Full-scale implementation of partial denitrification-anammox in IFAS processes: Cost savings and operational...

This paper examines the design and implementation of a full-scale integrated fixed-film activated sludge (IFAS) partial denitrification-anammox (PdNA) process at the Hampton Roads Sanitation District (HRSD) James River Treatment Plant (JRTP) in Newport News, VA, USA. The study assesses the operational outcomes of PdNA in the postanoxic zone of two full-scale demonstration treatment trains. Over 650 days, the first implementation, IFAS 1, underwent three supplemental carbon combinations for partial denitrification (PdN): step-fed primary clarifier effluent (PCE), methanol and PCE, and glycerol and PCE. Anammox bacteria were established in IFAS 1 144 days post-startup, during the second phase of carbon addition, marking the first successful full-scale deliberate application of an integrated PdNA process. Once IFAS 1's maximum anammox activity reached steady state during the final phase of carbon addition, IFAS 1 achieved an average in situ total inorganic nitrogen (TIN) removal rate of 0.93 ± 0.52 g/m²/day (0.35 ± 0.24 g/m²/day due to anammox). The second reactor, IFAS 2, was implemented a year later, using only step-fed PCE as an external carbon source. Anammox bacteria were confirmed in IFAS 2 192 days post-startup, demonstrating the potential for establishing anammox without an external carbon source and highlighting anammox bacteria's ability to establish and persist under limited nitrite (NO₂ ^-) conditions. Although IFAS 2 demonstrated that PCE was sufficient for anammox establishment, the more limited carbon available for maintaining anoxic conditions and promoting PdN resulted in minimal in situ anammox activity and a lower maximum anammox activity (0.18 ± 0.05 g-N/m²/day). However, IFAS 1 demonstrated that supplementing external carbon with PCE can result in substantial carbon savings. At steady state, supplementing glycerol addition with PCE in IFAS 1 increased carbon savings from 43% to 75% compared to full denitrification. This study offers valuable insights into the operational dynamics, challenges, and benefits of implementing full-scale mainstream PdNA, thereby contributing to the intensification of wastewater treatment processes. PRACTITIONER POINTS: For the first time, a deliberate design and implementation of a full-scale mainstream IFAS PdNA process was successfully completed. Anammox activity was established without biomass seeding, and it was not prevented by using carbons with lower PdN efficiencies. Significant carbon cost savings were achieved by supplementing external carbon with carbon provided via step feed to the PdNA zone. Anammox's ability to remove ammonia coming with step feed to the second anoxic zone is a unique benefit of PdNA.