化学需氧量现有2种标准分析方法若干问题研究

Research of Two Current Analytical Methods of the Chemical Oxygen Demand

《水质化学需氧量的测定重铬酸盐法》(HJ 828—2017)和《高氯废水化学需氧量的测定氯气校正法》(HJ/T 70—2001)是测定水中COD_(Cr)现有有效的2种标准方法。针对这2种方法存在的问题,通过实验给出操作建议。指出,对高氯废水稀释后采用《HJ 828—2017》方法测定水中COD_(Cr)时,稀释倍数太大或稀释后COD_(Cr)质量浓度<20 mg/L,将降低测定结果的准确度;采用《HJ/T 70—2001》方法测定高氯废水中COD_(Cr)时,硫酸亚铁铵浓度应为0.10 mol/L;《HJ 828—2017》方法中高、低质量浓度分界点建议从50 mg/L改为60 mg/L,试验结果可行且对部分行业排放标准适用性更好;鉴于低浓度样品的精密度结果相对偏大,建议按照COD_(Cr)的浓度大小分级设定精密度的质控要求,更加科学合理。

“Water quality-Determination of chemical oxygen demand-Dichromate method”(HJ 828—2017)and“High chlorine wastewater-Determination of chemical oxygen demand-Chlorine emedation method”(HJ/T 70—2001)are currently two effective methods for determination of COD_(Cr) in water.This paper probes into the problems existing in the two methods.It is pointed out that the accuracy of the result will be reduced if the dilution ratio is too large or the diluted COD_(Cr) value is less than 20 mg/L when the method of“HJ 828—2017”is used to measure COD_(Cr) in high chlorine wastewater.When“HJ/T 70—2001”is used to determine the concentration of COD_(Cr) in high chlorine wastewater,ferrous ammonium sulfate should be 0.10 mol/L.If the cut-off point of high and low concentration can be changed from 50 to 60 mg/L in the“HJ 828—2017”method,the test results are more feasible and more applicable to some industries.The precision of low concentration samples is generally on the high side,and it is more scientific and reasonable to set the precision requirement according to the COD_(Cr) concentration level.