Biosolids and Energy Evaluation at Post Point Treatment Plant

The City of Bellingham (City) currently owns and operates the Post Point Wastewater Treatment Plant (Post Point Plant). At the Post Point Plant, the City currently processes its biosolids in two multiple hearth furnaces (MHFs). This approach of sludge incineration has proven to be a reliable technology for the City over the years, however, the age of the existing equipment and its capacity limitations necessitated development of a solids processing plan for the future. It also provided the City with the opportunity to examine the potential of capturing heat and power from its biosolids handling system and transform the plant into a bioenergy facility.The City decided to perform an evaluation to analyze and compare the various biosolids and energy alternatives available to the City. After screening out several alternatives in a preliminary screening process, four main biosolids handling approaches remained as viable options for the Post Point Plant:Incineration with Heat Recovery and Power ProductionDigestion with Combined Heat and PowerDigestion and Drying with Combined Heat and PowerGasificationThe evaluation carefully examined each biosolids handling process by outlining the process, exploring the existing condition, the history of its use, its cost, energy and carbon footprint and associated risks. The comparison was based on objectives including economic viability, environmental responsibility, operational flexibility and social acceptance. This evaluation that considered multiple objectives was designed to help the City gain insight into selecting a biosolids handling and energy approach that met the City's goals for stewardship and plant reliability well into the future. The results of the evaluation compare the solids alternatives in terms of life cycle cost, carbon footprint, actual footprint, and operational considerations. Insights into the beneficial use of wastewater solids from land application to heat and power generation are discussed. Site specific conditions of a tight site with limited available land makes for an interesting comparison between carbon footprint and site footprint. The implementation of the recommended alternative strives to maximize the use of the existing equipment while providing reliable solids processing.