P-inactivation Agents Research Articles

Inactivation of phosphorus in a highly eutrophic pond using Zeofixer® to eliminate the free-floating aquatic plant (Spirodela polyrhiza)

Free-floating aquatic plants are important invasive alien species whose excessive growth strongly affects freshwater ecosystems and their ecological service functions worldwide. Due to their rapid reproduction rate and the difficulty in their removal using common methods, the management of these aquatic weeds is still challenging. In this study, we proposed a strategy to control giant duckweed (Spirodela polyrhiza) in a highly eutrophic pond by blocking the supply of phosphorus by greatly lowering the phosphorus concentration in water using Zeofixer®, a novel lanthanum-containing P-inactivation agent. We found that the application of Zeofixer® satisfactorily eliminated the aquatic weed from the study pond. Zeofixer® had a high affinity for phosphate with a maximum adsorption capacity of 21.19 mgP/g, and it reduced the concentration of dissolved inorganic P, which was the major form of P species in the pond, from 1.60 to 0.005 mg/L. Amendment of pond sediment with Zeofixer® greatly diminished the P concentration in water under either oxic or anoxic conditions, although the latter caused a great release of P from sediment when compared with the former. After Zeofixer® treatment, the releasable P fractions in the sediment were substantially converted to stable P fractions, enabling the inactivation of P and the retardation of future P release. In conclusion, the free-floating aquatic plants in bodies of water could be thoroughly and permanently controlled using P-inactivation agents.

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.

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

Controlling the release of sediment phosphorus (P) using chemical agents is a promising method for controlling internal P in eutrophic lakes. However, mineral P formation and changes in the organic P composition after sediment amendment with P-inactivation agents remain poorly understood. Furthermore, little is known about the changes in the sediment microbial community composition after remediation. Here, various ratios of poly aluminum chloride (PAC) and lanthanum-modified bentonite (LMB) were added to nutrient-rich sediments and incubated. Sequential P extraction, solution/solid-state 31P nuclear magnetic resonance (NMR), and microbial analyses were periodically performed on the inactivated sediments. The results indicate that PAC and LMB effectively reduced sediment iron-bound P and organic P, respectively, markedly increasing the content of aluminum- and calcium-bound P in the sediment, respectively. Solid-state 31P NMR results confirmed the formation of rhabdophane (LaPO4. nH2O) in the LMB-amended sediment. Solution 31P NMR results showed that PAC preferentially reduced the organic P fractions of pyrophosphate, whereas LMB efficiently reduced the organic P fractions of orthophosphate, monoesters, and diesters in the sediment. Compared with the control sediment, PAC addition can cause short-term negative effects on sediment microbes at high doses, whereas LMB addition can increase bacterial diversity or richness in the sediment. These results provide a deeper understanding of the differences between PAC and LMB in internal sediment P control.

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.

Effect of aluminum-based P-inactivation agent (Al-PIA) capping on bacterial community in sediment

Effect of aluminum-based P-inactivation agent (Al-PIA) capping on bacterial community in sediment

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.

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).

Portuguese shallow eutrophic lakes: evaluation under the Water Framework Directive and possible physicochemical restoration measures

Eutrophication has become the primary water quality issue for most of the freshwater ecosystems in the world. It is one of the most remarkable examples of the biosphere’s alterations due to agricultural and industrial activities affecting aquatic ecosystems. As eutrophication becomes frequent and many eutrophic ecosystems have difficulties in meeting the EU Water Framework Directive (WFD) criteria, the removal of phosphate gains great importance in water treatment. The objective of this study is to highlight the remediation methods that have been implemented in Portuguese eutrophic shallow lakes to accomplish the WFD requirements, particularly for the control of external loading of nutrients. However, the reduction of external nutrient loads per se often does not result in a change back to the original state, and additional internal lake restoration measures may therefore be needed to decrease the concentration of total phosphorus and increase water quality. In this context, this review paper also describes the chemical approaches available to mitigate the eutrophication of shallow freshwater ecosystems based on phosphate inactivation agents, their capacity and application methods, as well as the results that generically have been obtained. The P-inactivation agents can also be complemented with physical approaches in order to improve the treatment effectiveness. Although these remediation techniques can have significant benefits in reducing the proliferation of cyanobacterial blooms, other potential adverse ecological effects may occur. For this reason, the costs, the application strategy, the potential stressor(s) effect(s), both for human and key species, are factors that should be taken into account before its effective application.

