Integration of methane removal in aerobic anammox-based granular sludge reactors.

Combined partial nitritation-anaerobic ammonium oxidation (anammox) processes have been widely applied for nitrogen removal from anaerobic digestion reject water. However, such streams also contain dissolved methane that can escape to the atmosphere, hence contributing to global warming. This study investigates the possibility of integrating methane removal in aerobic anammox-based granular sludge reactors, through modelling and simulation. Methane removal could be established through aerobic methane-oxidizing bacteria (MOB), denitrifying anaerobic methane-oxidizing bacteria (damoB, NO2- + CH4 → N2 + CO2), and/or archaea (damoA, NO3- + CH4 → NO2- + CO2). The simulation results demonstrated that the combined removal of nitrogen and methane was feasible at low dissolved oxygen conditions. Aerobic MOB were the main responsible microorganisms for removing methane. A sensitivity analysis of key kinetic parameters showed a shift in the methanotrophic populations depending on the most favourable parameters for each microbial group, while keeping high nitrogen and methane removal efficiencies. Possible methane stripping during aeration could be limited by increasing the depth within the reactor column at which aeration was supplied. Overall, the integration of methane removal in aerobic anammox-based granular sludge reactors seems to be a promising process option to reduce the carbon footprint from wastewater treatment.

Evaluating the potential for dissimilatory nitrate reduction by anammox bacteria for municipal wastewater treatment.

Anammox bacteria can perform dissimilatory nitrate reduction to ammonium (DNRA) with nitrite as intermediate coupled to the oxidation of volatile fatty acids (VFA). Batch tests with enriched anammox and a co-culture of anammox and heterotrophic bacteria showed the capacity of Candidatus 'Brocadia fulgida' to perform the DNRA coupled to the anammox reaction (DNRA-anammox) at a high rate although the culture was not previously adapted to VFA. From thermodynamic calculations it could be stated that low COD/N influent ratios favour the DNRA-anammox transformation over heterotrophic conversions since more free energy is gained. A process scheme is proposed for an innovative nitrogen removal system in which the nitrate produced by nitrite oxidizing bacteria and/or anammox bacteria is converted during DNRA-anammox pathway, resulting in a sustainable nitrogen removal from municipal wastewater while circumventing the troublesome out-selection of nitrite oxidizing bacteria encountered in mainstream applications.