Investigating the use of anaerobically stored carbon in post-anoxic denitrification
Significant methanol savings are hypothesized to result from anaerobic storage of internal carbon that is used for post-anoxic denitrification. An investigation into this internal carbon-driven denitrification was performed via a series of batch tests using biomass from Hampton Roads Sanitation District's (HRSD's) water resource recovery facilities (WRRFs): the Virginia Initiative Plant (VIP), Nansemond Plant (NP), and Army Base (AB) Treatment Plant. Internal carbon specific denitrification rates (SDNRs) increased during winter, by as much as 1 mg N/g MLVSS/h for VIP. Increasing the aeration time by 2-4 h lowered the SDNR by an average of 0.21-0.35 mg N/g MLVSS/h. No internal carbon denitrification was observed for biomass from non-nitrifying/denitrifying, biological phosphorus removal (bio-P) WRRFs. The increase in internal carbon SDNRs when the anaerobic acetate dose increased from 20 to 100 mg COD/L ranged from 0.06 to 0.28 mg N/g MLVSS/h. Higher phosphorus uptake rates were found to correlate to higher internal carbon SDNRs, but no significant post-anoxic P uptake was observed. The first steps are taken towards developing a strategy for full-scale implementation of this relatively novel type of denitrification by evaluating how some factors affect its occurrence. Practitioner Points Significant methanol savings at a full-scale facility may result from use of internally stored carbon for post-anoxic denitrification. Short aerobic HRTs and high anaerobic zone VFA loading increase the post-anoxic internal carbon-driven denitrification. Non-nitrifying, bio-P biomass is not capable of internal carbon-driven denitrification. Internal carbon-driven denitrification is correlated with the activity of polyphosphate accumulating organisms.