Control Of Phosphorus Release Research Articles

Suppression of phosphorus release from sediment by Vallisneria natans combined with iron- and zirconium-modified bentonites: Effectiveness, mechanism, and response of sedimentary microbial communities

The efficiency and mechanism in the reduction of internal phosphorus loading from sediment by Vallisneria natans combined with iron- and zirconium-modified bentonites (abbreviated as FeBT and ZrBT, respectively) were studied, and the responses of the microbial communities in sediments to Vallisneria natans combined with FeBT and ZrBT were also explored. ZrBT had stronger phosphate adsorption ability than FeBT. The greatest phosphate adsorption capacities for FeBT and ZrBT in the simultaneous presence of common ions can attain 1.60 and 4.29 mg P/g, respectively, and those for the loaded iron in FeBT and zirconium in ZrBT can attain 55.2 mg P/g Fe2O3 and 164 mg P/g ZrO2, respectively. The combined utilization of FeBT and Vallisneria natans and that of ZrBT and Vallisneria natans can effectively lower the releasing risk of phosphorus from sediment into the overlying water (OW), and the combined use of ZrBT and Vallisneria natans had a higher controlling efficiency than that of FeBT and Vallisneria natans. The passivation of diffusion gradient in thin film (DGT)-labile phosphorus in the sediment layer was vital to the control of phosphorus release from sediment by Vallisneria natans combined with FeBT and ZrBT. The bacterial communities in the sediments under the conditions of FeBT + Vallisneria natans and ZrBT + Vallisneria natans can exert well ecological functions. This work indicates that the combined utilization of ZrBT and Vallisneria natans is a better method to lower the releasing risk of phosphorus from sediment into OW than that of FeBT and Vallisneria natans.

Control of phosphorus release from sediment by the combined use of Elodea nuttallii, hydrous ferric oxide, zeolite and calcite: Efficiency, mechanism and response of bacterial communities

The effectiveness of Elodea nuttallii combined with a mixture of hydrous ferric oxide, zeolite and calcite (HZC) to reduce the internal loading of phosphorus (P) from sediment and its mechanism were studied, and the effect of Elodea nuttallii combined with HZC on the composition and function of the microbial communities in the surface sediment was also investigated. The results showed that the combination utilization of Elodea nuttallii and HZC can decrease the risk of phosphorus liberation from sediment to the overlying water, and the controlling efficiency of Elodea nuttallii combined with HZC was higher than that of Elodea nuttallii or HZC alone. The passivation of labile P measured by diffusive gradient in thin film device and mobile P played a crucial role in the control of internal P loading from sediment by the combined Elodea nuttallii + HZC treatment. HZC capping had a promoting effect on the growth of Elodea nuttallii. This was beneficial to the absorption of phosphorus from sediment by Elodea nuttallii. The combined application of Elodea nuttallii and HZC not only had a certain negative effect on the diversity of bacteria in the surface sediment, but also changed the microbial compositions of the surface sediment at the levels of phylum and genus. However, the microbial communities in the surface sediment still can perform good ecological function. The above results suggest that the combined application of Elodea nuttallii and HZC has a high potential in the management of internal P loading from sediment.

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 11.2mg 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 Ca Modified Biochar on the Chemical Speciation of Soil Phosphorus and Its Stabilization Mechanism

