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Author      Title/Abstract      

Removal of Selenium Using a Novel Algal-Bacterial Process
Author: Matthew B. Gerhardt, F. Bailey Green, Robert D. Newman, Tryg. J. Lundquist, R. Blake Tresan, William. J. Oswald
Date: 7/191
Reprinted from Research Journal Water Pollution Control Federation, July/August 1991

A process for removing selenium and nitrate from agricultural drainage water using algae and anaerobic bacteria was studied in a field system. Algae were grown in high-rate ponds containing drainage water, and the 178-± 99-mg/L culture took up 18 ± 13 mg/L NO3- - N. The algae and drainage water were then transferred to anoxic units where denitrifying and selenate-reducing bacteria, feeding on algae, reduced NO3--N from 100 ± 24 mg/L to less than 10 mg/L at times. Soluble selenium concentration, which was 200–400 mg/L in the influent, decreased only slightly in anoxic units, but speciation of effluent selenium showed that selenate was completely reduced to selenite and other reduced forms. Addition of 10–20 mg/L ferric chloride to the effluent reduced soluble selenium to 7–12 mg/L. Selenium reduction was not inhibited by 2000–4000 mg/L sulfate. Algae not used by denitrifying and selenate-reducing bacteria were fermented to methane in unmixed cylindrical digesters where methane production averaged 0.16 L/g volatile solids introduced.

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