Phosphate Adsorption Isotherms Research Articles

Development of rare earth element doped magnetic biochars with enhanced phosphate adsorption performance

To improve the biochar’s adsorption performance towards phosphate as well as to endow the biochar with magnetic property, novel rare earth element doped magnetic biochars, Ce/Fe3O4-BC and La/Fe3O4-BC, were prepared by separately co-precipitating cerium (Ce) and lanthanum (La) with FeCl3, FeCl2 and biochar. For comparison, Fe3O4-BC without doping Ce or La was also synthesized. The characterization results indicated that Ce and La ions were successfully doped into the magnetite. The La/Fe3O4-BC had higher magnetic saturation and point of zero charge than Ce/Fe3O4-BC. A series of batch experiment results demonstrated that the phosphate adsorption capacity of biochar has been greatly improved after Ce or La doping, especially La. The phosphate adsorption capacity of La/Fe3O4-BC was 20.5 mg/g at pH 6.5, which was 1.6 and 2.9 times than that of Ce/Fe3O4-BC and Fe3O4-BC, respectively. The adsorption kinetics and isotherms of phosphate onto La/Fe3O4-BC and Ce/Fe3O4-BC were best fitted by the pseudo-second order and Freundich model, respectively, indicating that the adsorption process was a multilayer process and controlled by chemical reaction. The combined results of batch experiments and physiochemical analyses revealed that the possible mechanisms were the formation of inner-sphere complex at neutral conditions and electrostatic attraction between positively charged adsorption sites and phosphate under acid conditions. The enhanced phosphate adsorption performance and endowed magnetic property indicated La/Fe3O4-BC could be used as a promising adsorbent in phosphate removal.

Application of raw and modified Uruguayan clays to phosphate adsorption for water remediation

ABSTRACTA raw clay from Uruguay was modified with aluminium to obtain an aluminium pillared clay (Al-PILC). The solids were characterized by scanning electron microscopy, X-ray diffraction and nitrogen adsorption-desorption isotherms. The Al-PILC retained the typical laminar structure of montmorillonite. The specific surface area and the microporous volume of the Al-PILC, 235 m2 g-1 and 0.096 cm3 g-1, respectively, were much higher than those of the clay. The phosphate adsorption capacity of the Al-PILC was higher than those of the clay. The phosphate adsorption kinetic followed the pseudo-first-order model for both, the clay and the Al-PILC, and the phosphate adsorption isotherm for the Al-PILC fit the Freundlich model.

Performance and adsorption mechanism of a magnetic calcium silicate hydrate composite for phosphate removal and recovery.

A novel magnetic calcium silicate hydrate composite (Fe3O4@CSH) was proposed for phosphorus (P) removal and recovery from a synthetic phosphate solution, facilitated by a magnetic separation technique. The Fe3O4@CSH material was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), powder Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), zeta-potential and magnetic curves. The chemical composition and structure of Fe3O4@CSH and the successful surface loading of hydroxyl functional groups were confirmed. Phosphate adsorption kinetics, isotherm, and thermodynamic experiments showed that adsorption reaches equilibrium at 24 h, with a maximum adsorption capacity of 55.84 mg P/g under optimized experimental conditions. Adsorption kinetics fitted well to the pseudo second-order model, and equilibrium data fit the Freundlich isotherm model. Thermodynamic analysis provided a positive value for ΔH° (129.84 KJ/mol) and confirmed that phosphate adsorption on these materials is endothermic. The P-laden Fe3O4@CSH materials could be rapidly separated from aqueous solution by a magnetic separation technique within 1 min. A removal rate of more than 60% was still obtained after eight adsorption/desorption cycles, demonstrating the excellent reusability of the particles. The results demonstrated that the Fe3O4@CSH materials had high P-adsorption efficiency and were reusable.

