Equilibrium Phosphate Concentration Research Articles

Modeling of phosphate speciation on goethite surface: Effects of humic acid

Iron (hydr)oxides and humic acid (HA) are important active components in soils and usually coexist in the environment. The effects of HA on the adsorption and subsequent immobilization of phosphate on iron (hydr)oxide surface are of great importance in studies of soil fertility and eutrophication. In this study, two types of goethite with different particle sizes were prepared to investigate the phosphate adsorption behaviors and complexation mechanisms in the absence or presence of HA by combining multiple characterization and modeling studies. The adsorption capacity of micro- (M-Goe) and nano-sized goethite (N-Goe) for phosphate was 2.02 and 2.04 μmol/m2, which decreased by ∼25% and ∼45% in the presence of 100 and 200 mg/L HA, respectively. Moreover, an increase in equilibrium phosphate concentration significantly decreased the adsorption amount of goethite for HA. Charge distribution-multisite surface complexation (CD-MUSIC) and natural organic matter-charge distribution (NOM-CD) modeling identified five phosphate complexes and their corresponding affinity constants (logKP). Among these phosphate complexes, FeOPO2OH, (FeO)2PO2, and (FeO)2POOH species were predominant complexes on the surface of both M-Goe and N-Goe across a wide range of pH and initial phosphate concentrations. The presence of HA had little effect on the coordination mode and logKP of phosphate on goethite surface. These results and the obtained model parameters shed new lights on the interfacial reactivity of phosphate at the goethite-water interface in the presence of HA, and may facilitate further prediction of the environmental fate of phosphate in soils and sediments.

Release Risk of Phosphorus by Sediments and Its Influencing Factors in Ponds and Ditches of a New Urban District Park

This study examined five ponds and three ditches in the Shufengwan Sports Park in a new urban district of Hefei City, from which surface-layer sediments and overlying water samples were collected during autumn, winter, and summer. The equilibrium phosphate concentrations (EPC0) of the sediments and its response to exogenous carbon or nitrogen were then measured. The resulting EPC0values were used to assess the risk of phosphorus release by the sediments. Finally, major factors influencing phosphorous release were identified using the Partial Least Squares Regression (PLSR) method. The sediments in the urban park exhibited a light-to-moderate level of phosphorous pollution, with the total phosphorus content (TP) ranging from 209.28 to 713.51 mg·kg-1 and biologically available phosphorus accounting for 18.51%-36.21% of the total phosphorus content. Under ambient background, the EPC0 values in pond sediments were 0.012-0.142 mg·L-1, with a mean value of 0.057 mg·L-1, while in ditches the values ranged from 0.036 to 0.156 mg·L-1 with an average value of 0.078 mg·L-1. The addition of exogenous carbon increased the EPC0 values (by approximately 47.5% in pond 3), and thus increased the risk of phosphorus release from sediments, in pond 1, 3, and ditch 1. However, EPC0 values of the other ponds and ditches decreased (in particular, by approximately 58.6% in pond 5), indicating that the risk of phosphorus release decreased. After the addition of exogenous nitrogen, the EPC0 values of almost all ponds and ditches declined to varying degrees (except in ditches 1 and 2 during the summer). In particular, in the EPC0 value of pond 2 declined by approximately 51.6%. The declining values imply that nitrogen was a limiting factor in phosphorus uptake by sediments in ponds and ditches. According to the results of PLSR, nitrogen and phosphorus had different effects on the EPC0 values of sediments in ponds and ditches.

Efficient phosphate removal by dendrite-like halloysite-zinc oxide nanocomposites prepared via noncovalent hybridization

