Mechanism Of Phosphate Removal Research Articles

Utilisation of waste material for environmental applications: calcination of mussel shells for waste water treatment

Waste mussel shells from the New Zealand aquaculture industry have been investigated as a potential source of lime for use in waste water treatment. The calcination of raw mussel shells to lime was studied as a function of particle size, temperature, heating rate, treatment time and atmosphere. Lime formation went through a maximum with respect to particle size for all heating conditions, as a result of competition between increased surface area and a tendency for particle to form necks resulting in caking. Optimised heat treatment conditions resulted in transformations of more than 95%. Preliminary experiments to investigate removal of phosphates from model waste water solutions showed that raw shells had limited ability due to a mechanism that relies on adsorption only. For these raw materials the finer particle sizes removed more phosphate due to increased surface area. The heat treated mussel shells on the other hand were shown to remove greater than 95% of the phosphates for both fine and coarse size ranges due to a precipitation mechanism of phosphate removal. This work demonstrates the potential for using mussels as an alternative to limestone for phosphate removal, at the same time overcoming the expensive and problematic issues of waste disposal.

Pyrolysed powdered mussel shells for eutrophication control: effect of particle size and powder concentration on the mechanism and extent of phosphate removal

AbstractThe international shellfish farming industry has a growing problem with respect to sustainability: the shells, a by‐product, are currently being mostly wasted to landfill. Instead, this calcium‐rich resource can be used to produce lime [calcium oxide (CaO)] and then used to remove phosphate from rural wastewaters. Powdered mussel shell was heat treated to form lime. Two different shell particle sizes (fine, 53–106 µm; coarse, 212–250 µm) as well as various pyrolysis times, heating rates, pyrolysis temperatures and shell concentrations were used to determine the effects of these parameters on the lime formation and subsequent phosphate removal from a synthetic wastewater. Furthermore, the mechanisms of phosphate removal were determined by quantifying the phosphate content in all components before and after reaction with the synthetic wastewater. It was found that with excess of partially calcined pyrolysed shells, at a concentration of 5 g l−1, more than 95% phosphate removal was achieved, irrespective of particle size or pyrolysis conditions. When using optimally heat‐treated shells (particle size: 53–106 µm, pyrolysed for 1 h at 750 °C), it was possible to achieve over 90% phosphate removal using just 196 mg l−1 of shell. For the pyrolysed shells, the main mechanisms of phosphate removal were homogeneous nucleation to form a suspended precipitate, as well as adsorption and heterogeneous precipitation on the surface of the remaining calcite shell particles. Copyright © 2010 Curtin University of Technology and John Wiley & Sons, Ltd.

Study on the phosphate removal from aqueous solution using modified fly ash

In this work the fly ash was modified by sulfuric acid for the removal of phosphate. It was found that modification of fly ash could significantly enhance the phosphate immobilization ability of the fly ash. The specific surface area of the fly ash increased from 8.8 to 32.5 m 2/g after treated with sulfuric acid. The modification of the fly ash also resulted in the mobilization of acid-soluble metal ions due to partial or complete dissolution of the metals under the acidic conditions. Both adsorption and precipitation contributed to the removal of phosphate by the modified fly ash but precipitation was a major mechanism of phosphate removal. The experimental results showed that adsorption of phosphate by the modified fly ash was rapid, the removal percentage of phosphate could reach maximum in 5 min. In the range of 5–9, pH did not significantly affect the removal of phosphate and the removal percentage of phosphate increased with the increase of adsorbent dosage. The adsorption of phosphate by the modified fly ash could be described well by Langmuir isotherm equation, the Langmuir constant Q 0 was 9.15 mg g −1. The XRD patterns and the SEM images of modified fly ash after sorption revealed that CaHPO 4·2H 2O was formed in the removal of phosphate. In addition, phosphate also formed precipitate with aluminum and iron.

