Enhanced performance of anaerobic two-phase reactor treating coal gasification wastewater with the assistance of zero valent iron under co-digestion conditions

[Display omitted] •A novel two-phase anaerobic process coupling co-digestion was built for CGW treatment.•Dosages of co-substrate in influent and ZVI in methanogenic phase were obtained.•The total phenols removal exceeded 96% with the total methane production rose to 250 mL/d.•The acidogenic phase had the most types of microbial species and complex community diversity. Coal gasification wastewater (CGW) is a typical industrial wastewater that is difficult to degrade as it contains a large number of refractory and toxic pollutants, such as high concentrations of phenols.The aim of this study is to investigate an anaerobic two-phase reactor treating synthetic CGW under co-digestion conditions. The optimum dosages of co-substrate (glucose = 1000 mg/L), zero valent iron (ZVI) (2 g/L), and hydrolysis acidification time (12 h) were explored by batch tests. The results indicated that the concentration of total phenols declined from 636 mg/L to 376 mg/L when the cumulative methane production increased to 145 mL. In the long-term operation of the anaerobic two-phase reactor, 1,000 mg/L glucose was added to the influent, and 2 g/L ZVI was added in the methanogenic phase, respectively. HRTs in acidogenic and methanogenic phases were kept at 12 h and 48 h, respectively. The average acetate and TVFAs concentrations remained at approximately 852 mg/L and 1042 mg/L, respectively. The result showed that the concentrations of influent and effluent COD were approximately 3,191 mg/L and 412 mg/L, respectively, while those of influent and effluent total phenols were approximately 655 mg/L and 23 mg/L, respectively. The removal efficiencies of total COD and total phenols were over 86% and 96%, respectively. In addition, the total methane production rose to 250 mL/d. Microbial community structure analysis demonstrated that the acidogenic phase contained most types of microbial species and the most complex community diversity in the anaerobic system and that direct interspecies electron transfer (DIET) might occur between the potential electroactive bacteria Chloroflexi and the archaea Methanobacteriales and Methanosaeta, respectively.