Optimization of the determination of chemical oxygen demand in wastewaters

Chemical oxygen demand (COD) is one of the most relevant chemical parameters for the management of wastewater treatment facilities including the control of the quality of an effluent. The adequacy of decisions based on COD values relies on the quality of the measurements. Cost effective management of the minor sources of uncertainty can be applied to the analytical procedure without affecting measurement quality. This work presents a detailed assessment of the determination of COD values in wastewaters, according to ISO6060:1989 standard, which can support reduction of both measurement uncertainty and cost of analysis. This assessment includes the definition of the measurement traceability chain and the validation of the measurement procedure supported on sound and objective criteria. Detailed models of the measurement performance, including uncertainty, developed from the Differential Approach, were successfully validated by proficiency tests. The assumption of the measurement function linearity of the uncertainty propagation law was tested through the comparison with the numerical Kragten method. The gathered information supported the definition of strategies for measurement uncertainty or cost reduction. The developed models are available as electronic supplementary material, in an MS-Excel file, to be updated with the user's data.     

基于紫外-可见光谱的水质TOC定量分析方法

地表水资源安全关系到国民健康、生态环境稳定和经济可持续发展,具有重要战略意义.总有机碳(T OC)是一种衡量水体中有机物含量的综合指标,其在水环境监管和治理中具有重要价值.传统检测方法通过高温催化氧化测定水样中T OC含量具有耗时较长、操作复杂的局限性,紫外-可见光谱技术具有检测速度快、操作简单的优势,因而在水质在线检...     

厦漳地区原水DOM的3-DEEM-FRI表征与分析研究

采用三维荧光光谱结合荧光区域积分分析法(3DEEM-FRI)研究了厦漳地区江东泵站、北溪水闸、汀溪水库、莲花水库、坂头水库以及石兜水库原水中溶解性有机物(DOM)的荧光特性、污染特征及其他水质指标与各荧光区域积分体积之间的相关性.结果表明,三种荧光组分—荧光类蛋白质组分(组分Ⅰ,C1)、荧光类蛋白质组分(组分Ⅱ,C2)...     

Organic carbons and TOC in waters: an overview of the international norm for its measurements

Many chemical measurements are subjected to international recommendations and rules. When applied to environment, they must also respect national rules. In this paper, rules to measure TOC issued in the period 1973–2002 are presented. Over 20 rules and guidelines, both national and international, are presented all aiming to increase the environmental monitoring capacity of ecologists and researchers through the use of the best instruments commercially available and manufactured by the market farms.The tracking of CO₂, obtained by oxidative system, is the heart of TOC modern analysers. Practically, all the methods foresee the determination of the CO₂ produced by the degradation of the organic matter present in solution, often IR devices are used. Also, other detectors can be used (conductivimeter, CO₂electrode) but they must be characterised by mechanical resistance and stability, not interfered by other gases, not easily corroded.The thermal oxidation methods are distinguished in low-temperature method (below 100 °C) and high-temperature method (between 600 and 1200 °C) with the presence also of mixed oxidation systems.In many countries, TOC determination is ruled in order to avoid that manufacturers of scientific equipment manage at their commercial convenience on this field. Anyway, the rules imposed by internationally recognised organisms must be actually followed. They establish the use of reference solutions, specific methods of measure and detection limits that must be respected by the analytical instruments.Due to the wide field of application involving TOC measurements, especially related to water (drinking, surface, waste), this kind of instruments is largely present everywhere.At present, definitive rules about TOC measurement are not laid down by law; so, we consider it interesting to present the chronological list of the rules with their content concerning the measurement method, the sensitivity and detection limit, and the matrices that must be subjected to the control. Consideration about the measurement quality and the correspondence between rules and analytical power are out of the interest of this work.     

Remarks on the measurement of the total organic carbon (TOC) in water at lower levels

Summary The question, whether measurements of TOC-values in the lower ppm range in water have any sense, is discussed. Analytical parameters, like the lack of standards, the natural CO₂-blank, the influence of large amounts of water vapour on the quantitative combustion, the possibility of extrapolation of calibration graphs, the catalyst efficiency and the final measurement, are critically examined.

