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The gradual increase in cattle farming has led to a huge production of cattle manure (CM), but the conventional treatment methods are less efficient. In this study, the treatment method of anaerobic digestion (AD) of high-solids CM by combining nanobubble water (NBW) with different gases was proposed to present a new idea for the reduction, harmlessness, and resourcefulness of CM. It was found that the performance of the digester with added NBW was better than the control. Among them, the cumulative methane yield T-Air: 227.09 mL g−1 VS added and T-CO 2 : 226.12 mL g−1 VS added increased by 17.72 % and 17.22 %, respectively, compared with the control T: 192.90 mL g−1 VS added under thermophilic conditions. Under mesophilic conditions, M-Air: 162.39 mL g−1 VS added increased by 9.68 % compared with control M: 148.05 mL g−1 VS added. Microbial communities analyzed at the genus level revealed that the relative abundance of bacteria favorable to hydrolysis and acid-producing processes, such as Defluviitalea , Haloplasma , and Bacillus , increased to varying degrees. Moreover, the relative abundance of archaea favorable for methanogenesis, such as Methanoculleus , Methanobrevibacter , and Methanosarcina , also increased to varying degrees. Therefore, the addition of NBW promoted the hydrolysis of high-solids CM, enhanced the stability of the reaction, improved the methanogenic performance, and increased the RA of favorable genera, which ultimately led to a better performance of the AD of high-solids CM. [Display omitted] • Compared with control, NBW increased CH 4 production by 5–17 %. • Compared with control, NBW contributes to the production/transformation of VFAs. • Incorporation of NBW improves stability of high solids anaerobic digestion. • Compared with control, NBW increased the RA of hydrolytic acidification-associated bacteria. • Compared with control, NBW increased the RA of methanogenic-associated archaea. [ABSTRACT FROM AUTHOR]

Abstract Digestate from biogas plants managing municipal solid waste needs to be stabilized prior to final utilization or disposal. Based on the concept of urban mining, aged refuse from a closed landfill was used to treat landfill leachate, but nitrogen removal by biological denitrification was limited. The aim of this study was to use a digestate layer in bioreactors containing aged refuse to enhance the biological denitrification capacity of the aged refuse, stabilize digestate, and mitigate the ammonia emissions from digestate leaching with leachate recirculation. Six identical landfill columns filled with 0% (R0), 5% (R5), and 15% (R15) of solid digestate above aged refuse (ratios based on Total Solids) were setup and nitrified leachate was periodically fed and recirculated to the columns. The nitrate removal rate in R5 and R15 was 3.4 and 10 times higher relative to the control (no digestate added). A 31.5–35.9% increase of solid digestate biostability was confirmed by tests performed under both aerobic and anaerobic conditions. The results showed that instead of land use, the solid fraction of digestate could be utilized as an inexpensive functional layer embedded in an old landfill site to enhance the denitrification capacity and achieve digestate stabilization with minimal ammonia leaching from digestate. Graphical abstract A combined approach to manage digestate and landfill leachate treatment. Image 1 Highlights • Bioreactors packed with aged refuse and digestate were used to treat landfill leachate. • Digestate addition enhanced the denitrification capacity of aged landfill waste tenfold. • The aged refuse mitigated the amount of ammonia leaching from the solid digestate by 67.2%–84.8%. • N removal of old landfill leachate was jointly gained with digestate stabilization. [ABSTRACT FROM AUTHOR]