The efficient capture of phosphate from contaminated water is crucial for aquatic ecosystem protection and drinking water utilities, but designing nanohybrid materials with high phosphate-adsorption capacity remains challenging. This study reports on a way to tackle this challenge, by creating a dendrite-like nanocomposite through the functionalization of tubular halloysite (Hal) clay mineral with ZnO nanoparticles. Specifically, ZnO nanoparticles were coated on the surfaces of Hal, thereby by providing adsorption sites capable of removing phosphate. Furthermore, dendrite-like ZnO-Hal can grasp phosphate firmly because of the strong binding of ZnO nanoparticles to phosphate. Thus, the ZnO coating with its high adsorption affinity provides a new benchmark for the scavenging of phosphate in water. The adsorption capacity of ZnO-Hal exhibits an exceptionally high phosphate capacity of 97.3 mg P·g−1 under the equilibrium phosphate concentration of 346 mg P·L−1, which is superior to most other reported phosphate adsorbents. After normalizing to the content of ZnO in the nanocomposite, the phosphate adsorption capacity of ZnO-Hal is higher than that of the pure ZnO particles. The equilibrium adsorption isotherm and kinetic data of ZnO-Hal were fitted well with Freundlich and pseudo-second-order models, respectively. Moreover, good adsorption performance of ZnO-Hal was confirmed in the presence of competitive anions at molar ratios of 1:10 or 1:100 (phosphate-to-anion ratio), both in the acidic and neutral pH ranges, and in domestic wastewater as well. The adsorption mechanism was investigated; those results revealed that phosphate was removed by the formation of a zinc phosphate mineral hopeite on the Hal surfaces. This work, therefore, provides a novel material for removing phosphate from water for environmental remediation purposes.

Theoretical and experimental investigation of phosphate removal from seawater by multi-stage coagulation

Abstract Phosphate removal from seawater is important for biofouling control on RO membranes because phosphorus is one of the nutrients for microbial growth. This paper is based on the hypothesis that multi-stage coagulation results in better phosphate removal. Therefore, comparison of phosphate removal with one-step and three-step dose coagulation from the aspects of both the theoretical calculation and experimental results is investigated in this paper. The result of theoretical calculation based on the Freundlich equation shows that the final phosphate concentration from a three-step dose, i.e. 0.43 μgP/L, is ten times lower than that from a one-step dose, i.e. 4.47 μgP/L. The experimental result shows that for the three-step dose, final phosphate concentration is 1.0 μgP/L, which is lower than for the one-step dose (i.e. 4.0 μgP/L), but not as low as the theoretical calculated value (0.43 μgP/L). This discrepancy between theoretical calculation and experimental result may be the impact of equilibrium phosphate concentration, different initial Fe:P molar ratio and NOM competition between one-step dose and three-step dose coagulation. Although this discrepancy exists, the experimental results still showed that multi-stage coagulation presented better phosphate removal in seawater to concentration levels that are lower than with conventional coagulation. In other words, the problem of the high coagulant dosage in the pretreatment process while removing phosphate from seawater may be solved by application of multi-stage coagulation instead of conventional coagulation.

Sediment phosphorus buffering in streams at baseflow: A meta-analysis.

Phosphorus (P) pollution of surface waters remains a challenge for protecting and improving water quality. Central to the challenge is understanding what regulates P concentrations in streams. This quantitative review synthesizes the literature on a major control of P concentrations in streams at baseflow-the sediment P buffer-to better understand streamwater-sediment P interactions. We conducted a global meta-analysis of sediment equilibrium phosphate concentrations at net zero sorption (EPC0 ), which is the dissolved reactive P (DRP) concentration toward which sediments buffer solution DRP. Our analysis of 45 studies and>900 paired observations of DRP and EPC0 showed that sediments often have potential to remove or release P to the streamwater (83% of observations), meaning that "equilibrium" between sediment and streamwater is rare. This potential for P exchange is moderated by sediment and stream characteristics, including sorption affinity, stream pH, exchangeable P concentration, and particle sizes. The potential for sediments to modify streamwater DRP concentrations is often not realized owing to other factors (e.g., hydrologic interactions). Sediment surface chemistry, hyporheic exchange, and biota can also influence the potential exchange of P between sediments and the streamwater. Methodological choices significantly influenced EPC0 determination and thus the estimated potential for P exchange; we therefore discuss how to measure and report EPC0 to best suit research objectives and aid in interstudy comparison. Our results enhance understanding of the sediment P buffer and inform how EPC0 can be effectively applied to improve management of aquatic P pollution and eutrophication.

