Comparison of ethanol and methanol as carbon sources for coupled partial denitrification-anammox secondary treatment with MBBR technology.

Two moving bed bioreactors (MBBRs) with AnoxK™K5 carriers were operated for 156 days to compare methanol and ethanol as carbon sources in a single-stage partial denitrification-anammox (PdNA) process treating real municipal secondary effluent. The ethanol-fed reactor demonstrated superior performance with nitrogen removal rates (NRR) of 0.54 ± 0.1 gN.m-2.d-1 and nitrogen removal efficiencies (NRE) of 76 ± 7% at 20 °C, compared to 0.43 ± 0.1 gN.m-2.d-1 and 61 ± 6% for the methanol-fed reactor. Anammox contribution in the ethanol reactor remained consistently high (80 ± 7%) compared to the methanol reactor (57 ± 9%), with microbial analysis revealing selective enrichment of methylotrophic denitrifiers (Hyphomicrobium_A) under methanol conditions, promoting complete denitrification at the expense of anammox. Both systems demonstrated robustness across three different wastewater compositions and rapid recovery from operational disturbances. At 15 °C, the ethanol reactor maintained 82 ± 4% NRE, although requiring ∼50% lower nitrogen loading rates. COD consumption ratios of 2.2 ± 0.3 gCOD/gN-NO3 for ethanol achieved 53 ± 7% carbon savings compared to full denitrification requirements. Thermodynamically derived PdN and anammox coupled stoichiometries accurately predicted performance (R2 = 0.99 for NRR), identifying optimal feeding ratios of 1.00 gN-NO3/gN-NH4 and 2.06 gCOD/gN-NO3 for ethanol systems. This long-term evaluation of ethanol-based PdNA in an MBBR system treating real municipal wastewater, a combination not previously assessed - demonstrates the superiority of ethanol over methanol through higher anammox contribution, lower carbon requirements, and robust performance across varying wastewater compositions and temperatures.