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Bemerkungen zur Messung von niedrigen Werten des Gesamtgehaltes an organischem Kohlenstoff (TOC) in Wasser

Zusammenfassung Es wird die Frage diskutiert, ob das Messen von TOC-Werten im Bereich von weniger als einigen ppm Sinn hat. Die Fragwürdigkeit einer solchen Messung wird an Hand einiger Analysenparameter erörtert, nämlich: Abwesenheit von Standardproben, natürlicher CO₂-Blindwert, Einfluß von großen Mengen Wasserdampf auf eine quantitative Verbrennung, Möglichkeit zur Extrapolation von Eichgeraden, Wirkung von Katalysatoren und Ermittlung der Analysenergebnisse.

     

Evaluation of a Freeze-Concentration Technique for Enrichment of Natural Organic Substances in Water

Abstract

A freeze concentration method was tested for its ability to concentrate uncharacterized organic carbon, measured by TOC analyzer, in tap water derived from a surface water reservoir in eastern Massachusetts. Freeze concentration was carried out in polypropylene bottles of 2 liter volume, stirred at either 140 rpm or 400 rpm, and placed in a freezer at either -15°C or -25°C. No effect of stirring speed or freezer temperature on the recovery efficiency was found except possibly at high (>10x) concentration factors. For theoretical concentration factors below approximately ten, measured TOC was reproducible but substantially less than the theoretical value (e.g., for a theoretical value of 10, the measured concentration factor was only 4.3. At higher concentration factors, the ratio of the actual to theoretical concentration decreased further and became variable from experiment to experiment. Lack of quantitative recovery of TOC indicates the likelihood that selective concentration of different components of this material occurred.     

基于CDPD的智能车辆管理系统

主要阐述智能车辆管理系统的结构和各部分的原理 ,并结合实际的车辆管理系统 ,介绍其工作原理 ,对系统中的不足及其修改提出了看法。     

气液滑动弧等离子体降解高浓度有机废水的研究

采用气液滑动弧放电非平衡等离子体进行降解高浓度苯酚模拟废水(初始浓度为872 mg／L)的研究。实验研究表明:由于液滴的存在改变了电极间的介电常数和局部电场,气液滑动弧放电的电压波形比纯气流滑动弧放电更加不规则,起弧电压更低;采用氧气作为载气能提高苯酚的降解效果,最后TOC值为44 mg／L;增大气液混合比,相应的加强了废水的雾化效果,增大水气接触表面积,进而提高了苯酚的降解效果;在尾气中检测到CO2的存在,最高浓度达到35357 mg/m3。     

Rapid estimation of TOC in a marine urban sewage area by UV spectral deconvolution

A simple and rapid procedure for on-site qualitative and quantitative analysis of organic matter from discharges of municipal wastewater in seawater has been developed. This method is based on the knowledge of the UV signal of both seawater and anthropogenic absorbing matter and on the mathematical deconvolution of the sample spectrum using reference spectra. The main application is the estimation of TOC at the direct outlet of the discharge. This quantitative application is obviously limited by the nature of organic compounds, but the UV estimation allowed us to have an overview of the composition and evolution of organic matter into the polluted area. The application of this procedure has been carried out to study the wastewater dilution into an area receiving urban discharges. Experiments showed satisfactory analytical features with a range of TOC values from 75 to 1500?µM C, and the comparison of the results with those obtained by reference method presented a reasonable correlation (r ²?=?0.9636) in the marine discharge. The results have also allowed us to quickly estimate the plume evolution at the sea surface and in depth. This alternative method could be integrated in a portable device for on-site analysis and multiplication of measurements for relevant results, or in a continuous flow analyser.     

Uncertainty of the result of TOC determination in water samples

It is becoming increasingly important to have a reliable and rapid technique for determining total organic carbon (TOC) in wastewater as procedures for wastewater purification could be better applied by knowing the amount of TOC in the wastewater. We describe here an evaluation of the uncertainties associated with TOC determinations in wastewater. TOC was determined by combustion and an infrared (IR) detection method, as described in the standard procedures of the International Organization for Standardization (1999; no. 8245). The major sources of uncertainty in the measurements were identified as being contributions from the linear least square calibration, repeatability, recovery and stability of the sample (storage conditions). A 10% relative expanded uncertainty of TOC measurement in the range of 0.2 to 500 mg L⁻¹ TOC was calculated, which also includes the uncertainty due to sampling.