Growing Up Together Lessons Learned During Startup: Commissioning Sidestream Deammonification Concurrent with THP Digestion to Meet Strict Recycle Limits

WSSC WATER will commission the Bio-Energy project in Q1 2024. The Bio-Energy project will centralize WSSC Water's biosolids processing at the Piscataway WRRF, including thermal hydrolysis pretreatment (THP) and mesophilic anaerobic digestion to provide the necessary stabilization to meet regulatory requirements for a Class A biosolids product as well as produce valuable digester gas, which is converted to renewable natural gas (RNG) suitable for pipeline injection. See Figure 1 for an overall process schematic. The Bio-Energy project has fundamentally changed how WSSC WATER manages biosolids, allowing a focus on long-term sustainable end products with a Class A dewatered cake biosolids, and RNG suitable for pipeline injection and use as vehicle fuel. The project will reduce greenhouse gas emissions and result in significant operational cost savings. But with these benefits comes one of the biggest challenges of the Bio-Energy Project - to treat the additional nutrient recycle loads that will be generated from sludge imported from the other WRFs and increased even more by THP and anaerobic digestion. Total nitrogen recycle loads from the Bio-Energy Project must be limited to ensure the Piscataway WRRF can maintain compliance with effluent discharge limits. Two ANITA Mox (TM) sidestream treatment reactors are undergoing startup concurrent with the digestion process to treat high ammonia filtrate from the Bio-Energy dewatering process. Managing nutrient recycle from filtrate generation in coordination with startup of both the Digester and Sidestream processes is essential to maintaining permit compliance at the Piscataway WRRF. Figures 2 and 3 present digester and sidestream treatment startup graphs. This presentation discusses the early challenges, successes, and lessons learned during concurrent biological startups of the anaerobic digestion and sidestream deammonification processes, as well as a reflective assessment of integrated startup plan assumptions and approaches presented during the 2023 WEF RBC. Phase 1 -Preparation and Seeding Commissioning begins with preparation and biological seeding of one digester and one sidestream reactor. Preparation of Digester 1 for liquid seed sludge import from the DC Water Blue Plains Advanced Wastewater Treatment Plant (AWWTP)(thermally hydrolyzed Class A). Lessons learned include: o Planning for and executing successful delivery of seed sludge during winter conditions. o Pre-heating digester to mesophilic temperature range. o Maintaining a Class A digester in preparation for seed sludge. Preparation of Sidestream Reactor 1 for seeded media from an operating ANITATM Mox process. Lessons learned include: o Delivery of annamox seeded media sludge during winter conditions o Conditioning of virgin media o Pre-heating reactor to annamox temperature range Phase 2 - Digester Ramp Up to Piscataway Load During initial digester ramp up, only Piscataway sludge is processed through the Bio-Energy process. Indigenous sludge from the Piscataway WRRF is thickened, screened and dewatered prior to THP. THP throughput is increased from 4 dry tons/day (dtpd) up to the full Piscataway load, approximately 16 dtpd, over 30 days. Lessons learned include: - Managing indigenous sludge management between THP and current pathway, while limiting increase in feed and overall organic loading. - Building volume in Digester 1 while maintaining conditions conducive to THP mesophilic community. Phase 3 - Sidestream Reactor 1 Startup and Initial Acclimation During Phase 3, THP throughput and digester feed is constant at the Piscataway WRRF load (16 dtpd). This period is used to build the volume under digestion, establish robust microbial communities in both digesters, and fine-tune operations prior to introduction of imported sludges. Digester withdrawal also begins during Phase 3 to generate filtrate to be used in the sidestream deammonification reactors biological startup. Lessons learned include: - Splitting contents between Digester 1 and Digester 2. -Dewatering optimization for thermally hydrolyzed digestate - Balancing digester filtrate generation with sidestream reactor capacity - Sidestream acclimation of annamox community in moving bed biofilm reactor (MBBR) mode Phase 4 - Sidestream Reactor 1 Acclimation and Reactor 2 Preparation Digester 1 and 2 continue building the volume under digestion, digester microbial communities, and fine-tuning operations during the 16 dtpd hold period. Sidestream reactor 1 influent ammonia concentration and load gradually increased, RAS recycle is initiated, and process is converted from MBBR to integrated fixed-film activated sludge (IFAS) mode. Sidestream Reactor 2 prepared for startup. Lessons learned include: - Managing Filtrate EQ Basin for nutrient load equalization and solids capture prior to introduction to sidestream reactors. - Sampling campaign to target biological startup concentrations and mass loading conditions. - Dilution water adjustments to meet competing biological needs. - Maintaining bypass flexibility and nitrogen recycle limitations to plant headworks. Phase 5 - Increased Digester Loadings, Sidestream Reactor 1 Fast Acclimation and Reactor 2 Initial Acclimation After the digester 16 dtpd hold period, sludge import from the four remote WSSC Water WRRFs was initiated to increase sludge to the Bio-Energy process. Both digesters reach normal operating level, and digester withdrawal is carefully managed to ensure filtrate does not overwhelm the sidestream reactor treatment capacity or exceed total allowable Bio-Energy recycle limits. Lessons learned include: - Growing sidestream treatment capacity to meet full load from digesters. - Impacts to filtrate quality and sidestream treatment during digester upsets or dewatering issues. Phase 6 Steady State Digestion and Sidestream Deammonification Phase 6 begins as the Bio-Energy process reaches full loading, with all indigenous and remote sludge being treated through THP and digestion. Both digesters will be in steady state operation. As Sidestream Reactors 1 and 2 complete ramp up to full treatment capacity; startup will be complete, sidestream will be in steady state, and final operation and performance testing will commence. Lessons learned and a high level assessment of integrated startup plan assumptions and approaches presented during the 2023 WEF RBC include: o Digester in-tank characteristics o Volatile Solids Loading Rate vs. Hydraulic Loading Rate for feed control o Volatile Solids Reduction o Nitrogen recycle o Biogas production o Sidestream removal efficiency o What went right and what would we do differently next time? o Recommendations moving forward. Conclusion Sidestream deammonification is critical to the successful implementation of WSSC Water's Bio-Energy Project, mitigating the impacts of increased nutrient recycle from THP and digestion and imported sludge from WSSC Water's remote WRRFs. The stability of the concurrent biological startups of sidestream treatment and digestion are critical to meeting nutrient recycle targets and ultimately effluent discharge limits, all while maintaining an advantageous startup and commissioning schedule. This presentation will share practical 'how to' lessons learned from the startup as well as a review of theoretical assumptions made during the planning phase vs. observed results to help inform future work.