Mechanism Of Chemical,Biological And Ecological Collaborative Remediation To River Sediment

With the rapid development of modern city and industrialization,river pollution has become one of the most serious environmental problems in China.Sediment,particularly at the bottom of large rivers,acts as a sink for a wide variety of anthropogenic contaminants,which has nagetive impacts on overlying water.To overcome limitations associated with the use of single method,combinations of different methods have been introduced to enhance removal of contaminants in sediment.In this study,chemical,biological and ecological collaborative methods were applied for remediation of river sediment.In the study on the optimal dosage of calcium nitrate,aerobic denitrifiers combined with calcium nitrate showed better performance when the dosage of calcium nitrate was0.15 g/L.The removal of the total nitrogen?TN?in the sediment was 16.5%,the total transferable nitrogen?TTN?content increased from 0.097 mg/g to 0.109 mg/g,and the urease activity increased.This indicates that more nitrogen in the sediment had the potential to be further degraded.The organic pollutants in the sediment were removed or converted to low molecular weight compounds through microbial biodegradation.Decreased phenol oxidase activity exhibited that low concentrations of recalcitrant aromatic compounds remained in the sediment.The community diversity of bacteria markedly increased,and dominant genera mainly removed nitrogen and organic compounds,especially recalcitrant compounds.This suggests that a more favorable environment existed in the sediment.In the study on the optimal dosage of the biostimulant,when the dosage of the denitrification agent was 0.1 g/L,aerobic denitrifiers combined with the denitrification agent showed better performance on the remediation of river sediment.In the sediment,the removal efficiency of the TN was 14.7%,the concentration of TTN increased from0.097 to 0.166 mg/g,and the urease activity increased.This suggests that more nitrogen in the sediment would be further biodegraded.Although the TOC in the sediment decreased slightly,the combination technology could improve the removal of COD_Cr in the overlying water.The community diversity of bacteria markedly increased in the later period,indicating a more favorable environment and the improvement of self-purification ability.Aerobic denitrifiers,denitrification agent and calcium nitrate were added at the same time and showed better permances in the process of collaborative remediation.After 70 d of treatment,the TN in the sediment decreased from 1.52 to 0.97 mg/g.After120 d,the TOC content decreased from 0.430%to 0.251%.The acitvities of urease and protease decreased significantly,indicating most available nitrogen in the sediment were biodegraded.However,the phenol oxidase activity increased in the initial period.The micro-ecological environment in the sediment was improved and the community diversity of bacteria increased,which guaranteed the sustainable remediation.During the process of phytoremediation combined with aerobic denitrifiers and calcium nitrate or aerobic denitrifiers and denitrification agent,the release of nitrogen and phosphorus from the sediment was reduced,and the ORP values and the removal of TN in the sediment was enhanced.Moreover,phytoremediation combined with aerobic denitrifiers and denitrification agent could improved the removal of the organic matter in the sediment.Plants play an important role in the bactetial community succession,and the relative abundance of the bacteria,which had the intergrowth relationship with the plants,would increase in the later period.Furthermore,the collaborative effects increased the content of TN,soluble sugar,soluble protein and chlorophyll in the plants.