Modeling Glycerol Acclimated Biomass: Using an Add-On in BioWin To Model the Nitrite Lock

Authors:

  • S. Galst, R. Sharp - Hazen and Sawyer
  • D. Houweling - CH2M Hill
  • W. Du, R. Jones - Envirosim Associates Ltd
  • A. Deur, K. Beckmann - New York City Department of Environmental Protection

The need for an effective, safe and sustainable supplemental carbon source has become increasingly important as more municipalities are required to meet stringent total nitrogen effluent standards. Glycerol-based carbon sources have gained a lot of attention from the wastewater industry because they are a sustainable alternative (waste product of biodiesel production), do not pose health and safety risks like methanol and ethanol, do not require a specialized bacterial population that is susceptible to washout in cold weather, and have proven to be effective at pilot and full-scale.

In January 2012, the New York City Department of Environmental Protection began a full-scale demonstration of an AT-3 Separate Centrate Treatment (SCT) process with glycerol as the added carbon source. During the evaluation of the process, a series of denitrification batch tests were carried out to better understand the kinetics of glycerol acclimated biomass (GAB). Numerous batch tests indicated that the GAB carried out denitratation (NO3 to NO2) at a very high rate, while nitrite accumulated until almost all of the nitrate was converted, then denitritation (NO2 to N2(g)) began at rates that were equivalent to over-all denitrification rates observed in previous studies using glycerol. The results indicated that the nitrite lock occurs following biomass acclimation to glycerol and possibly indicates a selection for GAB that are not present in unacclimated SCT biomass. It was hypothesized that glycerol addition selects for a bacterial community (GAB) that appears to preferentially convert nitrate to nitrite at a very rapid rate while storing some form of organic carbon. The motives for GAB to partially convert nitrate to nitrite are not clear but may provide a kinetic advantage to these organisms or be a response to substrate limiting conditions. Depending upon BNR process configuration and operation, this nitrite-lock may cause operational difficulties such as increased chlorine demand due to presence of nitrite in effluent, increased glycerol addition to meet effluent Nitrogen limits, and a potential for increased nitrous oxide emissions. At the time, commercially available wastewater process modeling software did not have a biomass population that could mimic this response. As such, a model add-on was developed and calibrated to match the observations from the 26th Ward SCT process.

A full description of the developed model and more simulation results will be provided in the paper.

For more information, please contact the author at rsharp@hazenandsawyer.com.

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