Effect of polyphenols on activated sludge biomass during the treatment of highly diluted olive mill wastewaters: biomass dynamics and purifying performances.

This study aims to investigate the feasibility of treating olive mill waste water (OMWW) by activated sludge pilot (AS) after its high dilution (1%) by urban waste water (UWW) and to study the effect of polyphenol compounds on the biomass during the treatment. Specific oxygen uptake rate (SOUR), mixed liquor volatile suspended solids (MLVSS), chemical oxygen demand (COD) and total polyphenols, were followed up over 100 days. In spite of the polyphenols' high concentration (up to 128 mg·L-1), successful biomass growth of 7.12 g MLVSS.L -1 and activity were achieved. Most of the bacteria (Pseudomonas sp., Klebsiella oxytoca, Citrobacter fereundii, Escherichia coli and Staphylococcus sp.) and fungi (Trichoderma sp., Rhizopus sp., Aspergillus niger, Penicillium sp., Fusarium sp., Alternaria) identified in the aerobic basin during the stabilization stage were known to be resistant to OMWW and showed effective adaptation of the biomass to polyphenols in high concentration. COD and polyphenols were highly eliminated (90%, 92% respectively). The sludge volume index in the pilot settling tank was almost constant at around 120 mL.g -1. This suggests the possibility of managing OMWW by simple injection at a given percentage in already functioning conventional AS treating UWW.

Quality by design compliant strategy for the development of a liquid chromatography-tandem mass spectrometry method for the determination of selected polyphenols in Diospyros kaki.

Diospyros kaki fruits possess great beneficial properties for human health due to their strong antioxidant and antiradical activities related to the high level of bioactive compounds and particularly polyphenols. In this paper a rapid and efficient liquid chromatography-tandem mass spectrometry method for the determination of 38 polyphenolic compounds in Diospyros kaki flesh was developed. The optimization of the chromatographic method was performed applying a Quality by Design approach, which is unexplored in the field of food analysis. The Critical Method Attributes (CMAs) were the critical resolutions of some isobaric compounds and analysis time. The Critical Methods Parameters (CMPs) were related to the characteristics of both the mobile phase and the column: flow rate, temperature, starting organic phase concentration of the mobile phase, formic acid percentage in the eluents, type of organic solvent in the mobile phase and gradient of organic eluents. The effects of the CMPs on the CMAs were evaluated by experimental design, at first carrying out a screening phase by an asymmetric screening matrix and then applying Response Surface Methodology by a Doehlert Design. The quadratic polynomial models postulated to link the CMAs to CMPs were calculated and the Method Operable Design Region was identified with the aid of Monte Carlo simulations as the multidimensional combination of the CMPs that satisfied the requirements for the CMAs with a probability ≥90%. The developed method was applied to real samples obtained by the extraction of Diospyros kaki flesh from two different cultivars (Rojo Brillante and Kaki Tipo), making it possible to obtain extensive information on their polyphenolic profiles.

A comprehensive strategy in the development of a cyclodextrin-modified microemulsion electrokinetic chromatographic method for the assay of diclofenac and its impurities: Mixture-process variable experiments and quality by design.

A comprehensive strategy involving the use of mixture-process variable (MPV) approach and Quality by Design principles has been applied in the development of a capillary electrophoresis method for the simultaneous determination of the anti-inflammatory drug diclofenac and its five related substances. The selected operative mode consisted in microemulsion electrokinetic chromatography with the addition of methyl-ß-cyclodextrin. The critical process parameters included both the mixture components (MCs) of the microemulsion and the process variables (PVs). The MPV approach allowed the simultaneous investigation of the effects of MCs and PVs on the critical resolution between diclofenac and its 2-deschloro-2-bromo analogue and on analysis time. MPV experiments were used both in the screening phase and in the Response Surface Methodology, making it possible to draw MCs and PVs contour plots and to find important interactions between MCs and PVs. Robustness testing was carried out by MPV experiments and validation was performed following International Conference on Harmonisation guidelines. The method was applied to a real sample of diclofenac gastro-resistant tablets.

