Study On Reduction Of Pollutants In Black-odorous River Sediment And Purification Of Water Quality By Iron-Carbon Micro-electrolysis Coupled With Denitrifying Bacteria

The direct discharge of domestic sewage and industrial wastewater causes a large amount of pollutants to deposit in the riverbed,and the urban rivers are turned into black-odorous water bodies.Governing black-odorous rivers has become an important task in Chinese urban environmental protection.In recent years,it has been found that the black-odorous river emergency treatment methods are flawed.The use of microbial methods to treat river courses is generally recognized.Among them,the technology of iron-carbon micro-electrolysis technology combined with microorganisms has received extensive attention.Therefore,a technical system of iron-carbon microelectrolysis coupled denitrifying bacteria was constructed in this paper,which was used to reduce black-odorous sediment pollutants and purify water quality.Indoor simulation was conducted to provide technical and theoretical basis for reduction of pollutants in black-odorous sediment and purification of water quality by iron-carbon micro-electrolysis coupled with denitrifying bacteria.The single-factor simulation experiment was carried out by using the control variable method.Influence of the dosage of iron-carbon filler,the dosage of denitrifying bacteria and the length of aeration on the effect of reduction for pollutants in black-odorous sediment and water purification were investigated.A comparative study of different combinations was conducted to analyze the fate and transformation of the four main pollutants of C,N,P and S in the sediment-overlying water system,and analyz the evolution of microbial communities,and explore the role of iron and carbon fillers,microorganisms and aeration,etc,and reveal the synergistic mechanism of the coupling system.The main results and conclusions are as follows.The single factor results showed that when the iron carbon filler dosage was 30 g/kg,the denitrifying bacteria dosage was 15 mg/kg,the aeration volume was 60 mL/min,and the aeration time was 9-12 h/d,ammonia in overlying water was reduced,dissolved oxygen and redox potential in overlying water was increased,transparency of water was improved.The coupling method can quickly reduce pollutants in black-odorous sediments and improve water quality.The self-cleaning ability and impact resistance capacity in treated sediment were effectively improved.The experimental results show that the coupling system has better effect on the removal of pollutants in black-odorous sediment and overlying water.Treating by the optimum combination after 28 days,the removal rate of COD,NH₄⁺-N,TN and TP were 85.67%,98.2%,65.71%and 96.41%,respectively,stabilized at 15.03±2.18,0.67±0.07,13.55±0.61,0.22±0.05mg/L,respectively.Except for TN,COD,NH₄⁺-N and TP reached the standard of Class IV in surface water quality.The removal rate of sediment TOC,transferbal nitrogen and AVS were 48.83%,41.83%and 83.47%respectively.The coupling system promoted the degradation of organic matter and nitrogen in sediment and overlying water.Phosphorus was precipitated from overlying water to sediment.Stability of phosphorus in sediment was enhanced.The reducing sulfide was oxidized to sulfate.The microorganisms on the surface of the sediment were transformed from the anaerobic flora to the aerobic flora.The microbial abundance associated with the processes of decarbonization,denitrification and phosphorus uptake were increased.The coupling system plays a synergistic role in the reduction of pollutants in sediment and purification of water quality.The functions of each coupling unit include:iron-carbon micro-electrolysis redox decarburization,Fe³⁺to form FePO₄ dephosphorization,Fe²⁺and[H]to provide denitrifying electron donors,activated carbon adsorbs pollutants;denitrifying bacteria act on traditional aerobic denitrification and denitrification;aeration can rapidly increase DO and promote the transformation of microbial communities on the surface of the sediment to aerobic,forming a virtuous cycle.