Enhancing methane production of synthetic brewery water with granular activated carbon modified with nanoscale zero-valent iron (NZVI) in anaerobic system.

Anaerobic digestion is an effective treatment technology for wastewater. However, long HRT and low CH4 production limit the application of anaerobic treatment. Iron-based materials, carbon-based materials and Fe-C composite particles have been used in anaerobic processes. However, the strengthening effect of Fe-C composite particles on anaerobic systems requires further research. In this study, granular activated carbon (GAC) loaded with nanoscale zero-valent iron (NZVI) was prepared by a co-precipitation method and its morphology was characterized. Different concentrations of GAC-NZVI particles were used in the batch experiment to study the enhancing effect of the anaerobic biological treatment process. The water quality, sludge properties and microbial community were analyzed. The degradation rate of COD and total CH4 production increased by 9.38% and 14.29% with particles at a concentration of 1000 mg/L, respectively. The average methane yield was 169.86 mL CH4/g-COD removed, which was 9.39% higher than that of the control. The measurement results of extracellular polymeric substance (EPS), conductivity, cyclic voltammetry (CV) and Fe concentration indicated that the composite particles showed excellent electrical conductivity and promoted microorganism metabolism, which accelerated the use of substrates and methane generation. The 3-dimensional excitation (Ex) - emission (Em) matrix (3D-EEM) fluorescence spectroscopy of soluble microbial product (SMP) and EPS indicated that the particles could affect the endogenous respiration of microorganisms. Microbial community analysis revealed that the dominant genus Methanothrix (acetoclastic methanogens) increased by 13.32%, which could strengthen acetoclastic methanogenesis and lead to higher CH4 production. The abundance of hydrogenotrophic archaea decreased after the addition of GAC-NZVI. These results provide an alternate method for enhancing anaerobic wastewater treatment using conductive particles.