Innovative combination of QuEChERS extraction with on-line solid-phase extract purification and pre-concentration, followed by liquid chromatography-tandem mass spectrometry for the determination of non-steroidal anti-inflammatory drugs and their metabolites in sewage sludge.

For the first time QuEChERS extraction of sewage sludge was combined with the automatic solid-phase pre-concentration and purification of the extract (following indicated as SPE) and LC-MS/MS analysis, for the determination of the non-steroidal anti-inflammatory drugs acetylsalicylic acid (ASA), diclofenac (DIC), fenbufen (FEN), flurbiprofen (FLU), ketoprofen (KET), ibuprofen (IBU) and naproxen (NAP), and their metabolites salicylic acid (SAL), 4'-hydroxydiclofenac (4'-HYDIC), 1-hydroxyibuprofen (1-HYIBU), 2-hydroxyibuprofen (2-HYIBU), 3-hydroxyibuprofen (3-HYIBU) and o-desmethylnaproxen (O-DMNAP). Various commercial pellicular stationary phases (i.e. silica gel functionalized with octadecyl, biphenyl, phenylhexyl and pentafluorophenyl groups) were preliminarily investigated for the resolution of target analytes and different sorbent phases (i.e. octyl or octadecyl functionalized silica gel and a polymeric phase functionalized with N-benzylpyrrolidone groups) were tested for the SPE phase. The optimized method involves the QuEChERS extraction of 1 g of freeze-dried sludge with 15 mL of water/acetonitrile 1/2 (v/v), the SPE of the extract with the N-benzylpyrrolidone polymeric phase and the water/acetonitrile gradient elution on the pentafluorophenyl stationary phase at room temperature. Matrix effect was always suppressive and in most cases low, being it ≤20% for ASA, DIC, FLU, KET, IBU, 1-HYIBU, 2-HYIBU, 3-HYIBU, NAP and O-DMNAP, and included in the range of 35-47% for the other analytes. Recoveries were evaluated at three spiking levels, evidencing almost quantitative values for HYIBUs and O-DMNAP; for ASA, SAL and KET the recoveries were included in between 50 and 76%, whereas for the other compounds they ranged from 36% to 55%. The proposed method showed better analytical performances than those so far published, being suitable for target compound determination in real samples from tens of pg g(-1) to ng g(-1) of freeze-dried sludge, with a total analysis time of 30 min per sample.

Enantioseparation and impurity determination of ambrisentan using cyclodextrin-modified micellar electrokinetic chromatography: Visualizing the design space within quality by design framework.

A capillary electrophoresis method for the simultaneous determination of the enantiomeric purity and of impurities of the chiral drug ambrisentan has been developed following the Quality by Design principles. The selected separation system consisted of a micellar pseudostationary phase made by sodium dodecyl sulphate with the addition of γ-cyclodextrin. The effects of critical process parameters (capillary length, temperature, voltage, borate concentration, pH, sodium dodecyl sulphate concentration, γ-cyclodextrin concentration) on enantioresolution of ambrisentan and analysis time were extensively investigated by multivariate strategies involving a screening phase and Response Surface Methodology. The Design Space was defined with a desired probability level π≥90%, and the working conditions, with the limits of the Design Space, corresponded to the following: capillary length, 64.5cm; temperature, 22°C; voltage, 30kV (26-30kV); background electrolyte, 100mM borate buffer pH 9.20 (8.80-9.60), 100mM sodium dodecyl sulphate, 50mM (43-50mM) γ-cyclodextrin. A Plackett-Burman design was applied for robustness testing, and a method control strategy was established. The method was fully validated according to the International Conference on Harmonisation guidelines and was applied to ambrisentan coated tablets.

Adsorption of bentazone herbicide onto mesoporous silica: application to environmental water purification.

