| Anaerobic biological treatment technology as an economical and effective sewage wastewater treatment method has been widely concerned and applied because it could combine sewage treatment with energy.However,anaerobic biological treatment technology has some problems including slow start-up and low methane production efficiency in practical applications.The use of electric fields and conductive exogenous mediators can promote the efficiency of anaerobic methane production.However,these methods had limitations in enhancing anaerobic biological treatment process of wastewater.For example,excessive current（>20 m A）or alternating current can lead to the death of anaerobic microorganisms,the addition of excessive external mediators can cause secondary pollution.Therefore,a low voltage electric field coupled iron-carbon composite mediators enhancing method was proposed in order to break through the limitation of the single strengthening method and further improve the efficiency of wastewater anaerobic biological treatment.Iron-carbon composite exogenous mediators were prepared,taking brewery wastewater as the research object,and the possibility of low-voltage electric field,exogenous mediators and low-voltage electric field coupled exogenous mediators to enhance anaerobic biological treatment of wastewater was investigated.A low voltage electric field coupled iron-carbon composite mediators enhancing UASB system was constructed to investigate the influence of the coupling enhancement method on the process performance.The mechanism of different enhancement methods was speculated through determinating the microbial communities of anaerobic system.Granular activated carbon（GAC）loaded with nanoscale zero-valent iron（NZVI）was prepared by a co-precipitation method（GAC-NZVI）.The conductivity of GAC-NZVI increased by 8.66 m S/cm and the electron exchange capacity increased by 1.19times comparing with GAC.The highest methane production rate and the average methane production rate were 212.63±2.12 m L CH4/g-COD and 169.86±2.58 m L CH4/g-COD when adding 1000 mg/L GAC-NZVI to the anaerobic system,which were 7.56±4.58%and 9.39±0.03%higher than those of control.The contents of LB-EPS and TB-EPS increased to 22.43±2.25 mg/g MLSS and 62.19±7.30 mg/g MLSS,the conductivity increased to 14.82±0.17μS/cm in the reactor with GAC-NZVI compared with the control group without particles（4.47±1.75 mg/g MLSS,25.69±3.09 mg/g MLSS,6.26±0.13μS/cm）.GAC-NZVI increased the relative abundance of acetoclastic Methanothrix.The degradation of the substrate acetic acid was promoted and methanogenesis efficiency was improved.The pollutant removal efficiency and CH4 production rate of the anaerobic system were improved when adding 100 mV low voltage electric field.The COD removal rate increased by 16.72%;the cumulative CH4 production increased by 23.39±0.28%and the average methane yield increased by 15.69±0.91%.The EPS contents in anaerobic sludge increased by 235±32.19%,the conductivity increased to 3.17±0.08μS/cm,and the current density was 0.82±0.03 A/m2.The relative abundance of Methanothrix and Geobacter which could exchange electrons via direct electron transfer increased,and 100 mV external voltage could make up for the loss of metabolic energy of Geobacter and promote electron transfer process between microorganisms.GAC-NZVI particles with a concentration of 1000 mg/L were added to the anaerobic system with 100 mV low voltage electric field.The average methane yield increased from 227.72 m L±5.85 CH4/g-COD to 234.19±1.78 m L CH4/g-COD.The contents of LB-EPS and TB-EPS increased to 84.56±1.62 mg/g MLSS and 107.29±1.64 mg/g MLSS,the conductivity increased to 2.25±0.02μS/cm in the reactor with GAC-NZVI compared with the control group（76.60±1.84 mg/g MLSS,71.86±1.76 mg/g MLSS,1.71±0.05μS/cm）.The relative abundance of acetoclastic Methanothrix and Methanobacterium with DIET ability increased,which promoted methanogenesis efficiency.The anaerobic UASB wastewater treatment systems enhanced by GAC-NZVI and 100 mV low voltage electric field coupled GAC-NZVI were built.The methane yield of anaerobic system increased by 16.86±3.09%when the organic load was 2.86kg COD/（m3·d）.The contents of LB-EPS and TB-EPS increased to 113.45±6.07mg/g MLVSS and 190.08±1.51 mg/g MLVSS,which promoted the flocculation of sludge.And when the external nutrients in the influent of the system were insufficient,EPS could be used as a source of nutrients,which improved the activity of microorganisms and ensured the stability of the system.The conductivity increased to 25.24±0.68μS/cm,which decreased gradually with the operation of the reactor.Through the measurement of microbial communities and the prediction of functional genes,the diversity and richness of microorganisms improved.The relative abundance of Anaerolineaceae,which had the function of“syntrophism”with methanogens and acetoclastic methanogen Methanothrix ncreased.The coupling enhancement method promoted the degradation of acetic acid.The methane production rate increased as the organic load of the influent increased.The adaptability of anaerobic microorganisms to the external environment improved through the starvation experiments after enhancement.Short-term starvation was beneficial to the growth of hydro-methanogens Methanolinea and Methanobacterium,which ensured the efficiency of anaerobic methane production.Comparing the results of sequencing batch experiments and continuous flow experiments,it is found that within the same and sufficient reaction time,the single strengthening method could be used to promote the efficiency of anaerobic digestion,and the coupling strengthening effect was mainly reflected in improving the rate of anaerobic digestion. |
