Impact of application mode on the control of phosphorus release from sediments using zirconium-modified bentonite as geo-engineering material

Immobilization of phosphorus in water-sediment system by iron-modified attapulgite, calcite, bentonite and dolomite under feed input condition: Efficiency, mechanism, application mode effect and response of microbial communities and iron mobilization

Four kinds of iron-based materials, i.e., iron-modified attapulgite, calcite, bentonite and dolomite (abbreviated as Fe-ATP, Fe-CA, Fe-BT and Fe-DOL, respectively) were prepared and used to immobilize the phosphorus in the system of overlying water (O-water) and sediment under the feed input condition, and their immobilization efficiencies and mechanisms were investigated. The influence of application mode on the immobilization of phosphorus in the water-sediment system by Fe-ATP, Fe-CA, Fe-BT and Fe-DOL was researched. The effects of Fe-ATP, Fe-CA, Fe-BT and Fe-DOL on the concentration of labile iron in the water-sediment system and the microbial communities in sediment were also studied. The results showed that the Fe-ATP, Fe-CA, Fe-BT and Fe-DOL addition all can effectively immobilize the soluble reactive phosphorus (SRP), dissolved total phosphorus (DTP) and diffusive gradients in thin-films (DGT)-labile phosphorus in O-water under the feed input condition, and also had the ability to inactivate the DGT-labile phosphorus in the top sediment. Although the change in the application mode from the one-time addition to the multiple addition reduced the inactivation efficiencies of SRP and DTP in O-water in the early period of application, it increased the immobilization efficiencies in the later period of application. Although Fe-ATP, Fe-CA, Fe-BT and Fe-DOL had a certain releasing risk of iron into the pore water, they had negligible risk of iron release into O-water. The addition of Fe-ATP, Fe-CA, Fe-BT or Fe-DOL reshaped the sediment bacterial community structure and can affect the microorganism-driven phosphorus cycle in the sediment. Results of this work suggest that Fe-ATP, Fe-CA, Fe-BT and Fe-DOL are promising phosphorus-inactivation materials to immobilize the phosphorus in the water-sediment system under the feed input condition.

Effect of common ions aging treatment on adsorption of phosphate onto and control of phosphorus release from sediment by lanthanum-modified bentonite

The objective of this work was to explore the influence of combined aging treatment using Na⁺, Ca²⁺, Cl^-, HCO₃^- and SO₄^2- on the adsorption of phosphate (H_iPO₄^i-3) onto and the restraint of internal phosphorus (P) migration into overlying water (OW) by lanthanum modified bentonite (LMB). To achieve this aim, the adsorption characteristics and mechanisms of H_iPO₄^i-3 onto the raw and aged LMBs (named as R-LMB and A-LMB, respectively) were comparatively studied, and the effects of R-LMB and A-LMB treatments (addition and capping) on the migration of P from sediment to OW were comparatively investigated. The results showed that the combined aging treatment of R-LMB with Na⁺, Ca²⁺, Cl^-, HCO₃^- and SO₄^2- inhibited the adsorption of H_iPO₄^i-3. Similar to R-LMB, the precipitation of H_iPO₄^i-3 with La³⁺ to form LaPO₄ and the ligand exchange between CO₃^2- and H_iPO₄^i-3 to form the inner-sphere lanthanum-phosphate complexes are the important mechanisms for the H_iPO₄^i-3 uptake by A-LMB. The R-LMB addition and capping can be effective in the suppression of endogenous P release to OW under hypoxia conditions. The inactivation of diffusive gradient in thin film-unstable P (DGT-UP) and potentially mobile P (PM-P) in sediment acted as a key role in the restraint of internal P release to OW by the R-LMB addition, and the immobilization of DGT-UP and PM-P in the topmost sediment played a key role in the interception of endogenous P migration into OW by the R-LMB capping. Although the Na⁺/Ca²⁺/Cl^-/HCO₃^-/SO₄^2- combined aging treatment had a certain negative effect on the efficiencies of LMB addition and capping to hinder the liberation of P from sediment into OW, the A-LMB addition and capping still can be effective in the control of sediment internal phosphorus pollution to a certain degree. The results of this work indicate that LMB has a high potential to be used as a capping/amendment material to control internal phosphorus pollution.