Within the last few years, the presence of bentazone herbicide has been observed in many water resources. For the first time, removal of bentazone using mesoporous silica was investigated revealing reversible adsorption. The adsorption isotherm was well described using the Freundlich model. The affinity towards bentazone is strongly affected by pH in the range of 2-7, decreasing with the increase of the pH, becoming negligible at the neutrality. Regeneration of the adsorbent was possible, and a recovery as high as 70 % was obtained using CH3OH-NaOH solution. Furthermore, appreciable recovery (47 %) was also obtained using water. Applications on the purification of lake water and wastewaters, both characterized by a significant organic carbon load, spiked with 2 mg L(-1) bentazone were tested, observing removal yields in the range of 61-73 %. Taking advantage of the fast adsorption kinetics observed, an in-flow purification treatment was set-up, with quantitative removal of bentazone from polluted water.

Quality by design in the chiral separation strategy for the determination of enantiomeric impurities: development of a capillary electrophoresis method based on dual cyclodextrin systems for the analysis of levosulpiride.

Quality by design (QbD) concepts, in accordance with International Conference on Harmonisation Pharmaceutical Development guideline Q8(R2), represent an innovative strategy for the development of analytical methods. In this paper QbD principles have been comprehensively applied in the set-up of a capillary electrophoresis method aimed to quantify enantiomeric impurities. The test compound was the chiral drug substance levosulpiride (S-SUL) and the developed method was intended to be used for routine analysis of the pharmaceutical product. The target of analytical QbD approach is to establish a design space (DS) of critical process parameters (CPPs) where the critical quality attributes (CQAs) of the method have been assured to fulfil the desired requirements with a selected probability. QbD can improve the understanding of the enantioseparation process, including both the electrophoretic behavior of enantiomers and their separation, therefore enabling its control. The CQAs were represented by enantioresolution and analysis time. The scouting phase made it possible to select a separation system made by sulfated-ß-cyclodextrin and a neutral cyclodextrin, operating in reverse polarity mode. The type of neutral cyclodextrin was included among other CPPs, both instrumental and related to background electrolyte composition, which were evaluated in a screening phase by an asymmetric screening matrix. Response surface methodology was carried out by a Doehlert design and allowed the contour plots to be drawn, highlighting significant interactions between some of the CPPs. DS was defined by applying Monte-Carlo simulations, and corresponded to the following intervals: sulfated-ß-cyclodextrin concentration, 9-12 mM; methyl-ß-cyclodextrin concentration, 29-38 mM; Britton-Robinson buffer pH, 3.24-3.50; voltage, 12-14 kV. Robustness of the method was examined by a Plackett-Burman matrix and the obtained results, together with system repeatability data, led to define a method control strategy. The method was validated and was finally applied to determine the enantiomeric purity of S-SUL in pharmaceutical dosage forms.

Liquid chromatographic-tandem mass spectrometric method for the simultaneous determination of alkylphenols polyethoxylates, alkylphenoxy carboxylates and alkylphenols in wastewater and surface-water.

Four different pellicular stationary phases (i.e. octadecylsilane, octasilane, Phenyl-Hexyl and pentafluorophenyl) were investigated for the chromatographic resolution of alkylphenols (APs), alkylphenols polyethoxylates (APnEOs) and alkylphenoxy carboxylates (APECs) using mixtures of water and organic solvents (i.e. methanol, acetonitrile and tetrahydrofuran) as eluents, in order to obtain their determination by a single LC-MS/MS run. In fact, alkylphenols and alkylphenoxy carboxylates must be analysed in negative ion mode, whereas alkylphenols polyethoxylates undergo ionisation only in positive ion mode, and therefore, two distinct LC-MS/MS analysis are commonly adopted. The best resolution among the aforementioned target analytes was achieved on the pentafluorophenyl column, eluting with an acidified water-acetonitrile-tetrahydrofuran mixture and using the post column addition of an ammonia solution in methanol for the detection of positively ionisable compounds. Under these optimized chromatographic conditions the investigated compounds were determined via a single chromatographic run, with only one polarity switch, in 15min, achieving the following instrumental detection limits: 600pg for AP1EOs, 0.8-14pg for AP2EOs, 10.4-150pg for APs and 4.4-4.8pg for APECs. The chromatographic method was coupled with solid-phase extraction and clean-up procedures and successfully applied to the analysis of wastewater and surface water samples, highlighting mean concentration ranging from 6ng/L for 4-t-OP1EC to 1434ng/L for 4-NP1121EC, depending on the sample analysed.