Interactions of riverine suspended particulate matter with phosphorus inactivation agents across sediment-water interface and the implications for eutrophic lake restoration

Phosphorus (P) inactivation agents (PIAs) have been widely used in lakes for eutrophic management. However, the interactions of riverine suspended particulate matter (SPM) with PIAs have not been elucidated to the point of complete confidence in the success of PIA application to eutrophic lakes. In this study, a long-term field incubation experiment was carried out to investigate the effects of riverine SPM on sediment internal P management. Fluorescence excitation emission matrix coupled with parallel factor (EEM–PARAFAC) was used to characterize dissolved organic matter (DOM) derived from SPM/sediment, and to study its complexation with La (III) and Ca (II) contained in two PIAs. The analysis identified one protein-and two humic-like components in these samples, which show variable quenching effects by La (III) and Ca (II). The continuous settling of SPM can bury PIAs deeper into the sediment layers and while increasing the mobile P content in surface sediments. This consequently made an increase of P fluxes and surface sediment reactivity, which was witnessed by the increased labile P concentration measured by diffusive gradient in film (DGT). However, the binding capacity of PIAs towards sediment mobile P was kept in a buried layer during the six months’ field experiment. This study indicates that the influence mechanism of riverine SPM on PIAs was through a decrease of the reactive sorption sites of PIAs by complexing with DOM and continuously increasing the mobile P content in surface sediment thereby largely surpassing their maximum P sorption capacity. Repeated dosing at scheduled times would be better for turbid eutrophic lake remediation with high input of riverine SPM in long-term management.

Bioavailable phosphorus (P) reduction is less than mobile P immobilization in lake sediment for eutrophication control by inactivating agents

Phosphorus (P) immobilization by inactivating agents in the sediment of eutrophic lakes to reduce immediately available P in lake water is often crucial for mitigating nuisance eutrophication symptoms, such as cyanobacterial blooms. Macrophytes and phytoplankton, however, can directly utilize P from the sediment for growth. Accordingly, a comprehensive analysis of the P bioavailability in lake sediment amended with two promising P-inactivation agents, namely Phoslock® and drinking water treatment residue (DWTR), was investigated in both short- and long-term studies (20 and 180 d). Phosphorus-availability was assessed using six chemical extraction methods and Hydrilla verticillata and Microcystis aeruginosa growth tests. The results showed that Phoslock® and DWTR significantly reduced mobile P (NH4Cl and Na2S2O4/NaHCO3 extractable P) in lake sediment, while P bioavailability that was assessed by different methods showed considerable deviations. Interestingly, appropriate bioavailable P chemical extraction methods were determined based on linear correlation analysis, and further comparison indicated that reduction of bioavailable P by DWTR (<55% for macrophyte available P) and Phoslock® (<17% for cyanobacteria available P) were clearly less than the mobile P immobilization (>75%) at recommended dosages, which was probably caused by the capability of macrophyte and cyanobacteria to utilize various fractions of P (except the residual P) in amended sediment under proper illumination. Therefore, DWTR and Phoslock® can effectively reduce P release from lake sediment, but the potential bioavailable P may pose uncertainties for eutrophication control in lakes that typically have regular sediment re-suspension. Overall, an evaluation of the bioavailable P pool in the lake ecosystem should be essential for successful lake geo-engineering.

Phosphorus sorption and supply from eutrophic lake sediment amended with thermally-treated calcium-rich attapulgite and a safety evaluation

Modified clays are being increasingly used as P-inactivation agents for lake eutrophic control. However, the interaction of P with these material amended sediments still remain unclear. This study investigates the P sorption and supply from the thermally treated calcium-rich attapulgite amended eutrophic lake sediments as well as the ecological safety of material addition. The results indicated that P sorption on material amended sediment can be well fitted by a modified Langmuir model. Material addition can greatly enhance the P sorption capacity of lake sediment and lower the zero equilibrium P concentration (EPC0), which can turn lake sediment from a source to a pool. P sorption on raw and material amended sediment generally decreases with an increase of the water pH value. But material amended sediment still can adsorb a large amount of P even in very alkaline conditions resulting from algal blooms. Furthermore, P sorption on amended lake sediment was less influenced by NO3− and HCO3− than by SO42− to a moderate degree and by SiO3− to a much larger degree. The results of diffusive gradients in thin films (DGT) measurement indicated the ability of P supply from lake sediment was largely inhibited by material addition. This was due to sediment mobile P had been transformed into stable Ca-P. A toxicity study indicated that material additions can increase pH value in lake sediment and can cause a toxic effect on benthic organisms when a large addition of material is involved, but this would be greatly attenuated in the field. The results of this study indicated that thermally treated calcium-rich attapulgite has the potential to be used as a P-inactivation agent for lake eutrophication control.

Eutrophication control using a novel bentonite humic-acid composite material Bephos™

The main objective of the present study was to estimate the efficiency of Bephos™ as an active capping agent preventing the phosphate release from eutrophic lake sediments. Bephos™ was compared with unmodified bentonite (N-bentonite) and natural zeolite (N-zeolite), in a ratio 1/10/10 respectively. Bephos™ as a P-inactivation agent resulted in about ∼96.6% reduction of the phosphate flux and ∼75.2% reduction of the ammonium flux from the sediments respectively. N-Zeolite and N-bentonite as capping materials resulted in about 64% and 91.8% reduction of the phosphorus flux and in about 70% and 35.6% reduction of the ammonium flux from the sediments respectively. Moreover, an additional purpose of this study was to investigate the different P-forms present in sediments, their contributions to the P-loadings of the ecosystem and also the effect of Bephos™ amendment on P-binding properties of sediments. The results show that Bephos™ restrained P release from the sediments, reducing the proportion of P-mobile in sediments, which was transformed into non-reactive species. The application of Bephos™ caused an increase in the mass of P present in the more refractory ‘apatite bound P’ fraction compared to P-mobile, and also more P was stored in the residual P fraction of sediment post-application.

