Evaluation of Alternative Electron Donors in Anoxic Moving Bed Biofilm Reactors (MBBRs) Configured for Post-Denitrification

Abstract

The effectiveness of four different electron donors, specifically methanol, ethanol, glycerol, and sulfide, was evaluated in post-denitrifying bench-scale moving bed biofilm reactors (MBBRs). With increased concern for wastewater treatment plants to meet lower effluent nitrogen levels, alternate substrates could promote quicker startup/acclimation times and higher denitrification rates than methanol, which is most commonly used. While application of alternative substrates in suspended growth processes has been studied extensively, fixed film post denitrification processes have been designed to use primarily low yield substrates like methanol. Preliminary results indicate that ethanol and glycerol both provide consistent denitrification, with average COD consumption factors of 0.96 and 1.07 at assumed anoxic yield values of 0.5 and 0.55, respectively. Both ethanol and glycerol have shown substantially shorter acclimation times and much higher removal rates at 20°C than either methanol or sulfide.

Evaluation of electron donors for biological perchlorate removal highlights the importance of diverse perchlorate-reducing populations

“…In a bench-scale study with denitrifying, moving bed biofilm reactors, biomass growth was observed to be thicker and heavier with glycerol as the electron donor compared with methanol or sulfide. 38 This study also reported that reactor operation with glycerol was associated with higher levels of effluent total suspended solids and greater plugging of media void spaces. 38 Their estimate of the observed biomass yield with a glycerol-based electron donor (0.5 g COD biomass g −1 COD substrate [based on average effluent volatile suspended solids data]) is close to the estimated yield with the glycerol product tested in the present study (0.54 g COD biomass g −1 COD substrate , Table 2).…”

“…38 This study also reported that reactor operation with glycerol was associated with higher levels of effluent total suspended solids and greater plugging of media void spaces. 38 Their estimate of the observed biomass yield with a glycerol-based electron donor (0.5 g COD biomass g −1 COD substrate [based on average effluent volatile suspended solids data]) is close to the estimated yield with the glycerol product tested in the present study (0.54 g COD biomass g −1 COD substrate , Table 2). Similarly, in a study with bench-scale, denitrifying sequencing batch reactors, the biomass yield increased over time as biomass grew on glycerol or a glycerol by-product from biodiesel fuel production.…”