Treatment of anaerobically digested effluent from kitchen waste using combined processes of anaerobic digestion-complete nitritation-ANAMMOX based on reflux dilution

Abstract

In this study, an anaerobically digested effluent from kitchen waste with high concentrations of chemical oxygen demand (COD) and ammonia nitrogen was treated using combined processes of anaerobic digestion (AD), complete nitritation (CN), and anaerobic ammonium oxidation (ANAMMOX). The COD and nitrogen removal efficiency of each treatment unit were investigated. The feasibility of using the final treatment effluent to dilute the original wastewater was also discussed. Findings showed that as a pretreatment step, AD resulted in the decline in biodegradability and increase in ${\text{NH}}_4^{+}\text{- N}$ concentration. CN was successfully and stably achieved for 106 days with an average nitritation rate of 95% by maintaining the dissolved oxygen at 2-3 mg/L and hydraulic retention time of 24 hr under 30 ± 1°C. High ${\text{NH}}_4^{+}\text{- N}$ and ${\text{NO}}_2^{-}\text{- N}$ . removal efficiencies of over 88% and 96% were attained in the following ANAMMOX reactor. The reflux of ANAMMOX-treated effluent for the dilution of raw wastewater or an influent of CN and ANAMMOX ensured the stable operation of the combined system. PRACTITIONER POINTS: Anaerobic digestion effluent of kitchen waste had low COD/ ${\text{NH}}_4^{+}-N$ ratio and poor biodegradability. Stable and efficient nitritation was realized by controlling DO, HRT and TEMP. High ${\text{NH}}_4^{+}-N$ and ${\text{NO}}_2^{-}\text{-N}$ removal efficiency were obtained by ANAMMOX process. Average nitrogen removal rate of 0.94 kg N/m³ /day were obtained by ANAMMOX. Reflux dilution with the effluent guaranteed the system's successful operation.

Keywords: ANAMMOX; anaerobic digestion; anaerobically digested effluent from kitchen waste; complete nitritation; reflux dilution.