Comamonas in the USB,Nitrosomonas in the ZBAF and Candidatus Kuenenia and Candidatus Anammoxoglobus in the Anammox reactor were demonstrated to be responsible for denitrification,partial nitritation and Anammox process,respectively. |
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