Grease-Stimulated Biogas Production in a Regional Sludge Pipeline

Colorado Springs Utilities (CSU) operates an 18-mile long sludge pipeline connecting the Las Vegas Wastewater Treatment Facility with its Clear Springs Ranch Solids Handling and Disposal Facility. In 2008 CSU undertook a trial program to add concentrated skimmings (grease) to the sludge flow in the pipeline in order to eliminate hauling the skimmings by truck. With concern about the generation and safe handling of the biogas, CSU authorized a monitoring program of the pipeline on a before-and-after basis. The objectives of the monitoring program were to develop an understanding of the biological and physical mechanisms involved in the production and accumulation of biogas at the pipeline highpoints. The results indicate that the CSU pipeline supports an acid phase digestion, and that the byproducts of the acid phase digestion are increased by the addition of a daily input of grease that adds about 10% more total and volatile solids to the pipeline.