In Situ Microscale Analyses of Activated Sludge Flocs in the Enhanced Biological Phosphate Removal Process by the Use of Microelectrodes and Fluorescent In Situ Hybridization

Phosphate concentration microprofiles were measured within activated sludge flocs in the enhanced biological phosphate removal EBPR process, and a fluorescent in situ hybridization and clone library analysis were conducted to indentify polyphosphate accumulating organisms PAOs. The center of the flocs had the highest phosphate concentrations, and the stratification of the flocs found by microprofiling indicated that the PAOs were probably distributed evenly throughout the flocs. Under the assumption that the phosphate, which was generated because of phosphate release by microbial activity, was not consumed by microbes and was only transferred from the flocs to the bulk by diffusion during anaerobic conditions, the effective diffusion coefficient Df for phosphate release within the flocs was calculated to be 3.3310 7 cm 2 /s at the end of the anaerobic phase of the EBPR process. These results provide a better under- standing of the phosphate removal mechanism, and this understanding of the internal function of flocs can lead to improvement in the modeling, design, and operation of the biological phosphorus removal process.

Phosphate removal in marine electrolytes by zeolite synthesized from coal fly ash

The aim of this study was to examine the influence of seawater electrolytes on removal of phosphate by zeolite synthesized from fly ash (ZFA). A low-calcium ZFA was initially saturated with Na +, Mg 2+, Ca 2+, Al 3+, and Fe 3+. Al- and Fe-ZFA showed nearly complete removal of phosphate regardless of the major seawater electrolytes, pH, and salinity. This result was explained primarily on the basis of the adsorption mechanism through the formation of inner-sphere complexes. The remaining ZFAs showed lower phosphate removal performance, in general with the order of Ca-ZFA > Mg-ZFA > Na-ZFA. Compared with pure water, increase of electrolyte concentration or salinity initially enhanced phosphate uptake but then reduced phosphate removal. The individual presence of major seawater electrolytes all facilitated the retention of phosphate, with CaCl 2 being the most effective. The mechanism for phosphate removal by Na-, Mg-, and Ca-ZFA was due mostly to precipitation. Repeated batch equilibration experiments indicated that, compared with pure water, ZFA had greater sorptive capacity for phosphate (except for Ca-ZFA, whose capacity decreased slightly) and had lower reversibility for sorbed phosphate in marine electrolytes. In conclusion, our results suggest that presence of seawater electrolytes had roughly no effect, or even positive effects, on the removal of phosphate by ZFA.

Characteristics and mechanisms of phosphate adsorption onto basic oxygen furnace slag

The adsorption characteristics of phosphate adsorption on the basic oxygen furnace (BOF) slag were identified as a function of pH and ion strengths in solution. In addition, adsorption mechanisms were investigated by conducting batch tests on both the hydrolysis and phosphate adsorption process of the BOF slag, and making a comparative analysis to gain newer insights into understanding the adsorption process. Results show that the adsorption capacity from 4.97 to 3.71 mg P/g slag when the solution pH was increased from 2.0 to 13.0 and phosphate initial concentration was 50 mg/L, indicating that adsorption capacity is largely dependent upon the pH of the system. The results of the competitive adsorption between phosphate and typical anions found in wastewater, such as NO 3 −, SO 4 2− and Cl −, onto BOF slag reveal that BOF slag can selectively adsorb phosphate ions. The insignificant effect of NO 3 −, SO 4 2− and Cl − on phosphate adsorption capacity indicates that phosphate adsorption is through a kind of inner-sphere complex reaction. During the adsorption process, the decrease of phosphate concentration in solution accompanied with an increase in pH values and concentrations of NO 3 −, SO 4 2− and Cl − suggests that phosphate replaced the functional groups from the surface of BOF slag which infers that ligand exchange is the dominating mechanism for phosphate removal. At the same time, the simultaneous decreases in PO 4 3− and total calcium, magnesium and aluminum concentration in solution indicate that chemical reaction and precipitation are other mechanisms of phosphate removal.

