High Ammonia Nitrogen Landfill Leachate Treatment By DN-PN-ANAMMOX Biofilm Process

The most common disposal method of solid waste at present is landfill,which is simple in operation and low in cost.However,the landfill would bring the by-product,landfill leachate,a kind of highly contaminated wastewater that is characterized by high ammonia nitrogen concentration,low C/N ratio,and poor biodegradability.Therefore,conventional heterotrophic denitrification would lead to high cost and low efficiency while treating landfill leachate.Combining heterotrophic and autotrophic nitrogen removal to improve nitrogen removal efficiency and reduce treatment costs,this paper designed a three-stage sequencing batch biofilm treatment process of denitrification-partial nitrification-anaerobic ammonium oxidation（DN-PN-ANAMMOX）.The nitrogen removal performance and factors in high ammonia nitrogen landfill leachate treatment,and the distribution of functional bacteria at various levels in reactors were discussed,in order to provide technical support for the application of this process.The denitrification,partial nitrification,and anammox biofilm reactors were fed with synthetic wastewater during start-up and their characteristics were discussed.After 17 days,the denitrification biofilm reactor was successfully operated,the total inorganic nitrogen（TIN）removal efficiency was over 99%,and the COD_Cr removal efficiency was over 85%.The intermittent aeration was adopted in the partial nitrification reactor to control the dissolved oxygen（DO）concentration of 0.25-1.38mg·L^-1;partial nitrification was achieved in 10 days.Furthermore,by controlling the low DO(0.18-1.06 mg·L^-1)and long HRT（96h）,the partial nitrification reactor would convert into partial nitrification-anammox reactor,achieving TIN removal efficiency of70%-90%.The anammox biofilm reactor was inoculated with anammox granular sludge;the influent NH₄⁺-N was 150 mg·L^-1,NO₂^--N was 200 mg·L^-1,and the HRT was 48h.TIN removal efficiency was over 80%in 25 days.The nitrogen removal performance of the anammox biofilm reactor was inhibited while the influent transitioned from synthetic wastewater to actual leachate.Therefore,a granular sludge batch experiment was designed to explore the effect of the concentration of organic matter in the leachate on the nitrogen removal performance of anammox.When the COD_Cr concentration was less than 300 mg·L^-1,the nitrogen removal rate increased with the increase of COD_Cr concentration;when the COD_Crconcentration was 300-500 mg·L^-1,the nitrogen removal rate decreased with the increase of COD_Cr concentration.The results of the granular sludge batch experiment showed that the organic matter in the leachate did not significantly inhibit the nitrogen removal performance of the anammox sludge,while the changes in the surface properties of the biofilm revealed by the SEM and EDS indicated that the biofilm surface will be enriched with salt and metal ions after the leachate was dosed for a period of time.Therefore,to avoid the impact of leachate as much as possible,the anammox biofilm reactor was used as the last stage of the three-stage process.The actual landfill leachate was treated by a three-stage process of heterotrophic denitrification-partial nitrification-anammox.Raw leachate contained 1500-1700mg·L^-1 NH₄⁺-N,and 2500-3000 mg·L^-1 COD_Cr.HRT of each stage was 72h.After 78days of acclimation and operation,the total removal efficiency of TIN in the heterotrophic-autotrophic system was stably above 85%under the conditions of feeding500mg·L^-1(calculated as COD_Cr)of sodium acetate every 144 hours and the reflux ratio of 50%.Among them,the nitrogen removal contribution of the denitrification reactor is basically between 65%and 80%.The partial nitrification reactor contributed 10%-25%nitrogen removal.The nitrogen removal contribution of the anammox reactor fluctuated between 10%and 20%.The COD_Cr removal efficiency was 60%-70%,mainly contributed by the denitrification reactor.The results of high-throughput sequencing analysis showed that after 78 days of operation,the denitrification functional bacteria genus Thauera was successfully enriched in the denitrification reactor;the dominant functional bacteria genera in the partial nitrification reactor were AOB genus Nitrosomonas and An AOB genus Candidatus Kuenenia;the dominant functional genus in the anammox reactor was changed from Candidatus Brocadia to Candidatus Kuenenia.The leachate had the greatest impact on the microbial community structure in the denitrification reactor,and the microbial community structure in the anammox reactor was least affected by the leachate.Treating the leachate resulted in a decrease in biodiversity in the denitrification and anammox reactors,and an increase in biodiversity in the partial nitrification reactor.