Improve Degradation Of Organic Wastewater In Anaerobic Digester By Adding Low-voltage Electric Field

The use of anaerobic methane techniques for removing organic pollutants in wastewater,not only can effectively reduce the environmental load impact,and recover biomass energy.This technology can meet the needs of environmental health and sustainable development at the same time.However,during the anaerobic digestion process,the generation and consumption of intermediate products-volatile acids?VFAs?was imbalance,which lead to the accumulation of high concentrations of VFAs,and then pH value decrease,and inhibit the activity of methanogenic bacteria,system stability get worse,significantly inhibited the production of methane.The aim of this study was to enhance system stability,eliminate the inhibitory of the accumulation of volatile acids and then improve the methane production.Adding power supply on anaerobic digesters,which could makes it possible to produce hydrogen and methane gas at the cathode.This work contends three parts,one of them was to explore the effect of power supply on the VFAs degradation;the other one was to study the assistant role of bioelectrode on anaerobic digester under ammonia inhibition;the third one was to investigate the treatment of high concentration brewery wastewater in particulate electrode MEC.The first two parts study were operated in the same reactors,i.e.R1?titanium electrode+closed circuit?,R2?graphite felt+closed circuit?,R3?graphite felt+open circuit?.?1?Firstly,sodium acetate was used as the experimental substrate in single-chamber MEC to investigate the role of phosphate buffer solution?PBS?.The result shows that PBS could reduce the ohmic resistance in the MECs and enhance proton transfer between anode and cathode chambers which can improve the substrate degradation.It is tried to reveal the role of biofilm development and electricity addition by comparing substrate degradation kinetics and microbial community variations in MECs with close or open circuit operation.The first-order kinetic analysis indicated that electricity improved the substrate degradation rate,but the influence on biofilm was insignificant.In close circuit MECs with biofilm,the degradation of butyric acid was accelerated by 12%in first 24 h,whereas,no much help on the propionic acid digestion;correspondingly,about 35%increment of methane evolution was achieved as compared with MECs in open circuit.High-throughput sequencing revealed the fraction of Geobacter sp.and Methanosarcina sp.was increased in the effect of electricity,which can help to facilitate direct interspecies electron transfer?DIET?and contribute to the accelerated degradation of acetate and butyrate.?2?The performance of methane-producing microbial electrolysis cells?MECs?to a series of NH₄⁺-N stress was explored.When increasing NH₄⁺-N to 4 g/L,VFAs degradation and methane generation were significantly inhibited;nevertheless,butyrate and propionate degradation were enhanced by 10-70%with the assistance of bioelectricity/biofilm.Under the extremely high stress of NH₄⁺-N?6 g/L?,insignificant difference was found among three tests and the methanogenesis were seriously hampered.Specifically,although methane production in all reactors were decreased rapidly and inhibited significantly,the similar trends were observed as R2>R3>R1 in each ammonia-nitrogen concentration.Under ammonium stress,abundance of Methanobacterium significantly increased in anaerobic digester without electricity stimulation,however,acetoclastic Methanosaeta was found to survive and even increase in MEC.?3?Using different particle sizes of activated carbon as biotic electrode,investigate the effect of power supply on the degradation of high concentrations brewery wastewater in up-flow anaerobic digester.The results show that electricity stimulation can enhance the up-flow anaerobic digester treating high concentration of brewery wastewater capacity,improve substrate conversion efficiency and methane production.However,when the adding voltage increased to 1.0 V,the substrate consumption of up-flow anaerobic digester with granular activated carbon?10-20mesh?was totally inhibited,while the TOC degradation rate and methane production of reactor with powered activated carbon?80-100 mesh?were decreased 25%and56%,respectively.At the same time,activated carbon can enhance the ability to resist the impact of organic loading in the reactor.The results of molecular biological analysis of biological communities showed that archaea was mainly residence to the inner core region of activated carbon,which ensure that the reactors stable in the face of hydraulic and load impact and remains the high efficiency;the abundance of hydrogenotrophic methanogens was increased by electricity which could enhance methane production.In addition,the electricity stimulates the growth of hydrogenotrophic methanogens which could improve the methane production.Compared with granule activated carbon,there are abound of Methanosarcina in the power activated carbon.Due to the alternative metabolism pathways of Methanosarcina sp.,its coupled growth with syntrophic acetate oxidizing bacteria could help to enhance reactor stability.Therefore,activated carbon could act as a buffer to maintain the balance and stability of the system.