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

Synchronous control of nitrogen and phosphorus release from sediments in shallow lakes under wind disturbance by modified zeolite and Ca/Al-based sludge combination

To inhibit eutrophication caused by endogenous pollutants release, the experiment explored the efficiency and mechanism of the synchronous control of nitrogen (N) and phosphorus (P) release from sediments in shallow lakes under wind disturbance by modified Ca/Al-based sludge (MS) and modified zeolite (MZ). High-temperature calcination and NaCl impregnation increased the pore volume of MS and Na+ content of MZ, and the adsorption capacity of MS for PO43--P and MZ for NH4+-N was as high as 42.01 and 20.28 mg g-1. The results of a 90-day incubation experiment showed that the addition of MS and MZ increased the abundance of Thauera, Nitrospira, Denitratisoma, and Clostridium, while decreasing the proportion of Proteus Hauser and Saccharimonadales, thereby reducing the active N and P contents in sediments through microbial transformation. At the same time, the efficient adsorption performance of the MS and MZ resulted in a significant decrease in pollutants in the interstitial water and sediments. In addition, sediment resuspension caused by wind disturbance increased the contact between sediments and remediation agents, resulting in the action depth of covering materials exceeding 100 mm. Compared to adding MS or MZ alone, the combination of the two (MSZG) could synchronously, efficiently, and stably inhibit N and P release. Under the coupling effects of physical interception, physicochemical adsorption, and biotransformation, the average TN, NH4+-N, TP, and PO43--P in the overlying water of the MSZG decreased by 72.13%, 88.92%, 69.28%, and 81.26%, respectively, compared to Control, which satisfying the Class III standard for surface water. Therefore, this study could provide reference for controlling endogenous release, improving eutrophication in shallow lakes under wind disturbance, and recycling residual sludge from sewage plants.

Efficacy of P-sorbent material combined with aquatic plants in controlling nutrient release from urban lake sediment: Field investigation

The release of stored nutrients from sediments is thought to substantially affect water quality in urban lakes. To explore the efficiency of different in-situ remediation methods on controlling high internal urban lake sediments, 120 days of field-enclosure experiments were conducted to investigate the efficacy of P-sorbent materials combined with aquatic plants in controlling nutrient release from urban-lake sediments. The lanthanum-modified clay (LMC) effectively reduced sediment P release flux and could temporarily lead to a small increase in N concentration in the overlying water. In contrast, Vallisneria spiralis (V. spiralis) has a relatively weak effect on controlling nutrient release and can even cause an increase in P concentration. The combined restoration technique of V. spiralis + LMC can overcome the drawbacks of a single method, reduce the nutrient content in overlying water, and inhibit the sediment internal release. Relative to the control, the V. spiralis + LMC treatment reduced mobile P content by 52.5% and increased Ca-P content by 34.5%. The added lanthanum contained material can quickly bind the readily released P in sediment and porewater, transforming it into intert P over time. Submerged macrophytes can absorb active P in water and sediments and transport oxygen to sediments promoting denitrification and N removal. The combined restoration technique synergistically combines the high P sorption affinity of LMC and the substrate improvement effect of V. spiralis, thus realizing the long-term control of endogenous release in urban lakes. This approach holds great promise for restoring urban lakes with high endogenous nutrient loading.

Combining effects of submerged macrophytes and lanthanum-modified bentonite on sediment enzyme activity: Evidence from mesocosm study

Lanthanum-modified bentonite (LMB) combined with submerged macrophytes (SM) has been a conventional means of eutrophication management in lakes in recent years, and is one of the most important methods for P removal. However, trends in nutrients and sediment enzymes at the water-sediment interface during this process have not been systematically assessed, and there are still some gaps in how abiotic properties drive changes in enzyme activity. Here, we show changes in aquatic environmental conditions under the action of different ratios of modified bentonite (0, 10%, 20%, and 30%) in combination with SM (Vallisneria natans, Potamogeton lucens, and Hydrilla verticillate) and quantify their effects on sediment enzyme activities. The results showed that the nutrient cycling at the water-sediment interface was facilitated by the combined effect of SM and LMB, which effectively reduced the overlying water nutrient concentration, increased the sediment enzyme activity and enhanced the N cycling process. Partial least squares structural equation model (PLS-SEM) showed that sediment parameters strongly influenced changes in enzyme activity, with NO3-N as the main controlling factors. Our study fills in the process of changing environmental conditions in lake water under geoengineered materials combined with macrophyte measures, especially the changes in biological properties enzyme activities, which contributes to a clearer understanding of nutrient fluxes during the management of eutrophication in lakes.

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.