Purification Of Black And Odorous Water By Iron-carbon Micro-electrolysis Coupled With Ipomoea Aquatica

Industrial wastewater and sewage are discharged to rivers,turning the water into black and odorous water.Black and odorous water not only lose the function of self-purification,drinking,irrigation and landscape,but also harm the ecological balance and cause many hygienic and healthy problems,which have been an urgent environmental issue nowadays.Bio-ecological technology have been widely recognized through the practice of black odorous water treatment in recent years,of which Ipomoea aquatica has been widely used in wastewater treatment because of high pollution resistance and broad adaptability.In addition,the combination of iron-carbon micro-electrolysis and biological technology has received attention because iron-carbon micro-electrolysis can improve the purification efficiency of biological technology.Therefore,iron-carbon micro-electrolysis coupled with Ipomoea aquatica was established to treat black and odorous water.Indoor simulation experiment was developed to provide theoretical basis and technical support for the application of iron-carbon micro-electrolysis coupled with emergent aquatic plants.The single factor experiment was developed through variable-controlling approach,studying on the effects of different planting density,dosage of iron-carbon,dosage of ceramsite on the purifying effect.The simulation experiment was carried out to investigate the purification effect of Ipomoea aquatica group,Ipomoea aquatica+ceramsite group and the coupled group?Ipomoea aquatica+ceramsite+iron-carbon group?on black and odorous water.The synergistic mechanism was also studied.The results indicated as follow:The results of the single factor experiment showed that the suitable range of planting density,dosage of iron-carbon and dosage of ceramsite were 80¹12 plants/m²,18²7 g/L and26⁵2 g/L,respectively.The optimum conditions of planting density,dosage of iron-carbon and dosage of ceramsite were 80 plants/m²,18 g/L and 52 g/L,respectively.Treated by the optimum combination after 10 days,DO was between 5 and 6 mg/L,ammonia was less than 8 mg/L,ORP was more than 100 mV and the water turned transparent,which indicated that the combined system could eliminate black color and odorous state quickly.Treated by the optimum combination after 22 days,removal rates of COD,TP,TN and NH₄⁺-N were 77.6%,97.2%,74.1%and 99.5%,respectively,stabilized below 26.72±2.61 mg/L,0.12±0.004 mg/L,13.65±1.24 mg/L,0.21±0.04 mg/L,respectively.In addition,the degradation of COD and the removal of TN followed apparent second order kinetics,while the removal of TP followed apparent first order kinetics.The experiments of different combinations showed that the purification of the the coupled group was much better than that of Ipomoea aquatica group and Ipomoea aquatica+ceramsite group.The removal rates of COD,TP and TN increased by 22.43%,21.98%,22.28%and12.34%,5.86%,17.44%,respectively,compared with Ipomoea aquatica group and Ipomoea aquatica+ceramsite group.Treated by the coupled group for 22 days,the microbial abundance and diversity were increased.The dominant phyla in aquatic environment were Proteobacteria,Firmicutes and Bacteroidetes,the dominant genera in aquatic environment were Pseudomonas,Escherichia-Shigella and Diaphorobacter,the dominant phyla in rhizosphere were Proteobacteria,Bacteroidetes and Actinobacteria,and the dominant genera in rhizosphere were Neorhizobium-Pararhizobium-Rhizobium,Arenimonas and Rhodobacter,enabling the microbial community to be more suitable for the degradation of COD,the removal of nitrogen and phosphorus in the direction of succession.The synergistic mechanism of the coupled system included:iron-carbon micro-electrolysis could generate[H]and Fe²⁺as electron donor of autotrophic denitrification and degrade COD by redox,Fe³⁺could precipitate phosphorus,ceramsite could absorb nutrient,radial oxygen loss and root exudates in Ipomoea aquatica could enhance the capacity of nitrogen removals,and biofilm of ceramic and rhizospheric microorganism could degrade organics and denitrify.