Comparison of magnetite, hematite and goethite amendment and capping in control of phosphorus release from sediment

The characteristics and mechanism of phosphate adsorption onto magnetite, hematite and goethite were comparatively studied, and the effects of magnetite, hematite and goethite amendment and capping on endogenous phosphorus (P) liberation from sediment into overlying water (OW) were comparatively investigated. The adsorption of phosphate onto magnetite, hematite and goethite mainly obeyed the inner-sphere complexation mechanism, and the phosphate adsorption capacity decreased in the order of magnetite > goethite > hematite. The magnetite, hematite and goethite amendment all can decrease the risk of endogenous Prelease into OW under anoxic conditions, and the inactivation of diffusion gradients in thin films-labile P in sediment made a great contribution to the restraint of endogenous P release into OW by the magnetite, hematite and goethite amendment. The efficiency of endogenous P release restraint by the iron oxide addition decreased in the order of magnetite > goethite > hematite. The magnetite, hematite and goethite capping all can be effective for the suppression of endogenous P release from sediment into OW under anoxic conditions, and most of P immobilized by the magnetite, hematite and goethite capping layers is relatively or very stable. The results obtained from this work suggest that magnetite is more suitably used a capping/amendment material to prevent P release from sediment than hematite and goethite, and magnetite capping is a promising approach for hindering sedimentary P release into OW.

Effects of calcination on the environmental behavior of sediments by phosphorus speciation and interface characterization

Dredged sediments derived from eutrophicated lakes poses hardness of sludge disposal and ecological risks. The proper pretreatment and utilization of dredged sediments presented a challenge. In this study, Dianchi Lake sediments were dredged, thermally treated and utilized as particle capping material in batch experiments. The effects of calcination on phosphorus speciation and sediment-water interface environment as well as P immobility mechanism were predominantly explored. The microstructures and chemical compositions of calcined sediments were investigated, indicating the porosity and mineralization components were greatly enhanced. The fractional analysis of phosphorus revealed that the calcination process reduced the percentage of unsteady phosphorus, transforming into stable inert phosphorus fractions (Al-P, Ca-P and Res-P), respectively, thereby minimized its mobility and eutrophication risk. Interestingly, calcination temperatures of 700 °C and 800 °C resulted in smaller releasing potentials and equilibrium phosphorus concentrations, despite having lower adsorption capacities than 550 °C. Furthermore, the results of redox potential monitoring showed that the thermally treated Dianchi Lake sediments could enhance the redox potential and dissolved oxygen in the surface sediment, indicating the amelioration of interfacial environment. The practical monitoring experiments confirmed the capping depressed the DTP to 0.031 mg L^-1. The investigation of this study provided explicit evidence of Ca coupled P and aerobic Fe bound P strengthened the immobilization effects, and the development of sediment calcination demonstrates a promising strategy for alleviating the burden of endogenous pollution and improving aerobic environment, which are of great significance for lake ecological remediation.

Inhibition of sediment internal phosphorus release in agricultural drainage ditches by ceria nanoparticle capping

In this study, ceria nanoparticles (CNPs) were introduced as an in-situ capping agent to inhibit the release of phosphorus (P) from sediments of agricultural drainage ditches. High-resolution dialysis (HR-Peeper) and diffusive gradients in thin film (DGT) techniques were used to measure the concentrations of P and iron (Fe) in the overlying water and sediments. The results showed that the CNP capping not only decreased the soluble reactive P (SRP) in the overlying water by 55.36% but also decreased the SRP in the pore water by 30.06%. More importantly, after the CNP capping, the flux of SRP from the pore water to the overlying water decreased by 34.12%, indicating that CNP capping can effectively inhibit the release of P from sediments to the overlying water. In addition, 38.38% of DGT-labile P was immobilized using CNP capping. Furthermore, the results of P speciation showed that CNP capping led to the change of P species from easily released NH4Cl-extractable P (NH4Cl-P) and Na2S2O4/NaHCO3-extractable P (BD-P) to more stable HCl-extractable P (HCl-P) and residual P (Res-P). These results show that CNP capping can further decrease the release of P from sediments to the overlying water. The present study shows that CNP is a feasible and effective capping material to inhibit the release of P from sediments of agricultural drainage ditches.

