From Master Planning to THP--Charlotte Water's Approach to Regionalize Solids Handling and Treatment

Charlotte Water (CLT Water) is the largest public water and wastewater utility in the Carolinas, serving more than a million customers in the City of Charlotte and greater Mecklenburg County. Charlotte Water currently owns and operates five major wastewater treatment plants (WWTPs), treating an average of 78.1 million gallons per day (MGD) of wastewater and is in design for a six plant, the Stowe Regional Water Resource Recovery Facility (WRRF) that will treat flows from the western portion of Mecklenburg County and will also accept and treat flow from two neighboring towns in a bordering county. Charlotte Water oversees one of the largest class B biosolids programs in the Southeastern United States, operating with 17,000 acres of permitted agricultural land in both North and South Carolina and producing over 100,000 wet tons of biosolids annually. In 2013, Charlotte Water working with CDM Smith completed a Biosolids and Residuals Master Plan that consisted of a comprehensive review and evaluation of biosolids and residuals management alternatives and treatment technologies for all CLT Water's Water Treatment Plants (WTPs) and WWTPs (including the future Stowe Regional WRRF). This Biosolids and Residuals Master Plan presented a balanced life-cycle cost-based, environmentally sound, and publicly acceptable approach to meet Charlotte Water's short- and long-term residuals processing needs. The plan revealed several limitations to the Utility's program, including Charlotte Water's need -to transition a major portion of the biosolids program to a Class A product in order to diversify disposal outlet options -to centralize and optimize solids operations to the most extent possible in order to explore and engage more in Nutrient and Resource Recovery efforts The Master Plan identified implementation of a thermal hydrolysis process (THP) coupled with continued operation of existing anaerobic digesters and future thermal drying as the best treatment methods to achieve the desires of Charlotte Water. A 20-year life cycle cost analysis was prepared to compare the implementation of various alternatives for solids treatment and associated end-product management. Regionalization of solids coupled with the implementation of pre-digestion THP showed a lower 20-year life cycle cost by ~$10M. Implementing THP also affords other avenues for revenue generation including possible marketing of the end-product as well as increasing and consolidating biogas production at one facility to allow consideration of selling the gas for offsite uses. The project will be implemented as a phased program aimed at consolidating biosolids treatment at the McAlpine Creek Wastewater Management Facility (WWMF) and will include infrastructure that will convey biosolids from the Stowe Regional WRRF to the McAlpine Creek WWMF for treatment. Planned future phases include extension of the pipeline from Stowe RWRRF to the Irwin Creek WWTP and conveyance of combined Stowe and Irwin solids from the Irwin Creek WWTP to the McAlpine Creek WWMF. Upon completion of the project solids from four of CLT Water's six major WWTPs will be treated at McAlpine to produce a Class A product. This presentation will review and detail the current implementation of the Biosolids Program which will ultimately create a biosolids treatment system at Charlotte Water's largest Water Resource Recovery Facility, the McAlpine Creek WWMF, capable of processing upwards of 175 dry tons/day which is a significant increase compared to current capacity. Much of this capacity will be used to regionalize solids from three of Charlotte Waters other treatment facilities the Irwin Creek, Sugar Creek, and Stowe treatment facilities but will also leave some excess capacity for partnerships with other utilities as well as freeing up the older 4 digesters for other uses including possible future solids treatment capacity expansions.