The biotic contribution to the benthic stream sediment phosphorus buffer

Benthic stream sediments interact strongly with phosphorus (P) and can buffer dissolved reactive P (DRP) concentrations. The sediment P buffer can be measured with the sediment equilibrium phosphate concentration at net zero sorption (EPC0), which often correlates well with DRP. Yet, it is unclear how much of this P affinity in sediments is attributable to biotic (microbial P demand) or abiotic (sorption) processes. To clarify the role of biotic processes on EPC0, we used two experiments with benthic sediment from 12 streams. First, sediments sterilized by γ-irradiation increased in EPC0 compared to fresh sediments by a median of 83%. This increase in EPC0 was likely a result of cell lysis, where microbial biomass P (2.4 to 22.6 mg P kg−1) was re-adsorbed to sediment surfaces. This data also shows that the sediment microbial biomass is a significant, yet under-reported biotic stock of P in streams compared to their photic zone counterpart (i.e., periphyton). In a second experiment, fresh sediment EPC0 was measured after alleviating potential limitation of carbon (C) and nitrogen (N) for microbial growth. Sediment EPC0 did not change with C addition and decreased slightly (0.5 µg P L−1 or ~ 5% decrease) with N addition, suggesting these sediments strongly buffered DRP towards the EPC0 in spite of biotic demand. Together, these experiments suggest that sediment EPC0 was primarily abiotic in nature but that sediments may subsidize biotic P requirements through desorption. Further work is needed on whether this relation holds for streams with different substrate, geology, and nutrient inputs.

Trophic degradation predispositions and intensity in a high-flow, silted reservoir.

The objective of the work was to demonstrate the relationship between the natural environmental characteristics of a reservoir and its catchment and severity of trophic degradation. The shallow, highly-silted Rzeszów Reservoir (SE Poland) was the object of study. The impact on degradation of internal supply from accumulated bottom sediments was also assessed, using water and sediment sampled in 2013 and 2014. A high value for trophic state was identified for the reservoir on the basis of TSI indexes, while assessed natural resilience to degradation and analysis of the catchment as a supplier of biogenic and organic matter both indicate high susceptibility to cultural eutrophication. Obtained values for equilibrium phosphate concentrations under anoxic conditions (EPC-0) point to the possibility of a more intensive process of internal supply in phosphorus. However, the presence of sediments poor in organic matter suggest no major threat of ongoing eutrophication. Desludging and/or dredging are likely to entail elimination from the ecosystem of a large part of the pollutants accumulated in sediments, as well as the internal supply of phosphate to the water column. However, as external sources are responsible for the advanced degradation of Rzeszów Reservoir, any attempts at reclamation within the water will fail to yield persistent effects if appropriate protective procedures in the catchment are not implemented.

Phosphorus Forms and Release Risk of Sediments in Urban Sewage Treatment Plant Effluent and Receiving Stream Reach

From October 2018 to April 2019, the surface sediment and overlying water samples were collected every two months from the upstream and downstream of the effluent outlet of the Caitianpu sewage treatment plant in the Banqiao River, Hefei City. The effects of the sewage treatment plant effluent on both phosphorus forms and the equilibrium phosphate concentration (EPC0) in sediments were analyzed. The response of equilibrium phosphate concentration to external carbon (sodium acetate) and the release risk of phosphorus in sediments were investigated. Result show that the phosphorus pollution in Banqiao River was more severe. The average values of total phosphorus in the sediments at the upper and lower effluent outlet were 789.39 mg·kg-1 and 854.41 mg·kg-1, respectively, and the average bio-available phosphorus amounts were 157.19 mg·kg-1 and 173.37 mg·kg-1, respectively. The EPC0 values of the four sampling points decreased in the order SP1 > SP2 > SP3 > CP, indicating that the sewage treatment plant effluent increased the EPC0 level and phosphorus release risk of the stream sediments. Moreover, the addition of exogenous carbon significantly decreased the EPC0 value of the sediment, especially in SP1, suggesting that the addition of exogenous carbon decreased the risk of phosphorus release from sediments.

Some aspects of restoration of degradated sewage receivers

Bottom sediments are naturally connected with water body of the river and it is essential inpollutant balance, Natural phosphorus cycle in water environment is sedimentation cycle,Once introduced to water ecosystem can be removed by different chemical, biological andphysical processes and loses its environmental mobility as a sediment component,In studied case the contaminants load was radically reduced by construction of wastewatertreatment plant in city of Lodz, But the water quality improvement was not commensurate tothis reduction, Such situation could be the result of increased phosphorus release fromsediments deposed in the course of decades in river bed, On the distance the phosphateconcentration increases up to 25 km downstream the WWfP outlet and it can not beexplained by other pollution sources. The phosphorus content in the sediment is as high as 27 1 mg kg- dw, The equilibrium phosphate concentration (EPCo) experiment showed that itcould be released to water body, The preliminary results showed that EPCo value exceed in 3 some points limit polish water quality norm and amount to 1.2 mg PO4 dm- in oxic condition,