To control of phosphorus release from soil after farmland inundation around the lake and reservoir， calcium modified biochar （Ca-BC） was prepared using the coprecipitation method. Through X-ray photoelectron spectroscopy （XPS）， X-ray polycrystalline powder diffraction （XRD）， adsorption experiments， and simulated culture experiments， the effects of Ca-based biochar on the fraction of soil phosphorus （P） and its stabilization mechanism were studied. The results showed that the adsorption process of Ca-based modified biochar conformed to Langmuir （R2 = 0.940） and the first-order adsorption kinetic model （R2 = 0.961）， indicating that the P adsorption was a single-layer adsorption dominated by chemical action， and the maximum adsorption capacity was 267.93 mg·g-1. The simulated culture experiment indicated that when the modified biochar was 1%， the exchangeable fraction of phosphorus in the soil decreased from 7.42% to 4.59%. The XRD results demonstrated that Ca3（PO4）2 and hydroxyapatite absorption peaks appeared after adsorbed phosphorus on biochar， which proved that phosphate formed a relatively stable crystal precipitation. As shown in the XPS spectrum analysis， the carbonyl functional groups participated in the phosphorus fixation process， which improved the adsorption capacity of biochar for phosphorus. In general， when the concentration of Ca-based modified biochar was greater than 1%， it had a good fixation capacity for phosphorus release and had potential application value for controlling phosphorus release in soil.

Effect of capping mode on control of phosphorus release from sediment by lanthanum hydroxide.

The use of in situ active capping to control phosphorus release from sediment has attracted more and more attentions in recent years. It is important to identify the effect of capping mode on the control of phosphorus release from sediment by the in situ active capping method. In this study, the impact of capping mode on the restraint of phosphorus migration from sediment into overlying water (OW) by lanthanum hydroxide (LH) was studied. Under no suspended particulate matter (SPM) deposition condition, LH capping effectively restrained the liberation of endogenous phosphorus into OW during anoxia, and the inactivation of diffusive gradient in thin film-unstable phosphorus (UPDGT) and mobile phosphorus (PMobile) in the topmost sediment served as a significant role in the restraint of endogenous phosphorus migration into OW by LH capping. Under no SPM deposition, although the transformation of capping mode from the single high dose capping to the multiple smaller doses capping had a certain negative impact on the restraint efficiency of endogenous phosphorus liberation to OW by LH in the early period of application, it increased the stability of phosphorus in the static layer in the later period of application. Under SPM deposition condition, LH capping had the capability to mitigate the risk of endogenous phosphorus liberation into OW under anoxia conditions, and the inactivation of UPDGT and PMobile in the topmost sediment was a significant mechanism for the control of sediment phosphorus liberation into OW by LH capping. Under SPM deposition condition, the change in the covering mode from the one-time high dose covering to the multiple smaller doses covering decreased the efficiency of LH to limit the endogenous phosphorus transport into OW in the early period of application, but it increased the performance of LH to restrain the sedimentary P liberation during the later period of application. The results of this work suggest that the multiple LH capping is a promising approach for controlling the internal phosphorus loading in freshwater bodies where SPM deposition often occurs in the long run.

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 SO42− on the adsorption of phosphate (HiPO4i−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 HiPO4i−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 SO42− inhibited the adsorption of HiPO4i−3. Similar to R-LMB, the precipitation of HiPO4i−3 with La3+ to form LaPO4 and the ligand exchange between CO32− and HiPO4i−3 to form the inner-sphere lanthanum-phosphate complexes are the important mechanisms for the HiPO4i−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−/SO42− 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.

Control of phosphorus release from sediment by hydrous zirconium oxide combined with calcite, bentonite and zeolite

This study investigated the effectiveness and mechanism for the control of internal phosphorus (P) liberation from sediment by hydrous zirconium oxide (HZrO2) combined with calcite, bentonite and zeolite. The results suggested that coexisting calcite, calcium-modified bentonite (CaBT) and calcium-modified zeolite (CaZ) all had the ability to promote the adsorption of phosphate (PO43−) onto HZrO2. The mechanisms of PO43− elimination by HZrO2/calcite mixture involved the adsorption of PO43− on calcite, the precipitation of PO43− with Ca2+, and the inner-sphere complexation of PO43− with HZrO2. The amendment of sediment with HZrO2/calcite, HZrO2/CaBT or HZrO2/CaZ mixture can effectively prevent the sedimentary P release, and the immobilization of mobile P in the sediment and the uptake of dissolved reactive P (DRP) from the interstitial water by the amendment material played a key role in the control of P release from sediment by the combined amendment. Capping sediment with HZrO2/calcite, HZrO2/CaBT or HZrO2/CaZ mixture also can effectively intercept sediment P release, and the formation of P static layer attributed to the uptake of interstitial water DRP and DGT (diffusive gradient in thin-films)-unstable P in the upper sediment by the capping material was a key to the inhibition of sedimentary P migration into the overlying water by the combined capping. The great majority of P immobilized by the HZrO2/calcite, HZrO2/CaBT or HZrO2/CaZ combined covering layer is stable P and it has a low re-releasing risk under dissolved oxygen-deficit and pH 5–9 condition. The stability of P bound by the combined covering layer was larger than that by the single HZrO2 covering layer. The results of this research show that the combined use of HZrO2 and calcite, HZrO2 and CaBT, or HZrO2 and CaZ as a capping material has great potential in the reduction of sediment P loading.

