Anoxic processes are used for removal of total nitrogen and selenium from wastewater. In this process, organic matter (COD or BOD) is used by biological organisms to reduce nitrate and nitrites to nitrogen gas, and selenate and selenite ions to elemental selenium. The nitrates/nitrites are used as an energy source to oxidize organic matter, which result in the reduction of nitrate/nitrites to nitrogen gas.
The selenate (Se6+) and selenite (Se4+) ions present in aqueous forms are difficult to remove as they exist in a dissolved state. In anoxic processes, biological organisms use selenate and selenite ions as electron acceptors and reduce them to elemental selenium. Thus, in anoxic processes there is no need for aeration to provide oxygen, which is an energy-intensive process in aerobic systems.
In the ActiveCell Anoxic MBBR process, Headworks uses proprietary media, developed in-house, which is the main component of this system. This provides high surface area to support attachment of a large microbial population in the form of biofilms, which promote biochemical reactions in the wastewater treatment process at enhanced rates within limited reactor volume and footprint area. In absence of aeration, mixing inside the reactor tank is conducted by mechanical mixers in anoxic treatment processes.