Chemical modification of coal fly ash for the removal of phosphate from aqueous solution

This study investigated the chemical modifications of coal fly ash treated with HCl and NaOH. Sorption behavior of phosphate from water solution on treated fly ash was examined. Results showed that the HCl-treated fly ash (TFA-HCl) had a greater specific surface area (SSA) than the NaOH-treated fly ash (TFA-NaOH) and untreated fly ash (FA). The XRF, XRD patterns, and SEM images revealed the decreased CaO content in the TFA-HCl and observed the presence of NaP1 and sodalite zeolites in the TFA-NaOH. The P sorption capacity of all studied fly ashes increased with increasing initial P concentration and mechanisms of P sorption were influenced by the equilibrium pH. Maximum phosphate immobilization capacity obtained from Langmuir model was in the following manner, TFA-NaOH > FA > TFA-HCl (57.14, 23.20, and 6.90 mg P g −1, respectively). The decreased CaO content and acidic pH in the TFA-HCl were responsible for the lowest capacity of phosphate immobilization, because of unfavorable condition for calcium phosphate precipitation. In contrast, due to alkaline condition and relatively high calcium content, the precipitation of calcium phosphate was a key mechanism for phosphate removal in the FA and TFA-NaOH. The TFA-NaOH had a greatest phosphate immobilization, due to high CaO content and an increased SSA after the conversion of fly ash to zeolite. Both Langmuir and Freundlich models were good fitted for the TFA-NaOH, while was only Langmuir model for the FA and Freundlich model for the TFA-HCl. Results suggested that treating fly ash with alkaline solution was a promising way to enhance phosphate immobilization.

Phosphate biosorption characteristics of a submerged macrophyte Hydrilla verticillata

Phosphate biosorption of Hydrilla verticillata was investigated and compared with its bioaccumulation characteristics. Results obtained from the biosorption isotherms and kinetics showed that maximal phosphate biosorption was 286 mg kg −1, approximately equal to 6–9% of the phosphate bioaccumulation. The biosorption mainly occurred within 5 h, and was highest during the first 30 min. The initial phosphate concentration was an important factor affecting the biosorption process. Phosphate biosorption on H. verticillata was not the main phosphate removal mechanism in our experiments, but it cannot be ignored.

Mechanisms of phosphate removal from aqueous solution by blast furnace slag and steel furnace slag

We report the adsorption of phosphate and discuss the mechanisms of phosphate removal from aqueous solution by burst furnace slag (BFS) and steel furnace slag (SFS). The results show that the adsorption of phosphate on the slag was rapid and the majority of adsorption was completed in 5∼10 min. The adsorption capacity of phosphate by the slag was reduced dramatically by acid treatment. The relative contribution of adsorption to the total removal of phosphate was 26%∼28%. Phosphate adsorption on BFS and SFS follows the Freundlich isotherm, with the related constants of k 6.372 and 1/n 1.739 for BFS, and of k 1.705 and 1/n 1.718 for SFS. The pH and Ca2+ concentration were decreased with the addition of phosphate, suggesting the formation of calcium phosphate precipitation. At pH 2.93 and 6.93, phosphate was desorbed by about 36%∼43% and 9%∼11%, respectively. These results indicate that the P adsorption on the slag is not completely reversible and that the bond between the slag particles and adsorbed phosphate is strong. The X-ray diffraction (XRD) patterns of BFS and SFS before and after phosphate adsorption verify the formation of phosphate salts (CaHPO4·2H2O) after adsorption process. We conclude that the removal of phosphate by BFS and SFS is related to the formation of phosphate calcium precipitation and the adsorption on hydroxylated oxides. The results show that BFS and SFS removed phosphate nearly 100%, indicating they are promising adsorbents for the phosphate removal in wastewater treatment and pollution control.

