Membrane aerated biofilm reactor(MABR)is a newly developed biofilm technology for organic wastewater treatment,but it is especially deficient in phosphate removal.Struvite crystallization(SC),as a chemical crystallization method,can recover the nitrogen and phosphate simultaneously from wastewater to make up for the defects of MABR.In this study,we studied the removal efficiency of pollutants and biological communities in MABR and struvite-enhanced membrane aerated biofilm reactor(MAPMABR)under different operation conditions.Through the detection of common sewage index and high-throughput sequencing technology,the law of removal of pollutants and the shift process of bacterial and archaeal community in biofilms under high ammonia nitrogen,COD and phosphate load was revealed.This result laid a solid foundation for further extensive promotion of MABR.In the struvite crystallization part,using MgCl2·6H2O as the precipitant and NaOH as the alkalinity regulator,the recovery efficiency of nitrogen and phosphate and the purity of struvite of the anaerobically digested cattle manure wastewater were optimized.Under the condition of pH 8.0 and Mg/P molar ratio of 1.8,the recovery of phosphate was 83%,and the precipitate struvite was pure according to X-ray result.s With gradual increase of pH,phosphate recovery can be higher than 97%,but impurities such as CaCO3 and Ca3(PO4)2 appeared in the precipitate.As to Mg/P molar ratio,lower ratio brought more calcium sediments while higher ratio caused waste of magnesium salts.Therefore,during the SC stage,pH 8.0 and the Mg/P molar ratio of 1.8 were the optimal parameters for the early recovery of nutrients.The experimental results showed that during the increasing process of aeration pressure from 0.01 MPa to 0.04 MPa and circulating flow rate from 50 r/min to 180 r/min,both COD and TOC removal efficiencies were more than 80% in MABR reactor,but the removal efficiency of ammonia nitrogen,total nitrogen was only maintained about 65%.Turbidity can be effectively removed,which reached to 85%.Effluent concentration of nitrate nitrogen and nitrite nitrogen was almost zero.The removal efficiency of MAPMABR was basically better than the MABR reactor.The removal efficiency,including ammonia nitrogen,TOC,COD and total nitrogen,can reach higher than 80%.Nitrate nitrogen,nitrite nitrogen concentration also approached to zero.Turbidity removal improved clearly and reached to 90 %.Phosphate removal efficiency was higher than 98%,the effluent concentration of phosphate was only 1 mg/L.In the impulse test,both reactors had strong anti-impulse cabability and quickly returned to their original status,due to the large amount of biomass and the complex communities of the species.By adjusting dissolved oxygen in the reactor to 0.5 mg/L,short-cut nitrification and denitrification(SND)was realized through the elimination of nitrite oxidizing bacteria(NOB)and the accumulation of ammonia oxidizing bacteria(AOB).In the later stage of the operation,ammonia solution without organic carbon source was added to the two reactors in order to test the existence of anaerobic ammonium oxidation(ANAMMOX)process.Nitrate nitrogen was found to stay below 10 mg/L in a HRT,while concentration of nitrite nitrogen was as high as 80 mg/L,with a maximum nitrosation rate of 89%.After a HRT in this experiment,the total nitrogen decreased significantly,about 70 mg/L,which indicated the process of anaerobic ammonium oxidation(ANAMMOX)and denitrifying phosphate removal in the reactor.As to biology characterization,abundant Euglyphida showed existence in MAPMABR which indicated lighter load of BOD and possibility of ANAMMOX.High concentration of phosphate promoted algae reproduction.The investigation of Excellular polymer substances(EPS)of sludge showed that the both reactors contained higher concentration of EPS than raw sludge.This result meant MABR can effectively retained organisms and provide a good environment for sludge adsorption.High-throughput data showed that the organism types of raw sludge(RS),MAP-MABR sludge(MMS)and MABR sludge(MS)were similar under phylum classification,but the numbers varied.The changes of Chloroflexi,Actinobacteria,,Proteobacteria,Firmicutes and Bacteroidetes were especially obvious,these organisms in both reactors had shown significant growth comparing to the RS.The Firmicutes and Bacteroidetes have a very strong ability to degrade complex organic matter,proteins and lipids.The Chloroflexi often exist in the sludge floccules of the sludge bacteria and exist in the form of a floc skeleton,which provides skeleton support for the formation of biofilms.However,a significant decrease of Nitrospirae was observed,which demonstrated the rapid reduction of NOB and provided a biological support for the existence of SND.At the level of class,Clostridia had a marked growth,this bacteria has the function of denitrifying phosphate removal,which provided the whereabouts of phosphate on speculation.At the genera level,the proportion of Nitrospira dropped from 1.13% to 0.1%,while the proportion of Nitrosomonas increased from 0.1% to above 0.5%.Candidatus Brocadia,usually participates in anammox,increased from 0% to about 0.174%,which indicated that ANAMMOX appeared in both reactors.But Candidatus Brocadia was not a leading species and the concentration was.The number of species in the MAP-MABR reactor was always larger than MABR.This may be explained by the changed proportion of nitrogen,magnesium and phosphate in the sewage due to earlier struvite crystallization. |