Effects of inorganic anions and dissolved organic matter on COD measurement in Lake Chenghai

Abstract

自2005年以来，程海水体的化学需氧量（COD）持续升高，而生化需氧量（BOD）却维持不变，高锰酸盐指数（COD_Mn）升高也较缓慢.为研究程海COD持续升高的原因，选取程海水体中具有代表性的无机阴离子（Cl^-、F^-、S^2-、HCO₃^-）和溶解性有机质（DOM）中不同浓度的胡敏酸（HA）、富里酸（FA）和商品化腐殖酸（SHA），研究其对COD和COD_Mn测定的影响，探讨Cl^-和DOM共同存在下对COD测定的影响.结果表明：程海水体中Cl^-浓度对COD存在显著影响，产生的COD值为5.42 mg/L，S^2-、F^-和HCO₃^-对COD影响较小；各离子对COD_Mn的影响很小；不同浓度梯度的HA、FA和SHA与COD测定结果呈显著线性相关，氧化1 mg C HA、FA和SHA所产生的COD值分别为2.164、1.964和2.362 mg；氧化1 mg C HA和FA所产生的COD_Mn值分别为0.646和0.344 mg；DOM对COD测定值的影响显著大于对COD_Mn测定值的影响；且一定浓度Cl^-的存在增强了FA与HA对COD测定的影响.该研究为进一步阐明程海COD逐步升高，COD_Mn值缓慢升高的内在原因奠定了基础.;In Lake Chenghai, annual increase in chemical oxygen demand (COD) has been observed since 2005, while biochemical oxygen demand (BOD) has remained almost constant and permanganate index(COD_Mn) has been increasing slowly. In order to reveal the reason for the phenomenon, typical inorganic anions such as Cl^-, F^-, S^2- and HCO₃^-, as well as dissolved organic matter (DOM) such as humic acid (HA), fulvic acid (FA) and commercial humic acid (SHA) in Lake Chenghai were surveyed for the effect of COD measurement. This study investigated the effects of inorganic anions and major DOM fractions, and their combined occurrences on COD measurement. Results showed that:Cl^- could significantly affect the COD measurement with the value of 5.42 mg/L, while the presence of S^2-, F^- and HCO₃^- may hardly impair accuracy of COD measurement; the inorganic anions also had a less impact on COD_Mn measurement. The different concentrations of HA, FA, SHA were significantly linearly correlated with COD values, the oxidation of 1 mg C HA, FA and SHA produced 2.164, 1.964 and 2.362 mg COD, respectively; while the oxidation of 1 mg C HA and FA produced 0.646 and 0.344 mg COD_Mn, respectively. The influence of DOM on COD measurement was significantly larger than that of COD_Mn; and the different concentrations of chloride ions enhanced the effect of FA and HA on COD determination. This study can build up the foundation for further exploring the internal causes for the increase in COD and COD_Mn in Lake Chenghai.