Nitrite denitrification using biomass acclimatized with methanol as complementary carbon source: long-term performance and kinetics study†
The objective of this study was to investigate the dynamic specific denitrification rates (SDNRs) from nitrite at various COD/N ratios in a system that used methanol as a complementary carbon source. An SBR fed with municipal wastewater (MWW), methanol and nitrite solution was operated at an HRT of 8.4 h and SRT of 16–17 days for 110 days. The SDNR from the SBR employing methanol as a complementary carbon source was compared with those determined in 23 batch reactors employing MWW, methanol, nitrite, and nitrate. The batch tests were conducted using the biomass acclimatized with nitrite and methanol as a complementary carbon source. The maximum SDNR was 0.52 mgN per mgVSS per d, corresponding to COD/N ratios of 5.9 in the SBR, which was about eight times higher than the literature reported value for systems fed with MWW. However, the maximum nitrite SDNR was lower than the observed batch nitrate 1.06 mgNO3−-N per mgVSS per d SDNR using the nitrite acclimatized biomass. In the batch test, a lower nitrite SDNR (0.38 mgNO2−-N per mgVSS per d) was achieved using methanol as a sole carbon source. The nitrite denitrifier yields were 0.39 and 0.34 mgVSS per mgCOD using methanol as a complementary and sole carbon source, respectively. The half-saturation coefficient of nitrite (KNO2) during post-denitrification with methanol was found to be 9.2 mg L−1, which confirmed the lower SDNR values at lower nitrite concentrations below the KNO2. The higher SDNR rates in methanol usage as a complementary carbon source versus sole carbon source could be translated into 37% capital and operating cost savings.