Effects of Exogenous Carbon Addition on Equilibrium Phosphate Concentration and Risk of Phosphorus Release from Sediments in the Shiwuli River, Chaohu Lake Basin

Five surface sediment samples were collected every two months from the Shiwuli River along an urban-rural gradient, Chaohu Lake Basin, from July 2017 to May 2018. Sediment phosphorus fractions were investigated, and equilibrium phosphate concentration (EPC0) and its response to exogenous carbon (sodium acetate) addition were explored. Moreover, the risk of phosphorus release from sediment into water column was also evaluated. Results show that the Shiwuli River was seriously polluted by phosphorus. The average values of total phosphorus content in sediments ranged from 915.04 to 1205.31 mg·kg-1, and it decreased slowly along the urban-rural gradient, while the bio-available phosphorus content remained stable. Exogenous carbon addition not only reduced the EPC0 values of sediments (about 29%), but changed the order of EPC0 values among the five sampling sites as well. In general, the ratio of overlying water SRP (soluble reactive phosphorus) concentration to EPC0 value was 66.7%, and phosphorus adsorption-desorption equilibrium saturation EPCsat<-20% accounted for about 60.0%, indicating that the surface sediments in the Shiwuli River were dominated by phosphorus adsorption, namely, keeping the phosphorus "sink" state. The inputs of exogenous carbon addition increased the proportion of EPCsat<-20% from 60.0% to 73.3%, which lowered the risk of phosphorus release from sediments.

The error in stream sediment phosphorus fractionation and sorption properties effected by drying pretreatments

Stream sediment can control phosphorus (P) in the water column at baseflow. Two common laboratory analyses of sediment P are the equilibrium phosphate concentration at net zero sorption (EPC0) and P fractionation. Good sample handling ensures representative results, but oftentimes, studies rely on air-dried or freeze-dried samples, which alters sediment biogeochemistry. How and to what extent this influences EPC0 and P fractionation remains unclear. We therefore examine pretreatment effects on sediment EPC0 and P fractionation. We collected fine sediments (< 2 mm) from streams in the Tukituki River and Reporoa Basins in New Zealand (n = 31 sediments). Subsamples were then either kept fresh, frozen then lyophilized (freeze-dried), or dried at 40 °C for 2 weeks (air-dried). Measurements of EPC0 and P fractionation were made in triplicate. The sequential P fractionation scheme determined five different P pools: NH4Cl (labile P), NaOH reactive P (RP; metal oxide-bound P) and unreactive P (URP; organic P), HCl (Ca-mineral P), and residual P. Along with statistical comparisons between fresh results and the two pre-treatments, we explored correlations between pre-treatment effects and sediment physicochemical characteristics. The sediments had generally low EPC0 (majority < 0.020 mg P L−1), and uncertainty in EPC0 increased with concentration magnitude. While there were sediment-specific changes in EPC0 with pre-treatment, there was no consistent bias caused by pre-treatment. However, the differences between the fresh and air-dried sediment EPC0 were larger and more variable than between fresh and freeze-dried sediment. For P fractionation, the Tukituki sediments were enriched in HCl-P, while Reporoa sediments had more NaOH-RP and NaOH-URP. Despite large sediment-specific changes, the overall effects of freeze- and air-drying sediment were increased NH4Cl-P (estimated average effect, $$ \widehat{\theta} $$ = + 0.63 and + 3.7 mg P kg−1), no significant changes for NaOH-RP, contrasting changes in NaOH-URP (− 3.4 and + 3.3 mg P kg−1), and decreased HCl-P (− 40 and − 33 mg P kg−1). We found that drying sediment significantly influenced EPC0 and P fractions (especially the NH4Cl-P fraction). Air-drying was particularly error-prone and should be avoided. The use of freeze-drying to preserve samples for later analyses and improve ease of handling may be used with appropriate consideration of the research objectives and the error introduced by freeze-drying. However, we recommend using fresh sediments for analyses whenever possible, as they best represent natural conditions.