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.

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−, CO32− and HA− had a negative effect on the phosphorus removal of MT-LHMT, while NO3−, Cl−, SO42−, 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-PDGT). 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.

Behavior characteristics of phosphorus and capping effect of microbubble flotation to control phosphorus release in the benthic sediment

Abstract Microbubbles were applied to remove phosphorus (P) and improve environmental water conditions on the surface of the benthic sediment in a eutrophic lake. Microbubble flotation (MF) was used to remove P in a laboratory-scale experiment device from the benthic sediment and overlying water field samples. The results of P tracing observation for MF treatment, which were identified based on the mass balance, showed P accumulated at a higher concentration in the floated scum than in the deposited sludge. Furthermore, while the amount of soluble P separated was insignificant, the removal efficiency of soluble P in the floated scum was higher than total P. As an additional effect, P release was suppressed by the injection of microbubbles, which reduced anaerobicization and improved environmental conditions in the overlying water of the lake. We also confirmed that the sludge that settled after flotation separation caused capping, which restrained P release by forming a layer on the surface of the sediment. The direct P flotation separation, provision of oxygen by injected microbubbles, and capping effect of re-deposited sludge are advantages associated with MF, and our results show that field application studies are warranted.

Distribution characteristics, influencing factors and releasing risk evaluation of phosphorus in the sediment of water-level-fluctuating zone in Lake Nansi

