Applying current-carrying-coil-based magnetic field (CCC-MF) to promote anaerobic digestion of chicken manure: Performance evaluation, mitigation of ammonia inhibition, microbial community analysis, and pilot-scale validation

This study aims to investigate the effectiveness of a current-carrying-coil-based magnetic field (CCC-MF) placed outside the digester in promoting anaerobic digestion (AD) of chicken manure through digester performance evaluation, microbial community analysis, and pilot-scale experiments. With the applied CCC-MF, a magnetic field of 1.12-3.54 mT was generated in the anaerobic digester, and a 40% average methane yield increment was obtained from the AD of chicken manure. AD experiments showed that CCC-MF increased the average CH4 percentage by 18.7% and decreased the average CO2 percentage by 22.9%. The ammonia nitrogen concentration was decreased by 10.4-64.9% due to CCC-MF, indicating that CCC-MF was beneficial to the mitigation of ammonia inhibition. The activities of acetate kinase and F420 were increased by 21.9% and 30% due to CCC-MF. Microbial community analysis indicated that the dominant bacterial phyla were Thermotogae, Firmicutes and Bacteroidetes while the dominant methanogenic archaeal genera were Methanoculleus, Methanosarcina, Methanothrix, Methanomassiliicoccus, Methanolinea, and Methanospirillum. Due to CCC-MF, the electrotrophic methanogenic genus Methanothrix and ammonia-tolerant methanogen genus Methanosarcina were enriched by 2.1-fold and 1.6-fold, respectively. The KEGG analysis of metabolic pathways showed that many key metabolic pathways were enhanced 9-20 times due to CCC-MF. Furthermore, the results of pilot-scale validation experiments confirmed the technical effectiveness of the CCC-MF assistance in enhancing AD of chicken manure. This study provides a novel and promising strategy by placing a current-carrying coil outside the AD system for enhancing methane production from AD of animal manure and reveals the enhancing mechanisms of the technology.

Automated summary

This study investigates the effectiveness of a current-carrying-coil-based magnetic field in promoting anaerobic digestion of chicken manure. The results show that the applied magnetic field increases methane yield, decreases carbon dioxide production, and reduces the concentration of ammonia nitrogen. Microbial community analysis reveals the enrichment of certain methanogenic genera and enhanced metabolic pathways. Pilot-scale experiments confirm the technical effectiveness of the magnetic field assistance in enhancing anaerobic digestion of chicken manure.