Phosphate removal using sludge from fuller's earth production

This study assesses the phosphate removal capacity and mechanism of precipitation or adsorption from aqueous solutions in batch experiments by an industrial sludge containing gypsum (CaSO 4·2H 2O) obtained as a by-product from a fuller's earth process. The potential capacity for phosphate removal was tested using various solution concentrations, pH values, reaction times, and amount of sludge. The maximum phosphate adsorption capacity calculated using the Langmuir equation was 2.0 g kg −1. The pH for the maximum adsorption by the sludge was neutral to alkaline (pH 7–12). Over 99% of phosphate was removed from a phosphate solution of 30 mg L −1 using 0.15 g of sludge in a 9-h reaction. Sulfate (SO 4 2−) concentration increased with increasing initial phosphate concentration, possibly because of dissolution of gypsum and adsorption of both sulfate and phosphate. At high phosphate concentration (>1000 mg L −1), relative constant concentration of Ca 2+ was not consistent with adsorption of the most important phosphate removal mechanism. Results suggest that precipitation of calcium phosphate is principally responsible for phosphate removal under its high concentration. Agglomerated precipitate in the reaction sludge was observed by SEM and identified as brushite (CaHPO 4·2H 2O) by XRD, FT-IR, and DTA. Based on thermodynamic considerations, it is suggested that the brushite will readily transform to more stable phases, such as hydroxyapatite (Ca 5(PO 4) 3·OH).

Assessing the geochemical reactivity of inorganic phosphorus along estuaries by means of laboratory simulation experiments

AbstractPhosphate behaviour in natural estuarine systems can be studied by performing field measurements and by undertaking laboratory simulation experiments. Thus, in this paper we describe the use of a dynamic automated estuarine simulator to characterize the geochemical reactivity of phosphate in varying salinity gradients in order to study possible mechanisms of phosphate removal from the dissolved phase (e.g. formation of some kind of apatite) and how changes in pH and salinity values influence this removal. Six laboratory assays, representing various salinity and pH gradients (average pH values between 7 and 8), were carried out. The geochemical equilibrium model MINTEQA2 was employed to characterize removal of phosphate. Among the minerals from which dissolved phosphate can originate, it seems that hydroxyapatite is by far the mineral that shows the greatest saturation indexes in the experiments. Thus, there is evidence that a type of calcium phosphate (hydroxyapatite) is involved in phosphate removal in the assays. Phosphate removal by Ca2+ occurs sharply at salinity values of 1–2, whereas by Fe3+ it is relatively gradual, at least until a salinity value of 7. Copyright © 2006 John Wiley & Sons, Ltd.

Characteristics and mechanisms of phosphate adsorption on dewatered alum sludge

The adsorption characteristics of phosphate adsorption on the dewatered alum sludge were identified as a function of pH and ion strengths in solution. In addition, adsorption mechanisms were investigated by conducting batch tests on both the hydrolysis and P-adsorption process of the alum sludge, and making a comparative analysis to gain newer insights into understanding the adsorption process. Results show that the adsorption capacity decreased from 3.5 to 0.7 mg P/g sludge when the solution pH was increased from 4.3 to 9.0, indicating that adsorption capacity is largely dependent upon the pH of the system. The results of the competitive adsorption between phosphate and typical anions found in wastewater, such as SO 4 2− and Cl −, onto alum sludge reveal that alum sludge can selectively adsorb phosphate ions. The insignificant effect of SO 4 2− and Cl − on P-adsorption capacity indicates that phosphate adsorption is through a kind of inner-sphere complex reaction. During the adsorption process, the decrease of phosphate concentration in solution accompanied with an increase in pH values and concentrations of SO 4 2−, Cl − and TOC (total organic carbon) suggests that phosphate replaced the functional groups from the surface of alum sludge which infers that ligand exchange is the dominating mechanism for phosphate removal. At the same time, the simultaneous decreases in PO 4 3− and total aluminium concentration in solution indicate that chemical reaction and precipitation are other mechanisms of phosphate removal.

