Effect Of Mn²⁺ On Simultaneous Nitrification-Denitrification And Phosphorus And Manganese Removal By MBBR And Its Performance Optimization

The residual nutrients in the wastewater can lead to eutrophication of the water body if not completely treated,such as nitrogen and phosphorus.In recent years,moving bed biofilm reactor（MBBR）has been widely used to treat various wastewaters and emerging pollutants.The biological carriers in the MBBR not only promote the enrichment of ammonia oxidizing bacteria（AOB）and nitrite oxidizing bacteria（NOB）,but also create favorable aerobic/aerobic/anoxic conditions for the biological denitrification process,which can improve the MBBR robustness.Microbial in-situ oxidation of Mn²⁺to generate biogenic manganese oxides（BioMnO_x）by Mn²⁺oxidation with high redox potential can facilitate the pollutant degradation process.In this study,the effects of different concentrations of Mn²⁺on simultaneous nitrification denitrification and phosphorus and manganese removal by MBBR were investigated by constructing a laboratory-scale MBBR to treat simulated nitrogen-and phosphorus-containing wastewater;to further improve the total nitrogen（TN）removal,the performance ofβ-cyclodextrin（β-CD）driven MBBR for nitrogen conversion and denitrification for phosphorus and manganese removal was investigated.The main results obtained in this study are as follows:（1）With or without the addition of Mn²⁺,the average removal efficiency of MBBR for NO₃^--N and COD reached 95%and 89.9%,respectively,and the concentration of NO₂^--N hardly accumulated.The MBBR simultaneous nitrification denitrification（SND）and denitrification phosphorus removal efficiencies gradually increased with the increase of Mn²⁺concentration.Compared with the feed water Mn²⁺of 0 mg·L^-1,the average TN removal efficiency of MBBR at Mn²⁺concentrations of 5,10 and 15 mg·L^-1increased by3.8%,23.3%and 28.1%,respectively,the average TP removal efficiency increased by7.3%,29.1%and 41.9%,respectively,and the SND efficiency increased by 12.1%(Mn_inf²⁺=10 mg·L^-1)and 16.6%(Mn_inf²⁺=15 mg·L^-1),respectively.The biofilm EPS concentration and PN/PS ratio decreased with the increase of Mn²⁺concentration.When the concentration of Mn²⁺in the influent increased from 0 mg·L^-1to 5,10,and 15 mg·L^-1,the relative levels of reactive oxygen species（ROS）in MBBR increased by 8%,27%,and70%,respectively,while the activity of glutathione peroxidase（GSH-Px）decreased by219.43,481.54,and 1039.43 U·mgprot^-1,respectively.High-throughput sequencing showed that Proteobacteria,Bacteroidetes,and Actinobacteria were mainly involved in the biological nitrogen removal process.With the increase of Mn²⁺concentration,the richness of the microbial community decreased,but the relative abundance of major bacteria involved in biological nitrogen removal,such as Proteobacteria,increased continuously.（2）Neitherβ-CD nor a single nitrogen source alone could improve the performance of MBBR for nitrogen and manganese removal.The simultaneous addition ofβ-CD(0.1m M·L^-1)and Mn²⁺(10 mg·L^-1)could successfully optimize and improve the performance of MBBR for nitrogen and manganese removal.When bothβ-CD and Mn²⁺were added to the influent,the average removal efficiencies of MBBR for NO₃^--N,NH₄⁺-N,TN,TP,and COD were 96.12%,76.55%,84.88%,51.1%and 98.39%,respectively,when bothβ-CD and Mn²⁺were added to the influent.Compared with the MBBR with 10 mg·L^-1Mn²⁺in the influent,the average removal efficiencies of NH₄⁺-N,TN,COD,and Mn²⁺were increased by 23.45%,27.58%,9.49%,and 7.7%,respectively,and the SND efficiency was increased by 16.71%for the MBBR with bothβ-CD and Mn²⁺in the influent,and the average residual concentration of NO₂^--N decreased to 0.06 mg·L^-1.The MBBR optimized usingβ-CD and Mn²⁺showed a 14.5%decrease in the relative level of ROS and a 0.24μg O₂·g^-1·h^-1increase in electron transfer system activity（ETSA）compared to the MBBR with an influent Mn²⁺concentration of 10 mg·L^-1.The main dominant bacterial phylum species remained unchanged,including Proteobacteria,Bacteroidetes and Acidobacteria,while the dominant phyla mainly involved in denitrification were Betaproteobacteria,Alphaproteobacteria,Cytophagia and Sphingobacteria.