Three kinds of active thin-layer capping materials for reducing the phosphorus load in eutrophic water body: comparison in dynamic experiment

Control of phosphorus release from sediment by iron/aluminum co-modified zeolite: efficiency, mechanism, and response of microbial communities in sediment

The efficiency of iron/aluminum co-modified zeolite (FeAl-Z) covering and amendment for controlling the internal loading of phosphorus (P) from sediment to the overlying water (OW) and its controlling mechanism were explored. The response of the composition of sedimentary microbial communities in sediment and their function to the FeAl-Z capping and amendment was also examined. FeAl-Z showed good removal performance for phosphate in aqueous solution. The maximum phosphate adsorption quantity for FeAl-Z at pH 7 attained 11.2 mg P/g. The release of sediment endogenous phosphorus to OW can be successfully restrained by the FeAl-Z covering and amendment, and the suppression ability of FeAl-Z covering was stronger than that of FeAl-Z amendment. Under the capping or amendment condition, FeAl-Z can effectively inactivate the labile phosphorus measured by diffusion gradient in thin film (DGT-LP) in the overlying water and surface sediment. The added FeAl-Z transformed redox-sensitive phosphorus (BD-P) to metal oxide-bound phosphorus (NaOH-IP) and residual phosphorus (Res-P) in sediment, which increased the stability of inorganic phosphorus in the sediment. The passivation of soluble reactive phosphorus (SRP) and DGT-LP in the surface sediment by FeAl-Z significantly contributed to the inhibition of sediment endogenous phosphorus release to OW by the FeAl-Z capping, and the passivation of SRP, DGT-LP and mobile phosphorus in the surface sediment played a pivotal role in the control of sediment internal phosphorus release by the FeAl-Z amendment. The FeAl-Z amendment and capping did not increase the liberation risk of Fe from sediment, and the microorganisms in the sediments under the conditions of FeAl-Z amendment and covering still can perform good ecological functions. Results of this research demonstrate that FeAl-Z capping has high application potential in the control of phosphorus transfer from sediment to OW.

Effect of controlling nitrogen and phosphorus release from sediment using a biological aluminum-based P-inactivation agent (BA-PIA)

A biological aluminum-based P-inactivation agent (BA-PIA) has been developed and demonstrated to effectively remove nitrogen and phosphorus; however, whether it can control the release of nitrogen and phosphorus in sediment still needs study. This study aimed to examine the effect of BA-PIA on controlling sediment nitrogen and phosphorus release. BA-PIA was prepared by artificial aeration. The use of BA-PIA in controlling nitrogen and phosphorus release was studied using water and sediment from a landscape lake in static simulation experiments. The sediment microbial community was analyzed using high-throughput sequencing. Static simulation showed that the reduction rates of total nitrogen (TN) and total phosphorus (TP) by BA-PIA were 66.8 ± 1.46% and 96.0 ± 0.98%, respectively. In addition, capping of BA-PIA promotes the conversion of easily released nitrogen (free nitrogen) in the sediment to stable nitrogen (acid-hydrolyzable nitrogen). The content of weakly adsorbed phosphorus and iron-adsorbed phosphorus in the sediment was reduced. The relative abundance of nitrifying bacteria, denitrifying bacteria, and microorganisms carrying phosphatase genes (such as Actinobacteria) in the sediment increased by 109.78%. The capping of BA-PIA not only effectively removed the nitrogen and phosphorus in water but greatly reduced the risk of nitrogen and phosphorus release from sediment. BA-PIA was able to make up for the deficiency of the aluminum-based phosphorus-locking agent (Al-PIA) that only removes phosphorus, giving it improved application prospects.

Removal efficacy and mechanism of nitrogen and phosphorus by biological aluminum-based P-inactivation agent (BA-PIA)