Impact of Seaweed Extract and Phosphorus Application on Productivity of Dahlia Plants

A pot experiment was conducted for two successive seasons on a sandy soil and Dahlia pinnata plants grown on it. The randomized block design was used with two factors, the first was seaweed extracts (SWE) 0.0, 0.5, 1 and 1.5 % and the second was phosphorus (P) element treatment through soil application technique at four levels 0.0, 100, 200 and 300 ppm. The objective of this study was to determine the effect of different treatments of seaweed extract on chemical behavior and uptake of phosphorus at different levels in the sandy soil and on plant growth, flowering and chemical composition of growing plants and how the net negative surface charge and phosphate adsorption processes in a sandy soil were affected by seaweed and inorganic fertilizer applications. Soil samples ware collected from a field experiment where seaweed (SWE) and triple superphosphate (TSP) were applied annually on an equivalent plant-available P basis. The results showed that adding seaweed extract (Oligo- x) at 1% and P at 200 ppm revealed significant increase in the studied parameters in both seasons. Significant increases were in the stem length, stem dry weight, number of leaves and their dry weight, leaf area as well as the flower diameter, duration and dry weight while a significant increase in number of days needed to reach flowering was recorded with all fertilizer treatments in both seasons. Tuberous root fresh weights and their number/Plant were obviously stimulated by the used treatments. Meanwhile the content of the leaves of N, P and K (%) as well as the total content of chlorophyll and carbohydrates were significantly stimulated in both seasons compared to the control. After 2 years, SWE-soils had 37% more negative surface charge in soil suspensions from pH 4 to 7 than TSP-fertilized soils. Phosphate adsorption was 23% lower in soils received SEW than TSP. The phosphate adsorption data (adsorption of added phosphate + native adsorbed phosphate) was modeled with the Langmuir 2-surface equation, which revealed that the binding strength for phosphate, including native adsorbed phosphate, was about 50% less in the SWE-fertilized soils than the TSP-fertilized soils. These results suggest that SWE applications increased the net negative surface charge also reduces the soil phosphate adsorption capacity. Phosphate adsorption isotherms showed that phosphate was weakly bound in SWE-fertilized soils, compared with TSP-fertilized soils. Data showed that seaweed not only decreased phosphate retention by the soil but also increased phosphate release into the soil solution. It could be recommended to grow dahlia bulbs in sandy soil by adding of seaweed extract (SWE) at rate (1%) with supplying phosphorus at a level of 200 ppm.

Zirconium-Modified Activated Sludge as a Low-Cost Adsorbent for Phosphate Removal in Aqueous Solution

A highly effective zirconium-modified activated sludge (Zr(IV)-AS) adsorbent was prepared from activated sludge and applied to remove phosphate from aqueous solutions by batch and column experiments. Characterized results revealed that zirconium was successfully loaded onto the activated sludge (AS), and the specific surface area and pore volume were substantially improved after zirconium loading on the AS. Zr(IV)-AS exhibited a high adsorption affinity for phosphate and the maximum adsorption amount was 27.55 mg P·g−1 at 25 °C. Adsorption isotherms of phosphate could be described by the Langmuir model, and the adsorption kinetics were well described by the pseudo-second-order model. Phosphate adsorption on Zr(IV)-AS increased monotonically with decreasing solution pH. The presence of SO42− in water resulted in slightly decreased phosphate adsorption on the adsorbent even at a high concentration (25 mmol/L), and a greater influence of HCO3− on adsorption could be ascribed to the increased solution pH with the addition of the HCO3−. Column adsorption experimental results showed that the adsorbent has excellent phosphate adsorption properties and that the effluent can meet the requirement of phosphorus in the national wastewater discharge standard of China. Phosphate-saturated Zr(IV)-AS can be effectively desorbed in 0.1 mol L−1 NaOH solution, and the regenerated adsorbent still possessed the high capacity. The adsorption between the adsorbent and the phosphate is due to the electrostatic interaction and anionic exchange at the surface of the Zr(IV)-AS. Furthermore, this approach provides a possibility of treating wastewater with waste and has the potential for industrial applications for the removal of phosphate from wastewater.

