Improving water quality and mitigating CH₄ and N₂O production in urban landscape water simultaneously by optimizing...

Recent studies show that greenhouse gas (GHG) emissions from urban landscape water are significant and cannot be overlooked, underscoring the need to develop effective strategies for mitigating GHG production from global freshwater systems. Calcium peroxide (CaO₂) is commonly used as an eco-friendly reagent for controlling eutrophication in water bodies, but whether CaO₂ can reduce GHG emissions remains unclear. This study investigated the effects of CaO₂ dosage on the production of methane (CH₄) and nitrous oxide (N₂O) in urban landscape water under anoxic conditions during summer. The findings reveal that CaO₂ addition not only improved the physicochemical and organoleptic properties of simulated urban landscape water but also reduced N₂O production by inhibiting the activity of denitrifying bacteria across various dosages. Moreover, CaO₂ exhibited selective effects on methanogens. Specifically, the abundance of acetoclastic methanogen Methanosaeta and methylotrophic methanogen Candidatus_Methanofastidiosum increased whereas the abundance of the hydrogenotrophic methanogen Methanoregula decreased at low, medium, and high dosages, leading to higher CH₄ production at increased CaO₂ dosage. A comprehensive multi-objective evaluation indicated that an optimal dosage of 60 g CaO₂/m² achieved 41.21 % and 84.40 % reductions in CH₄ and N₂O production, respectively, over a 50-day period compared to the control. This paper not only introduces a novel approach for controlling the production of GHGs, such as CH₄ and N₂O, from urban landscape water but also suggests a methodology for optimizing CaO₂ dosage, providing valuable insights for its practical application.