Dissolved Oxygen Requirements for the Indirect Photolysis Treatment of Two Refractory Herbicides
- Richard J. Watts *,
- V. Dean Adams and
- E. Joe Middlebrooks
Indirect photolysis in lagoons under solar radiation has been proposed for the treatment of pesticide-laden agricultural runoff, pesticide container rinsate, and industrial wastes. A common indirect photolysis mechanism, singlet oxygen generation, consumes oxygen through electrophilic attack on the organic waste components. Photolysis lagoons will require optimum oxygen input to achieve economical treatment. Dissolved oxygen requirements were investigated for the photolysis of bromacil (5-bromo-3-sec-butyl-6-methyluracil) sensitized by methylene blue and terbacil (3-tert-butyl-5-chloro-6-methyluracil) sensitized by riboflavin. Indirect photolysis rate as a function of dissolved oxygen residual followed saturation curves. Methylene blue-sensitized photolysis of bromacil reached maximum rate at 1 to 2 mg L−1 O2 and the maximum rate of riboflavin-sensitized photolysis of terbacil was reached at approximately 5 mg L−1 O2. Dissolved oxygen uptake rates for the indirect photolysis reactions correlated with electrophilic attack of singlet oxygen on the substrates. Aeration requirements for indirect photolysis treatment systems may be calculated based on the criteria presented.
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