Effect of application mode (capping and amendment) on the control of cadmium release from sediment by apatite/calcite mixture and its phosphorus release risk

In this research, the influence of application mode (capping and amendment) on the control of cadmium (Cd) liberation from sediment by apatite/calcite mixture and its phosphorus release risk were investigated. The results showed that calcite addition had a limited effect on the speciation of Cd in sediment, but apatite addition had a significant impact on the fractionation of Cd in sediment. Apatite amendment could effectively immobilize the most readily mobilized Cd by transferring the acid-soluble fraction to the reducible and residual fractions. Apatite addition also could effectively reduce the concentration of toxicity characteristic leaching procedure (TCLP)-leachable Cd in sediment, and apatite had a much higher reduction efficiency of TCLP-leachable Cd than calcite. Apatite/calcite mixture capping could reduce the risk of Cd liberation from sediment into the overlying water, and the controlling efficiency of apatite/calcite mixture capping was higher than that of apatite/calcite mixture amendment. The effect of apatite/calcite mixture addition on the concentration of reactive soluble phosphorus (SRP) in the overlying water was limited. The introduction of calcite into the apatite capping layer could lower the risk of phosphorus release from apatite to the overlying water as compared to single apatite capping. However, the apatite/calcite mixture capping layer still had a relatively high risk of phosphorus liberation into the overlying water. Results of this work suggest that apatite/calcite mixture has a high potential to be used as a capping material to control Cd release from sediment from the perspective of controlling efficiency and application convenience.

Contrasting effect of zirconium-, iron-, and zirconium/iron-modified attapulgites capping and amendment on phosphorus mobilization in sediment

In this research, the sorption characteristics and mechanism of phosphate on zirconium-modified attapulgite (Zr-ATP), iron-modified attapulgite (Fe-ATP), and zirconium/iron co-modified attapulgite (Zr/Fe-ATP) prepared by a simple impregnation method were studied, and the impacts of Zr-ATP, Fe-ATP, and Zr/Fe-ATP amendment and capping on the migration of phosphorus (P) from sediments to overlying waters were investigated. The results showed that Zr-ATP and Zr/Fe-ATP possessed stronger adsorption ability for phosphate in aqueous solution than Fe-ATP. The ligand replacement of the hydroxyl group with the phosphate anion to form the inner-sphere phosphate complex played a crucial role in the adsorption process of phosphate on Zr-ATP, Fe-ATP, and Zr/Fe-ATP. Most of the phosphate ions bound by Zr-ATP and Zr/Fe-ATP were in the form of caustic soda solution-extractable inorganic P (NaOH-IP) and residual P (Res-P), and it is hard for these P species to be re-released into water under the circumstances of reducing environment and normal pH (5-9). The ratio of mobile P to total P of Fe-ATP loaded with phosphate was much higher than those of Zr-ATP and Zr/Fe-ATP loaded with phosphate, indicating that Fe-ATP-bound phosphate has a higher re-releasing risk than Zr-ATP-bound and Zr/Fe-ATP-bound phosphate. Zr-ATP, Fe-ATP, and Zr/Fe-ATP amendment all can reduce the releasing risk of P from sediments to overlying waters. The amendment of sediment with Zr-ATP and Zr/Fe-ATP can both induce the conversion of redox-sensitive P (BD-P) to NaOH-IP and Res-P in the sediment, making the phosphorus in the sediment more stable. However, the amendment of sediment with Fe-ATP can only induce the conversion of HCl-P to NaOH-IP in the sediment and had a negligible effect on the inorganic P activity in the sediment. Zr-ATP, Fe-ATP, and Zr/Fe-ATP capping all can reduce the risk of P release from sediment into the overlying water, and Zr-ATP and Zr/Fe-ATP capping had a better reduction efficiency of internal P liberation to the overlying water than Fe-ATP capping. Zr-ATP, Fe-ATP, and Zr/Fe-ATP capping all can give rise to the reduction of pore water SRP and diffusive gradient in thin-film (DGT)-labile P in the upper sediment. This is beneficial to the control of P releasing from sediment into the overlying water by the Zr-ATP, Fe-ATP, and Zr/Fe-ATP capping. The findings of this work suggest that Zr-ATP and Zr/Fe-ATP are promising active capping or amendment materials for internal P loading management in surface water bodies.

