ABSTRACT
Selenium (Se) is part of the 16th group of the periodic table and is a non-metal or chalcogen with strong metal-like properties. Selenium is a unique element that is both an essential nutrient and a toxic element to living organisms with a narrow range. This chapter focuses on the different reactor configurations used for selenium removal focusing on both granular and biofilm systems. It presents different selenium microbial pathway and reduction process and describes special properties of selenium as an anti-biofilm agent. Reduction of Se-oxyanions is widespread in natural environments and is more likely that biotic mechanisms are responsible for the presence of selenide in the environment rather than abiotic reduction. Upflow anaerobic sludge blanket (UASB) reactors are most commonly employed for anaerobic treatment of industrial effluents worldwide. Fluidized bed reactor (FBR) has close similarity with both UASB and PBR where both fluidization of the packing material and mixing of the liquid occur in the FBR.