Comparison of adsorption and desorption of phosphate on synthesized Zn-Al LDH by two methods in a simulated soil solution

Abstract Zinc aluminum layered double hydroxides (LDH) with Zn/Al molar ratios of 2 and 3 were synthesized by general (Zn 2G -Al, Zn 3G -Al) and modified (Zn 2M -Al, Zn 3M -Al) urea hydrolysis methods. The effects of time, pH, selectivity and initial phosphorous concentration were investigated on phosphate uptake by synthesized LDH in a simulated soil solution. Moreover, phosphate desorption from studied LDH was evaluated. Based on the results, nitrate containing Zn-Al LDH were synthesized by both methods. However, the presence of carbonate ion in the interlayer space of Zn 3G -Al was recorded. The kinetics experiments indicated that the pseudo-second order model well described phosphate uptake on all LDH. The lowest uptake (1.09 mmol g − 1 ) was observed for Zn 3G -Al likely due to Zn/Al molar ratio, the presence of carbonate in the interlayer space and incomplete phosphate intercalation mechanism. Phosphate adsorption isotherms of LDH were in agreement with Freundlich model. Although phosphate uptake decreased in the presence of other anions, the highest selectivity especially in the pure nitrate containing LDH were measured for phosphate anion. Phosphate uptake declined with increasing the pH from 6 to 8. The amounts of phosphate desorption from prepared LDH were between 23.2 and 36.3% suggesting that synthesized LDH may have potential to be used as a slow release phosphate fertilizer in soils.

English

The Eastern flank of Mount Cameroon is made up of human settlement and agricultural activities. Determination of phosphorus (P) fixation characteristics of soils around this region is important for a clean environment and economic fertilizer application. The objectives of this study were to evaluate P-fixation characteristics of soils within the region and identify factors contributing to P-fixation. Composite surface soil samples from five sites (between 36 to 1006 m) were collected and analyzed for physicochemical properties and P-fixation capacity. Fixation data were obtained by equilibrating the five soil samples with 25 ml of KH2PO4 in 0.01 M CaCl2, containing 0, 10, 50, 100, 250 and 500 mg L-1. Phosphorus-fixation data were fitted to Langmuir and Freundlich adsorption models and the relationship between P-fixation and soil properties was determined. The adsorption maximum (KL) for Freundlich model was the highest for Limbe - Man O’War Bay Road (LMR, 174.58 mg P kg-1), followed by SLR (34.12 mg P kg-1), Dibanda-Mutengene Road (DMR, 24.72 mg P kg-1), VAS and UPD (16.87 mg P kg-1). The Langmuir adsorption maximum for Vasingi (VAS), Upper Boduma (UPD), Sasse-Limbe Road (SLR), DMR, and LMR were 0.01, 0.02, 0.01, 0.02 and 0.05 mg P kg-1, respectively. The phosphate adsorption isotherm gave good fit adopting Freundlich (r = 0.98 to 0.99). KF correlated with pH (r = - 0.87), Ca (r = - 0.87), exchange acidity (r = 0.87), and clay (r = 0.67). This study illustrated that P sorption isotherm in relation to soil properties can be used as a tool for P management in sustainable crop production.   Key words: Phosphorus fixation, adsorption isotherms, soil physicochemical properties, volcanic soils, Mount Cameroon.

High sorption of phosphate on Mg-Al layered double hydroxides: Kinetics and equilibrium

The development of new materials for environmental remediation is a topic of high priority due to the increasing contamination of water. Although phosphate is not toxic, it has been recognized as one the main species responsible for eutrophication of fresh water bodies, and thus remediation techniques are continuously investigated to remove it from aqueous media. A Mg-Al layered double hydroxide (Mg-Al LDH) was synthesized by the co-precipitation method at constant pH 9. It was characterized by XRD, FTIR, TG-DSC, SEM and TEM, together with dissolution kinetics, phosphate adsorption kinetics, adsorption isotherms and electrophoretic mobilities. The solid was stable at pH >5 in NaCl aqueous solutions. Lower pH resulted in a fast dissolution, and at pH 3 dissolution was complete after 100min. Phosphate adsorption kinetics, isotherms and electrophoretic mobility enabled to establish that phosphate adsorbs via three different adsorption modes: anion exchange, electrostatic attraction and surface complexation. The phosphate adsorption capacity of the LDH at pH 5 was 2.25mmolg−1. This is the highest adsorption value when compared with the performance of other phosphate sorbents in the literature. The synthesized LDH, therefore, is a promising environmentally friendly solid to be used in wastewater treatment systems or to remove phosphate from aquatic environments.