南四湖是南水北调东线最大的调蓄湖泊，周期性水位涨落会形成大面积消落带，认知消落带底泥磷形态赋存特征、影响因素及释放潜能，对于保障东线调水水质具有重要的科学意义.本研究分析了南四湖消落带底泥磷形态分布特征，探讨了各形态磷与土地利用、母质类型及底泥理化因素之间的关系，评价了南四湖消落带底泥磷的污染程度并分析了其释放风险.结果发现，消落带底泥中总磷（TP）、无机磷（IP）、NaOH提取态磷（NaOH-P）、HCl提取态磷（HCl-P）和有机磷（OP）含量的平均值分别为745.37、510.51、50.42、460.09和234.86 mg/kg，以HCl-P为主的IP占比较高.南四湖消落带底泥各形态磷含量具有较高的空间异质性，TP、IP、OP、HCl-P和NaOH-P含量的变异系数分别为30.7%、36.9%、29.6%、37.6%和51.2%.自然湿地、乔木林地和水浇地等土地利用方式下的底泥NaOH-P、HCl-P、IP、OP和TP含量差异不显著.土壤类型对消落带底泥OP含量影响明显，但对TP、IP、NaOH-P和HCl-P含量则影响不大.NaOH-P含量与HCl-P含量具有显著正相关，与OP含量则具有极显著正相关.南四湖周边30多km²消落带底泥磷污染程度相对较高，轻度、中度和重度污染底泥分别占5.9%、76.5%和17.6%，部分区域底泥磷释放潜能较高.研究结果可为南四湖消落带内源磷释放控制以及水质保障提供科技支撑.;As an important storage hub of the Eastern line of the South-to-North Water Transfer Project, the periodic fluctuation of water level in Lake Nansi leads to the formation of a large-area water-level-fluctuating zone (WLFZ), which affects the water quality of Lake Nansi. Understanding the distribution characteristics, influencing factors and release potential of phosphorus in the sediment of the WLFZ of Lake Nansi is of great scientific significance to ensure the water quality of the Eastern line of South-to-North Water Transfer Project. In this work, the distribution characteristics, influencing factors and releasing risk evaluation of phosphorus in the sediment in the WLFZ of Lake Nansi were investigated. The results showed that the average contents of total phosphorus (TP), inorganic phosphorus (IP), NaOH-extractable phosphorus (NaOH-P), HCl-extractable phosphorus (HCl-P) and organic phosphorus (OP) in the sediment of the WLFZ of Lake Nansi were 745.37, 510.51, 50.42, 460.09 and 234.86 mg/kg, respectively. The percentages of IP to TP in the sediments of the WLFZ of Lake Nansi were higher than those of OP to TP. The contents of different P species in the sediments of the WLFZ of Lake Nansi had great spatial heterogeneity, with TP, IP, OP, HCl-P and NaOH-P at 30.7%, 36.9%, 29.6%, 37.6% and 51.2% respectively. There was no significant difference in the contents of NaOH-P, HCl-P, IP, OP and TP in the sediments of natural wetland, arbor forest land and irrigated land. The type of sediment parent material could affect the content of OP in the sediment, but it had a negligible effect on the contents of TP, IP, NaOH-P and HCl-P in the sediment. There was a significant positive correlation between NaOH-P content and HCl-P content, and a very significant positive correlation between NaOH-P content and OP content. The pollution evaluation results showed that 5.9% of the sediment samples were slightly contaminated with phosphorus, 76.5% were moderately contaminated with phosphorus, and 17.6% were heavily contaminated with phosphorus. On the whole, the phosphorus pollution in the sediments of the 30 km² WLFZ of Lake Nansi was relatively serious. The results can provide scientific and technical support for the control of phosphorus release from sediments and the protection of water quality in the WLFZ of Lake Nansi.

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.

Efficiency and mechanism for the control of phosphorus release from sediment by the combined use of hydrous ferric oxide, calcite and zeolite as a geo-engineering tool

In this research, the efficiency and mechanism for the suppression of phosphorus (P) liberation from sediment by the combined use of hydrous ferric oxide (HFO), calcite and zeolite as a geo-engineering tool were investigated. The results showed that the coexisting calcite enhanced the adsorption of phosphate onto HFO via the release of Ca2+ from calcite and the formation of phosphate-bridged Fe-P-Ca ternary complex on the surface of HFO. HFO/calcite/zeolite mixture exhibited good phosphate sorption performance, and the maximum phosphate sorption capacity was 35.9 mg P/g. The sorption of phosphate on HCZ could be primarily due to the surface adsorption of phosphate onto calcite and zeolite, the surface adsorption of phosphate onto HFO via the mechanisms of inner-sphere Fe-phosphate complex and phosphate-bridged Fe-P-Ca complex formation, and the precipitation of calcium phosphate. HFO/calcite/zeolite combined capping and amendment both can greatly cut down on the risk of the release of sedimentary P to the overlying water under the oxygen-poor condition, and the generation of a static layer with low concentrations of soluble reactive P and diffusive gradients in thin film-labile P in sediment was vital to the control of phosphorus liberation from sediment into the overlying water by these methods. Most (approximately 70%) of the total P bound by the HFO/calcite/zeolite combined capping layer existed in the form of moderately or highly stable P, which is not easy to be re-released under the circumstances of normal pH and reducing environment. Results of this work demonstrate that the combined used of HFO, calcite and zeolite as a geo-engineering tool is a sediment remediation strategy with a great application prospect for managing the internal loading of P in surface waterbodies.

