Economics of Selenium Removal from Drainage Water

Abstract

A treatment system consisting of biological reactors and microfiltration has been developed to remove soluble selenium species from agricultural drainage water. The process was evaluated over a two‐year period, and the reactor configurations and specific removal rates of nitrate and selenium were optimized. Trials on the operation of a pilot solar salt works to concentrate the detoxified water after treatment to recover salts were also carried out. The treatment process reduced the selenium concentration of the drainage water from over 500 μg/L to 10‐50 μg/L as Se. Boron in the drainage water was reduced from 6‐8 mg/L to 0.5 mg/L by an ion exchange post‐treatment. This resin also removed residual seleniuni to below 10 (ig/L. Trials on high‐salinity drainage waters, similar to those found in evaporation ponds, were successful and gave enhanced specific selenium removal rates. The costs of removing selenium or selenium and boron from the drainage water were estimated to be $\$0.038‐0.052/m^3$ and $\$0.050‐0.071/m^3\text{,}$ respectively, after allowance for by‐product recovery (boric acid and sodium sulfate) credits.