THE DEVELOPMENT AND DESIGN OF BIOSOLIDS DEWATERING AND COMPOSTING FACILITIES FOR THE CITY OF BOULDER, COLORADO

The City of Boulder, Colorado is in the process of developing biosolids dewatering and composting facilities to generate a Class A biosolids product. The City evaluated and analyzed the viability of various dewatering and composting alternatives before selecting high solids centrifuges and enclosed agitated bed composting as the technologies of choice in the development of a 12 dry ton per day capacity facility. The City and the engineering team of Rothberg, Tamburini & Winsor, Inc. (RTW) and Tetra Tech, Inc. determined that siting facilities at a location remote from the existing wastewater treatment plant was the best choice. Various dewatering and composting technologies were compared using economic and non-economic considerations before the final technologies of choice were selected. This paper presents the preliminary design process used in selecting these technologies including:Evaluation of dewatering at the wastewater plant versus pumping liquid biosolids and dewatering at a remote compost site.Selection of high solids centrifuges for dewatering.Comparison of aerated static pile versus agitated bed composting.Equipment selection and procurementProjected capital and operating costs for these facilitiesRealizing that land application is facing heightened scrutiny and continual opposition, dewatering and composting will provide the City of Boulder a proven process that generates a more versatile product with multiple end use options. Dewatering and composting on the Front Range in Colorado requires facilities that can manage biosolids in varying conditions of severe cold, wind, and low humidity without generating nuisance odor conditions. The resultant product has numerous potential uses in horticulture, landscaping and agriculture applications.