Direct resolution and quantitative analysis of flurbiprofen enantiomers using microcrystalline cellulose triacetate plates: applications to the enantiomeric purity control and optical isomer determination in widely consumed drugs.

Flurbiprofen enantiomers have very different pharmacological properties, since the (S)-(+) form has a much higher anti-inflammatory activity than the (R)-(-) isomer, the latter being responsible for very undesirable side effects, such as gastrointestinal irritation. Based on the different biological properties of flurbiprofen enantiomers, the development of chiral chromatographic methods for the control of the enantiomeric purity is a very important topic. In this study the separation of flurbiprofen enantiomers was achieved using for the first time noncommercial MCTA layers with polyvinyl alcohol as binder, which gives to these plates a mechanical stability equivalent to that of marketed ones. Baseline resolution (α = 1.31; RS = 2.0) was obtained with ethanol-acetic acid solution (pH 3.0 ± 0.1; 60:40, v/v) as eluent and a migration distance of about 14.5 cm. Under these experimental conditions, the thin-layer chromatography determination of the enantiomeric purity of the pharmacologically active (S)-(+)-flurbiprofen in the presence of 1% of the undesired (R)-(-) form was demonstrated. Moreover, the quantitative analysis of flurbiprofen enantiomers was achieved, obtaining quantification limits and detection limits of 50 and 25 ng of each enantiomer applied to the plate, respectively. The method was succesfully applied to the enantiomer determination in widely consumed drugs, obtaining results consistent with the flurbiprofen content declared in the drug facts.

Quality by Design approach in the development of a solvent-modified micellar electrokinetic chromatography method: finding the design space for the determination of amitriptyline and its impurities.

A solvent-modified micellar electrokinetic chromatography method was set up for the simultaneous determination of the tricyclic antidepressant amitriptyline (AMI) and its main impurities. The method was developed following Quality by Design (QbD) principles according to ICH Guideline Q8(R2). QbD approach made it possible to find the design space (DS), where quality was assured. After a scouting phase, aimed at selecting a suitable capillary electrophoresis pseudostationary phase, risk assessment tools were employed to define the critical process parameters (CPPs) to be considered in a screening phase (applied voltage, concentration and pH of the background electrolyte, concentration of the surfactant sodium dodecyl sulphate, of the cosurfactant n-butanol and of the organic modifiers acetonitrile and urea). The effects of the seven selected CPPs on critical quality attributes (CQAs), namely resolution values between critical peak pairs and analysis time, were investigated throughout the knowledge space by means of a symmetric screening matrix. Response surface study was then carried out on four selected CPPs by applying a Doehlert Design. Monte-Carlo simulations were performed in order to estimate the probability of meeting the desired specifications on CQAs, and thus to define the DS by means of a risk of failure map. Additional points at the edges of the DS were tested in order to verify the requirements for CQAs to be fulfilled. A control strategy was implemented by defining system suitability tests. The developed method was validated following ICH Guideline Q2(R1), including robustness assessment by Plackett-Burman design, and was applied to the analysis of real samples of amitriptyline coated tablets.

Fully-automated on-line solid phase extraction coupled to high-performance liquid chromatography-tandem mass spectrometric analysis at sub-ng/L levels of selected estrogens in surface water and wastewater.

A fully-automated on-line solid phase extraction liquid chromatographic/electrospray ionization tandem mass spectrometric method for the analysis of estrone (E1), 17-ß-estradiol (ß-E2), 17-α-ethinylestradiol (EE2), 17-α-estradiol (α-E2) and estriol (E3) in surface water and wastewater was developed. The method showed a very good linearity from 250 ng/L down to compound specific quantification limits, which were included between 0.25 and 2.00 ng/L. These limits were obtained with 2.5 mL aliquots of injected sample and the total analysis time per sample was slightly less than 10 min. Under these conditions, detection limits were 0.15 ng/L for E1, 0.31 ng/L for ß-E2, 0.52 ng/L for EE2, 0.59 ng/L for α-E2 and 0.95 ng/L for E3. The method reliability was tested on different kinds of real samples spiked with the estrogens, obtaining recoveries approximately included between 71 and 95%. The application to samples collected in rivers, lakes and wastewater treatment plants evidenced the presence of the investigated compounds at sub-ng/L or low ng/L concentration levels.

