Air nanobubble simultaneously enhances hydrolysis and methane yield of sludge temperature phased-anaerobic digestion

Nanobubble water (NBW) or temperature-phased anaerobic digestion assisted by microbial electrolysis cell (MEC-TPAD) can promote sludge hydrolysis and methanogenesis. However, the role of the combined application of NBW and MEC-TPAD in terms of anaerobic performance and related microbial properties remains unclear. This study investigated the impact of Air-NBW on hydrolysis and methanogenesis of dewatered sludge MEC-TPAD. Under different temperatures, NBW increased ammonia nitrogen by 7.8%-13.7% in the hydrolysis phase and ultimate methane yield by 23.3%-41.5%. NBW can significantly promote hydrolysis under mesophilic-mesophilic conditions, while it can promote substantially methanogenesis under thermophilic-thermophilic conditions. Moreover, NBW increased the diversity and richness of microorganisms in hydrolysis. As to bacteria, NBW increased the relative abundance (RA) of Firmicutes but decreased the RA of Proteobacteria. As to archaea, NBW increased the RA of Methanosarcina in hydrolysis but decreased it in methanogenesis. NBW synchronized with MEC-TPAD improved hydrolysis and methanogenesis of the dewatered sludge digestion process.