High Quality Biosolids Product Enhancement Using Windrow Management

Beneficial use of biosolids plays an essential role in wastewater resource recovery. High quality biosolids (HQB) products meeting regulatory requirements for land application or public distribution are not automatically qualified for high-value markets because of their odor characteristics. The Blue Plains Advanced Wastewater Treatment Plant (Washington, DC) produces a cured HQB product (Bloom®) that is marketed commercially for bulk application and public distribution. The goal of the project was to identify windrow management strategies (curing time, turning frequency, open versus covered conditions) that would consistently produce odor and handling characteristics that meet or exceed those of locally available bag products sold through retail outlets. Products were extensively tested for physical and chemical characteristics, respiratory activity, maturity (SOLVITA®), and various odor metrics, with odor detection threshold (DT) as the key parameter. Research findings indicate that post-dewatered biosolids processing using a combination of agitation and passive drying can substantially improve product quality and marketability. Both Open-Air and Roof-Shelter windrow processing approaches were successful in reducing product odors, and each showed positive attributes, and challenges. Findings confirm that handleability can be improved using Open-Air systems, but optimal processing time is vulnerable to inclement weather, which is hard to predict and plan around. A practical and objective windrow management procedure was developed to guide production of customer-ready products. The process involves passive windrow treatment with agitation 3-days per week. Windrow processing for at least 3-weeks is recommended to avoid initial odor peaks that were observed in field trials. SOLVITA compost maturity testing is then performed to verify minimum recommended NH3 and CO2 scores, and TS is determined to ensure customer requirements are satisfied. This procedure is inexpensive, quick and simple, and uses readily available objective information. It can be routinely performed by operation personnel to determine in-progress windrow material status and ultimately confirm finished product quality prior to distribution.