Removal of phosphate species from solution by adsorption onto calcite used as natural adsorbent

Phosphates are very important basic materials in agricultural and other industrial applications. Phosphorus is often present in low concentrations in wastewater, almost solely in the form of organic and inorganic phosphates (ortho- and poly-phosphates). The removal of phosphates from surface waters is generally necessary to avoid problems, such as eutrophication, particularly near urban areas. The usual methods of treatment are either biological or physicochemical by sedimentation. This paper studies the removal of phosphate species by adsorption onto calcite used as natural adsorbent. The phosphate solutions were prepared artificially by adding certain quantities of K 2HPO 4 in water. The effect of equilibrium pH, phosphate/mineral ratio and contact time was studied. The results showed that pH plays an important role in the removal of phosphate species from solution, with removal being more efficient in the basic pH region. The experimental results also show that adsorption is also efficient for high ratios phosphate/adsorbent. Finally, the adsorption process is time dependant. Based on the experimental results a possible mechanism of phosphate removal onto calcite surface is proposed. As a general conclusion, phosphate species seem to be efficiently removed from solutions using calcite as natural adsorbent. In addition, the adsorption product can be used as fertilizer for acid soils.

Fundamental Mechanisms of Phosphate Removal by Anaerobic/Aerobic Activated Sludge in Treating Municipal Wastewater

Acetate is thought to be an important substrate for phosphate removal in anaerobic/aerobic activated sludge (AS) processes. The acetate content in municipal wastewater is low, and the main organic compounds in such wastewater are particulate organic matters (POMs) that are converted to endogenous substrates in AS processes when municipal wastewater is introduced into AS reactors. The question which then arises is which substrate, acetate or POM, is important for phosphate removal in full-scale AS plants. The rates of phosphate release and substrate uptake were determined using AS harvested from a full-scale anaerobic/aerobic AS plant and also AS acclimated to peptone under alternate anaerobic and aerobic conditions for 26 months. The rate of phosphate release upon POM addition per AS concentration per unit of time was about 0.84 mg PO 4 -P/(g MLSS·h) irrespective of the wastewater quality. This value was about 0.05 in the case of AS acclimated to peptone for 26 months. When the AS concentration is 2.5 g/L and the mixed liquor retention time is 2 h in the anaerobic zone, about 4.2 mg/L PO 4 -P is released upon POM addition. Hence, phosphate can be removed from municipal wastewater using full-scale AS plants running under these conditions.

Sorption of phosphate from solid/liquid interface by fly ash

In this study, fly ash was used to remove phosphate from aqueous solutions. The influence of suspension pH (3, 8 and 11.5), temperature (20, 30 and 40 °C), agitation rate (150, 200 and 250 rpm) and fly ash dosage on phosphate removal was investigated by conducting a series of batch sorption experiments. In addition, the mechanisms of phosphate removal were explained on the basis of the results of X-ray spectroscopy. The maximum phosphate sorption capacity of the fly ash was defined as 71.87 (mg/g). In this study, phosphate removal efficiency in excess of 99% was obtained. As the result of this study, it was thought that the removal of phosphate from solid/liquid interface by fly ash predominantly took place by precipitation mechanism, ion exchange and weak physical interactions between the surface of sorbent and the metallic salts of phosphate.

Removal of phosphate from aqueous solution with blast furnace slag

Blast furnace slag was used to remove phosphate from aqueous solutions. The influence of pH, temperature, agitation rate, and blast furnace slag dosage on phosphate removal was investigated by conducting a series of batch adsorption experiments. In addition, the yield and mechanisms of phosphate removal were explained on the basis of the results of X-ray spectroscopy, measurements of zeta potential of particles, specific surface area, and images of scanning electron microscopy (SEM) of the particles before and after adsorption. The specific surface area of the blast furnace slag was 0.4 m 2 g −1. The removal of phosphate predominantly has taken place by a precipitation mechanism and weak physical interactions between the surface of adsorbent and the metallic salts of phosphate. In this study, phosphate removal in excess of 99% was obtained, and it was concluded that blast furnace slag is an efficient adsorbent for the removal of phosphate from solution.

Removal of phosphate from wastewaters

Gas concrete waste was used to remove phosphate from aqueous solutions in this study. The influence of suspension pH, temperature, mixing rate, and gas concrete dosage on phosphate removal was investigated by conducting a series of batch adsorption experiments. In addition, the yield and mechanisms of phosphate removal were explained on the basis of the results of X-ray spectroscopy, measurements of zeta potential of particles, both values of BET–N 2 specific surface area, and images of scanning electron microscopy (SEM) of the particles before and after adsorption. In this study, phosphate removal in excess of 99% was obtained and it was concluded that wastes of gas concrete are an efficient adsorbent for the removal of phosphate. The removal of phosphate predominantly takes place by precipitation mechanism and the weak physical interactions between the surface of adsorbent and the metallic salts of phosphate.

