Combining lanthanum-modified bentonite and calcium peroxide to enhance phosphorus removal from lake sediments

Effects of the combined use of lanthanum carbonate and activated carbon capping materials on phosphorus and dissolved organic matter in lake sediments

Lanthanum carbonate (LC) represents a novel material for the immobilization of internal phosphorus (P) in sediments. Activated carbon (AC) is a traditional adsorbent that has been employed in the remediation of sediments on a wide scale. The objective of this study is to examine the mechanisms and effects of the combined use of LC and AC capping materials on the immobilization of P and dissolved organic matter (DOM) in sediments, through a 90-day incubation experiment. The results of isotherm experiments showed that the adsorption mechanism of P on LC and AC was mainly chemisorption. The XPS analyses showed the adsorption mechanism of P on LC was mainly ligand exchange and inner-sphere complexation; while the adsorption mechanism of P on AC was mainly ligand exchange and electrostatic adsorption. The results demonstrated that the concentrations of soluble reactive phosphorus (SRP) and DOM in the 0 to -100 mm sediment layer were reduced by 69.79% and 33.93%, respectively, in comparison to the control group with the LC + AC group. Moreover, the HCl-P and Res-P (stable P) in the 0-5 cm sediment layer were increased by 50.07% and 21.04%, respectively, in the LC + AC group. This indicates that the combined application of LC and AC has the potential to reduce the risk of P release. Furthermore, the formation of Fe(III)/Mn(IV) oxyhydroxides by LC + AC treatment resulted in an increased adsorption of SRP and DOM. Moreover, the effect of LC + AC capping on microbial community was smaller than that of LC/AC capping alone. The findings of this study indicated that the combined use of LC and AC represents a novel approach to the effective treatment of internal P and DOM in eutrophic lake sediments.

Effects of modified sediments on the growth of submerged macrophyte Vallisneria natans under low light conditions

Submerged plants are an important part of aquatic ecosystems, and the restoration of submerged plants is a key step in the reconstruction of aquatic ecosystems. However, little is known about the role of modified sediments in helping submerged plants recover under low light. In this study, we set up four sediment types and two light intensities to explore the effects of modified sediments on the growth of Vallisneria natans under two low light conditions. The results showed that the independent and interactive effects of light intensity and sediment type significantly affected the biomass, morphology, photosynthetic pigment content and antioxidant enzyme activity of V. natans. At 5% and 20% natural light intensity, the sediment modified with 40% peat soil had a larger root biomass and the highest leaf and root C/N ratio, the sediment modified with 40% vermiculite had a longer root length and more ramets. At 5% natural light intensity, the sediments modified with fly ash had shorter root length and smaller leaf biomass. The sediments modified with fly ash had the greatest chlorophyll content at 20% natural light intensity. It can be concluded that the addition of 40% peat soil or 40% vermiculite in sediment is conducive to the growth of V. natans under low light conditions. Our study indicates the positive effects of the modified sediment on the growth of V. natans under low light conditions, and our study will provide a reference for the restoration of submerged plants in aquatic ecosystems.

Improving water quality and mitigating CH4 and N2O production in urban landscape water simultaneously by optimizing calcium peroxide dosage

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.