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.