Effect Of Ca²⁺ And Mg²⁺ On Nitrification Performance And Microbial Community Structure Of Sludge Using SBR Process

Metal smelting,printing and dyeing,papermaking,petrochemical and other industries often produce a large amount of wastewater containing Ca²⁺and Mg²⁺.The Ca²⁺and Mg²⁺enter the sewage treatment plant and contact with activated sludge,which can affect microbial activity,sludge flocculation and sedimentation performance.In this study,the effects of Ca²⁺and Mg²⁺on the removal efficiencies of COD,NH₄⁺-N and TN were investigated.The changes of the flocculation and settling properties of activated sludge were studied and the composition and structure of extracellular polymeric substances?EPS?were analyzed by infrared spectroscopy?FTIR?and three-dimensional fluorescence spectroscopy?EEM?.The microbial community structure was explored by high-throughput sequencing?amplification sequencing?.The influence mechanisms of Ca²⁺and Mg²⁺on the nitrification activity and microbial community structure of activated sludge was revealed using SBR process,which would provide a theoretical and practical foundation for the improvement of nitrogen removal efficiency and sludge settling performance in the sewage treatment plant.The results showed that Ca²⁺promoted the activity of nitrifying bacteria when the influent Ca²⁺concentration was lower than 1.1 mmol·L^-1under the influent COD of 300 mg·L^-1,NH₄⁺-N of 25 mg·L^-11 and TN of 27 mg·L^-1.As the influent concentration of Ca²⁺increased,the removal efficiencies of NH₄⁺-N and TN increased from 93%and 67%to 96%and 72%,respectively.SOUR_AOBOB and SOUR_NOBOB increased from 6.3 and 2.3 to 10.8 and 4.8 mg O₂·?g VSS?^-1·h^-1,respectively.When the influent concentration of Ca²⁺was 3 mmol·L^-1,Ca²⁺began to inhibit the activity of nitrifying bacteria.Removal efficiencies of NH₄⁺-N and TN were not affected,but SOUR_AOBOB and SOUR_NOBOB decreased slightly.Ca²⁺promoted the production of EPS and PN and the ratio of LB-EPS/EPS was reduced.Based on EEM analysis,aromatic proteins,fulvic acids and humic acids were found in EPS.Based on FTIR analysis,the increase of Ca²⁺concentration did not influence the composition of main functional groups and the functional group of LB-EPS and TB-EPS was identical.Ca²⁺mainly bonded with amide I,carboxyl and polysaccharide representative groups.The richness and diversity of microbial communities was the highest when the Ca²⁺concentration was 1.1 mmol·L^-1.Mg²⁺promoted the activity of nitrifying bacteria when the influent Mg²⁺concentration was lower than 1.1 mmol·L^-1.As the influent Mg²⁺concentration increased,the removal efficiencies of NH₄⁺-N and TN increased from 92%and 65%to 98%and 74%,respectively.SOUR_AOBOB and SOUR_NOBOB increased from 5.0 and 3.3 to 8.8 and 4.4 mg O₂·?g VSS?^-1·h^-1,respectively.When the influent Mg²⁺concentration was 3 mmol·L^-1,Mg²⁺began to inhibit the activity of nitrifying bacteria,and SOUR_AOBOB and SOUR_NOBOB decreased slightly.However,the removal efficiencies of NH₄⁺-N and TN were not affected.Mg²⁺inhibited the production of EPS,PN and PS,and reduced the ratio of LB-EPS/EPS.Based on EEM analysis,aromatic proteins,fulvic acids and humic acids were found in EPS.Based on FTIR analysis,the increase of Mg²⁺concentration did not influence the composition of the main functional groups and the functional group of LB-EPS and TB-EPS was identical.Mg²⁺mainly bonded with amide I and polysaccharide representative groups.The richness and diversity of microbial communities was the highest when the Mg²⁺concentration was 1.1 mmol·L^-1.When the molar ratio of influent Ca²⁺/Mg²⁺was 0.5,denitrification efficiency was the highest,nitrifying bacteria activity was strongest and flocculation and settleability of sludge was optimal.The removal efficiencies of COD,NH₄⁺-N and TN were 93%,96%and 70%,respectively.SOUR_AOBOB and SOUR_NOBOB were 10.2 and 6.9 mg O₂·?g VSS?^-1·h^-1,and SVI and FA were 52 mL·g^-11 and 46%,respectively.Based on EEM analysis,aromatic proteins was detected in LB-EPS and TB-EPS,and fulvic acids appeared in LB-EPS when the molar ratio of Ca²⁺/Mg²⁺was 0.5.Based on FTIR analysis,Ca²⁺/Mg²⁺molar ratios did not influence the composition of main functional groups of EPS.When the molar ratio of influent Ca²⁺/Mg²⁺was 0.5,the richness and diversity of microbial community were highest.