Removal of phosphate from aqueous solution using modified zeolite clays

Phosphate adsorption capabilities of different treated zeolite clays were assessed from aqueous solution. Natural zeolites were treated by thermal activation over 120–800 °C for 2 h, and by hydrochloric ac-id solution from 1%-9%, respectively. The mechanisms of phosphate adsorption of these modified products were also studied through adsorption isotherms and adsorption kinetics experiments. The acid activation in-creased the phosphate sorption capacity and the highest phosphate sorption capacity occurred at AZT9 (zeo-lite activated by 9% hydrochloric acid), while thermal activation did not have the same effect. AZT9 showed higher adsorption rate than natural zeolite (ZT). The phosphate adsorption isotherms of ZT, H400 and AZT9 are fitted well with Langmuir equation in terms of R2 values. It suggested that the adsorption of phosphate on zeolite was homogeneous multilayer adsorption. Based on R2 values, the kinetics of phosphate adsorption on these three zeolites can be satisfactorily described by pseudo-second-order kinetic equation. Results of this study suggested that acid modified zeolite could be potentially used as a promising adsorption media for phosphate removal.

Novel nano-conjugate materials for effective arsenic(V) and phosphate capturing in aqueous media

In this study, the ligand functionalized nano-conjugate material was developed for the sensitive and selective detection and removal of toxic arsenic(V) and phosphate ions in aqueous media. The nano-conjugate material was fabricated based on the use of metal-organic frameworks with exhibited of high surface area, pore morphology, and tuneable shape. The newly design nano-conjugate material was exhibited the naked eye monitoring of the ultra-trace arsenic(V) and phosphate in a simple, fast, cost-effective and easy-to-use approach. The data clarified that the arsenic(V) and phosphate adsorption process were found to be relatively fast. The adsorption isotherms of arsenic(V) and phosphate from aqueous solutions to the nano-conjugate material were measured, and the results showed that the Langmuir isotherm was found to be the best represent the measured adsorption data. The maximum adsorption capacity was 82.40 and 70.47mg/g for arsenic(V) and phosphate, respectively. The arsenic(V) and phosphate detection and removal were not affected in the presence of co-existing divers ions. Calibration curves were demonstrated by using UV–Vis spectrophotometric and digital image-based colorimetric analysis. The linear correlation obtained from the two methods, and the detection limit of arsenic(V) and phosphate were 0.15 and 0.13μg/L, respectively. In addition, the nano-conjugate material was regenerated by 0.20M NaOH treatment the arsenic(V) and phosphate detection or removal efficiency was retained almost as that of the original performance. In addition, the nano-conjugate material was applied to the determination and removal of arsenic(V) and phosphate in natural and industrial water samples. Therefore, the newly developed nanomaterial has potentiality for efficient detection and removal of arsenic(V) and phosphate in the real wastewater samples.

Application of different activated attapulgites to purify phosphate contaminated wastewater

Phosphate adsorption capabilities of different activated attapulgites were investigated. The natural attapulgites were treated by thermal activation over 120–800 °C for 2 h, and by hydrochloric acid solution from 1%-9%, respectively. The mechanisms of phosphate adsorption of these modified products were also studied through adsorption isotherms and adsorption kinetics experiments. The acid activation increased the phosphate sorption capacity and the highest phosphate sorption capacity occurred at AAT3 (attapulgite activated by 3% hydrochloric acid), while thermal activation did not have the same effect. AAT3 showed higher adsorption rate than natural attapulgite (AT). The phosphate adsorption isotherms of AT, H400 and AAT3 are fitted well with Langmuir equation in terms of R2 values. It suggested that the adsorption of phosphate on attapulgite was homogeneous multilayer adsorption. Based on R2 values, the kinetics of phosphate adsorption on these three attapulgites can be satisfactorily described by pseudo-second-order kinetic equation. Results of this study suggested that acid modified attapulgite could be potentially used as a promising adsorption media for phosphate removal.

