| Water is an important source of energy on which human beings depend for survival.Desalination of seawater and brackish water,recycling and utilization of municipal sewage,agricultural and industrial wastewater are important ways to increase water resources.The technologies of desalination and wastewater treatment of high-efficiency and low-consumption have become the focus of current research and development in the field of environmental engineering.Microbial Desalination Cells are a new water treatment process integrating sewage purification,electricity generation and desalination.Up to now,most researches have remained at the laboratory level and few results have been reported when applied to actual wastewater treatment.The subject design traditional small microbial desalination cell,improvement middle and large microbial desalination cell based on the microbial desalination cells as the research object.The effects of organics concentration,electrode spacing and salinity conditions on MDC performance were studied.By optimizing the reactor,we finally explored the effect of MDC on the treatment of washing water from saline-alkali soil.The long-term operation stability and practicability of the reactor were further evaluated from the aspects of electrochemical polarization characteristics,pollutant degradation,desalination efficiency and functional microbial diversity.The results show:S-MDC and M-MDC as experimental object,the concentration of organic matter from 100 to 800mg/L,degradation rate showed a trend of increase after decreases first.Coulomb efficiency and desalination efficiency were no significant difference.The concentration of organic matter change impact on microbial desalination cells performance,this study select best organic matter concentration of 600mg/L.In addition,according to the results of start-up and operation of the reactor,the middle microbial desalination cell can be used as a follow-up experimental study.Taking M-MDC as the experimental object and designed electrode spacing gradually decreased,the results showed that the power density increased first and then decreased,and the COD removal and desalination rate in the closed-circuit system with different spacing conditions were both higher than that in the open-circuit system,and there were significant differences,M-MDC2had the best effect.SEM showed that a large number of microorganisms were attached to the electrode surface,and sequencing showed that the electric-producing bacteria were mainly Bacillus,Arcobacter and Pseudomonas with a total abundance of 21.9 percent,while the hydrolyzed fermentation bacteria were mainly Bacteroides of 18.1 percent.By metabolizing organic matter,the electric-producing bacteria could accelerate the metabolism of the common matrix,assist the activity of electric-producing bacteria and improve the activity.L-MDC was used as the experimental object with the salinity changing successively from 30,15 and 5g/L,the results showed that the desalination cycle and rate gradually became shorter and the desalination rate gradually increased,with the desalination rate of 5g/L being the highest.The peak voltage was 742m V,the maximum power density was 2.84W/m3,and the desalination rate was 99.13 percent in actual washing water.Sequencing showed that three electric-producing bacteria of the Pseudomonas,Arcobacter and Bacillus?22.9%?,two hydrolyzed fermentation bacteria of the Bacteroides and Propionibacterium?20.9%?,two denitrifying bacteria of the Pseudomonas and Acinetobacter?17.5%?were found in the anodes biofilm.Three denitrifying bacteria belonging to Pseudomonas,Acinetobacter and Stenotrophomonas were found in the salt-chamber water with a total abundance of 10.5%,which was lower than that of denitrifying bacteria in the anode biofilm.The experimental results show that the desalination effect of L-MDC can meet the conditions,but the output power density can not meet the actual demand,and there is a limit of treatment water,which needs further optimization and improvement. |
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