Understanding the controls on sediment-P interactions and dynamics along a non-tidal river system in a rural–urban catchment: The River Nene

The release of Phosphorus (P) from river sediments has been identified as a contributing factor to waters failing the criteria for ‘Good Ecological Status’ under the EU Water Framework Directive (WFD). To identify the contribution of sediment-P to river systems, an understanding of the factors that influence its distribution within the entire non-tidal system is required. Thus the aims of this work were to examine the (i) total (PTotal) and labile (PLabile) concentrations in sediment, (ii) the sequestration processes and (iii) the interactions between sediment P and the river water in the six non-tidal water bodies of the River Nene, U.K. Collection of sediments followed a long period of flooding and high stream flow. In each water body, five cores were extracted and homogenised for analysis with an additional core being taken and sampled by depth increments. Comparing the distribution of sediment particle size and PTotal data with soil catchment geochemical survey data, large increases in PTotal were identified in sediments from water body 4–6, where median concentrations of PTotal in the sediment (3603 mg kg−1) were up to double those of the catchment soils. A large proportion of this increase may be related to in-stream sorption of P, particularly from sewage treatment facilities where the catchment becomes more urbanised after water body 3. A linear correlation (r = 0.8) between soluble reactive phosphate (SRP) and Boron in the sampled river waters was found suggesting increased STW input in water bodies 4–6.PLabile concentrations in homogenised cores were up to 100 mg kg−1 PO4–P (generally < 2% of PTotal) and showed a general increase with distance from the headwaters. A general increase in Equilibrium Phosphate Concentrations (EPC0) from an average of 0.9–∼1.7 μm L−1 was found between water bodies 1–3 and 4–6. Fixation within oxalate extractable phases (Al, Fe and Mn) accounted for ∼90% of P binding in water bodies 4–6, but only between 31 and 74% in water bodies 1–3. Statistical models predicting PTotal (R2 = 0.78), oxalate extractable P (R2 = 0.78) and Olsen P (R2 = 0.73) concentrations in river sediments identified Mn oxy-hydroxides (MnOx) as a strong predictive variable along with the location within the river system. It is suggested that MnOx within model predictions is identifying a pool of mixed Fe–Mn oxy-hydroxides (MnOx–FeOOH) or Fe oxy-hydroxide (FeOOH) from the wider FeOxalate pool that are particularly effective at sorbing and fixing P. The findings demonstrate how sediment and P may accumulate along a 100 km non-tidal river system, the extent to which a range of processes can fix P within mineral phases and how natural flooding processes may flush sediment from the river channel. The processes identified in this study are likely to be applicable to similar river systems over their non-tidal water bodies in eastern England.

Phosphorus adsorption and release characteristics of surface sediments in Dianchi Lake, China

Phosphorus adsorption and release characteristics of surface sediments from Dianchi Lake were investigated through indoor simulation experiments. Kinetics and thermodynamics of adsorption and release of phosphorus in sediments were studied, and the influence of different phosphorus fractions on adsorption and release was analysed. Results show that the total phosphorus content in the sediments ranged from 843.96 to 8144.44 mg kg−1, which was 2–8 times as much as those in other lakes in China (e.g. Erhai Lake and Taihu Lake). The average values of different phosphorus forms in the sediment samples were ranked in the order of organic P (OP), calcium-bound P (Ca-P), metal oxide-bound P (Al-P), residual P (Res-P), Fe-bound P (Fe-P) and weakly absorbed P(NH4Cl-P). Compared with the case of other lakes in China, the sedimentary phosphorus adsorption capacity of Dianchi Lake was at a higher level, but its maximal release rate and release capacity were low, indicating a relatively low release risk. By comparing the equilibrium phosphate concentration in the sediments and the soluble reactive phosphorus in the overlying water, the risks of phosphorus release from sediments in Caohai, Lake Central and Southern Waihai were found to be relatively low in the short term, but were high in Northern Waihai. The release behaviour of sedimentary phosphorus in Dianchi Lake was mainly determined by NH4Cl-P, Fe-P and Al-P, among which NH4Cl-P and Fe-P served a greater function. Therefore, the contents of different fractions of phosphorus and their distribution characterization should be considered when characterizing the adsorption and release status of lake sedimentary phosphorus.

