Implications on Using Glycerol as Supplemental Carbon Source for BNR
- Robert Sharp - Hazen and Sawyer
A series of glycerol batch tests were conducted to evaluate the denitrification kinetics of the glycerol acclimated biomass (GAB) obtained from an AT-3 separate centrate treatment (SCT) process at the 26th Ward WWTP in New York City. Testing was carried out to determine the cause and extent of the nitrite accumulation observed in AT-3 nitrogen profiles and initial batch tests. Denitrification batch tests were conducted using procedures and protocols provided by the Water Environment Research Foundation, with supplemental nitrate and/or nitrite added to supplement NOx to ~ 100 mg/l.
Nitrogen profiles on the SCT process indicated that nitrate was being converted to nitrite in the anoxic zones of each pass, , and much of the remaining nitrite was then converted back to nitrate in the subsequent aerobic zone. Nitrite accumulation had not been seen in previous glycerol pilot testing. Initial batch tests on the glycerol-fed AT-3 SCT process confirmed the profile results, showing very rapid denitratation (0.8¬0.5 mg NO3-N/mg VSS-day) and subsequent nitrite accumulation equal to ~70% of the initial nitrate added. Nitrite began to decrease once nitrate levels reached low levels, and the denitritation rates averaged 0.10 mg NOx-N/mg VSS-day. Similar results were found for batch tests using main plant sludge, indicating that the GAB was significant and well-established in the activated sludge. Nitrite accumulation was also observed at high glycerol doses (COD:N = 20:1), but not when primary effluent was used as a carbon source.
All results from kinetic and microbiological testing will be presented, along with a discussion of possible implications of GAB on operations and performance of both main plant BNR and SCT, including: 1) need for staged glycerol dosing or overdosing to optimize nitrogen removal; 2) impacts of elevated nitrite levels on plant operations; and 3) potential changes in anoxic/aerobic zone configuration to optimize performance.
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