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Monitoring of the degradation of chlorinated organic impurities in water by automated flow injection analysis

University of British Columbia

Chlorinated organics are a major concern because of their persistence in the environment, possible toxicity and carcinogenicity. One of the substances of most concern, chloroform, has been classified as a priority pollutant by U.S. Environmental Protection Agency. It is present at trace levels in man-made drinking water and in waste water from industries such as pulp and paper. The scope of this thesis has been to develop instrumentation and methods for destruction and detection of chloroform and related contaminants in such samples. Attack of chloroform by free radicals (e.g., HO.) can result in complete mineralization: i.e., quantitative liberation of the innocuous free chloride and generation of carbon dioxide. Free radicals are formed when a suspension of a semiconductor material such as titanium dioxide is illuminated with ultraviolet light. They are also formed when aqueous solutions are subjected to a high intensity ultrasonic field. In this thesis we report use of both UV and ultrasound to degrade chloroform, and have monitored the rate and extent of conversion via real-time on-line measurement of free chloride concentration and conductivity. The technique used for these studies is Flow Injection Analysis. Specific objectives of this research were as follows: (i) To develop a photo-reactor within which to carry out the degradation experiments. This contained two mercury lamps and used either suspended titanium dioxide powder (anatase) or titania glass as photocatalyst. The two UV lamps were directly immersed in the solution to provide the most efficient UV irradiation. A 23 kHz sonicator probe was situated in the centre of the vessel for those experiments which required it. (ii) To develop an automated sampling system by which the progress of the reaction within the reactor could be followed. This was comprised of polytetrafluoroethylene (Teflon®) tubing and contained an in-line microfiltering system to remove catalyst solids. It was used to take samples from the reactor and deliver them to the detection system. (iii) To develop an automated Flow Injection Analysis system to detect products from the photodegradation of the organic species. A flow-through conductivity detector was constructed and used to monitor the change in total free ions. A chloride ion selective electrode with its flow-through cell was used to quantitatively monitor the change in concentration of free chloride ion. In both cases the output was observed as a series of skewed Gaussian peaks. (iv) To characterize the instrumentation developed and to use it to study the degradation of chlorinated organics - specifically chloroform. The instrumentation was able to monitor the progress of reactions over a period of several hours without human supervision. With the presence of UV light and titania powder catalyst it was found that chloroform was totally degraded after about 50 mm. The chlorine was quantitatively recovered as chloride ions. A kinetic analysis showed that the reaction curve followed A—B--*C reactions. A mechanism for the reaction is proposed in the thesis. When using a heterogeneous chloroform system, introduction of power ultrasound into the reactor improved the yield after 20 mm by 41 % based on the detection of chloride ions. A preliminary investigation of a glassy form of titanium dioxide showed a reaction rate which was four times slower than for the anatase form, given equal masses. This rate difference may be due to decreased contacting surface area. However, the glassy form is much easier to use. The system developed has strong potential for rapid, semi-automatic development of optimal catalytic treatments to detoxify industrial waste water and purify municipal drinking water. As such it has significant economic and environmental applications.

Thesis/Dissertation

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2009-02-26

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http://hdl.handle.net/2429/5229

Chemistry

University of British Columbia

UBCV

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