The blended, thickened sludge from the Water Reclamation Facility is pumped under the Cuyahoga River to the Akron Renewable Energy Facility, formerly the City of Akron Composting Facility.
The Akron Renewable Energy Facility is owned by the City of Akron and operated by KB BioEnergy, Inc., formerly known as KB Compost Services, Inc., a firm committed to protecting and improving the environment, all within the confines of federal and state regulatory requirements. Since 1986, the management of solids was successfully accomplished through “in-vessel composting”. Annually, 70 million gallons were dewatered and converted to a soil conditioner known by the local residents as “Soil Magic” or “TechnaGro”. Each year 75,000 cubic yards were generated and sold as an “Exceptional Quality Biosolid.”
As with all processes, technology is constantly changing, and this is no different in the way wastewater solids are managed. A “high solids” anaerobic digestion (AD) process by the German firm of Schmack Biogas AG was considered to handle the wastewater solids. What made this AD process different than other traditional ADs was the plug flow digester that allowed up to 30% solids to be processed. Mainstream digesters process solids typically in the 3-5% solids range.
ADS PHASE I
In 2007, a pilot project was launched to determine the feasibility of using this high solids AD process as a means to manage the solids. The pilot project was designed to process 1/3 of the annual solids, with the by-product being biogas that would fuel a 335kW combined heat and power engine.
ADS PHASE II
The success of the pilot project, or Phase I, resulted in a full scale design that would process 100% of the wastewater solids by AD, known as Phase II today. With this development, on December 31, 2012, the composting process was shut down.
Phase II incorporates the Schmack Biogas technology used in Phase I, but on a larger scale. The wastewater solids are added as a food source to sustain a healthy population of anaerobic microorganisms living inside the digesters. Biogas generated will be used to fuel three 600kW combined heat and power units. Like Phase I, the expected parasitic load will be around 10% of the power generated. The remaining power will be used to reduce operational costs at the wastewater treatment facility.
The digestate coming from the AD tanks will be dewatered and processed through an indirect dryer, resulting in material that will be 95% or better dry solids. These “pellets” will meet the “Exceptional Quality Standard.” Approximately 15,000 cubic yards will be produced annually.
For more information about the Anaerobic Digestion System, review the pdf files in the sidebar!