Cross-flow Ultrafiltration System Research Articles

Investigation of the Distribution and Binding Affinity of Copper to Size-Fractioned Dissolved Organic Matter (DOM) in a Constructed Wetland

This study investigated the distribution and binding affinity of dissolved copper (Cu) and organic carbon (OC) in size-fractioned dissolved organic matter (DOM) in a constructed wetland (CW). Two sites were studied: one at the inflow (P-1) and one within the wetland (P-2). The DOMs (<0.45 μm) were separated into six size fractions using a cross-flow ultrafiltration system. In the wetland (P-2), the concentrations of dissolved organic carbon (DOC) increased while the concentrations of Cu decreased. The high molecular weight fraction (1 kDa–0.45 μm, HMW) contained most of the OC mass (57.4–71.2% averages). On the other hand, Cu was almost equally distributed in HMW and low molecular weight fractions (<1 kDa, LMW) with mean HMW percentages of 50.3–51.3%. The mean Cu binding affinity to DOM ratios (CuBADOM) was 74.9 ± 24.0 μmol/g-C at site P-1 and 17.3 ± 2.6 μmol/g-C at site P-2. The CuBADOM ratios were decreased in wetlands of bulk and size-fractioned DOM (p < 0.001 to p = 0.073). The SUVA254 values for bulk DOM solution were 2.54 ± 0.15 and 1.68 ± 0.18 L/mg-C/m, and humidification index (HIX) values were 1.74 ± 0.16 and 2.09 ± 0.19 for sites P-1 and P-2, respectively. Optical indicators suggested that the wetland process decreased aromaticity but increased the humification degree of DOM. Furthermore, the CuBADOM ratios positively correlated with SUVA254 and HIX within the constructed wetland DOM but not in the influent DOM. Understanding the Cu distribution and binding affinity to size-fractioned DOM makes it possible to develop strategies to mitigate the potential effects of copper pollution in wetlands.

Copper Distribution and Binding Affinity to Size-Fractioned Dissolved and Particulate Organic Matter in River Sediment

This study investigated the distribution of copper in sediment dissolved and particulate organic matter (DOM and POM) based on their size. The DOM and alkaline extracted POM (AEOM) were separated into five size fractions using a cross-flow ultrafiltration (CFUF) system. The results showed that Cu mass was mainly distributed in the low molecular weight (<1 kDa, LMW) fraction of the DOM with an average range of 78.1–83.1%. Conversely, the high molecular weight (1 kDa–0.45 μm, HMW) AEOM fraction had a higher distribution of Cu mass with an average range of 92.6–93.3%. The Cu and AEOM binding affinity ratios (CuBAAEOM) ranged from 17.0 to 149.6 μmol/g-C in site-1 and from 20.6 to 143.7 μmol/g-C in site-2. The HMW CuBAAEOM ratios were significantly higher than the LMW ratios. The Cu and DOM binding affinity ratios (CuBADOM) ranged from 5.6 to 358.6 μmol/g-C and 17.2 to 126.6 μmol/g-C in site-1 and site-2, respectively. However, the LMW CuBADOM ratios were significantly higher than the HMW ratios. Optical indices suggested that the AEOM had more aromaticity and terrestrial and allochthonous contributions than the DOM. The optical indices were significantly correlated with the CuBAAEOM ratios but weakly correlated with the CuBADOM ratios. Sediment exchange between POM and DOM may affect copper distribution. DOM has a low-molecular-weight composition, while POM retains high-molecular-weight organic matter.

Ag@BiOBr/PVDF photocatalytic membrane for remarkable BSA anti-fouling performance and insight of mechanism

Membrane technologies offer great potential in desalination and wastewater treatment. However, the serious issue of membrane fouling results in the unsatisfactory sustainability and reusability for treating wastewater containing high level of organic foulants. In this work, a photocatalytic membrane reactor system combining Ag@BiOBr photocatalyst and polyvinylidene fluoride (PVDF) ultrafiltration with remarkable anti-fouling property was constructed. The integrated Ag@BiOBr/PVDF photocatalytic ultrafiltration membranes were prepared by blending Ag@BiOBr nanoparticles (NPs) into PVDF membrane via phase inversion method. The membrane separation performance and fouling resistance were studied in a cross-flow ultrafiltration system using bovine serum albumin (BSA) as the model foulants. Compared with the pristine PVDF membrane, the hydrophilicity and surface smoothness of composite membranes were promoted by photocatalyst-incorporation, the Ag@BiOBr/PVDF membrane with the optimal Ag@BiOBr blending content of 2.0 wt% achieved both enhanced water flux and higher BSA rejection efficiency. More importantly, the mechanism of anti-fouling and self-cleaning performances were further studied, the photocatalysis process based on Ag@BiOBr/PVDF membrane effectively decomposed the BSA foulant into broken protein with induced change of carbonyl, ionic bond and hydrogen bond contents in BSA foulants via the active radicals, weakened the intermolecular force of BSA foulants to prevent membrane pore blockage. Meanwhile, the broken protein peptide chains with more negative charges could result in the strength of electrostatic repulsive forces between BSA molecules and membrane. As a result, the BSA foulant could be stably removed in the Ag@BiOBr/PVDF photocatalytic ultrafiltration system under visible light irradiation, achieving the excellent anti-fouling performance by preventing the membrane pore blockage and foulant adhesion. We believe the Ag@BiOBr/PVDF photocatalytic membrane presented in this study will be one example among many photocatalyst-membrane combinations that can be further pursued for organic pollutants removal. In particular, we expect the theoretical support can present a great opportunity to design novel photocatalytic membranes with sustainable anti-fouling performance.

