Alternate: Getting it Started with Alternative Delivery Approaches to THP

SUMMARY The cost and complexity of projects implementing thermal hydrolysis pretreatment (THP) at municipal water resource recovery facilities (WRRFs) has led many utilities to utilize alternative delivery approaches. Raleigh Water selected Construction Manager At Risk (CMAR) to deliver its Bioenergy Recovery Project at the Neuse River Resource Recover Facility (NRRRF). WSSC Water utilized Progressive Design Build (PDB) to deliver the Bio-Energy Project at the Piscataway WRRF. The benefits of THP-enhanced digestion are many, from increased volatile solids reduction and biogas production to higher digester loading and therefore less required digestion volume. Some of the considerations involved with implementing THP include sludge preconditioning and treatment of high-strength post-digestion recycle streams. The cost and constructability feedback made possible with alternative delivery helped the design teams for the Raleigh Water and WSSC Water projects identify the optimal solution for each project, with a collaborative approach to the site-specific benefits and challenges associated with THP implementation. This 'case study' provides a summary of these two projects from design, through construction, and commissioning. It will focus on the unique aspects of each project, highlighting the role that alternative delivery played in influencing the design and start-up of these projects. BACKGROUND & Raleigh Water's Bioenergy Recovery Project Raleigh Water is implementing a Bioenergy Recovery Project to produce green energy and a Class A biosolids product, demonstrating the City of Raleigh's commitment to sustainable local government operations. By transitioning to THP and anaerobic digestion, Raleigh Water can convert the methane generated in the process to renewable natural gas (RNG) to fuel the City's bus fleet. Using RNG for vehicle fuel will offset greenhouse gas (GHG) emissions, supporting the City's aggressive community-wide goal of an 80-percent reduction in GHG emissions by 2050. The Bioenergy Recovery Project will be net energy producing, qualifying Raleigh Water for a $50M zero percent interest loan under the Clean Water State Revolving Fund (CWSRF) Green Project Reserve. The project was recognized nationally as Exceptional under CWSRF's Performance and Innovation in the SRF Creating Environmental Success (PISCES) program. Raleigh Water manages residuals from all three of its wastewater treatment plants at the Neuse River Resource Recovery Facility (NRRRF), the largest permitted treatment works in North Carolina with a rated capacity of 75 mgd. Current biosolids management includes lime stabilization, aerobic digestion, and off-site composting. As the existing solids handling equipment neared the end of its useful life, the utility was motivated to explore alternative biosolids management strategies, specifically those that maximize the potential for resource recovery and minimize GHG production. The Bioenergy Recovery Project will use THP to maximize the efficiency of new anaerobic digesters, achieving a nearly 50-percent reduction in mass and generating enough RNG to fuel 50 City buses. €ƒ BACKGROUND & WSSC Water's Bio-Energy Project The WSSC Bio-Energy project centralizes biosolids processing from WSSC Water's five WRRFs at the 30 mgd Piscataway WRRF to produce a Class A biosolids product. In addition to the THP and anaerobic digestion processes, the overall project also includes cake receiving, solids screening, pre-dewatering, cake pumping, pre-THP cake storage, post-dewatering, cake conveyance, Class A cake storage, sidestream nitrogen removal, odor control, renewable natural gas production, gas storage, combined heat and power generation and steam boilers. The Bio-Energy project will fundamentally change how WSSC produces biosolids, allowing a focus on long-term sustainable end products with a Class A dewatered cake biosolids and renewable natural gas suitable for pipeline injection and vehicle fuel. The project will overall reduce the greenhouse gas emissions from WSSC by 15% and result in nearly $3 million per year in operation cost savings. COLLABORATIVE DELIVERY DURING DESIGN Some of the biggest benefits of alternative delivery include quick cost and constructability feedback during design. After the CMAR came onboard the Raleigh Water Bioenergy Recovery Project, cost estimates were provided at the 60-percent design level to inform value engineering for the project. Cost feedback continued throughout design, which progressed to 100-percent completion level for Guaranteed Maximum Price (GMP) development. At the beginning of the detailed design process of WSSC Water Bio-Energy Project, the PDB team considered how best to approach a series of critical decisions related to the digestion process to provide the best long-term solution for process performance, energy efficiency, and accommodation of potentially high volume expansion considerations while balancing capital costs. The critical decision areas that needed review and discussion included: digester construction method; digester mixing approach; digester volume/dimensions; rapid volume expansion containment approach; and digested sludge storage approach. These five decision areas were considered individually and collectively to understand the range of advantages and disadvantages that each would have on the overall project. SUCCESSFUL COMMISIONING Commissioning new equipment and processes can be challenging, especially when facilities must maintain operations and compliance with treatment standards. Discussions began during design to identify the optimal start-up and commissioning approach for each project. The different alternative delivery methods employed led to different roles, responsibilities, and contractual requirements for each project. This paper will review the start-up and commissioning plan for both projects.