| COD, BOD and TOC are the three important indexes of environmental monitoring, which can be obtained by measuring the content of produces after oxidized and decomposed those organic substances. But these methods neglect the properties of organic substances and we cannot know the existing form of organic substances in water body. Further, these analytical methods have many disadvantages such as high cost, long time spent, and uses some venomous chemical medicines causing the second pollution. Organic substances in sewage, that have hydrophilic group and hydrophobic group, are easily enriched on the gas-water interface, which will change the surface membrane pressure. Just in a certain concentration range, surface excess and concentration are obey the law of Gibbs. As a result, the best and direct way to determine the organic substance is the method of membrane pressure: no pretreatment with the sample, no destruction the organic substance. And dissimilar organic material in different concentration can get diverse chart with the instrument of membrane pressure, which can show some useful information of the molecular structure and the interaction between molecules. To exploit the instrument of determination of dynamical surface pressure in line can extend the research field of the method of membrane pressure, detect continuously the whole water treatment process, and study the resolvability of surface membrane of the organic substance in the wastewater, in order to apply it to environment protection.Good linear relation between area of hysteresis loop and CODcr value had been derived through the survey of surface membrane of different sewage factories on early stage, and preliminary analysis of cause and physical meaning of hystersis loop are also made by Jianbiao Yang and Fei Qin; Caiyang Xu had studied the membrane of naphthalene and crude oil; Hua Sun had researched the influence of some metalline ions on the membrane of humic acid. On these bases, we continue to do some reseaches of the method of membrane pressure. In the one hand we apply it into soluble membrane instead of insoluble one, study the membrane pressure and the formof area of hysteresis loop of different kinds of surfactants at the gas-water interface, and compare the results to the experiences of dilatational rheological viscoelastic properties to get some information of surface membrane in the interface, such as state, constitute, form and interaction etc; on the other hand, we use the instrument of dynamic membrane pressure in line to determine the content of the organic substance in the city sewage in order to do some primary researches for application of this method into water quality monitor.In the first part of this article, we study some kinds of soluble surfactants like citric acid (CA), anionic surfactants including sodium dodecyl sulfate(SDS), sodium dodecyl sulphonate and sodium dodecyl benzene sulfonic (SDBS), cationic surfactant cetyl trimethyl ammonium bromide(CTAB), nonionic surfactant OP, and the second one, use the instrument of dynamic membrane press in line to determine the content of the organic substance in the city sewage. The results are as follows:1. Relation between surface membrane pressure and concentration According to the experiences of CA, SDS, SDBS, CTAB, and OP, we can find the same trend, that is: with the addition of concentration of surfactants, surface membrane pressure augment rapid and then hold the line in a certain concentration below the CMC, it is means that the surface adsorption arrive saturated concentration; in the range of this experiment, surface membrane pressure of CA has a good linear relation with concentration (R>0.95);2. Relation between area of hysteresis loop and concentration Excluding SDS, CTAB, all the substances in this experiment show the same result: when concentration added, area of hysteresis loop has a large number in the same concentration of experiment of dilatational rheological viscoelasticity properties, and in low concentration, SDS, SDBS and sodium dodecyl sulphonate... |
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