New Water Treatment Index System toward Zero Liquid Discharge for Sustainable Coal Chemical Processes

The shortage of water resources is the major bottleneck for coal chemical industry development. It is imperative to approach zero liquid discharge for coal chemical processes. Varieties of wastewater treatment processes have been developed, but none of them have yet achieved zero discharge in practice. The water quality of reuse does not meet the requirements, resulting in inactivation of microorganisms in the biochemical system and accelerated corrosion and fouling of heat exchangers. These problems can even threaten production and operation. Current water treatment units are pieced simply together leading to unsatisfactory water quality for reuse. Therefore, a new water treatment index system is proposed for ensuring water quality for reuse and zero liquid discharge. In order to establish the water treatment index system, this paper focuses on the study of the whole water treatment process. For better illustration, a water treatment process for zero liquid discharge is established. A mass balance is calculated depending on several practical industrial cases. Analysis shows that the content of polyphenols, PAHs, long-chain alkanes, and ammonia nitrogen is the key for water reuse quality. Therefore, concentration limits for these components in the indexes are carefully studied and determined. The indexes at each joint point between units are determined based on data from current existing treatment processes and technical demands of specific treatment units. Depending on the index system, appropriate treating technologies are selected and optimized. We finally give suggestions on improvement and optimization of water treatment processes for zero liquid discharge.