Navigating the Seas of Settling Process Advancements
- Cory Hopkins - Hazen and Sawyer
Sedimentation has been widely utilized in the water industry for the effective removal of many constituents following coagulation and flocculation processes in conventional treatment plants. Utilities facing a near-term need for expansion in the midst of economic hardships are evaluating the implementation of high-rate settling technologies and more efficient residuals collection systems to provide a cost-conscious means to treat greater plant flows while maintaining high settled water quality standards.
On the surface, conventional settling appears fairly straight-forward with widely accepted values for critical design parameters including loading rates and detention time. Yet, several advancements to the settling process, particularly regarding high-rate technologies such as tubes and plates, provide a utility with an array of options to implement that can make a utility feel as though they are “lost at sea”. To further complicate matters, utilizing such a technology may require the use of new residuals collection equipment that complement the operation of the high-rate equipment.
An assessment of the available high-rate settling technologies available in the market today will be presented discussing critical design considerations including, but not limited to, raw water quality, hydraulic capacity, life expectancy, materials of construction, flow distribution, new structural requirements, maintenance, and costs. Likewise, a similar impartial review of advances in residuals collection technologies will be given outlining key design factors. This discussion will assist a utility in identifying the optimal high-rate settling technology and complementary residuals collection equipment selection going forward for implementation at the expanding facility.
Case studies from the Cities of Fayetteville and Raleigh, two utilities contemplating near-term facility expansion, will be presented detailing their experiences in the selection process. Both utilities expressed interest in making use of existing basin infrastructure to mitigate the cost of additional basins and conserve valuable plant real estate. Each case study will review the utility’s unique experience regarding equipment comparisons, hydraulic evaluations, particular basin geometry challenges, and costs. Further, lessons learned from these experiences will be shared in an effort to assist other utilities to make the most efficient, educated and economical decision for future sedimentation basin improvement or expansion efforts.
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