Isolation And Immobilization Of Aerobic Denitrifiers To Enhance Denitrification Of Rural Domestic Sewage

Nitrogen pollution of rural domestic sewage affects the quality of the local water environment and restricts the development of rural areas.In order to improve the living environment and ensure the ecological health of the water environment in rural areas,it is particularly important to seek an economical,safe and efficient denitrification technology.As an important part of the new denitrification processes,aerobic denitrification enriches the theory of biological nitrogen removal process.In comparison with traditional denitrifiers,aerobic denitrifiers can complete both the nitrification and denitrification processes under aerobic conditions.It simplifies the process flows and facilitate management,which has attracted extensive attention from domestic and foreign scholars.Combined with previous experience,aerobic denitrification bacterial consortium LHJ-1 was isolated from the sediment of Longhongjian pond in this study.Meanwhile,the denitrification characteristics,functional genes and immobilization studies were carried out to further investigate the characteristics of the bacterial consortium.Finally,the immobilized bacterial consortium were added into the experimental reactor to enhance the denitrification for artificial domestic sewage.The main conclusions are as follows:?1?Bacterial consortium LHJ-1 was mainly composed of Pseudomonas,Acinetobacter,Acidovorax,Cupriavidus and Pseudoduganella with NapA,NirK,NirS and NosZ genes.Cupriavidus was the main aerobic denitrification bacteria among this bacterial consortium,which could conduct a complete denitrification process.The bacterial consortium LHJ-1 showed great aerobic denitrification and heterotrophic nitrification characteristics with NO₃^--N,NO₂^--N and NH₄⁺-N as nitrogen sources,and the nitrogen removal rate was 76.73%,72.11%and 93.58%,respectively.The bacterial consortium could use different carbon sources and had a good adaptability to the change of pH and dissolved oxygen concentration.Additionally,it was more suitable to grow with high C/N ratio.The bacterial consortium was acclimated with C/N up to 8 to adapt to rural domestic sewage while the results showed that the denitrification efficiency continued to be above 70%.The model of bacterial denitrification predicted that the highest denitrification efficiency of LHJ-1 could be up to 81.21%,while the final denitrification efficiency of verification experiment was76.00±2.59%.The result was consistent with expectation.?2?It was found that the optimal carrier ratio was 12%polyvinyl alcohol?PVA?,8%sodium alginate?SA?,0.5 g rice husk powder and 10 mL bacterial solution,which were cross-linked for 4 h in 3%CaCl₂-boric acid satiation solution and then cross-linked for 1 h in 0.5 mol/L Na₂SO₄ solution to form immobilized pellets.It showed that the pellets had good stability and mass transfer performance,and the removal rate of TN at 48 h was about 90%.Compared with free bacteria,the efficiency was significantly improved.The pellets had good tolerance to the change of pH and rotation speed.However,they were seriously affected by low temperature while can obtain good denitrification efficiency in a high temperature environment.?3?In the stable stage,the average removal rate of COD,TN,NH₄⁺-N in the control group were 90.84%,65.58%and 79.48%,respectively,while that in the experimental group were 91.22%,77.96%and 89.74%,respectively.Moreover,the effluent water quality of the experimental group reached class 1A which implied that the removal rate of pollutants in the experimental group was better and more stable than the control group.The results of microbial diversity study suggested that there were aerobic denitrifiers in both groups.Due to the addition of pellets,the abundance of Cupriavidus was highest among the experimental group while which was lower in the control group.The results showed that the bacterial consortium LHJ-1 had great potential in practical application.