OZONATION OF DISSOLVED ORGANIC MATTER IN SUBSTRATE-VARIED AND OPERATIONALLY-VARIED ACTIVATED SLUDGE EFFLUENTS (WASTEWATER, KINETICS, TERTIARY TREATMENT)
Abstract
The dissolved organic matter in activated sludge effluents includes microbial by-products, so manipulating bioreactor variables could indirectly affect downstream processes. This research studied ozonation and ozonated effluent character as affected by three activated sludge variables. These variables were each tested at two levels, including pH levels of 6.0 and 8.0, dissolved oxygen (DO) levels of 1 and 7 mg/L, and organic substrates of complex and simple compositions. All eight possible combinations of these levels were tested in laboratory reactors, yielding eight long-term composite samples, which were then filtered and adjusted to pH 7. Data from the unozonated samples showed that complex feed, a pH of 8, or a DO of 7 mg/L had resulted in higher organic levels. Molecular size and adsorption tests indicated that the bioreactor variables had also influenced the qualitative character of effluent organics. The relative ozone demand of each sample was measured by a test that found the ozone dose required to yield a dissolved ozone residual of 0.30-0.35 mg/L after five minutes of mixing in a gas-liquid batch reactor. Resulting doses ranged from 3 to 16 mg/L and correlated to organic level, especially after accounting for nitrite. Another test measured ozone consumption rates. The data fit pseudo-first-order kinetics that were modified by replacing the "rate constant" by a "rate-constant function," which decreased as ozone was consumed. Sample comparison suggested that kinetic behaviour was also related to organic and nitrite levels. Ozonating each sample with its dose as determined in the demand test resulted in organics with lower molecular sizes, greater biodegradability, different activated carbon adsorption isotherms, and higher non-adsorbable fractions. Organic level measured by chemical oxygen demand or ultraviolet absorbance decreased due to ozonation, but changes in dissolved organic carbon level depended on bioreactor feed composition. In most cases, ozonated organic character and changes due to ozonation were related to initial organic character or ozone dose. In general, ozone demand and final organic character were influenced more by quantitative, rather than qualitative, differences. That is, the three bioreactor variables affected ozonation mainly by their effects on the levels of organic matter and nitrite in the effluents.
Degree
Ph.D.
Subject Area
Civil engineering
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