Distribution of endocrine-disrupting chemicals in colloidal and soluble phases in municipal secondary effluents and their removal by different advanced treatment processes

In this work, the partition of endocrine-disrupting chemicals (EDCs) in colloid-bound and truly dissolved phases in municipal wastewater before and after advanced treatment processes was determined. The effluents, which were filtered using a 0.45 μm membrane, were further separated with the 1 kDa cross-flow ultrafiltration system into two phases, namely, colloidal phase (0.45 μm-1 kDa) and soluble phase (<1 kDa), and the partition coefficients of typical EDCs to colloids (Kcoc) were calculated. The removal of typical EDCs and their estrogenic activity in secondary effluent by coagulation sedimentation (CS), granular activated carbon (GAC) adsorption, magnetic ion exchange resin (NDMP), and ozone processes was compared. Results show that the percentages of colloid-bound EDCs were noteworthy and ranged between 7.8% and 44.3% in secondary effluents. The reduction in EDCs resulting from the GAC adsorption process was positively correlated to their logKcoc, thus suggesting that the adsorption of EDCs onto granular activated carbon and colloids exhibited a similar phenomenal character. Ozone oxidation was most effective in removing both colloidal phase and soluble phase EDCs, whereas CS displayed a relatively adequate performance in reducing colloidal EDCs. EDCs with lower Kow values exhibited higher removal by ion exchange resin. The combination of modified NDMP and ozonation processes achieved the best performance in reducing estrogenic activity and satisfying the predicted no-effect concentration (PNEC).

Concentration and characterization of groundwater colloids from the northwest edge of Sichuan basin, China

Natural groundwater colloids are significantly important since they are closely related with toxic substances migration in subsurface systems. In this paper, a cross-flow ultrafiltration (CFUF) system equipped with 100kDa cartridges was developed to enrich groundwater colloids and multiple analytical techniques were used to characterize colloid properties. Analytical techniques included scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), transmission electron microscopy (TEM) with energy dispersive X-ray spectra (EDS), excitation-emission matrix (EEM) fluorescence spectra, inverted fluorescence microscopy (IFM), and 16S rDNA sequencing. SEM and AFM results indicated that the mean diameter and height of colloids were 322±90nm and 10.4±2.1nm respectively and two different morphologies of colloids existed which seem to be hollow and platy structure. XRD analysis showed that the mineralogical composition of inorganic colloids consisted of albite (NaAlSi3O8), orthoclase (KAlSi3O8), clinochlore ((Mg,Fe)6(Si,Al)4O10(OH)8, lepidocrocite (FeIIIO(OH)), muscovite (KAl2(Si3Al)O10(OH,F)2), calcite (CaCO3) and quartz (SiO2), most of which was confirmed by TEM-EDS information. Different types of dissolved organic matter (DOM) were characterized by EEM fluorescence spectra, while a larger fraction of ‘protein-like’ fluorescent DOM was found. Bacteria was observed under 488nm laser excitation by IFM and 16S rDNA sequencing revealed that Thermomonas was the most likely genus the bacteria may belong to.