Effect of pore size distribution on iron oxide coated granular activated carbons for phosphate adsorption – Importance of mesopores

Adsorption is often suggested for to reach very low phosphate levels in municipal wastewater effluent and even to recover phosphate. Adsorbent performance is usually associated with surface area but the exact role of the pore size distribution (PSD) is unclear. Here, we show the effect of the PSD on phosphate adsorption. Granular activated carbons (GACs) with varying PSDs were treated with potassium permanganate followed by reaction with ferric chloride to form iron oxide coated GACs (Fe-GACs). Energy dispersive X-ray and kinetics experiments confirmed that manganese anchored on the GAC is important for subsequent iron attachment. Mössbauer spectroscopy showed presence of ferrihydrite in Fe-GAC. Transmission electron microscopy showed that the iron oxide particles are not present in the micropores of the GACs. Phosphate adsorption isotherms were performed with the Fe-GACs and adsorption at lower phosphate concentrations correlated with the porous area of >3nm of the adsorbents, a high fraction of which is contributed by mesopores. These results show that high surface areas of GACs resulting from micropores do not contribute to adsorption at low phosphate concentrations. This can be explained by the micropores being difficult to coat with iron oxide nanoparticles, but in addition the diffusion of phosphate into these pores could also be hindered. It is therefore recommended to use backbones having high mesoporous areas. This information is useful for developing adsorbents particularly for applications treating low phosphate concentrations, for e.g. in municipal wastewater effluent polishing.

Adsorption kinetics and isotherms of phosphate and its removal from wastewater using mesoporous titanium oxide

The adsorption of phosphate onto mesoporous TiO2 was investigated in order to reduce phosphorus concentrations in wastewater and provide a potential mode of phosphorus recovery. Three equilibrium isotherms were used to optimize and properly describe phosphate adsorption (R2>0.95). The maximum capacity of phosphate on the adsorbent was found to be 50.4 mg/g, which indicated that mesoporous TiO2 could be an alternative to mesoporous ZrO2 as an adsorbent. A pseudo-second order model was appropriately fitted with experimental data (R2>0.93). Furthermore, the suitable pH for phosphate removal by TiO2 was observed to be in the range of pH 3-7 in accordance with ion dissociation. In contrast, increasing the pH to produce more basic conditions noticeably disturbed the adsorption process. Moreover, the kinetics of the conducted temperature study revealed that phosphate adsorption onto the TiO2 adsorbent is an exothermic process that could have spontaneously occurred and resulted in a higher randomness of the system. In this study, the maximum adsorption using real wastewater was observed at 30 C.

Using desulfurization slag as the aquacultural amendment for fish pond water quality improvement: Mechanisms and effectiveness studies

The objective of this study was to evaluate the potential of applying desulfurization slag (DS) as pavement materials and amendments in the aquacultural industry for water quality improvement. The results of characteristic analyses and a mobile factor calculation show that the bonding patterns of heavy metals in DS were stable and had low bioavailability and mobility. DS can effectively adsorb ammonia and phosphate according to the pseudo second-order kinetics model. The adsorption isotherm for ammonia can be described by the Langmuir model. Both the Langmuir and Freundlich models can be used for phosphate adsorption isotherm evaluation. Ammonia adsorption involved physical adsorption, and the mechanisms for phosphate removal included adsorption and chemical precipitation. The adsorption of ammonia by DS was a non-spontaneous endothermic process, and the adsorption of phosphate was a spontaneous exothermic process. The results from excitation emission fluorescence matrix analysis show that the organic substances in the fish pond with DS addition included a soluble microbial product, protein-like substance, and humic acid-like substance. This indicates that algal growth and biomass accumulation could be enhanced by DS addition because the released trace elements and hydroxide ions from DS are beneficial to algal growth. Using DS as an amendment and construction material for the fish pond would increase the water alkalinity and prevent acidification of pond water. The results indicate that DS can be used in the aquacultural industry as construction material as well as for pH control and algal growth enhancement.

