Exploring nanobubble technology for enhanced anaerobic digestion of thermal-hydrolysis pre-treated sewage sludge

Nanobubble technology was used to enhance anaerobic digestion (AD) of thermal-hydrolysis pre-treated sewage sludge for bioenergy recovery. The prepared air, CO₂, and H₂ nanobubble solutions, with concentrations of 9.88–10.2 × 10⁷ bubbles/mL, remained stable for at least 7 days. After adding them into AD reactors, significantly higher CH₄ production (37.1 %) was observed for the CO₂ nanobubble treatment, followed by air (25.6 %) and H₂ (14.5 %) nanobubble treatments, compared to the control group. CO₂ nanobubble treatment performed the best in improving acidogenesis/acetogenesis, resulting in significantly higher volatile fatty acid generation during the initial 3–4 days. A comparison of reactors supersaturated and non-saturated with oxygen has demonstrated most of the biogas uplift observed to result from the nanobubbles rather than from initial oxygen soluble levels, demonstrating the crucial role of nanobubbles in upgrading AD. This study demonstrates, for the first time, that nanobubbles can provide additional benefits when combined with stablished sludge pre-treatment technologies.