Kinetic study on biological reduction of selenium compounds

Biological treatment of selenium-containing wastewater was investigated using the selenium-reducing sludge acclimatized from denitrifying sludge. The kinetic behavior of selenium reduction was evaluated for both selenate- and selenite-acclimatized sludge using methanol as an electron donor in batch and continuous runs. Selenate and selenite concentrations decreased linearly till the end of reaction, indicating the zero-order kinetics of the consecutive reduction paths. The temperature dependency was satisfactorily expressed by the Arrhenius type equation with different activation energy in selenate and selenite reduction. The pH dependency was quite different, too. The inhibitory effects of nitrate coexistence in reacting fluid were different depending on the type of selenium and sludge employed. The continuous runs with actual industrial wastewater could be performed satisfactorily resulting in full reduction of the aqueous selenium species to native Se, which was reflected in quite low selenium concentration of the effluent.