Total and hexavalent chromium removal in a subsurface horizontal flow (h-SSF) constructed wetland operating as post-treatment of textile wastewater for water reuse.

In this study we investigated total and hexavalent chromium removal in an h-SSF constructed wetland (CW) planted with Phragmites australis and operating as post-treatment of effluent wastewater from an activated sludge plant serving the textile industrial district of Prato (Italy). Two measurement campaigns were carried out in 2006 and 2008-2010 in which more than 950 inlet and outlet samples were analyzed. When inlet and outlet concentrations were compared one to the other, the latter were found to be significantly lower than the former (p < 0.001); during the entire period of investigation, removal of hexavalent chromium equal to about 70% was achieved. Outlet concentrations ranged between values lower than the quantification limit (0.5 microg L(-1)) and 4.5 microg L(-1), and in all cases were therefore lower than the limit indicated for hexavalent chromium in the Italian regulation for water reuse (5 microg L(-1)). The comparison of the removal efficiencies achieved for hexavalent and trivalent chromium during the two campaigns suggested that the removal of the former can be sustained in the long term, while for the latter, the treatment efficiency is more sensitive to the age of the CW, being that it is it based on trivalent chromium retention in the reed bed.

Influence of the application renewal of glutamate and tartrate on Cd, Cu, Pb and Zn distribution between contaminated soil and Paulownia tomentosa in a pilot-scale assisted phytoremediation study.

The influence of repeated applications of tartrate (TAR) and glutamate (GLU) at 50-mmol kg(-1) of soil on Cd, Cu, Pb, and Zn distribution between a contaminated soil and Paulownia tomentosa was investigated. TAR and GLU were applied by a single or a double dosage, the latter carried out with an interval between the two applications of thirty days. The comparison of the differences in mean amounts of metals accumulated in the whole plant at the end of single and double TAR and GLU application experiments indicated the positive effect of repeated GLU applications on the accumulation of Cu, Pb, and Zn by Paulownia tomentosa as compared to untreated controls. A similar effect was not observed for the TAR treatments. When soil treated with either TAR or GLU was compared with untreated controls, no significant effect on heavy-metal concentrations in the soil solution was observed 30 days after treatment, suggesting the absence of an increase of the long-term leaching risk of heavy metals in aquifers and surface waters due to the ligand application. A cost analysis of the treatment is also reported.

Chiral separations and quantitative analysis of optical isomers on cellulose tribenzoate plates.

In this paper new cellulose tribenzoate/gypsum layers in the ratio up to 8/1 (w/w) were investigated for the chiral resolution of closely related aromatic ketones (e.g. tetralones and indanones), alcohols (e.g. benzhydrols) and racemates or enantiomers of other compound classes (e.g. dinitrophenyl amino acids). Among 22 investigated compounds, 16 racemates were baseline or partially resolved by eluting with methanol or 2-propanol/water mixtures on 4/1 (w/w) layers. The best results were compared with those achieved on microcrystalline cellulose triacetate plates and on cellulose tribenzoate columns. The study of structurally related solutes allowed us to increase the knowledge of the retention and resolution mechanisms on this chiral stationary phase and to highlight the role of π-π interactions between cellulose tribenzoate and solutes with different substituents on the aromatic ring. However, some results were unexpected and confirmed the complexity of enantioseparation mechanisms, thus evidencing the importance of experimental tests. Densitometric scan in the visible region of cellulose tribenzoate/gypsum plates after their exposure to iodine vapours allowed us to successfully perform the quantitative analysis of the investigated compounds, thus overcoming the detection problems normally encountered with this stationary phase.

