The most widely applied processes used to treat coal gasification
wastewater (CGW) include solvent extraction and steam stripping
to reduce the contaminants of phenolic compounds and
ammonia, followed by biological treatment, mostly the activated
sludge process, anoxic–oxic (A/O) process and anaerobic–anoxic–
oxic (A1/A2/O) process (Guclu et al., 2013). However, with the
implementation of the increasingly stringent environmental
regulations, the quality of secondary effluent is unable to satisfy
the discharge standards due to the high concentration of organic
matter, ammonium nitrogen and COLOR (Zhuang et al., 2014a).