The Mechanism And Process Parameter Optimization In Black-odor River Sediments Treated With Calcium Nitrate For Quick Remediation

The phenomena of odorous and black are still a common problem of sediments in most urban river in South China area.And calcium nitrate addition has been proved to be one of the cost-effective technologies for sediment in-situ treatment.However,few of current researches focus on the co-oxidation effect of typical reductive pollutants?such as ferrous,sulfide,ammonium and TOC?in sediments and the community structure of related functional microbes.Besides,the mechanism after nitrate addition into sediment needs to be further clarified and process parameters need to be optimized.Thus,in this work,site investigation was firstly conducted to identify the spatial distribution of main reductive pollutants in the typical odor-black urban rivers in Guangzhou city.Also process parameters such as seasonal changes and dosing ratio were optimized by in situ sediment experiment treated with calcium nitrate.It can find out the co-oxidation process of reductive pollutants and the related functional microbes responding to those processes.The findings in this work could provide technical and theoretical experiences for quick sediment in-situ treatment in urban rivers at South China area.The results showed as follows:?1?Significant variation of spatial distribution of reductive-pollutants?including ferrous,sulfide,ammonium and TOC?in sediments was observed in Guangzhou typical black-odored sediment,whose microorganisms are mainly Proteobacteria and Bacteroidetes.In addition,Thiobacillus?was affirmed to be able to oxidize sulfide and ferrous?within Proteobacteria has been dominated.After nitrate addition,the change of sediment color was related to the oxidation of sulfide and ferrous,and the fast-efficient elimination of black-odored sediment can be achieved in 14 days.?2?The results in this work revealed that microbial community in sediments treated with calcium nitrate would be remarkably restructured by temperature variation.Meanwhile,the process of sulfide/ferrous oxidation was significantly influenced due to the change of dominant bacteria determined by temperature variation.Thus,nitrate-driven sulfide and ferrous oxidation were proportionally promoted only when temperature increased above15?,in which nitrate-driven sulfide and ferrous oxidizing associated bacteria?e.g.Thiobacillus?became dominant.As a result,a higher treatment efficiency by calcium nitrate addition for odor control would be achieved in summer than any other seasons in south China areas.?3?In this work,the ratio of nitrate dosing showed a significant impact on the process of sulfide/ferrous oxidation?ammonia nitrogen oxidation and microbial diversity in sediments.With an appropriate nNO₃/n?S+Fe?ratio,sulfide and ferrous could be simultaneously oxidized completely in two weeks and no sulfide regeneration appeared in two months.These results indicated that for sulfide-and ferrous-rich sediments treatment,n_NO3/n_?S+Fe?ratio was feasible as an index for calcium nitrate dosage calculation and the ratio nearly 1.2 was applicable for a short-term sediment odor control.And the related functional microbes in this progress included Thiobacillus?Sulfurimonas?Candidatus_Brocadia and so on.While the appearance of Candidatus_Brocadia explains the cause of ammonia nitrogen decrease is the reaction of anaerobic ammonia oxidation.