Heavy metal distribution between contaminated soil and Paulownia tomentosa, in a pilot-scale assisted phytoremediation study: influence of different complexing agents.

The distribution of Cd, Cu, Pb and Zn between a contaminated soil and the tree species Paulownia tomentosa was investigated in a pilot-scale assisted phytoremediation study. The influence of the addition of EDTA, tartrate and glutamate at 1, 5 and 10mM concentrations on metal accumulation by the plant and on metal mobilization in soil was evaluated. Root/shoot metal concentration ratios were in the range of 3-5 for Zn, 7-17 for Cu, 9-18 for Cd and 11-39 for Pb, depending on the type and concentration of complexing agent. A significant enhancement of metal uptake in response to complexing agent application was mainly obtained in roots for Pb (i.e. 359 mg kg(-1) for EDTA 10mM and 128 mg kg(-1) for the control), Cu (i.e. 594 mg kg(-1) for glutamate 10mM and 146 mg kg(-1) for the control) and, with the exception of glutamate, also for Zn (i.e. 670 mg kg(-1) for tartrate 10mM and 237 mg kg(-1) for the control). Despite its higher metal mobilization capacity, EDTA produced a metal accumulation in plants quite similar to those obtained with tartrate and glutamate. Consequently the concentration gradient between soil pore water and plant tissues does not seem to be the predominant mechanism for metal accumulation in Paulownia tomentosa and a role of the plant should be invoked in the selection of the chemical species taken up. Metal bioavailability in soil at the end of the experiment was higher in the trials treated with EDTA than in those treated with tartrate and glutamate, the latter not being significantly different from the control. These findings indicated the persistence of a leaching risk associated to the use of this chelator, while an increase of the environmental impact is not expected when glutamate and tartrate are applied.

Polycyclic aromatic hydrocarbons (PAHs) in human milk from Italian women: influence of cigarette smoking and residential area.

The presence of PAH in breast milk collected from 32 smoking and non-smoking lactating women, residing in urban and rural areas of Tuscany (Italy) was investigated. The results indicated a significant contribution of tobacco smoke to the PAH contamination of milk: the condensate contained in the cigarettes smoked daily by each subject was strongly related with the polynuclear hydrocarbon content (R(2)=0.92, P<0.005). An experiment carried out under controlled exposure conditions to cigarette smoke allowed to demonstrate that individual metabolic activity and smoking habits affect the PAH concentration in milk samples. Mothers living in rural environments showed significantly lower PAH concentrations than those observed in urban subjects. The risk evaluation due to PAH ingestion via breast milk was assessed on the basis of the acceptable daily intake of Benzo(a)pyrene in drinking water, evidencing that a hazard cannot be excluded for heavy smokers residing in urban areas.

Performance of horizontal subsurface-flow treatment wetlands in fecal bacteria removal.

This work evaluated sub-surface flow (SSF) constructed wetlands and activated sludge plant efficiency in pathogen removal. The two were also compared. The removal of fecal bacteria (total coliforms, fecal coliforms, fecal streptococci) was evaluated. Analysis was carried out during one year by determining the amount of bacteria in the inflow and the outflow of four systems: three SSF systems (two were pilot plants and one a fully operating plant) and an activated sludge plant. MPN techniques were used to determine the quantity-value of the microorganisms. Percentages of fecal bacteria removal in wetlands systems were as good as (and sometimes better than) those recorded in the activated sludge plant. Optimal values of these bacteria were obtained in the outflow of the post-treatment pilot plant: very high bacterial removal percentages (>99%) were recorded. SFS constructed wetlands are a valid solution for the final treatment of the outflow of existing plants.

Phosphorus adsorption maximum of sands for use as media in subsurface flow constructed reed beds as measured by the Langmuir isotherm.