In this study, aluminum-based P-inactivation agent (Al-PIA) was used as a high-efficiency microbial carrier, and the biological Al-PIA (BA-PIA) was prepared by artificial aeration. Laboratory static experiments were conducted to study the effect of BA-PIA on reducing nitrogen and phosphorus contents in water. Physicochemical characterization and isotope tracing method were applied to analyze the removal mechanism of nitrogen and phosphorus. High-throughput techniques were used to analyze the characteristic bacterial genus in the BA-PIA system. The nitrogen and phosphorus removal experiment was conducted for 30 days, and the removal rates of NH₄⁺-N, TN and TP by BA-PIA were 81.87%, 66.08% and 87.97%, respectively. The nitrogen removal pathways of BA-PIA were as follows: the nitrification reaction accounted for 59.0% (of which denitrification reaction accounted for 56.4%), microbial assimilation accounted for 18.1%, and the unreacted part accounted for 22.9%. The characteristic bacteria in the BA-PIA system were Streptomyces, Nocardioides, Saccharopolyspora, Nitrosomonas, and Marinobacter. The loading of microorganisms only changed the surface physical properties of Al-PIA (such as specific surface area, pore volume and pore size), without changing its surface chemical properties. The removal mechanism of nitrogen by BA-PIA is the conversion of NH₄⁺-N into NO₂^--N and NO₃^--N by nitrifying bacteria, which are then reduced to nitrogen-containing gas by aerobic denitrifying bacteria. The phosphorus removal mechanism is that metal compounds (such as Al) on the surface of BA-PIA fix phosphorus through chemisorption processes, such as ligand exchange. Therefore, BA-PIA overcomes the deficiency of Al-PIA with only phosphorus removal ability, and has better application prospects.

Study on the management efficiency of lanthanum/iron co-modified attapulgite on sediment phosphorus load

Attapulgite co-modified by lanthanum-iron (MT-LHMT) was used to study its effectiveness and mechanism in controlling phosphorus release from sediments. MT-LHMT has high adsorption capacity for phosphate and the maximum adsorption capacity of MT-LHMT to phosphate can reach 75.79 mg/g. The mechanism mainly involved electrostatic action, surface precipitation and ligand exchange between MT-LHMT bonded hydroxyl and phosphate to form La-O-P and Fe-O-P inner-sphere complexes. MT-LHMT has excellent adsorption performance in the pH range of 3-8. In addition to HCO₃^-, CO₃^2- and HA^- had a negative effect on the phosphorus removal of MT-LHMT, while NO₃^-, Cl^-, SO₄^2-, K⁺, Ca²⁺ and Mg²⁺ had a positive or no effect on phosphorus removal. MT-LHMT significantly reduced the risk of phosphorus release from overlying water in different dose effects and covering methods, as well as the unstable inactivation of flowing phosphorus, sediment dissolved reactive phosphorus (DRP) and available phosphorus with medium diffusion gradient in thin film in the sediment-water interface (Labile-P_DGT). The MT-LHMT capping wrapped with fabric can reduce the risk of nitrogen release from sediment to overlying water more than only MT-LHMT capping. The results of this study showed that the MT-LHMT capping wrapped with fabric has high potential and can be used as an active capping material to manage the nitrogen and phosphorus load in surface water.

Control of Endogenous Phosphorus Release at the Sediment–Water Interface by Lanthanum-Modified Fly Ash

This study optimizes the modification and granulation of fly ash to make it more stable at the sediment–water interface. Through laboratory simulations, the modified fly ash pellets were optimally granulated to cover the sediment–water interface, and its control effect and mechanism were evaluated. The results showed that the phosphorus adsorption effect of lanthanum-modified fly ash was 34% and 40% higher compared with those of acid-modified and alkali-modified fly ash, respectively, with the phosphorus adsorption effect reaching 85%. The best dosing ratio was about 0.3 g/L. Adsorption was affected by pH and was more effective under weak alkalinity, close to the Langmuir adsorption model, which was consistent with the unimolecular layer adsorption characteristics and the presence of chemisorption and physical adsorption. The saturation adsorption amount of phosphate by lanthanum-modified fly ash was 8.89 mg/g. The optimized granulation conditions for lanthanum-modified fly ash pellets were a fly ash/montmorillonite ratio of 7:3, a roasting temperature of 900 °C, a roasting time of 4 h, and a particle size of 3 mm. After 20 days, the orthophosphate removal rate was more than 60% higher than that of the control group, with a total phosphorus removal rate of 43%. After covering for 60 days, active phosphorus in the surface layer of the sediment was gradually transformed into a stable phosphorus form, with calcium phosphorus accounting for 70% of the total inorganic phosphorus. The ability of the sediment to release phosphorus to the overlying water body was also significantly weakened. Meanwhile, the total phosphorus removal rate in the overlying water at the sediment–water interface reached more than 40%, and orthophosphate removal reached more than 60%, indicating an obvious phosphorus control effect. Transmission electron microscopy analysis showed that lanthanum was present at locations enriched with elemental phosphorus and was adsorbed onto the material surface. Therefore, lanthanum-modified fly ash pellets are a promising in situ phosphorus control agent with good endogenous phosphorus pollution control abilities in eutrophic water bodies.