Study On The Purification Of Black Odorous Water From Rivers By Iron-carbon Microelectrolysis Coupled With Vallisneria Natans

Due to the rapid and extensive development of industry and agriculture and the lag of sewage collection and treatment rate,the phenomenon of black and odor in urban rivers is frequent in China.The long-term existence of black and odorous water has seriously damaged the balance of aquatic ecosystem,endangered human health,and hindered the sustainable development of industry and agriculture.The treatment of black and odorous water has become an urgent problem to be solved.In recent years,bio-ecological methods have been widely recognized through the treatment practice of black and odorous water.Among them,Vallisneria has been widely used in sewage treatment because of its pollution resistance,alkali resistance and good purification effect.In addition,iron-carbon micro-electrolysis combined with biological treatment technology has been well applied to sewage treatment.Iron-carbon micro-electrolysis can degrade COD through oxidation and reduction,and improve the biodegradability of sewage.Phosphorus removal and organic matter removal by flocculation and coprecipitation can accelerate electron mass transfer and provide electron donors to promote microbial denitrification.In order to provide theoretical basis and technical support for the rapid and efficient purification of river black odor water by iron-carbon micro-electrolysis coupled Vallisneria natans,a technical system of iron-carbon micro-electrolysis coupled with Vallisneria natans was constructed to purify river black odor water and carry out laboratory simulation experiments.A single-factor simulation experiment was carried out to study the effects of the amount of iron-carbon filler and the density of Vallisneria natans on the purification efficiency of the black odor water.The purification performance of the best combined coupling system was determined,and the purification efficiency of the iron-carbon group,the Vallisneria natans group and the iron-carbon and the Vallisneria natans coupling group was studied.The contribution of each component of the coupling system to nitrogen,phosphorus and carbon removal was analyzed.The degradation kinetics of main pollutants was discussed.The synergistic mechanism of iron-carbon micro-electrolysis coupling with Vallisneria natans was clarified by combining the principle of iron-carbon micro-electrolysis reaction,plant growth,matrix biofilm and microbial community evolution information.The results showed that:Plant density 88-148 plants/m² and iron-carbon filler dosage 8-16 g/L were suitable.After20 days of operation,the water purification effect of the two groups increased first and then decreased with the increase of iron and carbon filler dosage and the density of Vallisneria natans.There were significant differences in TN removal between iron and carbon dosage and the density of Vallisneria natans,which indicated that appropriate iron and carbon dosage and density of Vallisneria natans were beneficial to microbial nitrogen removal.Under the optimum combination of iron and carbon dosage and the density of Vallisneria natans.The coupling effect of the coupling group on black odor water was significantly better than that of the single iron-carbon filler group.After treatment for 6 days,the black odor of the coupling group was quickly eliminated,the transparency was quickly increased to 30 cm?the device has bottomed out?,and the DO and ORP increased rapidly to 3.42±0.17 mg/L and 125±6mv,and NH₄⁺-N was 10.45±0.67 mg/L.After 20 days,the removal rates of COD,NH₄⁺-N,TN and TP were 85.7%,94.2%,82.9%and 96.1%,respectively,which were stable at13.68±1.81 mg/L,1.41±0.75 mg/L,0.21±0.05 mg/L and5.02±0.28 mg/L respectively,COD,NH₄⁺-N,and TP reached the surface water standard of Class IV,and the effect was remarkable.The COD degradation and TP removal in the coupling group accorded with the apparent second-order kinetic equation,and the TN removal accorded with the apparent first-order kinetic equation.After 20 days of treatment of the black odorous water body,the microbial abundance and diversity were significantly improved.The coupled system water samples and root dominant bacteria were Proteobacteria,Bacteroidetes,Actinobacteria and Firmicutes,and the dominant genus was Sediminibacterium,Acidovorax and Flavobacterium,Mycobacterium,Pseudomonas and Candidatus Nitrotoga.The relative abundance of microbial communities in the coupling system related to organic matter degradation,nitrogen and phosphorus removal and other processes showed an increasing trend.The Vallisneria natans and iron carbon filler can promote the microbial community succession,and the iron-carbon filler can affect the microbial community distribution.The synergistic purification of black and odorous water by coupling system includes:iron-carbon microelectrolysis electrode product redox degradation of COD,anode Fe³⁺to form FePO₄ precipitate,[H]and Fe²⁺provide electron donor for autotrophic denitrification;The granules adsorb nitrogen,phosphorus,organic matter,photosynthetic oxygen production and rhizosphere oxygen secretion to promote ceramsite biofilm and rhizosphere microbial degradation of organic matter and nitrification and denitrification.