Significance of homogeneous operation in light-assisted fixed-bed bioprocess under ammonia stress: Optimization, long-term operation and metagenomic analysis

Abstract

Activating microbes with light is a promising strategy for addressing ammonia-stressed anaerobic digestion (AD). However, as a critical in-process parameter, homogenous operation, in light-assisted AD amended by bio-fixed bed has received limited attention. This research endeavors to establish a uniform-illuminated biosystem and assess its practical feasibility through a 90-day semi-continuous operation at pilot scale under solar light illumination. With optimal stirring mode (intermittent stirring for 3 min every 15 min), robust methane yields were achieved across various organic loads, reaching 88.7-94.3% of theoretical yield under high ammonium stress (3500 mg/L). The metagenomic analysis unveiled that uniform illumination triggered synergistic effects in AD, fostering a diversified microbial consortium, enhancing carbohydrate and methane metabolism, and facilitating the formation of an electroactive bio-cluster. This study underscores the significance of homogenous illumination in AD systems for efficient waste-to-energy conversion, highlighting the implementation of solar light as a greener approach for scale-up application.

Keywords: Ammonia inhibition; Bioinformatics analysis; Light stimulation; Pilot-scale evaluation; Stirring strategy.