Building and Correlating Process & Cost Models to Support A Major Biosolids Management Program

DC Water's Biosolids Management Program (407M) for the Blue Plains AWTP (370 MGD) using new innovative processes of thermal hydrolysis & mesophilic anaerobic digestion (TH+MAD) will provide major cost savings in land application and energy. Unique biosolids process and cost models were developed for DC Water to evaluate technological and financial sustainability by comparing process options and financial consequences. This paper starts with understanding recent solids quantities and qualities generated by the Blue Plains AWTP including peak, minimum and average solids loadings to biosolids treatment. Seasonal variations and various primary/biological solids ratios were evaluated followed by an analysis of solids loadings on new processes or modified existing processes.The Biosolids Process Model includes primary and biological solids thickening, solids blending, screening, pre–CAMBI thickening , thermal hydrolysis (CAMBI), anaerobic digestion and final dewatering. Existing Lime Stabilization uses dewatering, lime addition and mixing.Present and future solids loadings analyzed in the biosolids process model were then analyzed by the Biosolids Cost Model that forecasts capital, O&M and financing costs. Savings in land application, biosolids volume reductions and energy savings were particularly important. Based on differences between process options, the Biosolids Cost Model identified cost savings, schedule of costs, pay back periods and break-even points. Early in the program adverse impacts of traditional bonding costs were identified…despite the new facilities yielding extensive savings. This led to deferred bond funding based upon borrowing added funds to pay the bond payments during the years of construction.This paper illustrates how to develop key biosolids information and correlate it with costs as needed to thoroughly understand process and funding options, thereby guiding optimum choices. It also explains how financing biosolids programs can be equally important in making the projects viable during difficult funding conditions now facing our country.