Effectiveness and mechanism of aluminum/iron co-modified calcite capping and amendment for controlling phosphorus release from sediments

The effectiveness and mechanism of aluminum/iron co-modified calcite (Al/Fe-CA) for the control of phosphorus (P) liberation from sediments was investigated. The results showed that Al/Fe-CA possessed good sorption performance for phosphate, and the maximum phosphate sorption capacity for Al/Fe-CA could reach 27.0 mg/g. The major mechanisms involved the surface adsorption of phosphate on calcite, the precipitation between phosphate and Ca²⁺ leached from calcite, and the ligand exchange between Al/Fe-bound hydroxyl groups and phosphate to form the Al-O-P and Fe-O-P inner-sphere complexes. The re-releasing risk of Al/Fe-CA-bound P under the circumstances of normal pH (5-9) and reducing environment was very low. Al/Fe-CA addition could significantly reduce the risk of P releasing from sediment to overlying water (OL-water), and the inactivation of mobile P, reactive soluble P (SRP) and diffusive gradient in thin-films (DGT)-labile P in sediment by Al/Fe-CA had a great part in the suppression of sediment-P liberation to OL-water by the Al/Fe-CA amendment. Al/Fe-CA capping and fabric-wrapped Al/Fe-CA capping both could greatly reduce the risk of P releasing from sediment into OL-water, and the formation of a static layer with low concentrations of SRP and DGT-labile P in the upper sediment was the key to sustaining a high P controlling efficiency. When the applied mode of Al/Fe-CA varied from capping to amendment, although the inactivation efficiency of DGT-labile P in the overlying water and upper sediment by Al/Fe-CA would decrease to a certain degree, the inactivation efficiency of DGT-labile P in the lower sediment by Al/Fe-CA would increase. Results of this study suggest that Al/Fe-CA has the high potential to be used as an active capping or amendment material for the management of internal P loading in surface water bodies.

Feasibility of using Mg/Al-based layered double hydroxides as an inactivating agent to interrupt phosphorus release from contaminated agricultural drainage ditch sediments

This study aimed to evaluate the feasibility of using Mg/Al-based layered double hydroxides (Mg/Al-LDHs) treatment to prevent phosphorus release from sediments of agricultural drainage ditches. A high-resolution diffusive gradient film technique and a high-resolution peeper technique were used to measure the phosphorus and iron concentrations in the overlying water and sediment profiles at sub-millimeter vertical resolution. Results demonstrated that Mg/Al-LDHs effectively reduced the concentrations of soluble reactive P (SRP) (about 69%) in the overlying water and the concentrations of SRP (about 37.42%) and labile P (about 36.72%) in the pore water. The highly positive correlation (p < 0.01) between SRP and soluble Fe, labile P and labile Fe in the sediment profiles provided high-resolution evidence for the simultaneous release of iron and phosphorus in sediments. Furthermore, Mg/Al-LDHs inactivated mobile P (NH₄Cl-P and BD-P) in the uppermost sediment (0-50 mm) and then transformed the mobile P to more stable P (NaOH-rP, HCl-P, and Res-P) (about 81% of total extractable P). An inactivation layer with low phosphorus concentrations was observed in the upper sediment. In brief, the addition of Mg/Al-LDHs to the sediment surface of agricultural drainage ditches was effective in reducing SRP concentrations in the overlying water while effectively hindering the release of sediment internal phosphorus from the pore water to the overlying water.

