盐度对海水化学需氧量测定的影响及校正方法研究

发布时间：2018-06-03 09:10

本文选题：化学需氧量 + 河口及近岸海区　；参考：《中国海洋大学》2015年硕士论文

【摘要】：海水化学需氧量(chemical oxygen demand, COD)是海水水质的重要监测指标,通常用于表征海水综合有机污染程度,并在海域生态环境质量评价、海区富营养化研究等方面得到广泛应用。然而,在低盐的河口及近岸海区,海水COD和淡水高锰酸盐指数(CODMn)的测定均受到C1-的影响,其实测值无法准确反映近岸盐度较低海域的有机污染程度,而且这两种方法的测定结果不能对应,这使得陆源污染物输入量与海区污染物现存量的对比分析缺乏依据,河口及近岸海域自净能力的评估失真,难以全面、准确地评价近岸水质有机污染状况,难以提出以溯源为主有针对性的污染治理方案。本文通过研究不同盐度条件下海水COD测定方法的氧化效率,分析盐度对海水COD测定的影响,并初步阐释其影响过程；在考虑盐度影响的基础上,比较海水COD与淡水碱性CODMn两种指标的测定结果；根据海水COD测定值随盐度的变化规律,提出河口及近岸海域水质评价中COD实测结果的校正式,结合黄河口淡咸水混合区水质现场调查数据分析,说明进行该校正是必要的,从而为COD这一常规有机污染指标在河口及近岸海域水质评价中的应用提供参考。本文主要结论如下：(1)海水COD测定结果在盐度约为0-25的低盐区明显偏低,而在盐度约为25-35范围内该测定方法稳定。有机物浓度也是海水COD测定的影响因素,盐度越低,有机物浓度对COD实测值的偏差影响越大。在盐度约为0-25范围,海水COD测定方法的平均氧化率随盐度的降低而下降。C1-对海水COD测定的影响发生在碱性KMnO4加热氧化有机物阶段,而对后续的KI还原过量的KMnO4和MnO2以及Na2S2O3滴定生成的游离碘等过程无影响。(2)淡水碱性CODMn测定方法在盐度约为0-5范围内稳定,不受盐度变化的影响：但随着盐度升高,其测定结果迅速升高。在盐度约为5-35范围内,碱性CODMn测定方法的平均氧化率随C1-浓度的升高而显著增大。淡水碱性CODMn测定方法的氧化效率比海水COD方法普遍偏高,其在盐度约为0-5范围内的氧化效率与海水COD方法在盐度约为25-35范围内的氧化率相近(以葡萄糖为底物)。(3)通过将有机物溶液在不同盐度条件下的COD实测值与其在盐度为25-35条件下测定值的差值进行拟合得到的公式,可对盐度低于25的河口及近岸低盐区域的海水COD实测值进行校正。校正后COD值可以与盐度为25-35范围内的COD实测值直接对比,也可以与盐度0～5范围内的淡水碱性CODMn测定结果直接对应。校正后的海水COD值与淡水碱性CODMn的相对误差不超过3.6%。
[Abstract]:Chemical oxygen demand, COD) is an important monitoring index of seawater quality. It is usually used to characterize the degree of comprehensive organic pollution of seawater and is widely used in the evaluation of ecological environment quality and eutrophication of sea area. However, in the low-salt estuaries and inshore areas, the determination of COD in seawater and the index of permanganate in fresh water are affected by C1-, and the measured values can not accurately reflect the degree of organic pollution in the lower salinity coastal waters. Moreover, the results of the two methods can not be matched, which makes the comparative analysis of the input amount of pollutants from land sources and the standing quantity of pollutants in the sea area lack the basis, and the evaluation of self-purification ability of estuaries and coastal waters is distorted, and it is difficult to be comprehensive. In order to evaluate the organic pollution of coastal water quality accurately, it is difficult to put forward a targeted pollution control scheme with traceability as the main source. In this paper, the oxidation efficiency of COD determination method in seawater under different salinity is studied, the influence of salinity on COD determination in seawater is analyzed, and the influence process is preliminarily explained, on the basis of considering the effect of salinity, Comparing the determination results of COD in seawater with alkaline CODMn in fresh water, according to the variation rule of COD value with salinity in seawater, the formal calibration of COD measured results in water quality evaluation of estuaries and inshore waters is put forward. Based on the analysis of the field investigation data of water quality in the mixed area of the Yellow River estuary, it is proved that it is necessary to carry out this study, thus providing a reference for the application of COD, a conventional organic pollution index, in the evaluation of water quality in estuaries and inshore waters. The main conclusions of this paper are as follows: (1) the determination results of COD in seawater are obviously low in low salt areas with salinity of 0 to 25, but stable in the range of salinity of 25 to 35. The lower the salinity, the greater the effect of the concentration of organic matter on the deviation of the measured value of COD. In the salinity range of 0-25, the average oxidation rate of COD in seawater decreases with the decrease of salinity. The effect of C1- on the determination of COD in seawater occurs in the stage of oxidation of organic compounds by alkaline KMnO4 heating. However, this method has no effect on the subsequent processes such as excessive KMnO4 and MnO2 reduction by Ki and free iodine generated by Na2S2O3 titration.) the basic CODMn method for the determination of freshwater alkalinity is stable in the range of about 0-5 salinity, and is not affected by the salinity change: however, with the increase of salinity, The results of determination were rapidly increased. In the salinity range of 5-35, the average oxidation rate of alkaline CODMn method increases significantly with the increase of C1- concentration. The oxidation efficiency of fresh water alkaline CODMn method is generally higher than that of seawater COD method. Its oxidation efficiency in the range of 0-5 salinity is similar to that of seawater COD method in the range of 25-35 salinity (glucose as substrate) by measuring the COD value of organic solution under different salinity and salt. The formula obtained by fitting the difference value of the measured value under the condition of 25-35 degrees, The COD values of the estuaries and coastal low salt areas with salinity less than 25 can be corrected. The corrected COD values can be compared directly with the measured values of COD in the range of 25-35 salinity, or with the results of alkaline CODMn measurements of fresh water in the range of 0 ~ 5 salinity. The relative error between the corrected COD value of seawater and the fresh water alkaline CODMn is not more than 3.6.
【学位授予单位】：中国海洋大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：X834

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