Photon number based anaerobic digestion process for efficient bio-methane conversion from ammonium-rich feedstock: Performance evaluation and practical potential

Abstract In this study, an innovative photon number-based illuminated anaerobic digestion process for bio-methane conversion from ammonium-rich waste has been investigated. The photon flux density and illumination time showed significant effect on ammonium-rich anaerobic digestion. Further, the number of photons, as the integration of two lighting parameters, was found to be a determining factor in illuminated bioprocess for the first time. The effective range of photon number for mitigating ammonium inhibition was observed at 1.16 × 104–1.86 × 104 μmol∙day−1∙L−1. Correspondingly, the result of ATP and coenzyme F420 indicated that illumination with effective number of photons could activate the methanogens responsible for alleviation of ammonia inhibition. In addition, at different ammonium nitrogen concentration, the illuminated bioreactors with effective photon number of 1.25 × 104 μmol∙day−1∙L−1 always showed 2-fold higher methane yield than dark bioreactors. Moreover, the bioreactors with different working volumes under the same photon number condition showed similar methane yield, revealing that the photon number is the key factor for optimizing the illumination condition of anaerobic digestion in treating ammonium-rich substrate. Besides, the illuminated bioreactor with effective photon number condition was stable and well-performed under high ammonium concentration with long-term 89-day semi-continuous operation. This work provides a promising approach to build an easy-operated green recovery system for efficient bio-methane conversion from ammonium-rich waste.