Mainstream partial nitritation/anammox: Balancing overall sustainability with energy savings

Abstract

Implementation of one-stage nitritation/anammox (i.e. deammonification) for the treatment of sludge digestates allowed net energy positive operation in the wastewater treatment plant (WWTP) in Strass (Austria). To further optimize the overall energy efficiency a first trial to expand the deammonification process to the full-plant wastewater treatment system was performed. The effluent quality, greenhouse gas emissions, energy balance and overall CO 2 footprint before and after implementation of mainstream DEMON® were evaluated in this study after one year of operation. In the effluent, a shift from nitrate over nitrite ratios of 31 to ratios of 2 was observed. The higher nitrite levels caused higher N 2 O emissions up to 2.3% of the N load in the B-stage, increasing the overall greenhouse gas emission of the plant significantly. For the present situation with mainstream DEMON, 11% of the electricity demand in the B-stage could be saved allowing higher net energy productions. These higher energy recoveries could not totally counteract the increased N 2 O emissions, resulting in a higher CO 2 footprint of 36 kg CO 2 -eq PE -1 year -1 compared to 7 kg CO 2 -eq PE -1 year -1 before mainstream DEMON. Further optimization of the operational conditions in the mainstream will reveal if higher energy savings can be obtained at lower N 2 O emissions. First hints towards this can be given based on experimental trials carried out for this study.

Nitric oxide preferentially inhibits nitrite oxidizing communities with high affinity for nitrite

“…The differential in AOB and NOB rates can be obtained by for example operation close to washout sludge retention time of AOB and cyclic oxic-anoxic conditions (Regmi et al, 2014;Wett et al, 2012) and is a prerequisite of the success of the novel mainstream processes partial nitritation/anammox (PN/A) (Kuai and Verstraete, 1998). However, an AOB/NOB activity differential (specifically, owing to relatively lower NOB activity) and thus nitrite accumulation often results in increased nitrous oxide (N 2 O) and nitric oxide (NO) emissions (Chandran et al, 2011;De Clippeleir et al, 2012;Kampschreur et al, 2009). The similarity in conditions allowing for an AOB/NOB activity differential and NO/N 2 O emissions is remarkable (De Clippeleir et al, 2013) and raised the question if the emissions are a mere result of the nitrite accumulation after establishment of NOB out-selection or if the emissions can play a role in the NOB out-selection itself.…”

Measuring Nitrite - The Key to Controlling Deammonification Systems

“…The importance of nitrite sensors measurements in side stream applications was demonstrated by investigators at the Strass, Austria WWTP who showed that there was a significant potential of reducing greenhouse gas emissions from anammox reactors if nitrite concentration could be controlled in the liquid phase (De Clippeleir et al, 2012;Lemaire et al, 2011).…”