Sustainability Analysis for the Wastewater Treatment Technical Route for Coal-to-Synthetic Natural Gas Industry through Zero Liquid Discharge Versus Standard Liquid Discharge

In recent years, the rapid development of the coal chemical industry has triggered problems related to supply and demand imbalances of the regional water resources in China. Water resources have become the main bottleneck restricting the sustainable development of the coal chemical industry. To achieve cleaner production, China has issued policies on zero liquid discharge for the coal chemical industry, especially for coal gasification wastewater. However, to achieve zero liquid discharge targets, coal gasification companies have to add more processes to support and complete the sustainable reuse of wastewater. To scientifically evaluate this sustainability problem, in this study, we conducted a life cycle assessment of water consumption, costs, and environmental impacts for the zero liquid discharge route of the fixed-bed coal gasification wastewater treatment process. The results reveal that the total water consumption of the zero liquid discharge route is greater than the one of the standard liquid discharge route. Reusing 1 m³ of water would consume an extra 1.64 m³ of water. This is because of the large amount of indirect water consumption caused by the extra high power consumption. Moreover, the life cycle cost of the zero liquid discharge route is approximately twice that of the standard liquid discharge route while the total environmental impact is 1.15 times that of the standard liquid discharge route and 1.03 times for total human health impact. The zero liquid discharge route increases water consumption, incurs higher costs, and causes more serious environmental impacts. Therefore, the zero liquid discharge route does not meet the requirements of cleaner production and sustainable development.