The effectiveness of four different electron donors, specifically methanol, ethanol, glycerol, and sulfide (added as Na(2)S), were evaluated in post-denitrifying bench-scale moving bed biofilm reactors (MBBRs). With the requirement for more wastewater treatment plants to reach effluent total nitrogen levels approaching 3 mg/L, alternative electron donors could promote more rapid MBBR startup/acclimation times and increased cold weather denitrification rates compared to methanol, which has been most commonly used for post-denitrification processes due to low cost and effectiveness. While the 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. Bench-scale MBBRs were operated continuously at 12 degrees Celsius, and performance was monitored by weekly sampling and insitu batch profile testing. Ethanol and glycerol, though visually exhibited much higher biofilm carrier biomass content, performed better than methanol in terms of removal rate (0.9 and 1.0 versus 0.6 g N/m(2)/day, respectively.) Maximum denitrification rate measurements from profile testing suggested that ethanol and glycerol (2.2 and 1.9 g N/m(2)/day, respectively) exhibited rates that were four times that of methanol (0.49 g N/m(2)/day.) Sulfide also performed much better than either of the other three electron donors with maximum rates at 3.6 g N/m(2)/day and with yield (COD/NO(3)-N) that was similar to or slightly less than that of methanol.

While the 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. Autotrophic denitrification using reduced sulfur compounds could be a low yield alternative to conventional heterotrophic denitrification to polish effluent nitrate. Three lab-scale MBBRs (using sulfide, methanol and ethanol as electron donor sources) were operated continuously at 12°C. The performance of each reactor was monitored by weekly sampling and batch rate profile testing. Sulfide visually exhibited biofilm carrier biomass content similar to or slightly less than that of methanol, yet provided increased removal rates (1.1±0.5 versus 0.6±0.3 g NO X -N/m 2 /day, respectively.) SDNR profile testing also suggested that maximum NO X -N removal rates for sulfide (1.8 g NO X -N/m 2 /day) were more than three times that of methanol (0.57 g NO X -N/m 2 /day.) Although the sulfide reactor produced the highest removal rates, significant uncertainties must be addressed prior to full-scale implementation.

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.