Effects of different chemical agents on changes in sediment phosphorus composition and the response of sediment microbial community

The combined effects of lanthanum-modified bentonite and Vallisneria spiralis on phosphorus, dissolved organic matter, and heavy metal(loid)s

The use of lanthanum-modified bentonite (LMB) combined with Vallisneria spiralis (V∙s) (LMB + V∙s) is a common method for controlling internal phosphorus (P) release from sediments. However, the behaviors of iron (Fe) and manganese (Mn) under LMB + V∙s treatments, as well as the associated coupling effect on P, dissolved organic matter (DOM), and heavy metal(loid)s (HMs), require further investigations. Therefore, we used in this study a microelectrode system and high-resolution dialysis technology (HR-Peeper) to study the combined effects of LMB and V∙s on P, DOM, and HMs through a 66-day incubation experiment. The LMB + V∙s treatment increased the sediment DO concentration, promoting in-situ formations of Fe (III)/Mn (IV) oxyhydroxides, which, in turn, adsorbed P, soluble tungsten (W), DOM, and HMs. The increase in the concentrations of HCl-P, amorphous and poorly crystalline (oxyhydr) oxides-bound W, and oxidizable HMs forms demonstrated the capacity of the LMB + V∙s treatment to transform mobile P, W, and other HMs forms into more stable forms. The significant positive correlations between SRP, soluble W, UV254, and soluble Fe (II)/Mn, and the increased concentrations of the oxidizable HMs forms suggested the crucial role of the Fe/Mn redox in controlling the release of SRP, DOM, and HMs from sediments. The LMB + V∙s treatment resulted in SRP, W, and DOM removal rates of 74.49, 78.58, and 54.78 %, which were higher than those observed in the control group (without LMB and V∙s applications). On the other hand, the single and combined uses of LMB and V·s influenced the relative abundances of the sediment microbial communities without exhibiting effects on microbial diversity. This study demonstrated the key role of combined LMB and V∙s applications in controlling the release of P, W, DOM, and HMs in eutrophic lakes.

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

Lanthanum-modified bentonite (LMB) and calcium peroxide (CP) are known for their effective removal phosphorus (P) capacities. The present study aims to investigate the effects of the combined use of LMB and CP（LMB + CP）on the sediment P, dissolved organic matter (DOM) and iron (Fe) concentrations through a 90-day incubation experiment. The combined treatment showed strong removal effects on sediment P and DOM. Indeed, the SRP and DOM concentrations in the 0-10 cm sediment layer decreased following the combined application of LMB and CP by 40.67 and 28.95%, respectively, compared to those of the control group (CK). In contrast, the HCl-P in the 0-5 cm sediment layer increased following the combined treatment by 13.28%. In addition, compared with the single application of LMB, the LMB + CP treatment significantly reduced the soluble Fe (Ⅱ) in the sediment pore water and promoted the oxidation of Fe. Therefore, LMB + CP can enhance the removal of internal P from sediments. The DOM removal and Fe oxidation in sediment pore waters are beneficial for enhancing the adsorption of P by LMB. On the other hand, the single and combined applications of LMB and CP increased the richness of the sediment microbial communities while exhibiting slight effects on their diversity. According to the results of this study, the combined use of LMB and oxidizing materials represents a novel method for treating lakes with high internal phosphorus and DOM loads in sediments.

An overview of electrokinetically enhanced chemistry technologies for organochlorine compounds (OCs) remediation from soil

In recent years, electrokinetic (EK) remediation technology has gained significant attention among researchers. This technology has proven effective in the remediation of low-permeability polluted soil. Organochlorines (OCs) are highly toxic, persistent, bioaccumulative, and capable of long-distance migration. They can also accumulate through the food chain, posing significant environmental risks. This paper provides a review of the reaction mechanism of combining chemical technology with EK remediation for the removal of several typical OCs. Furthermore, the factors influencing the efficiency of EK remediation, such as pH and ζ potential, voltage gradients, electrode materials, electrolytes, electrode arrangements, and soil types, are summarized. The paper also presents an overview of recent advancements in the methods of combining chemical technology with EK remediation for the treatment of OCs contaminated soil. Specifically, the research progress in surfactants-combined EK technology, chemical oxidation-combined EK technology, chemical reduction-combined EK technology, and chemical adsorption-combined EK technology is summarized. These findings serve as a foundation for ongoing and future research endeavors in the field. Further exploration and investigation in this area are essential for advancing the field and improving environmental remediation strategies.