By Jenny Zhang, Scientist, Dow Water & Process Solution, Dow Chemical (China) Investment Ltd. and Juno Chen, Business Communications Manager, Dow Chemical (China) Investment Ltd.
Coking wastewater generated from the processes of coking, coke gas purification, and recovery of coking products, is highly toxic and carcinogenic. The wastewater usually contains phenolic, aromatic, heterocyclic, and polycyclic organics, and some inorganics, such as cyanides, sulfides, ammonium, ammonia, and so on, which makes it hardly degradable. Presently, coking wastewater is mainly treated by biochemical methods. However, due to the effluents still containing phenolic compounds and residual tars, it is hard to meet the discharge limits steadily or perform water recycle and reuse.
The end-user, Shandong Weijiao Group Co., Ltd., was facing problems to recycle its coking wastewater due to the low biodegradability and the high chemical oxygen demand (COD) of the coking wastewater, an issue facing many other coking plants in China.
To solve this issue, Dow successfully integrated its unique DE-COD technology to reduce the COD of the coking wastewater, achieving the national standards of wastewater discharge. Further combined with Dow™ UF and Dow FILMTEC™ RO technology, Dow SMART solution realized the desalination of the wastewater, so that the chlorine ion level and the total dissolved solids (TDS) level of the wastewater meets the standard of the plant’s circulation cooling system.
DE-COD technology is the key technology of the SMART solution, which could remove COD before RO desalination and can effectively remove hardly biodegradable components like phenols, heterocyclic, and polycyclic hydrocarbons, as well as ensure RO operation stably with high flux and yield as a pretreatment of RO.
The successful operation of Dow’s integrated water solutions has enabled Weijiao Group to recycle 70 percent of the coking wastewater as the plant’s circulation cooling water, profoundly advancing Weijiao Group’s production process into a green and sustainable model with a low carbon footprint.