Effect of Myriophyllum verticillatum on controlling phosphorus release from sediment for water environment purification

Eutrophication is one of the most common water pollution problems in the world. In this paper, the effects of Myriophyllum verticillatum on phosphorus content in water and sediment were studied. The results showed that Myriophyllum verticillatum had the strongest purification effect on water sample. Under the condition of sufficient light, suitable temperature and environmental factors not affected by the external environment, the phosphorus content in the overlying water increased first and then decreased. In addition to the external factors, the phosphorus content in the water decreased. The results show that the growth of Myriophyllum verticillatum depends on the change of phosphorus concentration in water. The increase of phosphorus concentration in water will increase the phosphorus concentration in plants and accelerate the growth of Myriophyllum verticillatum. However, the growth of Myriophyllum verticillatum will consume more phosphorus. Myriophyllum verticillatum in sufficient light, suitable temperature, environmental factors are not affected by the outside world. The contents of phosphorus in the sediments showed a downward trend. In addition to the external factors, the phosphorus content in the sediment was reduced by Myriophyllum verticillatum. The relationship between the growth of Myriophyllum verticillatum and the total phosphorus concentration in sediments is interdependent. The release of phosphorus in sediment will increase the phosphorus content in water, which will lead to the enrichment of phosphorus in plants and accelerate the growth of Myriophyllum verticillatum. The growth of Myriophyllum verticillatum will make Myriophyllum verticillatum need more phosphorus, which will accelerate the absorption of phosphorus in water and release more phosphorus from sediment. This is the reaction mechanism of phosphorus removal by Myriophyllum verticillatum; Under the conditions of sufficient light, warm climate and environmental factors not affected by the external environment, the total phosphorus content of Myriophyllum verticillatum was on the rise.

Dissolved Air Flotation to Control Phosphorus Release of Benthic Sediment in a Coastal Brackish Lake

When applying the flotation process for phosphorus (P) removal in a lake, it is important to separate as much P as possible from water bodies and sediments using microbubbles. Furthermore, for remo...

Influence of algal blooms on the efficacy of La/Al-based phoslock in the control of phosphorus release from sediment in shallow lakes: a microcosm study

One of the most significant problems in eutrophic lakes is the presence of algal blooms, which may affect phosphorus (P) inactivation agents (PIAs) in the control of P release from sediment. Therefore, in this study, lanthanum/aluminium co-modified thermally treated calcium-rich attapulgite (LA@TCAP) is used to analyse the influence and mechanisms of algal blooms on P inactivation effect to provide technical support for the application of PIAs. In August 2020, lake water, sediments, and algae were collected from Zhushan Bay in Lake Taihu and LA@TCAP was prepared in the laboratory. These samples were used to establish three groups of microscopic simulation experiments. Through sequential extraction and 31P nuclear magnetic resonance, the mobile forms of P (Mobile-P) of sediment in each experimental group were measured and analysed, and the influence of algal blooms on the inactivation effect of the P immobilisation of LA@TCAP was determined. Physical and chemical properties of overlying water (DO, pH, algae organic matter (AOM), etc) and microbial community structure of capping layers were used to understand the influence mechanisms of algal blooms on the inactivation effect of PIAs. The concentration of dissolved oxygen (DO) concentration in the overlying water was reduced due to the decomposition of algal blooms, which increased the relative abundance of P-solubilising bacteria, and transformed more inert forms of P (Inert-P) into Mobile-P in the capping layer. Simultaneously, the algal blooms released OP, which passed through the capping layer and increased the OP content in the sediment. Under this dual effect, the Mobile-P content in the sediment increased, making LA@TCAP unable to inactivate the increased mobile-P, which was bound to affect the inactivation effect of LA@TCAP. Besides, the AOM released from the algal blooms combined with the metal ions in LA@TCAP, resulting in the reduction of adsorption sites of LA@TCAP for P. The algal blooms significantly decreased the DO concentration in the overlying water, thereby affecting the microbial community and transforming more Inert-P into Mobile-P. In addition, the adsorption performance of LA@TCAP for P also reduced owing to AOM competed with P for the metal ions in the LA@TCAP. Thus, algal blooms reduced the ability of LA@TCAP to control the P release from sediment.

