Reducing CH₄ and CO₂ emissions and improving water quality in rural waterlogging ponds by injecting CaO₂ into surface...

In order to solve the problems of water quality deterioration, black-odor phenomenon, and greenhouse gas (GHG) emissions caused by hypoxia in rural waterlogging ponds, the experiment explored the improvements and mechanism of CaO₂ under coverage and injection methods. The incubation test results indicated that CaO₂ achieved the synchronous inhibition of the release of various nutrient pollutants from sediments and effectively improve the black-odor phenomenon by increasing DO and ORP, promoting sulfide oxidation, and enhancing the coupled biological nitrogen and phosphorus removal processes. Meanwhile, CaO₂ reduced the concentrations of NH₄⁺-N, NO₂^--N and PO₄^3--P in the pore water, which radically reduced the release potential for endogenous nitrogen and phosphorus. Furthermore, CaO₂ decreased the abundance of hydrolytic fermentation bacteria, syntrophic acetogenic bacteria, and methanogens (represented by Soehngenia, Syntrophus, and Methanobacterium) in sediments. In contrast, the increased abundance of Methylocystis and Methylobacter, which could oxidize CH₄ via O₂ and NO₃^- mediation, contributed to a marked decrease in GHG emissions. In comparison, injecting CaO₂ into surface sediments provided a prolonged and deeper action depth, yielding the most stable and optimal improvements in water quality and GHG reduction. Specifically, shallow injection of CaO₂ reduced turbidity, NH₄⁺-N, PO₄^3--P, and COD in the overlying water, while decreasing CH₄ and CO₂ emission fluxes by 91.37 %, 83.53 %, 82.68 %, 82.08 %, 88.99 %, and 81.14 %, respectively. Therefore, the experiment could provide ideas and references for black-odor improvement and GHG reduction in heavily polluted slow-flow water.