Full-Scale Methanol Optimization at a Step-Feed BNR Demonstration Facility

A study at a 25-mgd full-scale, four pass step-feed BNR treatment plant was carried out to optimize supplemental carbon addition. The study began with methanol addition to all four passes, which showed that carbon addition was only needed in the final two passes (Passes C and D) to achieve optimal denitrification. Further optimization to single-point (Pass D) carbon addition revealed that at low methanol doses, the traditional denitrification theory significantly over estimated the actual denitrification (nitrate removal) seen in the full-scale plant by 65%. Denitrification theory over-predicted methanol-driven nitrate removal by 900 lbs, with only 230 lbs being removed by methylotrophs. When the methanol dose was doubled, the amount of nitrate removal that was expected from the increased dose was achieved (∼1,130 lbs), yet the 65% short-fall (900 lbs of nitrate) seen at the lower dose was still observed indicating that the methanol denitrification kinetics at the low methanol dose do not accurately predict nitrate removal in this high rate system.