Modeling Greenhouse Gas Emissions Impacts in NYC Biosolids Management Planning

During development of the New York City Biosolids Management Plan, recommendations were made for future sludge handling upgrades at 13 water pollution control plants, from nine biosolids treatment process scenarios. Greenhouse gas emissions for these scenarios were evaluated and valued relative to incurred operating costs, using a model developed by Gould and Bandi (2008) and customized specifically for the project. The model analyzes energy and chemical consumption, sidestream electrical treatment demands, and other factors in the production of emissions sources and sinks at each process stage, to yield a net greenhouse gas carbon dioxide equivalent value as a function of the mass of solids processed. The model also applied cost factors derived from carbon credit market performance and projected market pricing, to assign a monetary value to the emissions.It was found that most treatment process and plant combinations resulted in a net greenhouse gas emissions offset, with peak offsets achieved in the neighborhood of 0.5 short tons of carbon dioxide equivalent per dry ton of sludge solids. At peak levels, total emissions offsets at all 13 plants ranged between 139,000 and 175,000 short tons of carbon dioxide equivalents. Peak offsets were valued at 0.35 to 0.45 percent of projected annual operating costs.Model results were used in conjunction with separate traditional evaluations of capital and operating costs involved in implementing selected process scenarios at each plant, to justify planning recommendations. Model sensitivity analyses identified significant contributing factors to greenhouse gas emissions associated with solids handling processes and promoted supplementary operational recommendations.