JEA's Measured Approach to Regional Biosolids Management with Drying - Setting a Trend for Utilities Concerned about Narrowing Management Options

APPLICABILITY Treatment and the security of disposal/beneficial use options for biosolids is constantly evolving due to more stringent regulations as new contaminants in wastewater raise concerns about potential migration into biosolids and subsequent impacts. Advancements in treatment technologies and development of new markets for different types of biosolids products offer opportunities to mitigate risks to current biosolids management options while maintaining a certain level of institutional control. Economics and utility-specific drivers and constraints play key roles in selecting the right combination of treatment technology and end use. DEMONSTRATED RESULTS/CONCLUSIONS JEA, one of the largest utilities in the State of Florida, has been highly proactive in evaluating and looking to the future with their biosolids program. In 2017, JEA prepared a master plan to evaluate replacing their aging biosolids handling facilities while charting a path for the future. The existing biosolids handling facilities are located at the Buckman Water Reclamation Facility (BWRF), JEA's largest WRF. The facility handles sludge from 9 of the 11 JEA owned and operated WRFs. Solids from the two remaining WRFs are dewatered and the cake is hauled to nearby landfills for disposal using separate, third-party hauling and disposal contracts. Currently, liquid sludge from JEA's three larger WRFs is pumped long distances via dedicated sludge force mains and received at the BWRF headworks. The solids are captured in the primary clarifiers at the BWRF and pumped to a raw sludge holding tank (RSHT). The solids from the remaining five JEA WRFs are hauled as liquid sludge and received at the RSHT. The existing biosolids handling facilities at BWRF include thickening, anaerobic digestion, dewatering and a thermal drum drying system producing a Class AA product. The Class AA product is hauled by a third party for polishing and product marketing for beneficial reuse. All the existing solids handling equipment is retrofitted in an old incinerator building that has also reached the end of its useful life. Since the equipment was retrofitted in an existing building, the layout has inherent inadequacies that result in operational challenges. Further, the thermal drum drying facility only includes a single drum that also reached its end of useful life, providing no redundancy. The 2017 master plan recommended decommissioning of the old thermal drying system and instead hiring the services of a third-party to receive the anaerobically digested Class B dewatered cake. The third-party would take full responsibility for further processing and final product marketing and ultimate disposal. The master plan recommended construction of a new solids handling building with new thickening and dewatering equipment to replace the aging infrastructure. However, this approach resulted in undue dependence on a third-party for cake hauling, further processing, and appropriate disposal of the biosolids, thus leading to uncertainty in capital and long-term operating costs, adherence to future regulations, and impacts of market conditions/changes on disposal of the product. As a result, in 2020, JEA revisited the findings of the earlier master plan. The 2020 master plan evaluated several short-term and long-term biosolids management strategies and recommended replacing the existing thermal drum drying system with two larger drum dryers providing greater process reliability and redundancy while continuing to produce a Class AA product with substantial volume reduction for ease of product transport and disposal. The 2020 master plan ultimately recommended constructing a new regional biosolids handling facility at BWRF, that can handle solids from all 12 WRFs owned and operated by JEA, thereby providing JEA the desired level of control for their biosolids handling and disposal options. Such regionalization could be adopted by other utilities seeking certainty and control for their solids treatment and disposal options. As part of the short-term strategy, JEA has refurbished several of the thermal drum drying system components. The utility is also in the process of rehabilitating the existing building for operator safety and extending the life of the building for the next 5 years until the completion of the new biosolids handling facilities. A new multi-story biosolids treatment facility (BTF) has been designed and is under construction as the long-term permanent solution for JEA. This facility, shown in Figure 1, will house new thickening equipment (5 gravity belt thickeners), new dewatering equipment (4 centrifuges), and two new thermal drum drying systems (evaporation rate of 10,000 kg/hr) with pellet storage and a truck loading station. As illustrated in Figure 2, the new BTF will be a regional facility sized to accommodate all solids generated by the 12 JEA WRFs. Unstabilized dewatered cake from three remote facilities will be shipped to the new BTF where plant effluent from BWRF will be used to dilute the dewatered cake to thickened sludge consistency and added to the anaerobic digestion process. This is intended to maintain a consistent feed to the drying process such that high-quality pellets are consistently produced and dust and fines formation is reduced. PROJECT INNOVATION A full-scale pilot of an in-line high-shear dynamic mixer coupled with a density meter was successfully conducted onsite to re-wet the dewatered cake solids (~21% total solids) from remote plants with plant effluent to produce a consistent product with a total solids concentration of ~4 to 5% to feed to the existing anaerobic digesters. This cake mixing concept, shown if Figure 3, could be a game changer for agencies seeking to ship their un-stabilized dewatered cake to regional facilities for stabilization and further treatment, while reducing transportation costs, truck traffic and avoiding significant capital expense at the smaller surrounding plants. This type of system could be integral to the regionalization that may be necessary to accommodate changes in biosolids management that could necessitate costly thermal processes to reduce potential impacts from constituents of emerging concern like PFAS.