The multifaceted role of nanobubbles in controlling composite fouling in biogas slurry irrigation pipelines

Irrigation with biogas slurry enables nutrient recovery and water reuse but is hindered by composite fouling in pipelines. While nanobubbles (NBs) are known to mitigate fouling, their mechanisms against composite fouling are poorly understood. This study evaluated oxygen, nitrogen, and helium NBs for controlling biofouling, scaling, and particulate fouling. Oxygen NBs were most effective due to their high oxidative capacity and ability to disrupt fouling structures. NBs attenuated the synergistic interactions among different fouling types, reducing overall accumulation. Oxygen nanobubbles reduced total fouling dry weight by 62.3% (p < 0.05), microbial abundance by 59.5%, and extracellular polymeric substances (EPS) by 52.4%, outperforming nitrogen and helium nanobubbles. NB treatment also decreased microbial diversity (Shannon index reduced by 18-32%) and altered mineral composition, promoting the transformation of calcite to aragonite (aragonite content increased by up to 591.9%). They also reduced microbial diversity, disrupted interaction networks, and inhibited biofilm formation. Furthermore, NBs promoted the transformation of calcite to less adhesive aragonite. These findings demonstrate that NBs are an effective and sustainable strategy for controlling composite fouling in biogas slurry irrigation, providing both mechanistic insights and practical implications.