Mitigation of nitrous oxide (N₂O) emissions from denitrifying fluidized bed bioreactors (DFBBRs) using calcium

Nitrous oxide (N₂O) is a significant anthropogenic greenhouse gases (AnGHGs) emitted from biological nutrient removal (BNR) processes. In this study, N₂O production from denitrifying fluidized bed bioreactors (DFBBR) was reduced using calcium (Ca²⁺) dosage. The DFBBRs were operated on a synthetic municipal wastewater at four different calcium concentrations ranging from the typical municipal wastewater Ca²⁺ concentration (60mg Ca²⁺/L) to 240mg Ca²⁺/L at two different COD/N ratios. N₂O emission rates, extracellular polymeric substances (EPS), water quality parameters, and microscopic images were monitored regularly in both phases. Calcium concentrations played a significant role in biofilm morphology with the detachment rates for R_120Ca, R_180Ca, and R_240Ca 75% lower than for R_60Ca, respectively. The N₂O conversion rate at the typical municipal wastewater Ca²⁺ concentration (R_60Ca) was about 0.53% of the influent nitrogen loading as compared with 0.34%, 0.42%, and 0.41% for R_120Ca, R_180Ca, and R_240Ca, respectively corresponding to 21-36% reduction.