Pilot-scale demonstration of an integrated process for efficient management of kitchen waste digestion liquid

Recovering organic waste as bioenergy from source-separated kitchen and food waste via anaerobic digestion is a sustainable approach; however, this process often generates large volumes of high-strength kitchen waste digestion liquid (KWDL) that require further treatment. This study proposes an integrated treatment train consisting of dissolved air flotation (DAF) pretreatment followed by a two-stage partial nitrification/anammox (PN/A) process. Results from long-term pilot-scale operation showed that the DAF process reduced chemical oxygen demand (COD) and suspended solids (SS) from 8204 ± 605 mg COD/L and 7317 ± 831 mg SS/L to 5580 ± 395 mg COD/L and 2424 ± 415 mg SS/L, respectively. In the subsequent PN reactor, a stable average nitrite accumulation ratio of 75.7% was achieved under low dissolved oxygen (<2 mg O₂/L) and elevated free ammonia concentrations (45.0 ± 47.2 mg N/L). The PN effluent, with an NO₂⁻/NH₄⁺ ratio of approximately 1.74, was then treated in the anammox reactor, where about 77.5% of total nitrogen (TN) was removed through the combined action of anammox and heterotrophic denitrification. Microbial community assessment revealed that Candidatus_Brocadia was the dominant anammox bacterial genus. Overall, the combined process achieved removal efficiencies of 91% COD, 98% SS, and 85% TN under pilot-scale operation, with overall COD and TN loading rates of 0.63 kg COD/m³/d and 0.12 kg N/m³/d, respectively, demonstrating a practical and controllable treatment route for high-strength food waste digestate and providing operational insights for future full-scale implementation. © 2026 The Authors.