Considering alternative wintertime supplemental carbon addition strategies can help wastewater treatment plants maintain efficient operations despite significant drops in temperature

By Amy Gao, CH2M HILL

Amy Gao, along with co-authors Mark Supplee, PE, CH2M HILL; Sue Liu, PE, NYC Department of Environmental Protection; and Robert Frost, Hazen and Sawyer P.C. will present their paper “The Impact of Cold Weather and Temperatures on the Design of Supplemental Carbon Facilities Using Glycerol as a Carbon Source for Biological Nitrogen Removal” on Tuesday, July 30 at Poster Session 2, during the 2013 WEF/IWA Nutrient Removal and Recovery Conference in Vancouver.

Temperature drops and bone chilling winds define New York City (NYC) winters.  The cold winters with frigid temperatures can have a negative impact on plant operations of supplemental carbon addition systems. NYC’s Department of Environmental Protection will use supplemental carbon in the form of glycerol. Cold temperatures cause significant increases in the viscosity of glycerol solutions used as supplemental carbon for the enhancement of biological nitrogen removal.

When designing supplemental carbon addition facilities, glycerol viscosity is a key variable to consider. Elevated viscosities, often the result of low temperatures, can lead to excessive headloss and backpressure in the glycerol feed system. When managed correctly, supplemental carbon in the form of glycerol can improve the nitrogen removal process, despite fluctuations in temperature. However, to date there have been limited resources available to help wastewater engineers with the design of these systems in relation to low temperatures, leading to the focus of our research.

The viscosity of glycerol solutions varies significantly with temperature and glycerol concentration. To determine the impact of NYC winter temperatures on the design of glycerol feed systems, viscosity was measured as a function of a wide range of NYC’s historical temperatures from 1970 to 2011 on four commercially available glycerol products at several different concentrations. Understanding the results of the viscosity tests helps to identify design criteria for supplemental carbon facilities during cold weather operations, and to consider provisions to accommodate a wider range of products to keep viscosities manageable.

Our presentation will review the three alternative cold weather carbon addition strategies that were identified from the NYC study, sharing lessons learned so that other WWTPs can think about how to best accommodate for impacts of low temperatures on glycerol viscosity and how to ensure that these plants operate effectively at extreme temperatures.

Amy Gao is a Water Engineer in CH2M HILL’s New York City Office. She holds an M.S. in Environmental Engineering from The University of Texas at Austin and B.S. in Earth and Environmental Engineering from Columbia University. She is an active participant with the Water Environment Federation.