Particulate phosphorus speciation and phosphate adsorption characteristics associated with sediment grain size

Phosphorus (P) speciation in size-fractionated sediments was studied, and the phosphate adsorption characteristics associated with grain size were investigated in the laboratory. Detrital P (De-P) was the most abundant form and had the highest proportion of total P (TP), followed by organic P (Or-P). Bioavailable P (BAP) was much more concentrated in fine sediments than sandy sediments, which meant that fine sediments played a dominant role in P transfer from sediments to overlying water and/or ambient pore water. Native adsorbed phosphorus (NAP) was close to the exchangeable P (Ex-P) concentrations in sediments. The adsorption capacity was 116.0, 84.8, 73.6 and 50.0μgg−1 for fine silt, medium silt, coarse silt and sand, respectively. The zero equilibrium phosphate concentration (EPC0) values obtained from the adsorption isotherms of size-fractionated sediments from the same sampling site were very close in value (55.0, 54.9, 51.7 and 49.0μgL−1 for fine silt, medium silt, coarse silt and sand, respectively), revealing a potential method for predicting the phosphate concentrations of overlying water and/or ambient pore water, which were also considered to be the equilibrium concentrations of phosphate through long-term adsorption and desorption processes by sediments. The adsorption capacity, adsorption rate and NAP were all largely controlled by sediment grain size. Based on our data, the maximum total phosphate adsorption amount (TQmax) of fine sediments (<32μm) was almost six times as large as that of sediments larger than 32μm. Due to the much higher phosphate adsorption capacity of fine sediments, compared to the sandy sediments, the mud belt in the East China Sea (ECS) inner shelf should play a key role in controlling the phosphate concentration in the overlying water and/or ambient pore water and may act as an efficient “trapper” for the overloaded phosphate discharged by the Changjiang, greatly reducing the risk of eutrophication on the outer shelf of the ECS.

Phosphorus sorption and buffering mechanisms in suspended sediments from the Yangtze Estuary and Hangzhou Bay, China

Abstract. The adsorption isotherm and the mechanism of the buffering effect are important controls on phosphorus (P) behaviors in estuaries and are important for estimating phosphate concentrations in aquatic environments. In this paper, we derive phosphate adsorption isotherms in order to investigate sediment adsorption and buffering capacity for phosphorus discharged from sewage outfalls in the Yangtze Estuary and Hangzhou Bay near Shanghai, China. Experiments were also carried out at different temperatures in order to explore the buffering effects for phosphate. The results show that P sorption in sediments with low fine particle fractions was best described using exponential equations. Some P interactions between water and sediment may be caused by the precipitation of CaHPO4 from Ca2&amp;amp;plus; and HPO42− when the phosphate concentration in the liquid phase is high. Results from the buffering experiments suggest that the Zero Equilibrium Phosphate Concentrations (EPC0) vary from 0.014 mg L−1 to 0.061 mg L−1, which are consistent with measured phosphate concentrations in water samples collected at the same time as sediment sampling. Values of EPC0 and linear sorption coefficients (K) in sediments with high fine particle and organic matter contents are relatively high, which implies that they have high buffering capacity. Both EPC0 and K increase with increasing temperature, indicating a higher P buffering capacity at high temperatures.

Zeolite (Na) modified by nano-Fe particles adsorbing phosphate in rainwater runoff

Zeolite (Na) modified by self-synthesized nano-Fe particles was used as infiltration media to adsorb phosphate in rainwater runoff. The adsorption capacities increased up to 75 times that of natural zeolite at a saturated equilibrium phosphate concentration of 0.42 mg/L. The correlation of capacity and material-specific surface area indicated that specific surface area was not the key factor contributing to the capacity improvement. SEM and XRD analysis showed that chemical reaction between Fe and P to form new products like cacoxenite is the main reason for the increased capacity, and that the method of adding metal ions or particles to improve the adsorption capacity for phosphate is feasible.

Phosphate uptake by TiO2: Batch studies and NMR spectroscopic evidence for multisite adsorption

Systematic studies, combining batch experiments with NMR spectroscopic methods, are carried out for phosphate sorption on titanium dioxide (TiO2). It is found that phosphate sorption on TiO2 decreases with increasing pH, whereas the phosphate uptake by TiO2 increases with increasing ionic strength of the solution. In I⩽0.1M, the sorption sharply increases and reaches a near maximum and then followed by little changes showing Langmuir-type behavior, whereas in I=0.7M, non-Langmuirian uptake becomes evident as equilibrium phosphate concentrations increase in solution. The sorption of phosphate on TiO2 is rapid and mostly irreversible at pH 4.5 and 7.0. At pH 9.0, however, the phosphate sorption is initially reversible and followed by resorption of phosphate on TiO2 at the system re-equilibration. 31P{1H} cross-polarization and magic angle spinning (CP/MAS) NMR spectra contain at least four main peaks which appear similar in position and width under all adsorption conditions, but vary in intensity with surface loading. The spectral characteristics of these peaks, including cross-polarization dynamics and chemical shift anisotropy obtained from spinning sideband analysis, suggest that they arise from distinct inner-sphere adsorption complexes, most of which are protonated. These results indicate that uptake of phosphate by TiO2 occurs by formation of several types of surface complexes.

