Effect And Mechanism Of In-situ Remediation Of Black And Odorous Water By Humic Acid Reducing Bacteria

With the urbanization and the improvement of living quality,urban rivers and natural freshwater suffered from more pollution input,resulting in frequent black and odorous phenomenon.River remediation has become an important task at present.Biological measures are widely used in river remediation.Humic-reducing bacteria can utilize the humic acid in sediment to accelerate the degradation of pollutants,which has attracted extensive attention.In this paper,the effects and mechanisms of humic-reducing bacteria,calcium nitrate and its synergy on the remediation of black and odorous were investigated.In the remediation experiment using humic-reducing bacteria and activated sludge capable of humic acid reduction,the decrements of the total organic matters(TOM)in the bacteria group and the activated sludge group were 26.4mg/kg-dry-sediment and 22.7 mg/kg-dry-sediment(42 d),respectively,higher than that in the control group.The decrements of acid volatile sulfur(AVS)were 817mg/kg-dry-sediment and 1399 mg/kg-dry-sediment(42 d),respectively.The relative abundance of heterotrophic microorganisms were significantly increased.The microbial activity of single bacteria group is higher,which indicates that humic acid reducing bacteria can use humic acid in sediment to improve the degradation rate of pollutants and promote the microbial activity of corresponding reactions.To enhance the removal of TOM and AVS,chemical agents addition was employed to strengthen remediation efficiency.Calcium nitrate can significantly improve the micro-ecological environment in sediment.The relative abundance of Proteobacteria(phylum level)increased from 32.11%(control group)to 65.97%.Sulfide bacteria became the predominant dominant(relative abundance 4.02%).The degradation rate of TOM in sediment was 45.2 mg/kg-dry-sediment(42 d)and the degradation rate of AVS in sediment was 1720 mg/kg-dry-sediment(7d),higher than that of the control group.The results showed that calcium nitrate can stimulate the activity of sulfur oxidizing bacteria and heterotrophic microorganisms in sediment and accelerate AVS and degradation in sediment.However,AVS would rebound,and the sulfate-reducing bacteria “Sulfurimonas” became dominant after 21 days' remediation with a relative abundance of 0.96%,and AVS rebounded over the initial level(3068 mg/kg-dry-sediment)after 77 days.In the synergetic remediation experiments using humic acid reducingbacteria+chemicals or activated sludge with humic acid reducing ability+chemicals,the measures can significantly improve the micro-ecological environment in sediment,the relative abundance of Proteobacteria(phylum level)were 63.74% and 59.76%,and the relative abundance of sulfide bacteria were 3.92%and 3.09%,respectively.The decrements of TOM were 32.6 mg/kg-dry-sediment and30.0 mg/kg-dry-sediment(42 d),respectively,higher than that of the control group.The decrements of AVS were 2026 mg/kg-dry-sediment and 2201mg/kg-dry-sediment(42 d),respectively.After 7 days,AVS rebounded slightly,and the rebound rate was only about 50% of that of the chemical group,which indicated that the coordinated chemical-biological remediation was positive to control AVS rebound.Using bio-remediation alone had limited effect on changing the micro-ecological environment and improving microbial activity in the sediment.Chemical remediation can rapidly reduce AVS,increase TOM degradation and enrich microbial community,while the AVS rebound phenomenon was remarkable,therefore,the AVS control cannot be long-lasting.Chemical-biological synergistic remediation can improve the micro-ecological environment of sediment and enhance microbial activity.It can improve the degradation rate of TOM and AVS,restrain the rebound phenomenon of AVS,and achieve the goal of long-lasting remediation.