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Abstract

In this thesis is described the development of a novel method and instrumentation for electrical pH control in aqueous solutions. The work is targeted to environmental and industrial on-line remote in-situ chemical and optical fibre sensors conditioning, measurement, and process control. The method is a more flexible alternative to the existing automatic pH controllers, based on correction buffer reagent addition and mixing. It operates free of chemicals and mechanical valve systems and involves only pure electrical bias and feedback control in conductive, especially aqueous solutions.

Dissolved gaseous species which produce acidic and basic waters are of great concern for the preservation of the environment. Significant research effort is aimed at the development of on-line, in-situ monitoring methods. The measurement of such pollutants has been previously maintained by using preconditioned water samples and ion-selective electrodes, or absorption spectrometry. A gas-permeable membrane has been successfully used in this application to separate the molecular form from the ionic form of the measured species. The solution pH has been controlled by chemical means to ensure the reversible transition of measured species from ionic to gaseous form and hence allow their permeation through the membrane.

An electrochemical pH controller based on electrolysis was developed and evaluated. Multiple feedback-control systems for biasing of the modulation electrodes were investigated, including constant voltage (potentiostatic), constant current (galvanostatic) and combined methods. The instrument’s speed, settling time, accuracy, power requirements and battery runtime are discussed. Battery power sources for on-line monitoring were evaluated and improved hybrid power supply was developed. Two different feedback control options, involving electrochemical and optical sensors, are presented. Real instruments implementing the two feedback approaches were built and analyzed, and the test results discussed. Possible applications of the new method for environmental monitoring and process control are demonstrated.

Publication Type:	Thesis (Doctoral)
Subjects:	Q Science > QA Mathematics T Technology > TA Engineering (General). Civil engineering (General)
Departments:	School of Science & Technology > Engineering School of Science & Technology > Mathematics Doctoral Theses

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