The effect of chronic exposure to phosphorus-inactivation agents on freshwater biota

The phosphorus (P)-inactivation agents alum or modified zeolite (Aqual-P TM ) are used in eutrophic lake remediation. Lake managers must evaluate the benefits of P-removal against potential adverse effects on lake biota. Laboratory mesocosms were used to determine whether a 2 month exposure to alum or Aqual-P had lethal or sublethal effects on native benthic-dwelling macroinvertebrates or fish. The P-inactivation agents were applied while the organisms were present to evaluate both acute- and longer-term effects. A gradient of doses up to 344 g alum m -2 ((7 mm capping layer thickness) and a single 200 g Aqual-P m -2 dose were applied with no detectable acute effects on survival or behaviour. After 2 months, there was no significant effect of alum or Aqual-P on the survival or growth of the crayfish, mussels or fish, but aluminium accumulation was measurable in some treatments. Fingernail clams were held in a sub-mesocosm to prevent predation, which resulted in exposure to intact capping layers. The highest alum dose significantly decreased fingernail clam survival and reburial rates, while 200 g Aqual-P m -2 caused highly variable survival. Our findings can be used by lake managers to assist the selection of site- specific application rates for these P-inactivation agents.

Comparison of efficacy of two P-inactivation agents on sediments from different regions of Lake Taihu: sediment core incubations

Comparison of efficacy of two P-inactivation agents on sediments from different regions of Lake Taihu: sediment core incubations

Sustainability assessment and comparison of efficacy of four P-inactivation agents for managing internal phosphorus loads in lakes: sediment incubations

A novel application of a continuous flow incubation system (CFIS) was used to assess four phosphorus (P) inactivation agents—alum, Phoslock™, a new modified zeolite (Z2G1 or Aqual-P™), and allophone—when used as sediment capping agents to manage internal P loads in lakes. The CFIS technique allowed combined efficacy and sustainability assessment, including: (1) flux measurements during simulation of stratified (anoxic) and mixed (aerobic) conditions on the same sediment through multiple cycles to assess the longevity of a range of product doses; (2) simulation of a summer algal bloom collapse and subsequent burial of the products; and (3) investigation of non-target effects on nitrification and denitrification processes at the sediment–water interface. Minimum P-removal dose rates were found to differ substantially at 80 g m−2 for alum, 190 g m−2 for Z2G1, 220 g m−2 for allophane and 280 g m−2 for Phoslock™, for similar capping layer thickness of about 2 mm, and would be effective for at least 4 years. All products temporarily suppressed nitrification and denitrification under aerobic conditions, and it may be important to minimise product application to any permanently aerobic zones, such as the littoral areas of a lake. While the aluminium (Al)-based products did not enhance Al fluxes in the CFIS, lanthanum (La) was released at a near constant rate of around 2 mg La m−2 day−1 from the Phoslock™ treatments over a period of at least 14 days. Spatial variability of sediment P, bioturbation, and burial are factors that will affect up-scaling these results to a whole lake.

Effects of a modified zeolite on P and N processes and fluxes across the lake sediment–water interface using core incubations

A new locally produced P-inactivation agent, Z2G1, was tested on sediment cores from Lake Okaro, New Zealand, for phosphorus (P) removal efficacy and any non-target side effects prior to a whole lake trial to manage internal P loading. Z2G1 is a granular product which settles rapidly, and was designed as a sediment capping material. It is a modified zeolite which acts as a carrier for the aluminium (Al)-based P-binding agent. It was found to have a high affinity for P and did not release Al into the water column. Continuous-flow incubation study results showed that a thin layer of Z2G1 (~2 mm) could completely block the release of P from the sediment under aerobic and anoxic conditions, and remove P from the overlying water in contact with the capping layer. The Z2G1 capping layer neither released metals itself nor did it induce the release of metals from the sediments, and the zeolite substrate absorbed arsenic and mercury from the geothermally influenced Lake Okaro sediments. In general, zeolites are strong cation absorbers and the zeolite substrate of Z2G1 absorbed ammoniacal nitrogen, making it the only sediment capping material to actively remove both P and N. There were, however, indications of a suppression effect on microbial denitrification by the Z2G1 capping layer under aerobic conditions. Overall, the Z2G1 sediment capping material is a highly effective P-inactivation agent which might be a useful material for managing internal P loads in eutrophic lakes.