| Human activities such as leakage of dyes used by printing and dyeing enterprises,wastewater discharged from sewage treatment plants and the use of small amounts of dyes in rural areas may cause low-concentration printing and dyeing wastewater to enter the water body,and the continuous accumulation of refractory pollutants in the environment may give Organisms and even the ecological environment cause obvious harm.In order to find a method for economically and effectively treating low-concentration printing and dyeing wastewater,this study combines the major scientific and technological special project of environmental governance and ecological protection in Sichuan Province,"Integrated Demonstration of R&D Integrated Demonstration of Non-point Source Pollution Control and Fine Management of Tuojiang River Basin"(2018SZDZX0024),Taking methylene blue(MB)as the representative of low-concentration printing and dyeing wastewater,MB was added to the micro-polluted river to simulate wastewater.The electrode materials,MB concentration,co-substrate dosage,and hydraulic retention time were investigated.Factors affect the construction of wetland-microbial fuel cell system(Constructed wetland-microbial fuel cell system,CW-MFC)in the treatment of methylene blue in low-concentration printing and dyeing wastewater.At the same time,the basic effects of the system on COD,total phosphorus,ammonia nitrogen and total nitrogen in wastewater were investigated.Some conclusions have been drawn on the improvement effect of the water quality index and the power generation performance of the system under different conditions.(1)After the introduction of graphite felt in the electrode,the effect on MB removal is not obvious,and the effluent can meet the chromaticity requirements of the discharged water body in the natural water environment.The introduction of graphite felt can also slightly increase the removal rate of COD,total phosphorus,ammonia nitrogen and total nitrogen by the CW-MFC system.Especially for the CW-MFC system after the graphite anode is introduced into the cathode and anode,the COD removal rate can reach a maximum of 81.38%.The total phosphorus removal rate can reach 76.56%,and the ammonia nitrogen and total nitrogen removal rates can reach89.12% and 81.15%.During the experiment,the maximum average voltage appeared in the CW-MFC with graphite felt introduced into the anode,which was 241.6 m V.It shows that the introduction of graphite felt material in the electrode can improve the MB removal ability of CW-MFC,other pollutants removal ability and power generation efficiency.Among them,the graphite blanket is introduced into the cathode and anode.The performance of the CW-MFC system is the best,and the effluent is basically close to Surface water class III standard.(2)When the MB concentration in the wastewater is 10 mg/L,20 mg/L,and 30mg/L,the MB removal rate can reach more than 98% steadily,meeting the chromaticity requirements of the discharged water in natural water environment.The highest removal rates of COD,total phosphorus and ammonia nitrogen appeared at MB concentration of 10 mg/L,which were COD 58.47%,total phosphorus 60.24%and ammonia nitrogen 63.82%.In wastewater containing MB,the lower the MB concentration,the better the system performance,but lower than the system performance without MB in wastewater.During the experiment,the maximum average voltage appeared when the MB concentration in the wastewater was 30 mg/L,reaching 345.4 m V.It shows that the increase of MB concentration will cause the purification effect of CW-MFC to the water quality indicators such as COD,total phosphorus,ammonia nitrogen and total nitrogen to a certain extent,resulting in the effluent unable to meet the class III standard of surface water,but it can slightly increase the electricity production.(3)The dosage of co-substrate has little effect on the removal rate of MB.When the dosage of glucose co-substrate is 50 mg/L,150 mg/L,250 mg/L,350 mg/L,MB is removed on average The rates are all above 98%,which meets the chromaticity requirements of the discharged water body in the natural water environment.When the dosage of glucose co-substrate is 350 mg/L,CW-MFC has the best removal performance for other pollutants,with a COD removal rate of up to 87.14%;total phosphorus removal rate of up to 87.55%;and ammonia nitrogen removal rate of the highest It can reach 84.13%;the total nitrogen removal rate can reach 84.09%.Total phosphorus,ammonia nitrogen and total nitrogen can all meet the surface water class III standard.Although COD fails to meet this standard,it also removes most of the organic matter in the influent water.During the experiment,the maximum average voltage appeared when the dosage of glucose co-matrix was 350 mg/L,reaching413.0 m V.Therefore,increasing the amount of co-substrate can increase the MB removal capacity of CW-MFC,other pollutants removal capacity and power generation performance.When the dosage of glucose co-substrate is 350 mg/L,the overall performance of the system is the best,and the nitrogen and phosphorus in the effluent can meet the standard ? of surface water.(4)When the HRT is 0.5 d,1.0 d,2.0 d,and 3.0 d,respectively,when the HRT is2.0 d,the CW-MFC system has the best ability to remove MB,and the average removal rate reaches 99.39%,which satisfies the natural water environment.The color requirements for the water discharged into the water.Similarly,when the HRT is2.0 days,CW-MFC has the best removal performance for other pollutants.The average removal rate of COD is 85.72%,up to 87.94%;the average removal rate of total phosphorus is 79.31%,up to 92.63%;The average removal rate of ammonia nitrogen is 73.58%,up to 78.40%;the total nitrogen is basically the same as ammonia nitrogen.Total phosphorus can meet the Class III standard of surface water,and COD,ammonia nitrogen and total nitrogen can all be close to Class III standard of surface water.During the experiment,the maximum average voltage appeared when the HRT was 2.0 d,reaching 450.0 m V,and the system had the best power generation performance.Therefore,proper extension of HRT can improve the MB removal capacity of CW-MFC,other pollutants removal capacity and power generation performance.When the HRT is 2.0 days,the overall performance of the system is the best,and the total phosphorus in the effluent can meet the surface water class III standard.(5)CW-MFC can effectively treat low-concentration MB wastewater,combined with MB removal capacity,other pollutant removal capacity and power generation performance,it is concluded that in the CW-MFC system,both the cathode and anode are graphite felt electrodes,MB The system performance is the best when the concentration is 10 mg/L,the glucose co-substrate dosage is 350 mg/L,and the HRT is 2.0 d,which can meet the emission standards for textile dyeing and finishing industrial water pollutants(GB4287-2012)after the discharge,but the concentration of pollutants in the tail water will still be higher than the limit value of the type III water body in the "Surface Water Environmental Quality Standards(GB3838-2002)" to provide new ideas. |
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