Salt exposure and emission reduction strategies in typical industrial wastewater treatment processes

Zero-discharge industrial wastewater treatment is an inevitable goal that enterprises seek for the green and sustainable development. However, the generation and treatment of mixed salt present an enormous challenge. This study, taking the practical case of coking wastewater treatment, analyzes the influencing factors of salt and proposes a load salt reduction strategy. The results show that chemical oxygen demand (COD) is the main factor for the change in salt content. When the influent COD of coking wastewater is 3863.93 ± 466.61 mg/L, the relationship between salt reduction (y) and the COD change rate (x) in the treatment process follows the ExpGro1 natural exponential function: y = −2.2378 × exp (-x/17.0839) + 2.2570, with a fitting degree of 0.9938. In the case where the economic and environmental benefits of this strategy are positive (with a maximum COD reduction of 0.5796 kg/m³), every 1.0 kg/m³ reduction in COD will result in a reduction of 2.5002 ± 0.2980 mS/cm·m³ in salinity, 3.7391 ± 0.9245 CNY/m³ in operating costs, and 1.4989 ± 0.6509 kg CO₂/m³ in carbon emissions. Moreover, this study proves that the adsorption - oxic/hydrolytic & heterotrophic denitrification/oxic (A-OHO) process can effectively reduce the load salt. Other salt reduction strategies (technology salt reduction and cycle salt reduction) and the concept of strategic cooperative operation are also further explored.