Conference Agenda

Partial denitrification (PD) is being considered as a potential alternative to partial nitrification (PN) for generating nitrite. This is due to the difficulty of suppressing nitrite oxidizing bacteria (NOB) at low mainstream temperatures and nitrogen levels. The Partial Nitrification/Denitrification/Anammox (PdNA/PANDA) process is an innovative way to remove ammonia from the mainstream by partially nitrifying it to nitrate, while leaving some residual ammonia in the post-anoxic phase. In this phase, the residual ammonia and nitrite generated by PD are removed via Anammox. The moving bed biofilm reactors (MBBRs) are often used as a tertiary polishing process for biological nitrogen removal (BNR) to meet the permissible total nitrogen (TN) limit of 3 mg/L. However, this requires large amounts of external organic carbon for denitrification. By replacing conventional BNR with PdNA/PANDA, energy savings and chemical savings of up to 60% and 80%, respectively, are projected. While PdNA/PANDA has been used to reduce carbon and aeration demand in mainstream biological nitrogen removal, its applicability in tertiary processes with low influent nitrogen loading (TN < 7 mg/L), frequent storm-related loading fluctuation, and stringent effluent TN limit (< 3 mg/L) has not been explored. Additionally, previous PdNA/PANDA studies have only been performed in lab- or pilot-scale systems. This presentation will highlight the experience and lessons learned from two pilot-scale PdNA/PANDA systems from two different utilities (Fairfax VA and Everett WA), and some ongoing works that effectively demonstrate full-scale mainstream deammonification via PANDA while meeting stringent nutrient limits. The major insights from pilot-scale studies are: 1. the PdNA/PANDA system can achieve effluent TIN limit of 3 mg/L at the design HRT/load/flux; 2. practical savings ranging from 20% to 30%; 3. feed forward methanol feeding control strategy can provide means for achieving stable PdN; 4. optimizing the influent NO3/NH3 ratio is the most critical step for successfully PdNA/PANDA. The major insights from the full-scale study are: 1. startup without seeding can be achieved in under 3 months while still meeting very low TN and ammonia limits; 2. chemical savings of approximately 30% are in line with pilot-scale studies.

The purpose of this presentation is to share the commissioning and start-up (C&SU) approach, execution and lessons learned of the first Thermal Hydrolysis Process (THP) built in Texas, and the second largest THP system in the United States, designed to process 375,750 dry lbs/day.

The Trinity River Authority’s (TRA) Central Regional Wastewater System (CRWS) serves 1.4 million customers in Dallas metropolitan area, with a treatment capacity of 189 MGD. CRWS’s Phase III B Solids Management Improvement Project includes replacement of the current lime stabilization treatment process with THP and anaerobic digestion. The goal of the Project is to significantly reduce the volume of biosolids produced and improve the classification from Class “B” to a Class “A” biosolid, which can be land applied or sold as fertilizer.

The biosolids treatment conversion from lime stabilization to THP and anaerobic digestion required both processes to operate in parallel. Due to the volume of equipment, impact to existing operations and risk associated with the activity MWH, in collaboration with TRA operations, developed a C&SU phased approach to facilitate the transition. The goal of the phased approach was to mitigate unknown process risk and minimize the impact to TRA’s daily operation. One example of risk mitigation occurred during Pre-THP Process Startup phase. Upstream of the THP system, there is a series of pre-dewatering equipment needed to be optimized with process fluids prior to introduction to the THP system. During process start-up the C&SU team identified the centrifuges were rotating backwards, despite extensive factory acceptance testing, field inspections, and water startup with the equipment vendor. This issue could only have been identified when process fluids were introduced into the system. If the team had not completed Pre-THP Process Startup the equipment reconfiguration would have impacted THP startup and Digester ramping, risking the loss of biomass following Digester Seeding.

Throughout the Pre-THP and THP startup, the team worked through numerous challenges to troubleshoot and optimize the systems. This presentation will explain how the team resolved each challenge and share lessons learned, resulting in the successful C&SU of the pre-dewatering equipment and THP system.