7. Concluding remarks
This review sheds light into various biological processes for treating CGW. Given highly complex recalcitrant nature of CGW, it appears still challenging to handle this type of wastewater in a cost-effective and environmentally friendly manner even after decades of effort, especially when zero liquid discharge has been set to be the ultimate target. Various combinations of anaerobic and aerobic processes have been successfully applied for removing phenols, PAHs, NHCs and long chain nchains from CGW at industrial scale. In order to achieve the targeted zero liquid discharge from CGWTP, biological treated effluent should inevitably be further concentrated via HERO, evaporation and crystallization, while likely by their combinations which are all considered as highly-energy intensive operation. So far, most studies on biological treatment of CGW have a narrow focus on biological performance, but without attention to looking into integrated engineering system for properly handling CGW. In fact, an integrated biological and advanced treatment system is urgently needed for in-plant zero liquid discharge by coal gasification and related industry globally. Moving forward, the design, operation and optimization of biological processes for CGW treatment should be considered together with downstream advanced treatment units in a more holistic approach. Only such integrated effort may ultimately lead to a total solution for zero liquid discharge from CGWTP. Also, it is necessary to conduct a comprehensive cost-benefit and system life cycle analysis to ensure a good sustainability without sacrificing the environment.
