Investigation of nitrite accumulation by hydrogenotrophic denitrification in a moving bed biofilm reactor for partial denitrification and anammox process.

The partial denitrification and anammox (PDA) process has received attention for its ability to optimize treatment of wastewater containing a low NH4+-N concentration. This study investigated the suitable operational conditions for NO2--N accumulation by hydrogenotrophic denitrification (HD) in operation of a laboratory-scale moving bed biofilm reactor, for future application in the PDA process. NO2--N accumulation was achieved by minimizing the H2 flow rate under optimized conditions (i.e., 15 mL/min H2 flow rate, 40 mg-N/L influent NO3--N, 7.0 h hydraulic retention time, and 2 L working volume). Hydrogenophaga comprised 39.2% of the bacterial abundance after NO2--N accumulated, indicating its contribution to the NO2--N accumulation. In addition, an intermittent H2 supply maintained the NO2--N accumulation rate (NAR) and maximized the nitrite accumulation efficiency (NAE). A H2 supply ratio of 0.7 (i.e., ON: 7 min, OFF: 3 min) was optimal, which induced increases in NAR, NAE, and the NO3--N removal efficiency that reached 0.07±0.01 kg-N/m3/d, 64.4±14.5%, and 89.2±8.9%, respectively. The ratio of H2 supply rate to the NO3--N loading rate was calculated as 4.3 in this experiment, which may represent the optimal balance for maximization of NO2--N accumulation by HD.

Newly established process combining partial hydrogenotrophic denitrification and anammox for nitrogen removal.

The anaerobic ammonium oxidation (anammox) process holds great promise for treating nitrogen-contaminated water; stable nitrite-nitrogen (NO2 --N) production is significant to anammox performance. In this study, partial hydrogenotrophic denitrification (PHD) was used to stably and efficiently produce NO2 --N from nitrate-nitrogen (NO3 --N). An investigation of the effects of initial pH on the PHD process revealed that a high NO2 --N production efficiency (77.9%) could be ensured by setting an initial pH of 10.5. A combined PHD-anammox process was run for more than three months with maximal ammonium-nitrogen (NH4 +-N), NO3 --N, and total dissolved inorganic nitrogen removal efficiencies of 93.4, 98.0, and 86.9%, respectively. The NO2 --N to NH4 +-N and NO3 --N to NH4 +-N ratios indicated that various bioprocesses were involved in nitrogen removal during the anammox stage, and a 16S rRNA gene amplicon sequencing was performed to further clarify the composition of microbial communities and mechanisms involved in the nitrogen removal process.