基于技术和水质相结合的排污许可限值核定技术研究

“十三五”期间，我国排污许可管理制度已基本建立；“十四五”时期，我国排污许可管理将逐步过渡到注重水质达标的管理阶段.为适应我国排污许可新的管理需求，研究了基于技术和水质相结合的排污许可限值核定技术.其中，基于技术的排放限值核定主要根据企业的行业属性和核定产能，结合环境影响评价批复的污染物排放额度，确定其排放浓度限值和排放总量限值；基于水质的排放限值核定需建立污染源与水质之间的响应关系，以地表水水质达标为目标，计算各污染源的最大允许排放量.最终的排污许可限值为基于技术的排污许可限值和基于水质的排污许可限值的最小值.以常州为例，从常州排污许可证核发重点行业选取了两家化工企业A和B，核算其基于技术的排放限值；采用水质模拟和污染物最大允许排放量分配技术，计算了污染物最大允许排放量，并分配到两家化工企业，作为基于水质的排放限值.结果表明:A化工企业COD_Cr和NH₃-N的最终排污许可限值分别为6.53和0.075 t/a，其中，COD_Cr的最终取值为基于水质的排放限值，NH₃-N基于技术和基于水质的排放取值相同；B化工企业COD_Cr和NH₃-N的最终排放限值分别为11.60和0.17 t/a，最终取值均为基于技术的排放限值.研究显示，基于水质的排许可限值受到企业自身和外部水环境容量的双重影响，应从严制定排污许可限值，既能达到企业行业排放标准和环境影响评价批复的要求，又能满足水环境质量达标的目标. 

Revision and Determination of Wastewater Discharge Permit Limit Based on Technology and Water Quality Target

China's discharge permit system is mainly established in the '13th Five-Year Plan'. In the '14th Five-Year Plan', the management of the discharge permit system should pay more attention to the supervision over the water quality compliance. To adopt to the new management demands for the wastewater discharge permit limit, this work discussed revision and determination of wastewater discharge permit limit based on technology and water quality target. The revision and determination of the technology-based effluent limits (TBELs) was determined based on the industry sector and its approved production capacity, combined with the ratified pollutant discharge quota by the environmental impact assessment. The water quality based effluent limits (WQBELs) was determined based on the response relationship between the pollutant loads and the water quality, and the maximum allowable pollutant loads was calculated for the individual pollution sources, aiming to achieve the water quality compliance of surface waters. The value of the final pollution discharge limit will be the lower one of the TBELs and WQBELs so that both requirements can be met. Taking Changzhou as an example, this study selected two chemical enterprises A and B to assess their TBELs because chemical industry was one of the most important industries for pollutant discharge permit work. The water quality model and the allocation technology for the maximum allowable pollutant loads were used to calculate the allowed maximum load for each pollution source, and the calculated allowed maximum load was allocated to the two chemical enterprises as their discharge limit based on the water quality. The result showed that the final discharge permit limit of COD_Cr and NH₃-N for enterprise A was 6.53 and 0.075 t/a, respectively, in which the final COD_Cr value was based on the WQBEL, and the TBEL and WQBEL of NH₃-N were the same. The final discharge permit limit of COD_Cr and NH₃-N for enterprise B was 11.60 and 0.17 t/a, respectively, with both COD_Cr and NH₃-N limits determined by the TBELs. The study indicates that the water quality-based wastewater pollutant discharge permit limit is affected by both the enterprise itself and the water environmental capacity, and the more strict discharge permit limit, i.e., the lower of TBEL and WQBEL should be selected as the limit value so as either to meet the discharge standards for the enterprises and the requirements ratified by the environment impact assessment, or to meet the target of the water environment quality.