Effects Of Inorganic Anions And Dissolved Organic Matter On COD Measurement In Chenghai Lake

As one of the nine high plateau lakes in Yunnan Province,Chenghai Lake is the core of maintaining the ecological balance of its basin and supports the ecological foundation of Lijiang City,s national economic construction and social development.In Chenghai Lake,an annual increase of chemical oxygen demand(CODCr)has been observed since 2005,while biochemical oxygen demand(BOD5)has remained almost constant and permanganate index(CODMn)has been increasing slowly.In order to explore the reasons for the increase of CODCr,this study analyzed the source of CODCr from both inorganic anions and dissolved organic matter.First,typical inorganic anions such as Cl-,F-,S2-and HCO3-,as well as dissolved organic matter(DOM)such as humic acid(HA),fulvic acid(FA)and commercial humic acid(SHA)in Chenghai Lake were researched for the effect of CODcr measurement.This study investigated the effects of inorganic anions and major DOM fractions,and their combined occurrences on CODcr measurement.Next,select samples from monitoring places and testing sections of Chenghai Lake,offshore water and waste water in the pollution origin,and testify the restored polluted indicators,analyze the organic matter with DAX-8 resin and DAX-4 resin.Meanwhile,analyze samples from other plateau lakes(Yangzong Lake,Dianchi Lake)and Kunming wastewater treatment plants to further understand water quality change of Chenghai Lake.Study results are as follows:(1)Cl-could significantly affect the CODcr measurement and the value is 5.42 mg/L,while the presence of S2-,F-and HCO3-may hardly impair accuracy of CODCr measurement in Chenghai Lake;the inorganic anions also had a less impact on CODMn measurement in Chenghai Lake;the different concentrations of HA,FA,SHA were significantly linearly correlated with CODCr values,oxidation of 1 mgC HA,FA and SHA produced 2.164,1.964 and 2.362 mg CODcr,respectively;oxidation of 1 mgC HA and FA produced 0.646 and 0.344 mg CODMn,respectively;the influence of DOM on CODCr measurement was significantly greater than CODMn;and the different concentrations of chloride ions enhanced the effect of FA and HA on CODcr determination.(2)Chemical oxygen demand(CODCr)in Chenghai Lake monitoring data show:Cl-contributes 14.00%to CODCr,algae and suspended matter contribute 33.05%(parts retained by 0.45 μm filter)to CODCr,hydrophobic organic matters adsorbed by DAX-8 resin contribute 28.57%to CODCr,organic matters adsorbed by DAX-4 resin contribute 8.63%to CODCr,others contribute to 15.75%.Hydrophobic substances mainly come from the rapid degradated hydrophilic organic matters,contribute 10.2 mg/L to CODCr value.(3)Yangzong Lake has better quality,whose suspended insolubles and algae contribute less to CODCr value while Dianchi Lake and Chenghai Lake have more and roughly the same suspended substance.Yangzong Lake waters has more hydrophilic organic matter than hydrophobic one(0.4:1),Dianchi Lake has the same hydrophilic organic matter and hydrophobic organic matter(1:1),while Chenghai Lake has more hydrophobic organic matter than hydrophilic one(3.3:1),indicating the differences among Yunnan’s three typical major lakes in CODCr contribution origin and in pollution process.The ratio of both hydrophobic and hydrophilic organic matter in the fifth,sixth,eighth water purification plants in Kunming is1.3:1,same with that of Dianchi Lake,while the ratio of the fourth water purification plant is 3.7:1,closer to that of Chenghai Lake.