Performance Of One-stage Bioreactor For Treating Low C/N Ratio Wastewater And Its Microbial Mechanism

Nitrogen pollution control in wastewater is a hot issue in environmental field in recent years.Through continuous research,scholars from home and abroad have successfully developed a number of novel wastewater biological nitrogen removal process represented by partial nitrification-anammox process(PNA).However,when partial nitrification-anammox(PNA)is used to treat low C/N wastewater,there are still problems remained such as excessive nitrate production,which lead to excessive effluent total nitrogen and complex multi-stage process.Therefore,it is of great significance to develop a new nitrogen completed removal process for low C/N wastewater.This study describes the development of a single-stage partial nitrification,anammox and denitratation(SPANADA)integrated bioprocess for the treatment of low C/N ratio wastewater in an air-lift internal circulation reactor.During 245 days of operation,the reactor demonstrated an excellent total nitrogen(TN)removal efficiency of 91.4%under the conditions of influent ammonia nitrogen of 100 mg/L,COD/N ratio of 3.0 and limited dissolved oxygen concentration of 0.5～1.0 mg/L.The effluent TN meets the first-class discharge standard in Integrated Wastewater Discharge Standard(DB 31-199-2018).Reads-based metagenomics coupled metatranscriptomics analysis found that the main reason for high TN removal efficiency in the reactor may lie in that the synergism of partial nitrification and anammox plays a leading role,and denitritation leads to a higher TN removal efficiency.The expression of the amoA and hao genes for partial nitrification were as high as 3053.4 RPM and 1394.6 RPM,respectively.In addition,the expression of hzsA and hdh genes for anammox reached 2706.5 RPM and 4290.6 RPM,respectively.Another notable trend was that the expression of napA and narG gene for denitratation were 78.7 RPM and 321.8 RPM,respectively,and the sum of the reads from these genes was 3-fold higher than the combined reads for nirK and nirS.Genome-based analysis revealed that the dominant genera of ammonia-oxidizing bacteria and anammox bacteria were members of either Nitrosomonas and Candidatus Brocadia,respectively.They accounted for 5.5%and 10.0%of the total reads in the transcriptome,respectively.For denitratation,Thiolinea,which only contained narG,accounted for 8.5%of the total reads in the transcriptome and,remarkably,84.1%of narG expression.Stoichiometric and kinetic evaluations confirmed that anammox was the dominant nitrogen removal pathway,accounting for 67.0%of the TN removed.Partial nitrification and denitratation accounted for 82.7%and 17.3%of the nitrite production,respectively.This study describes a novel and effective one-stage nitrogen completed removal alternative for low C/N wastewater and gains insight into the underlying microbial mechanism through the use of meta-omics as well.