As previously mentioned, the dyes used in the industry contain various nitrogenous compounds. This, combined with the stringent regulations on discharging effluent water, makes it necessary to remove nitrogen from wastewater discharges to meet the requirements. This can be achieved by nitrification and denitrification following a combination of anoxic and aerobic biological treatment processes.
In nitrification, organic nitrogen compounds and ammonia are converted into nitrate ions. In denitrification the nitrates are reduced to nitrogen gas by using carbonaceous material. The nitrification reaction occurs in the moving bed bioreactor tank (MBBR) itself, and the denitrification process occurs in an anoxic zone which can be created within the MBBR tank. The following biochemical reactions take place in nitrification and denitrification respectively:
NH3 + O2 → NO2 – + 3H+ + 2e-
NO2 – + H2O → NO3 – + 2H+ +2e-
6 NO3– + 5 CH3OH → 5 CO2 + 3 N2 + 7 H2O + 6 OH-
(Note: here methanol (CH3OH) has been used to represent an easily biodegradable organic matter expressed as COD or BOD).
There are several biological wastewater treatment processes. Moving bed bioreactor is one of the state-of-the art technologies used to treat wastewater. It has a dynamic fixed film which allows it to prevent adverse effects like channeling, poor distribution of wastewater and air to biomass attached onto the media surface. These are the advantages that MBBR has over traditional fixed film treatments like rotating bio-reactor (RBC), trickling filters. MBBR also offers several folds of effective solids retention time (SRT) in comparison with Conventional activated sludge (CAS). As a result, for equivalent levels of treatment an MBBR treatment requires much lower reactor volume and footprint area compared to suspended growth treatments.