Study On In-situ Remediation Performance Of Black-odor River Enhanced By Chemical Oxygenate-immobilized Microorganisms Coupled Technology

Black-odor river is a problem existing in many cities in China.Black-odor river not only affects the appearance of city,but also poses a huge threat to the health of surrounding residents.There are two main reasons for the black-odor river course:constant inflow of exogenous pollutants and continuous release of sediment pollutants.At present,the import of exogenous pollutants in most river has been effectively controlled after the treatment measures such as sewage interception and management,so the remediation of polluted sediment is the key to solve the problem of black-odor river.In this study,the overlying water and sediment collected from polluted river were used as research objects.First,calcium peroxide（Ca O₂）was prepared into slow-release Ca O₂ tablets（Calcium peroxide tablets,CPT）by embedding method,and the in-situ remediation potential and optimal dosage of CPT were investigated under laboratory simulation conditions.Then,CPT was used as oxygenating agent to study the effect of the in-situ remediation of simulated river by adding nitrogen removal bacteria agent,and the synergistic effect of nitrogen removal bacteria agent and CPT was investigated.Finally,the immobilized microorganism technology combined with CPT was used to in-situ repair the simulated river,and the remediation effect and pollutant degradation rule was analyzed.The main results of this study were as follows:（1）The optimal conditions for the preparation of CPT:concentration of PVA solution is2.5%;filling material is biochar;filling material adding ratio is 1:2（biochar:Ca O₂）.The mass of each CPT prepared under the optimal conditions is 0.60 g,the oxygen release time is 362.3h,and the oxygen release speed at first ten days is 0.165 mg·h^-1.CPT could effectively slow down the consumption rate of Ca O₂,achieve sustained oxygen release for a long time,and had little effect on the p H of water.After adding CPT,the removal rate of TP in overlying water reached 90.6%,the proportion of easy-released phosphorus in sediment decreased,and the proportion of hard-released Ca-P increased to 31.3%.CPT could significantly improve the sediment biodegradation capacity（G value）.When the CPT dosage was 1.5 times of the theoretical dosage,the sediment G value could be increased to 1.98 g·（kg·h）^-1.（2）The addition of nitrogen removal bacteria agent BT1 could improve the degradation effect of pollutants in simulated river,after repairing for 40 d,the overlying water NH₄⁺-N,TN,COD and TP concentration decreased to 0.76,1.67,26.5 and 0.16 mg·L^-1 respectively,the removal rates of sediment organic matter（OM）,total transformable nitrogen（TTN）and acid volatile sulfide（AVS）were 12.2%,17.6%and 51.1%respectively.The repair effect of the BT1treated group was significantly better than that of the untreated group.The nitrification process of NH₄⁺-N was coordinated by AOA and AOB under the combined remediation mode of CPT and BT1.The copy number of AOA＿amo A gene and AOB＿amo A gene in sediment reached2.72 and 10.88 times of that in initial sediment.The addition of BT1 significantly increased the nir K gene copy number to 4.54×10⁵ copies·g^-1 at 10 d,which enhanced the nir K denitrification process at the early stage of this experiment.The oxygen slow-release characteristics of CPT inhibited the growth of anaerobic microorganisms in sediment,and the relative abundance of aerobic bacteria increased significantly.Among them,the relative abundance of BT1 was up to3.27%,which was the dominant nitrifying bacterium in sediment.（3）Volcanic rock has the best effect of microbial immobilization.The optimal conditions of DO concentration,p H and temperature for the preparation of volcanic rock immobilized microorganisms are 5 mg·L^-1,9 and 35℃respectively.The combined remediation mode of CPT and immobilized microorganisms could effectively promote the degradation of organic pollutants in simulated river.Increasing the dosage of immobilized microorganisms is beneficial to decrease the concentration of NH₄⁺-N in overlying water,but not conducive to the removal of NO₃^--N.The combined remediation mode inhibited the release of nitrogen from sediment,and the decreasing amplitude of NH₄⁺-N and TN diffusion flux was:3 kg·m^-2group>5 kg·m^-2 group>1 kg·m^-2 groups.The combined remediation mode could reduce the content of IEF-N and WAEF-N（easy-released form）in sediment,and increase the content of SAEF-N（hard-released form）.Meanwhile,the content of SOEF-N（organic form）decreases by27.6%.When the immobilized microorganism dosage was 3 kg·m^-2,the TTN reduction effect was the best,and the removal rate reached 26.1%.By comprehensive comparison,the 3 kg·m^-2 dosage of immobilized microorganism had the best effect for simulated river in-situ remediation.