Suppression of phosphorus release from sediment using lanthanum carbonate as amendment

The performance of lanthanum carbonate (LC) pertaining to the adsorption of phosphate (H_wPO₄^w-3) was investigated, and the possible adsorption mechanism was elucidated. The stabilization of H_wPO₄^w-3 adsorbed to LC was evaluated. The influence of LC addition on the upward transport of phosphorus (P) from sediment to overlying water (OL-W) was studied, and the adsorption performance of H_wPO₄^w-3 on the LC-amended sediment was explored. The results of this work indicated that LC performed well in the elimination of H_wPO₄^w-3 from water in the pH range of 4 to 11, and the commercial and self-prepared LC samples afforded the maximum H_wPO₄^w-3 adsorption capacities of 57.9 and 99.4 mg P/g, respectively, at pH 7. The presence of coexisting species including chloride, bicarbonate, and sulfate had a small influence on the H_wPO₄^w-3 adsorption onto LC. The main H_wPO₄^w-3 adsorption mechanism of LC at pH 7 was the ligand exchange reaction between carbonate and H_wPO₄^w-3 forming the inner-sphere La-phosphate complexation. The self-synthesized LC exhibited much higher H_wPO₄^w-3 adsorption performance than the commercial LC. The overwhelming majority (> 97.0%) of H_wPO₄^w-3 adsorbed to LC primarily existed in the form of muriatic acid-extractable P, which has relatively low re-releasing risk. The addition of LC into sediment could significantly prevent the release of P from the sediment solid into the OL-W, thereby leading to a lower concentration level of reactive soluble P (RSP) in the OL-W compared with no LC treatment. The addition of LC into sediment could greatly improve the H_wPO₄^w-3 uptake ability for the sediment, and the enhancement of H_wPO₄^w-3 adsorption onto the sediment by the added LC increased as the increase of the amendment dosage and the initial H_wPO₄^w-3 concentration. All results suggest that LC could serve as a promising amendment material for the control of sedimentary P release.

Interception of phosphorus release from sediments using Mg/Fe-based layered double hydroxide (MF-LDH) and MF-LDH coated magnetite as geo-engineering tools

A magnesium/iron-based layered double hydroxide (MF-LDH) and a composite of MF-LDH and magnetite (MF-LDH@Fe₃O₄) were synthesized, characterized and used as solid-phase phosphorus (P)-sorbents (SPPSs) to control the release of sedimentary P. The behavior and mechanism of phosphate adsorption onto MF-LDH and MF-LDH@Fe₃O₄ were studied. The effect of MF-LDH capping and amendment on the migration of P in sediments were comparatively investigated, and the impact of fabric-wrapped and unwrapped MF-LDH@Fe₃O₄ capping on P mobilization in sediments were also comparatively investigated. Results showed that both MF-LDH and MF-LDH@Fe₃O₄ had good phosphate adsorption performance, and the adsorption mechanisms included cation exchange, electrostatic attraction, ligand exchange and inner-sphere complex formation. Sediment capping and amendment using MF-LDH both could dramatically reduce the risk of the release of soluble reactive P (SRP) and diffusive gradient in thin-films-labile P (P-DGT) from sediments into overlying waters (OLY-Ws), and the MF-LDH capping had a better suppressing efficiency of sediment-P release into OLY-W than the MF-LDH amendment. Sediment capping with the fabric-wrapped and unwrapped MF-LDH@Fe₃O₄ both greatly decreased the risk of SRP and P-DGT released from sediment into OLY-W, and the efficiency of the prevention of SRP released from sediment into OLY-W by the fabric-wrapped MF-LDH@Fe₃O₄ capping layer (about 81-90%) was slightly lower than that by the unwrapped MF-LDH@Fe₃O₄ capping layer (about 94-99%). The reduction of P-DGT in the top sediment and the direct interception of the soluble P from pore water (POR-W) to OLY-W by the MF-LDH@Fe₃O₄ capping layer were the keys to the management of P released from sediment by the MF-LDH@Fe₃O₄ capping. From the standpoint of the efficiency of sedimentary P suppression, the convenience of application and the sustainability of sediment remediation, sediment capping with the fabric-wrapped MF-LDH@Fe₃O₄ is a promising approach to manage the release of sedimentary P into OLY-W.