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/m 3 ), every 1.0 kg/m 3 reduction in COD will result in a reduction of 2.5002 ± 0.2980 mS/cm·m 3 in salinity, 3.7391 ± 0.9245 CNY/m 3 in operating costs, and 1.4989 ± 0.6509 kg CO 2 /m 3 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.
Siqi Tong,Guangbing Liu,Xi Meng,Chunkai Huang,Siwen Chen,Zhiquan Xiang,Weijing Liu,Jinyou Shen,Yi Wang
With increasing wastewater treatment demands and decarbonization goals, synergistic reduction in pollutants and green house gas (GHG) emissions is crucial. High process emissions like N2O pose significant challenges, yet optimized carbon reduction strategies for conventional plants are lacking. This study developed three mathematical models to quantify the impact of dissolved oxygen (DO), influent salinity, and C/N ratio on direct emissions (CH4, N2O) and indirect emissions. Response Surface Methodology (RSM) optimized these factors to minimize GHG emissions under three accounting scenarios: (1) plants with CH4reuse systems: salinity = 0.5 g L−1, DO = 3.67 mg L−1, C/N = 12.75; (2) plants focusing solely on direct emissions: salinity = 0.5 g L−1, DO = 3.35 mg L−1, C/N = 3; and (3) plants assessing total emissions: salinity = 0.5 g L−1, DO = 2.5 mg L−1, C/N = 7.18. Key findings indicated that increasing salinity exacerbated greenhouse gas emissions. Elevated DO levels in the aerobic stage reduced N2O emissions but increased indirect emissions in the A2/O process. Higher C/N ratios promoted anaerobic CH4production, but sufficient carbon reduced N2O by enabling complete heterotrophic denitrification. A 60−day continuous GHG emissions monitoring campaign was conducted at a WWTP to validate the actual emission reductions achievable under the identified optimal control conditions. An analysis and comparison of operational and economic costs were also performed. The findings provide practical insights into sustainable GHG emission management and offer potential solutions to advance the synergistic reduction in GHG emissions and pollutants.
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