基于不同时间周期排放量的排污许可限值

理论和实践表明,受生产和生活活动的影响,污染源的排放具有明显的波动性. 我国污染物总量控制往往为年排放量,在颁发排污许可证时,为避免污染源短时间大量排放对水质造成的冲击性影响,同时也方便对企业进行监管,需要制订更短时间平均周期的排污许可限值. 以铁岭市各污水处理厂出水ρ(COD_Cr)和流量在线监测数据为研究对象,采用在线监测数据方法和NPDES(美国国家污染物排放削减系统)中关于各类限值的计算方法,对污水处理厂MDL(日最大限值)、AWL(周平均限值)、AML(月平均限值)与LTA(长期平均限值)进行了研究. 结果表明,随着污水处理量的增加,MDL、AWL、AML与LTA的比值基本保持稳定并略有减少,说明污水处理厂规模越小,比值波动性越大；从MDL、AWL和AML的比较来看,排污许可限值计算的时间周期越短,波动性越大. 铁岭市各污水处理厂出水ρ(COD_Cr)的MDL、AWL、AML与LTA比值的平均值分别为1.52、1.19和1.09,变差系数分别为4.9%、2.5%和1.0%；出水COD_Cr负荷的MDL、AWL、AML与LTA比值的平均值分别为1.74、1.27和1.12,变差系数分别为7.8%、4.1%和2.3%. 研究结果有助于根据LTA(如年均值)推导较短周期的MDL、AWL和AML. 

Discharge Permit Limits Based on Different Temporal Periods

Abstract: Due to changes in industrial production and domestic living activities, the discharge of pollutants often differs between theoretical study and practical experience. Usually, total pollutant load control is based on an annual period in China, but it is extremely necessary to give discharge permits over shorter time periods to avoid side effects of impulsive pollutant discharge, as well as to facilitate supervision of enterprises. The relationship between pollutant loads discharged over different periods provides a scientific basis to formulate different temporal discharge permits. Taking COD and flow on-line monitoring data of wastewater treatment plants (WWTPs) in Tieling city as an example, the maximum daily limits (MDL), average weekly limits (AWL), average monthly limits (AML) and long term average (LTA) were calculated and compared with the on-line monitoring data and NPDES. It was found that the smaller WWTP was likely to have a greater temporal variation, and shorter temporal average values were more unstable than longer ones. For the Tieling case, the average concentrations of MDL, AWL and AML were 1.52,1.19 and 1.09, and their variation coefficients were 4.9%, 2.5% and 1.0%; the average load MDL, AWL, AML were 1.74,1.27 and 1.12, and their variation coefficients were 7.8%, 4.1% and 2.3%. These results can be used to estimate the MDL, AWL and AML based on the LTA for other enterprises.