Phosphate sorption parameters in relation to soil properties in some major agricultural soils of India

Phosphorus sorption characteristics of some Indian representative agricultural soils belonging to four soil orders namely Vertisol, Inceptisol, Alfisol and Ultisol were investigated for adsorption behaviour of P and sorption data were fitted to Langmuir and Freundlich equations. The Langmuir constant i.e. adsorption maxima was highest for Vertisol (716.85 ?g g-1), followed by Ultisol (633.3 ?g g-1), Alfisol (501.46 ?g g-1) and Inceptisol (522.93 ?g g-1) respectively. The Freundlich ‘k’ value for Vertisol, Inceptisol, Alfisol and Ultisol were 159.12, 59.41, 110.57 and 181.36 ?g g-1 respectively, whereas the ‘n’ values were 2.05, 1.92, 2.49 and 3.07 g ml-1 respectively. The phosphate adsorption isotherm gave good fit adopting Langmuir (r2 = 0.96 to 0.99) and Freundlich (r2= 0.95 to 0.99) for the four soils. Phosphorus sorption maxima was significantly correlated with clay (r2=0.70), Al (r2= 0.73) and Fe (r2=0.81) forms, MPBC (r2=0.67) and Freundlich constants (r2=0.82). Among the various soil properties which correlated with P sorption maxima of significance was clay content (r2=0.97) was significantly correlated. The study illustrated that P sorption isotherm in relation to soil properties can be used as a tool of P management in sustainable crop production.SAARC J. Agri., 14(1): 1-9 (2016)

Novel ferrihydrite sand coating process as a first step for designed technosols

The production of technosols to remediate polluted or sealed urban soils to sustain new green areas is mainly empirical. For this, our research aims to contribute with the scientific knowledge base for purpose designing of technosols. Since iron minerals play an important role for many different functions of soils, we simplified a technique to incorporate and stabilize iron minerals in a substrate: a sand coated with an amorphous iron (hydr)oxide, a 2-line ferrihydrite (2L-FH). The 2L-FH was precipitated by neutralization of a concentrated FeCl3 solution. The suspension was homogeneously mixed with the sand and the mixture was dried at 35 °C. The mechanical stability of the 21 2L-FH-coated sand was determined by shaking the aggregates in water for 0, 1, 10, 100, and 1 000 min. The degree of coating detachment and the properties of the coating after shaking were characterized through (a) Fe content, (b) zeta-potential and particle size of the detached particles, (c) the specific surface area (SSA) of the coated sand, and (d) its surface structure using scanning electron microscopy (SEM). A phosphate adsorption isotherm was performed to measure the P-sorption capacity of the shaken samples and to test the 2L-FH-quartz attachment stability against the surface charge reduction of the 2L-FH associated with P adsorption. A reduced Fe loss (30 %) and smaller sizes of the coating detached particles in the sample shaken for 1 000 min indicate that a fractioning and reattachment of these aggregates occurred during the agitation process, resulting in a smoother surface (SEM), and a larger SSA and P-sorption capacity. The coated shaken samples showed P-adsorption capacities (5.3–6.34 μmol P g−1) comparable to high loadings of phosphate in soils, and low detachment of Fe (7–14 %) in spite of negativity surface charge increase. The practical novel coating process along with the 1 000-min shaking produced a mechanical resistant and P-adsorptive effective coated sand that could sustain the needs of plants in further experiments.