Effect of Temperature and Salinity on Phosphate Sorption on Marine Sediments

Our previous studies on the phosphate sorption on sediments in Florida Bay at 25 °C in salinity 36 seawater revealed that the sorption capacity varies considerably within the bay but can be attributed to the content of sedimentary P and Fe. It is known that both temperature and salinity influence the sorption process and their natural variations are the greatest in estuaries. To provide useful sorption parameters for modeling phosphate cycle in Florida Bay, a systematic study was carried out to quantify the effects of salinity and temperature on phosphate sorption on sediments. For a given sample, the zero equilibrium phosphate concentration and the distribution coefficient were measured over a range of salinity (2-72) and temperature (15-35 °C) conditions. Such a suite of experiments with combinations of different temperature and salinity were performed for 14 selected stations that cover a range of sediment characteristics and geographic locations of the bay. Phosphate sorption was found to increase with increasing temperature or decreasing salinity and their effects depended upon sediment's exchangeable P content. This study provided the first estimate of the phosphate sorption parameters as a function of salinity and temperature in marine sediments. Incorporation of these parameters in water quality models will enable them to predict the effect of increasing freshwater input, as proposed by the Comprehensive Everglades Restoration Plan, on the seasonal cycle of phosphate in Florida Bay.

Distribution of bioavailable phosphorus between overlying water and SPM under abrupt expansion condition

Experiments on Phosphorus (P) fraction characteristics in sediment resuspension were performed under adequate hydrodynamic conditions. It is found that the concentration of Suspended Particulate Matter (SPM) in the eddy current region exhibits the “Matthew effect”. Velocity is an impact factor of the Equilibrium Phosphate Concentration (EPC), which is related to other hydraulic conditions. Overall bioavailable dissolved P in the SPM causes migration to overlying water and sediment, eventually being converted into a chemical speciation of P. Conditions of resuspension promote Al-P of SPM that migrated to the sediment and water. Concentrations of Al-P in SPM are reduced. P is released from SPM to water bodies, mainly through conversion into particulate P and dissolved total P. Meanwhile, exchange between SPM and sediments occur mainly through Ca-P migration. Al-P and BD-P possess similar geochemical characteristics or source. Ca-P and Al-P exhibit a negative correlation between migration and conversion.

Phosphorus release potential and pollution characteristics of sediment in downstream Nansi Lake, China

The research aimed to evaluate present and potential phosphorous pollution due to high sedimentary phosphorus load and release from sediment, when external phosphorus was reduced in downstream Nansi Lake. Pollution load of the sediment and overlying water was investigated. Kinetics and isotherms of adsorption/release of sedimentary phosphorus were studied to determine equilibrium phosphate concentration (EPC0) and release potential. Kinetics of phosphorus adsorption on sediment and release from sediment were well described by both the pseudo-first-order rate equation and the pseudo-second-order rate equation, but more appropriate to the pseudo-second-order rate equation with the adsorption/release capacity more close to the measured values, suggesting that the processes were chemically rate controlled and dependent on adsorption capacity. Soluble reactive phosphorus (SRP) sorption isotherms on sediment were best fitted by the modified Langmuir model indicating a monolayer adsorption. By comparing EPC0 and SRP of water, the status (adsorption, releasing or in equilibrium) of sediment phosphorus could be determined. The sediments at site S1, S3, S4, S5, and S7 where the EPC0s were greater than the SRPs, had a potential to release phosphorus into the water column. However, those sediments at S9, S10, and S12, where the EPC0s were approximately equal to the SRPs, were in impermanent equilibrium with overlying water in status of phosphorus, the sediments can be likely to release phosphorus to the water column once the equilibrium was broken. Therefore, sedimentary phosphorus can be a secondary pollution source in downstream Nansi Lake.