Donohue & Associates and the City of Stevens Point, WI received a 2023 ACEC Wisconsin Engineering Excellence Best of State Award for the Liquid to Dried Biosolids Conversion Project at their wastewater treatment facility.
The City of Stevens Point’s wastewater treatment plant operated a successful Class B liquid land application program for decades, but as land application restrictions grew tighter and weather related delays limited disposal timings, it became evident that a change was necessary. Donohue & Associates provided guidance in the planning, design, and construction of what became a major overhaul to not only the solids handling process, but also the water department’s main garage and office space.
Donohue researched options for alternative ways to continue the Class B land application process; however, these options would not be able to fully address the application issues. Upgrading to a Class A biosolids process was a natural path forward. Donohue designed significant changes to the solids handling program to facilitate the thermally treated/dried Class A biosolid fertilizer. The resulting solution identified relocating the non-wastewater department vehicles from a structure that was properly positioned to serve as a new solids processing building for wastewater treatment, enabling both departments to solve multiple system needs. The creation of a new, larger Water Garage enabled all the common departments (collection systems, water, stormwater, and wastewater) to have a common vehicle, equipment, and parts storage building. Recycled wastewater effluent is circulated to the new Water Garage for geothermal heating and cooling powered by a rooftop solar array, producing 150% of the power consumption and offsetting nearly all of the heat load.
The existing garage space was then converted to a solids processing space for dewatering and drying of the biosolids. The selected paddle dryer was one of few devices that could fit in the limited ceiling height and provide the necessary evaporative capacity. Being the first dryer of its type in the State, the team forged new ground, adapting it to run on the City’s over-abundance of anaerobic digester biogas (methane), saving 90% of the natural gas cost, equivalent to $300,000 per year.
Donohue and the City collaborated closely to generate a revised WDNR biosolids management plan, one which documents how the material will be generated, stored, and transferred. The resulting plan enabled the City to obtain Class A certification and pursue a commercial fertilizer license. The final product, distributed as “BIOPOINT,” is currently collected in a silo, hauled away in semi-trailers and utilized for agricultural fertilizer.
Awards judge Kevin Lyons noted “This project transformed the City’s liquid biosolids program to a salable Class A dried product program. I appreciated the complex and sustainable design elements, including new dryer technology, harnessing biogas as a fuel source, adding 200% more digestion capacity, and a new heat pump system. This project is a gem in Wisconsin.”