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Title: On-line Monitoring of a Photo-Fenton System
Author: Modrzejewska-Baudin, Barbara
Awarding Body: University of Glamorgan
Current Institution: University of South Wales
Date of Award: 2008
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A uv photo-Fenton process, utilising immobilised iron catalyst, was studied during the experimental work described here to treat the model recalcitrant waste: nonbiodegradable azo dye Orange II in concentrations ranging from 0.05 to 0.80 mM. The AOP reactor with capacity of 12l and headspace volume of 0.5l was constructed and used to study the oxidation of the dye waste stream during both batch and continuous experiments. The Fenton process was enhanced by light (with radiation centred at 253.7nm) through the decomposition of photo-active Fe(OH)2+, leading to the generation of additional ·OH radicals with concomitant partial recycling of the Fe3+ to Fe2+. The process utilised a novel immobilised Fe catalyst (initially Nafion membrane based and subsequently Fe-Silica fabrics) which allows the reduction of the amount of iron salts required to be fed into the process, reduces sludge production from the process and the risk of iron salts precipitating on the UV lamps. Both the aqueous and gas phase off-line process parameters were evaluated and a novel on-line gas phase monitoring system (analysing carbon dioxide from the complete oxidation of organic matter and oxygen from the self-decomposition of hydrogen peroxide) was also developed and employed. During the latter stages, a novel instrument measuring hydrogen peroxide levels, operating in conjunction with the AOP reactor, was evaluated. The hydrogen peroXide dosing was studied with molar ratios of hydrogen peroxide to Orange II dye within the range of 7.8:1 to .62.5:1. It was established that the optimum ratio for organic carbon removal was 31.25 M H202 to 1 M Orange II dye. Both under-dosing and over-dosing of hydrogen peroxide resulted in a decreased efficiency of the oxidation treatment due to a reduction in the number of hydroxyl radicals available for oxidation. The comparison of oxidation results initiated at both neutral and acidic conditions (pH <3) showed marginally higher efficiency in COD and Toe removal during epxen'ments W.ith lowered pH (0.4% and 3.2%, respectively). It was demonstrated that'In! the expen.ments at elevated liquor temperature of approximately 50°C (in contrary to experiments initiated at room temperature) promoted slightly higher efficiency of the photo-Fenton process and carbon removal was on average 2.5% higher during 50°C runs. Iron analyses conducted during the batch experiments showed gradual deterioration of Nafion membranes which led to significant reduction in oxidation efficiency; the TOe removal decreased from 97% to 29%. Subsequently Nafion membranes were replaced by Fe-Silica fabrics, which proved to be better suited to the UV-Fenton process. The comparison of batch and continuous studies indicated a higher efficiency of the photo-Fenton process during the continuous treatment: to reach the same level of TOC removal, the batch experiments reqUired on average 19 minutes more than the continuous experiments with an equivalent hydraUlic retention time (HRT). The oxidation treatment of initially non-biodegradable Orange II solutions (BODs/COD ratio of 0.001) resulted in increased biodegradability and the continuous experiment with HRT of 1.5h was enough to make the waste stream biodegradable (BODs/COD ratio of 0.62). The analysis of oxygen gas suggested that the hydrogen peroxide overdosing lead to the production of oxygen gas; this was likely due to the scavenging of hydroxyl radicals, as the excess hydrogen peroxide was successfully competing with organics for the radicals. In order to evaluate and control the usage of hydrogen peroxide during the oxidation process on waste-stream of varying load and strength, the AOP reactor was used in conjunction with the automated hydrogen peroxide monitor. The principle of the H20 2 monitor's operation was the measurement of the produced volumes of oxygen from the reaction of catalase enzyme with hydrogen peroxide. The monitor's response was found to be linear within the hydrogen peroxide range of 30 - 400 mg H20 2 with R2 correlation of 0.99. After the initial experiments with poor correlation between the off-line spectroscopy measurements and H20 2 monitor (R2 of 0.25), the sample conditioning was introduced. With sample conditioning the correlation with the off-line spectroscopy measurements was greatly improved with the correlation coefficients R2 of 0.957 and 0.995. This would enable the on-line process monitoring of hydrogen peroxide to be implemented in the AOPs.
Supervisor: Not available Sponsor: Not available
Qualification Name: University of Glamorgan, 2008 Qualification Level: Doctoral
EThOS ID:  DOI: Not available