The P-adsorption capacities of 13 Danish sands were studied by short-term isotherm batch experiments and related to the physico-chemical characteristics of the sands. The maximum P-adsorption capacities (Q) and P-binding energy constants (b) were calculated using the Langmuir-isotherm model. The Freundlich model was also used, but it was not useful for the description of adsorption phenomena per se since it fitted well P-removal data even if precipitation of P-salts occurred simultaneously. The Langmuir model described the data well (R(2)=0.90-0.99) when precipitation of phosphates did not occur and seems therefore to be useful for describing the adsorption processes per se. The relationships between maximum sorption capacities and physico-chemical characteristics of the sands were investigated using classical univariate and partial least squares regression analyses. Among the physico-chemical properties of the sands, Ca and Mg content, grain size, porosity, bulk density and hydraulic conductivity were significantly related (P<0.1) to the maximum adsorption capacity as estimated by the Langmuir model. Using the maximum P-adsorption capacities, it was estimated how long the P-removal can be sustained with the different sands in subsurface flow constructed reed beds. If the most efficient sand for P-adsorption was used, the adsorption capacity would be used up after about 1 year, while, for the less efficient sands, the P-retention would go on for about 2 months. This suggests that, in order to sustain a long-term P-removal in subsurface flow constructed reed beds, precipitation reactions of insoluble P-salts should be promoted. P-binding energy constants were not significantly related to the physico-chemical properties of the sands, except the Ca content, which showed, however, a low correlation coefficient.

Phosphorus removal by sands for use as media in subsurface flow constructed reed beds.

Sorption of P to the bed sand medium is a major removal mechanism for P in subsurface flow constructed reed beds. Selecting a sand medium with a high P-sorption capacity is therefore important to obtain a sustained P-removal. The objective of this study was to evaluate the P-removal capacities of 13 Danish sands and to relate the removal to their physico-chemical characteristics. The P-removal properties were evaluated in short-term isotherm batch-experiments as well as in 12-week percolation experiments mimicking the P-loading conditions in constructed reed bed systems. The P-removal properties of sands of different geographical origin varied considerably and the suitability of the sands for use as media in constructed reed beds thus differs. The P-removal capacity of some sands would be used up after only a few months in full-scale systems, whereas that of others would persist for a much longer time. The most important characteristic of the sands determining their P-removal capacity was their Ca-content. A high Ca content favours precipitation with P as sparingly soluble calcium phosphates particularly at the slightly alkaline conditions typical of domestic sewage. In situations where the wastewater to be treated is more acid, the contents of Fe and Al may be more important as the precipitation reactions with these ions are favoured at lower pH levels. The maximum P-sorption capacities estimated using the Langmuir-isotherm plots did not correspond to or correlate with the actual amount of P removed in the percolation columns. Hence, the Langmuir-isotherm does not estimate the P-removal capacities of sands. It is suggested that a suitable quick method of screening a selection of potential media for P-removal potential is to perform simple removal isotherm studies using water with a similar chemical composition as the wastewater to be treated. This method will not provide a direct estimate of the P-removal capacity that can be obtained in full-scale systems, but it is a means of comparing the relative performance of potential media.

Media selection for sustainable phosphorus removal in subsurface flow constructed wetlands.

Sorption of phosphorus (P) to the bed sand medium is a major removal mechanism for P in subsurface flow constructed wetlands. Selecting a sand medium with a high P-sorption capacity is therefore important to obtain a sustained P-removal. The P-removal capacities of 13 Danish sands were evaluated and related to their physico-chemical characteristics. The P-removal properties of sands of different geographical origin varied considerably and the suitability of the sands for use as media in constructed reed beds thus differs. The P-sorption capacity of some sands would be used up after only a few months in full-scale systems, whereas that of others would subsist for a much longer time. The most important characteristic of the sands determining their P-sorption capacity was their Ca-content. Also the P-binding capacities of various artificial media were tested (light-expanded-clay-aggregates (LECA), crushed marble, diatomaceous earth, vermiculite and calcite). Particularly calcite and crushed marble were found to have high P-binding capacities. It is suggested that mixing one of these materials into the sand or gravel medium can significantly enhance the P-sorption capacity of the bed medium in a subsurface-flow constructed wetland system. It is also possible to construct a separate unit containing one of these artificial media. The media may then be replaced when the P-binding capacity is used up.