Transiting from the inhibited steady-state to the steady-state through the ammonium bicarbonate mediation in the anaerobic digestion of low-C/N-ratio food wastes

Abstract

The current study aimed to determine the effects of NH₄⁺ on anaerobic digestion (AD) metabolism and the feasibility of using NH₄HCO₃ to improve methane production in an AD system when treating a low-C/N-ratio food waste (FW). Increasing the ammonium concentration (500-1000 mg NH₄Cl-N/L) added into the AD system did not limit the methane production but caused the volatile fatty acid (VFA) accumulation, forming an "inhibited steady-state" system. The addition of 200 mg NH₄HCO₃-N/L increased methane yield by 20% by aiding the microbial oxidation of VFAs. The high acetate content (65-85%) and abundance of acetoclastic methanogens (Methanosaeta and Methanosarcina) indicated an efficient acetoclastic methanogenesis process, which was facilitated by NH₄HCO₃. The long-term operation of the AD system demonstrated that NH₄HCO₃, at a concentration of 200 mg N/L, was capable of forming an active buffer system with NH₄⁺ and VFAs, enhancing methane production (221 ± 86 mL/g VS).

Keywords: Ammonia nitrogen; Anaerobic digestion; Buffer system; Methanogenesis; low C/N ratio; “inhibited steady-state”.