Study On Removal Of Cr(?) By Fe-C Microelectrolysis Coupled Constructed Wetland

In this study,a certain proportion of iron carbon was used in the matrices of constructed wetland to construct a coupling process constructed wetland with ferro-carbon micro-electrolysis.The galvanic cell formed by the principle of metal corrosion was used to improve the treatment of domestic sewage and hexavalent chromium as a heavy metal.Meanwhile this process was studied to support the nitrogen and phosphorus removal in constructed wetlands technically for the treatment of chromium-containing wastewater.Firstly,the effects on removal of COD,ammonia nitrogen,total nitrogen and total phosphorus in domestic wastewater were compared under different conditions of no aeration,intermittent aeration and continuous aeration.The results showed that the effect of iron and carbon on the removal of COD and ammonia nitrogen was not significant.The removal rates were relatively high,and they were stable at 96%and 98%,respectively.Under the three conditions of aeration,the removal rate of total nitrogen increased by 24.05%,11.41%,and 18.45%,respectively,in the coupling process.The removal rate of total phosphorus increased by 21.08%,16.98%,and 23.6%,respectively.The removal rate is highest under aeration conditions,so the coupling process and intermittent aeration can significantly improve the removal performance of total nitrogen and total phosphorus in wetland.Then,under the optimal working conditions,Cr(?)was added to the two systems to compare their effects on the removal of Cr(?).At the same time,the effect of Cr(?)addition on the removal of conventional pollutants from the coupling process was discussed.The effect of hydraulic retention time on the removal of hexavalent chromium from the coupling process was discussed.The results showed that the removal rates of Cr(?)in the two constructed wetlands firstly decreased,then increased,then decreased,and finally stabilized,and the removal efficiency of the coupled process for Cr(?)was 10%to 18%higher than that of the traditional wetland.It indicates that iron-carbon can enhance the removal efficiency of Cr(?)in constructed wetland systems;after adding Cr(?),the effluent quality of COD,ammonia nitrogen,total nitrogen,and total phosphorus in the coupling process decreases to varying degrees.The addition of Cr(?)has a great influence on the microbial community in the system.When the hydraulic retention time was 1 day,3 days and 5 days,the removal efficiency of Cr(?)by the coupling process was 53.8%,75.2%and 42.8%,respectively,and the removal effect reached the best under the condition of 3 days.Then,static experiments were conducted to study the adsorption kinetics of Cr(?)on the four substrates of ferro-carbon,volcanic rock,zeolite,and terra cotta,and analyzed from three aspects:isothermal adsorption,adsorption kinetics,and the effect of pH on adsorption.The results showed that the adsorption order of the four substrates is in the following order:iron-carbon>terra cotta>volcanic rock>zeolite.The adsorption of Cr(?)is more in line with the Langmuir equation and the second-order kinetic equation,indicating that the adsorption behavior belongs to chemical adsorption.And iron-carbon is more favorable for the adsorption of Cr(?).The pH value has little effect on the adsorption capacity of volcanic rocks,zeolites,and terra cotta,but has a significant effect on the adsorption of iron-carbon.The condition is better when the solution is acidic and alkaline.It is good for iron carbon to adsorb Cr(?).Finally,the high-throughput sequencing method was used to analyze the composition and changes of microbial community before and after the addition of Cr(?)to the wetland system.The results showed that after adding Cr(?),the microbial diversity in both wetlands decreased significantly,and the microbial diversity decreased.The influence of Cr(?)is significant.The chromium-binding microorganisms in the coupling process are Actinobacteria,Proteobacteria,Saccharibacteria,and the sum of abundances reaches 87%.However,the chromium-tolerant microorganisms in traditional wetlands are only Actinobacteria,Proteobacteria,and their demeanor.The sum reached 67%.Therefore,the removal of chromium by the microorganisms in the coupling process is greater than traditional wetland.