Adsorptive Removal of Nitrate and Phosphate Using MCM-48, SBA-15, Chitosan, and Volcanic Pumice

The nitrate and phosphate adsorption capacities of laboratory made and naturally available adsorbents were studied in this study. Two mesoporous silica materials, Mobil composition of matter no. 48 (MCM-48) and Santa Barbara Amorphous-15 (SBA-15), were hydrothermally synthesized, and chitosan was made by reacting crab shells with sodium hydroxide. Pumice powder was prepared by grinding volcanic rocks. All adsorbent powders were characterized by nitrogen adsorption/desorption, X-ray diffraction, Fourier transform infrared (FT-IR), scanning electron microscope (SEM), and high-resolution transmission electron microscopy (TEM) to check their physical properties and surface morphology as adsorbent materials. The adsorption isotherm data of nitrate and phosphate were described by both Langmuir and Freundlich isotherm models. In general, phosphate adsorption isotherms seem to be favorable while some of nitrate adsorption isotherms are slightly unfavorable and linear. Furthermore, the pseudo-second kinetic model is good in describing the batch adsorption rates. Among four adsorbent materials, MCM-48 shows the highest adsorption capacity for both nutrients while the adsorption capacity of SBA-15 is much lower than expected. It should be noted that pumice has considerably high adsorption ability for phosphate and chitosan has good capacity for nitrate even if they have much lower Brunauer, Emmett, and Teller (BET) surface area than mesoporous silica materials.

Effects of water temperature on phosphate adsorption onto sediments in an agricultural drainage canal in a paddy-field district

The phosphorus (P) dynamics in an agricultural drainage canal are dependent on the adsorption characteristics of the underlying sediments. Water temperature is a basic factor affecting P adsorption on the sediments, and this study was aimed at understanding the effects of water temperature on P adsorption onto the sediments in an agricultural drainage canal in a paddy-field district. Phosphate (PO4-P) adsorption kinetics experiments were conducted at 5, 15, 25, and 35°C to clarify temporal variations in the amount of PO4-P adsorption onto the sediments and the effect of water temperature on the PO4-P adsorption rate. We found that higher water temperatures enhanced the adsorption rate and the equilibrium concentration of PO4-P. Phosphate adsorption isotherm experiments were also conducted at 15, 25, 32, and 35°C and three isotherm models were used to characterize adsorption behavior. The amount of PO4-P adsorbed onto the sediments increased with water temperature. However, there was a strong positive correlation between the zero-equilibrium P concentrations estimated using the linear model and the water temperature. These results suggest that sediments may be a greater source of PO4-P for the overlying water with the lower PO4-P concentrations when water temperatures in a drainage canal are high.

Phosphorus and nitrogen removal from tertiary treated urban wastewaters by a vertical flow constructed wetland

Lake L’Albufera is a hypertrophic lake exposed to anthropic pressures. To reduce nutrient loads, a set of horizontal and vertical sub-surface flow constructed wetlands (CWs) were built to treat wastewater from a tertiary wastewater treatment plant (WWTP) before its discharge into the lake.These CWs were designed to remove nutrients, primarily total phosphorus (TP). This paper is focused on a vertical flow constructed wetland (VFCW), the primary objective of which was to remove TP by adsorption and biological uptake. Prior to construction, laboratory experiments were conducted to determine which materials and in what proportions are best suited to achieve that goal. Two different sands (types 0 and 1), as filling material, two types of clays (types 1 and 2) and two types of iron oxides (types a and b), as sorption agents, were used. The primary parameters studied were the phosphate adsorption isotherm, the filter medium hydraulic conductivity and the depletion of adsorption capacity in experimental columns.Laboratory results showed that the best mixture was formed by sand type 0 (Qmax=2.94mg Pkg−1) and 10% of iron oxide type b (Qmax=1666.67mg Pkg−1). Operation was established in a daily cycle with a hydraulic loading of 0.068md−1.Following this procedure, a VFCW planted with reeds and with 157.9m3 water capacity per cycle was constructed. The inflow contained 0.635mg TPl−1, 1.906mg NH4+-Nl−1, 8.9mg TNl−1 and 20.9mg CODl−1. During the first year of operation, total phosphorus removal was 77.0%, ammonium 95.0%, total nitrogen 24.4% and organic matter (COD) 49.3%.

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+ 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.