Al-PHOSLOCK thin-layer capping to control phosphorus release from sediment: effect of hydraulic retention time and phosphorus migration/transformation mechanism

This work aimed to (i) investigate the effect of hydraulic retention time (HRT) on controlling the release of phosphorus from sediment and (ii) interpret the phosphorus migration and transformation mechanism in the Al-PHOSLOCK thin-layer capping system. A 35-day laboratory dynamic simulation experiment was conducted by applying the Al-PHOSLOCK thin-layer capping to evaluate the effect of HRT on interrupting the release of phosphorus from contaminated sediments. The total phosphorus (TP), inorganic phosphorus (IP), organic phosphorus (OP), non-apatite inorganic phosphorus (NAIP), and apatite phosphorus (AP) were identified as different phosphorus species and analyzed during the experiment to further elucidate the migration and transformation of phosphorus. The release of phosphorus from contaminated sediment was successfully suppressed by the Al-PHOSLOCK capping layer with an efficiency of higher than 90%. The HRT exerted a dual role on phosphorus controlling: at low HRT, slight water flow facilitated phosphorus migrating out from sediment and diffusing to the overlying water; at high HRT, the migration of phosphorus from overlying water back to sediment was strengthened. It was demonstrated that the phosphorus release was effectively controlled by the Al-PHOSLOCK thin-layer capping under different HRT conditions (static, 0.5 d, 1.0 d, and 3.0 d). The mechanism of phosphorus migration and transformation in the Al-PHOSLOCK thin-layer capping system was elucidated, including three significant stages of physical interception, adsorption, and capture/hold/transform process. This study verified the good capacity of the Al-PHOSLOCK capping system for controlling the release of sediment phosphorus under different HRT. Therefore, it was expected to be a promising approach in the handling of water eutrophication.

The effect of secondary capping on the control of phosphorus release from sediment by activated thin-layer capping with Al-PIA.

It is well-known that the activated thin-layer capping covering by secondary capping of contaminated sediment poses a threat to the inactivation of activated material. In this study, the static simulation experiment was conducted to study the effect of secondary capping thickness by sediment on the control of TP release from the sediment by aluminum-based P-inactivation agent (Al-PIA), and to propose the phosphorus adsorption pathway of Al-PIA. The results showed that Al-PIA could effectively reduce the release of phosphorus pollutants from the sediment at the capping intensity of 2kg/m2. When the secondary capping thickness of sediment were 0, 2, 4, 7, 10, and 15mm, the average removal rates of TP were 87.57%, 76.39%, 61.22%, 51.32%, 41.93%, and 32.11%, respectively, indicating that the removal efficiency of phosphorus decreased with the increase of the secondary capping thickness of the sediment. The adsorbed phosphorus by Al-PIA was mainly non-apatite inorganic phosphorus (NAIP) in inorganic phosphorus. With the increase of the secondary capping thickness of sediment, the NAIP proportion of phosphorus adsorbed by Al-PIA increased. Meanwhile, the removal rate of phosphorus in the activated capping system showed a first increase and then decrease trend, and the removal rates of total phosphorus (TP), inorganic phosphorus (IP), and organic phosphorus (OP) were obvious except for that of organic phosphorus (OP).

Effect of addition of lanthanum-modified bentonite(Phoslock<sup>®</sup>) in sediments on growth of <i>Hydrilla verticillata</i> under different water nutrient concentration

