Effects of nano-bubble water on anaerobic co-digestion of cabbage waste and cow manure under mesophilic and thermophilic conditions

The impact of four nano-bubble water (NBW) additions on the hydrolysis rate, methane yield, and microbial community of co-digestion of cabbage waste (CW) and cow manure (CM) under mesophilic and thermophilic conditions were investigated. Adding NBW under mesophilic conditions promoted hydrolysis, and the highest soluble chemical oxygen demand of the mesophilic digesters with the addition of CO2-NBW increased by 15.86%. Methane yield in the mesophilic digesters with Air-NBW and CO2-NBW increased by 17.54% and 14.72%, respectively. Moreover, the addition of NBW further accelerated the methane yield rate under mesophilic conditions. Due to the influence of thermophilic temperature, the impact of NBW addition on hydrolysis, methane yield, and methane yield rate in the thermophilic digesters did not differ significantly from the control. The addition of Air-NBW and N-2-NBW in the thermophilic digesters resulted in only marginal increases in methane yield, by 1.09% and 5.61%, respectively. NBW addition enhanced both the abundance and diversity of microbial communities in both mesophilic and thermophilic digesters. The addition of NBW represents a promising technological advancement for enhancing the efficiency of anaerobic co-digestion of CW and CM. {GRAPHICAL ABSTRACT}