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The Town of Cary (Town) owns and operates two water reclamation facilities that treat wastewater and provide reclaimed water for the Town and neighboring areas. A residual product of the wastewater treatment process is waste activated sludge that requires proper processing before final reuse or disposal. The Town has a successful biosolids (stabilized sludge suitable for reuse) land application program that recycles Class B liquid biosolids to farmland in nearby counties. As development and growth continue in the area, available farmland for biosolids application is becoming scarce within a reasonable distance. In order to manage the continued increase in biosolids management costs, and to ensure the sustainability of the biosolids program, the Town contracted with CDM to conduct a biosolids dewatering and drying study. The objectives of the study were to evaluate and select a dewatering and drying system, which would allow the Town to implement a Class A biosolids management program that is reliable, sustainable, costeffective, and that recycles beneficial organics and nutrients to the land within the Town.

After reviewing plant records and defining the biosolids processing needs, CDM proceeded to conduct a site evaluation study to determine if it was beneficial to have a centralized biosolids processing center. Concurrently, a technology review was conducted to evaluate dewatering and drying applications. Belt filter press dewatering as well as centrifuge dewatering were evaluated. For biosolids drying, the technology review was complemented by a market survey to establish product quality needs. Various biosolids' drying technologies were reviewed including direct and indirect drying systems on the market. Thermal efficiencies, operational issues, materials of construction, proven track records, as well as product quality were among the key criteria for evaluation. Based on the criteria used, it was recommended that a direct drying system be used at the Town. Before the final decision was adopted for the drying system, several site visits were made by plant operational staff to drying facilities to observe operation, learn about maintenance and other issues, and to review product quality and market conditions.

This paper summarizes the process the Town undertook in its move towards Class A biosolids processing to secure a long-term biosolids management strategy for this fast-growing community. Factors influencing key decision- making are documented, as well as the Town's experience in developing this plan over a period of more than a decade.
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Document Type: Research Article

Publication date: 01 January 2003

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