轮叶黑藻（Hydrilla verticillata）是我国浅水湖泊常见的沉水植物，经常用于湖泊生态修复工程.然而在生态修复中后期，轮叶黑藻又往往会过度繁殖，影响其他湖泊功能的发挥.镧改性膨润土（锁磷剂）可以有效地降低沉积物中生物可利用磷含量，近年来被用于控制湖泊沉积物磷释放，其对轮叶黑藻生长和形态的影响还有待阐明.本研究在2种不同上覆水营养盐浓度条件下，设置添加和不添加锁磷剂2种处理，探究沉积物添加锁磷剂对轮叶黑藻生长及形态特征的影响.结果表明：1）沉积物添加锁磷剂之后，铁锰结合态磷、有机磷、铝结合态磷等生物可利用磷浓度显著降低，而生物不可用磷，如钙结合态磷浓度显著升高；2）沉积物添加锁磷剂显著降低了轮叶黑藻的生物量和生长率.添加锁磷剂的处理组植物的株高、地上部分生物量均明显低于无锁磷剂组；相反，添加锁磷剂显著增加了植物的根长和地下部分生物量，进而提高了植物的根冠比；3）锁磷剂对轮叶黑藻生长的影响程度与水体营养盐浓度有关，在低营养盐浓度水体中锁磷剂对植物生长和形态特征的影响更为显著.本研究表明，锁磷剂的添加能降低沉积物中生物可利用磷浓度，抑制轮叶黑藻的生长，同时这种影响程度与在水体营养盐浓度有关.;Hydrilla verticillata is a common submerged plant in shallow lakes in China, and is often used as a pioneer species in lake ecological restoration projects. However, the Hydrilla verticillata tends to overgrowth, forming a canopy which affects other functions of lakes. Lanthanum-modified bentonite (Phoslock^®) can effectively reduce the bioavailable phosphorus content in sediments. In recent years, it has been used to control phosphorus release from lake sediments. Its impact on the growth and morphology of Hydrilla verticillata remains to be clarified. In this study, two treatments with and without Phoslock^® in the sediments were set up to investigate the effects of Phoslock^® on the growth and morphological characteristics of Hydrilla verticillata under two different water nutrient concentrations. The results show that:1) After adding Phoslock^® to the sediments, the bioavailable phosphorus concentration, such as Fe/Mn combined phosphorus (BD-P), organic phosphorus (Org-P), Aluminum-bound phosphorus (Al-P), is significantly reduced, while the non-bioavailable phosphorus concentration, such as Calcium-bound phosphorus (Ca-P), is significantly increased. 2) The addition of Phoslock^® in the sediments significantly reduced the biomass and growth rate of the Hydrilla verticillata. The plant height and aboveground biomass of Phoslock^® group were significantly lower than those without Phoslock^®; on the contrary, the addition of Phoslock^® significantly increased the root length of the plant and the underground biomass, and increased the plant's root-shoot ratio. 3) The effect of Phoslock^® on the growth of Hydrilla verticillata is related to the concentration of nutrients in the water, and the effect of Phoslock^® on plant growth and morphological characteristics is more significant in low-nutrient water. Overall, this study shows that the addition of Phoslock^® can effectively reduce the concentration of bioavailable phosphorus in sediments and inhibit the growth of Hydrilla verticillata, and this effect is more significant when the concentration of nutrients in the water is reduced.

Polyurethane nanocomposites can increase the release control in granulated fertilizers by controlling nutrient diffusion

We proposed a nanocomposite system based on castor oil-derived polyurethane (PU) for controlling the release of fertilizers by an ion-exchange mechanism. PU coatings modified with less than 5% montmorillonite, a cation-exchange material, successfully retarded the nitrogen release from urea granules, with less than 50% of the nutrient released within 18 days of immersion, as confirmed by soil incubation experiments. The same profile was observed for the phosphate release from monoammonium phosphate (MAP) granules coated with PU modified with hydrotalcite (less than 5% by weight), an anion-exchange material. The release times were proportional to the contents of the cation- or anion-exchange materials, which exhibited specific correlations with the kind of nutrient released (i.e., cationic or anionic), confirming the diffusion barrier promoted by the PU coating structures. Our results demonstrated that the use of PU nanocomposites can significantly reduce the coating thickness with improved nitrogen and phosphorus release control, opening a new field for the investigation of controlled release fertilizers.