Air nanobubbles reduce methane and ammonia but increase nitrous oxide emissions from dairy lagoon wastewater

This study evaluated the effects of air nanobubbles and conventional aeration on emissions of methane (CH₄), nitrous oxide (N₂O), carbon dioxide (CO₂), and ammonia (NH₃) from dairy lagoon wastewater. Wastewater collected from a commercial dairy in California was treated in duplicate drum systems under nanobubbles aeration, conventional aeration, and control (no aeration) over 31 days. Nanobubbles aeration significantly reduced CH₄ emissions rates by 66.7% compared with the control. However, the reduction was not statistically significant relative to conventional aeration, although the average reduction was 29.4%, likely due to limited replication in this experiment. Nanobubbles aeration also significantly lowered NH₃ emissions rates relative to both treatments. However, nanobubbles aeration and the associated increase in temperature led to significantly higher N₂O and CO₂ emissions rates, particularly during the initial phase of treatment. Across treatments, N₂O became the dominant contributor to global warming potential (GWP₁₀₀), resulting in higher net climate impacts for nanobubbles (2265.34 g CO_2-eq/m³) and conventional aeration (1445.10 mg CO_2-eq/m³) compared with the control (418.00 CO_2-eq/m³). Changes in nitrogen dynamics indicated rapid nitrification under aerated conditions, with substantial decreases in ammonium and accumulation of nitrate, suggesting limited denitrification likely due to low organic carbon availability. Overall, under this controlled study, air nanobubbles aeration effectively reduced CH₄ and NH₃ emissions but shifted nitrogen losses toward N₂O, resulting in a higher net climate impact. These findings highlight the importance of evaluating dairy manure and wastewater management strategies using full greenhouse gas accounting to avoid unintended tradeoffs.