Removal of phosphate by seafood processing wasted sludge

There is a need for developing low cost, easily and abundantly available, yet efficient, adsorbents for the removal of phosphates during the tertiary treatment of wastewater. The wasted sludge from a cuttlefish processing factory prepared on a laboratory scale has been used to evaluate its performance for phosphate adsorption. The material has been shown to be a good alternative adsorbent. As much as 90% phosphate removal by the prepared sludge is possible in about 20 h under the test conditions. Phosphate removal is seen to increase with decreasing adsorbent particle size, increasing the relative concentration of phosphate to sludge and increasing adsorbent dose. Models for predicting phosphate removal incorporate operational variables such as the ratio of phosphate to wasted material and adsorbent dose. These models also manifest high values of the correlation coefficients. Calcium phosphate precipitation in the present experimental system is not a significant phosphate removal mechanism.

Removal of phosphate by layered double hydroxides containing iron

Iron-based layered double hydroxides (Ma2+Feb3+(OH)2(a+b)CO3b/22−mH2O) were synthesized. Removal of phosphate by the compounds was studied from the viewpoint of buffering pH effect of the compounds and buffering capacity of solution. The compounds released metal cations (Mg2+, Ca2+, Fe3+) and/or their hydroxides responding to various water environments due to their buffering pH function. The released cations and/or hydroxides worked effectively as coagulants for the phosphate removal. The removal of phosphate depended on the buffering capacity of the solution that is the function of the solution pH and the concentration of phosphate. The removal of phosphate from the solution with small buffering capacity followed a Langmuir-type isotherm. The removal of phosphate from the solution with larger buffering capacity was largely increased. The removal of phosphate by the compounds was analyzed based on the model describing the buffering pH effect of the compounds from which the amount of released cations (CB) can be determined. The removal was well correlated with the amount of dissolution of the compounds, CB. The mechanism of phosphate removal was examined based on the removal efficiency (mol of removed phosphate/mol of released alkali). The efficiencies showed below one in the solution with large buffering capacity and above one in the solution with small buffering capacity. The efficiency below one showed the removal of phosphate through coagulation by the released metal cations and hydroxides. The successful removal of dilute phosphate (0.2mg P/l) from the drain water was also demonstrated.

The effect of media on evaluating the phosphate uptake capacity of activated sludge bacterial isolates

Since the identification of Acinetobacter calcoaceticus as the primary agent responsible for biological phosphorus removal, much research has been conducted to either confirm or refute this claim. The majority of these studies was conducted under defined laboratory conditions using various artificial media; as a result, many conflicting reports exist regarding the role of A. calcoaceticus and other activated sludge isolates in their possible roles as true polyphosphate-accumulating bacteria. This study was therefore conducted to determine the effect of media type on biological phosphate removal when performed in the laboratory under defined conditions. Five isolates were obtained from a full-scale biological nutrient removal activated sludge system and a previously identified A. calcoaceticus isolate was inoculated into three different media types. The inoculated media were subjected to anaerobic and aerobic conditions to stimulate the phosphate removal mechanism. The test micro-organisms released phosphate, under anaerobic conditions, in the three test media. Synthetic wastewater was found to promote the release of higher concentrations of phosphate by the micro-organisms than in the other two media. During the aerobic phase, phosphate uptake was highest in synthetic wastewater and settled sewage. Due to inconsistencies obtained in the readily biodegradable chemical oxygen demand, total chemical oxygen demand and soluble oxygen demand tests, it was concluded that the medium formulation may skew qualitative or quantitative data regarding biological phosphate removal. It can be concluded that the media used for P uptake studies are of importance as it was observed that the organisms' removal/uptake capabilities were enhanced or reduced depending on the media used.