Biosolids Utilization – A Non Land Application Approach

The City of Wilmington owns the Wilmington Waste Water Treatment Plant (WWTP) located on the east side of the city along the Delaware River. The facility processes waste water for the Department of Public Works serving New Castle County (the northern 1/3 of Delaware) and a small portion of Pennsylvania. Operation of the WWTP has recently been privatized and is presently contracted to US Filters. US Filters, in turn, has contracted with VFL Technology Corporation for the treatment and ultimate disposition of the biosolids generated.The WWTP is designed to process 90 million gallons per day resulting in the production of 40,000 wet tons of anaerobically digested sewage sludge with a solids content ranging from 16% to as high as 25%, depending upon the dewatering technique employed (belt filter press vs. centrifuge). The sludge is delivered to the VFL processing facility in rolloff containers and stockpiled for processing. VFL, as an N-Viro licensee, utilizes the NViro process to create a stabilized soil like product that is suitable for a number of beneficial use applications. The N-Viro process uses a blend of alkaline reagents such as lime or kiln dust to control pH and maintain specified temperatures for the elimination of pathogenic organisms together with the addition of drying reagents which are incorporated to modify the consistency of the final product. The process is capable of producing a material meeting the requirements of 40 CFR Part 503 for a Class A (Exceptional Quality) product and qualifies as a “Process to Further Reduce Pathogens”, obtaining approval from the USEPA on January 25, 1988.In order to provide a consistent product at the lowest cost possible, VFL has implemented a strategy to use a variety of cost-effective by-products to serve as reagents. The byproducts consist primarily of Class F coal ash and dry scrubber residuals generated at local electric generating stations. The fly ash is utilized for bulking and drying properties, while the scrubber residuals are utilized for their alkaline characteristics.VFL has operated the facility on a full time basis since May 1993 and has beneficially utilized 100% of the end product in non-land application end uses. The primary outlets have been landfill cover, berm construction, and synthetic topsoil production.