Inhibition of ammonia on anaerobic digestion of synthetic coal gasification wastewater and recovery using struvite precipitation

Coal gasification wastewater (CGW) contains very high concentrations of phenols and ammonia. However, the potential impact of ammonia on the anaerobic digestion of phenols remained unclear. Firstly, the methanogens and phenols degraders had a good tolerance up to 1 g L−1 of total ammonia nitrogen (TAN), but the substrate utilization rate for phenol, and specific methanogenic activity of sludge were decreased by 89% and 67% at 5 g TAN L−1, and 94% and 100% at 10 g TAN L−1, respectively. Secondly, the optimum struvite crystallization conditions (pH = 8.5, 10 g TAN L−1, n(Mg2+):n(TAN):n(PO43−) = 1:1:1) were obtained by the orthogonal tests. Thirdly, the removal efficiencies of chemical oxygen demand (COD) and phenols were recovered to around 82% and 66%, respectively in the upflow anaerobic sludge blanket reactor using the pretreatment of struvite precipitation at 10 g TAN L−1 and 1 g phenols L−1. Therefore, anaerobic digestion coupled with struvite precipitation was considered as an alternative way for CGW treatment.