Effect of HNTs modification in nanocomposite membrane enhancement for bacterial removal by cross-flow ultrafiltration system

This study investigated the potential of silver lactate (SL)-holloysite nanotube clay (HNTs) nano-filler embedded into the polyvinylidene fluoride (PVDF) polymer matrix as an antibacterial separator. Three different nanocomposite membranes were fabricated via phase inversion technique aimed to enhance the permeation flux and fouling resistance with complete bacterial rejection. HNT has been modified by N-β-(aminoethyl)-ɣ-aminopropyltrimethoxy silane (AEAPTMS) aiming for immobilization of SL on the surface HNT during dope preparation. Salmonella and Enterobacter aerogenes (E. aerogenes) were considered as two types of bacteria to be removed from contaminated water in this experimental work. Nanocomposite membranes were characterized and analyzed by thermal gravimetric analysis (TGA), Fourier transform infrared (FTIR), field emission scanning electron microscopy (FESEM) combined with energy dispersive X-ray (EDX), X-ray photoelectron spectroscope (XPS), atomic force microscopy (AFM), contact angle, molecular weight cut-off (MWCO) and tensile strength. Potential silver ion loss was assessed by measuring the silver content in the coagulation bath and in the UF permeate using inductive-coupled plasma mass spectrometer (ICP-MS). Moreover, antibacterial effect of the membrane was examined in terms of removal of microorganisms by filtration, Log Reduction Value (LRV) and thickness of inhibition zone. From the experimental results, the prepared nanocomposite membranes have shown more than 99% bacterial rejection, LRV of more than 3 and broad inhibition zones in the agar plate. In particular, the nanocomposite membrane consisting M-HNTs/SL/PVDF showed significant improvement in permeation flux and flux declination among all the tested membranes. It was also found that modification of HNTs resulted in reduction of silver leaching by uniform distributing of SL, which contributed to significant inhibition for both types of growth bacteria within 24h of incubation.

Ultrasonic control of UF membrane fouling by natural waters: Effects of calcium, pH, and fractionated natural organic matter

Abstract Ultrasound at a frequency of 20 kHz and a power of 16 W was applied to a cross-flow ultrafiltration system to investigate the ultrasonic control of surface-water fouled ceramic membranes. Ultrasound was effective in improving the normalized permeate flux of a surface water, from 0.21 in the absence of ultrasound to 0.70 with the aid of ultrasound. Moreover, with ultrasound a stable permeate flux was obtained throughout the 2 h filtration process. Calcium and pH had little impact on the extent of membrane fouling in the absence of ultrasound; however, ultrasound was more effective at minimizing fouling at lower calcium concentration and moderate pH values, presumably due to weaker foulant–foulant and foulant–membrane interactions at these conditions. Fractionation of natural organic matter (NOM) showed that, in the absence of ultrasound, the hydrophilic fraction contributed greatest to fouling while the hydrophobic fraction contributed less. Also, the extent and rate of fouling caused by the hydrophilic NOM was not sensitive to the change of pH or calcium concentration in feed water. The ultrasonic control of membrane fouling caused by hydrophilic NOM was effective at both calcium concentrations (40 and 180 mg/L) investigated. Ultrasonic control of fouling by hydrophilic NOM was more effective at higher pH, presumably due to greater charge repulsion between the membrane and amino acids and peptides in the hydrophilic fraction.

Process intensification with a hybrid system: A tubular packed bed bioreactor with immobilized activated sludge culture coupled with membrane filtration

Performance of a hybrid system consisting of a tubular bioreactor and a membrane filter was studied for removing carbohydrate and protein. Microporous polyurethane (sponge) was used as the packing medium for immobilization activated sludge culture. The bioreactor was operated in series with a cross flow ultrafiltration system to study the effect of influent flow rate and chemical oxygen demand (COD) concentration on the overall system performance. The removal efficiency in the bioreactor decreased linearly with increase in loading. The decline of removal efficiency at higher loadings was more significant for protein than carbohydrate. Coupling the bioreactor with a membrane separation process increased the overall removal rates and provided a consistent effluent quality. The flux through ultrafiltration membrane did not change significantly even when the bioreactor effluent had high levels of protein. Morphological examination of the packing medium both visually and by SEM showed significant accumulation of organisms on the surface which indicates that biofilm thickness was controlled by diffusion limitations. Advantages of the hybrid system include small footprint, economical packing medium, and space savings by coupling the bioreactor with a membrane filtration process.

A combined model for the prediction of the permeation flux during the cross-flow ultrafiltration of a whey suspension

In the dairy industry, whey protein is concentrated by means of cross-flow ultrafiltration. In this membrane process, the thickness of the cake layer is assumed to be controlled by the shear stress exerted by the feed flow. In our prior work, we developed a model for the cross-flow ultrafiltration of a whey suspension that incorporated the effect of this shear stress. In this study, the model is extended to consider the permeation process as two periods determined by the dominant factor controlling the filtration resistance. In the first period, pore blockage dominates while in the latter, cake deposition is dominant. The models for each period were combined using the results of the model for the first period as the initial conditions for the second period. The combined model was compared with experimental results of cross-flow ultrafiltration. Results show that the permeation process was well described under the conditions of this study by the combined model and the possibility of the application of the model to the cross-flow ultrafiltration system was indicated.

Composition and characterization of colloidal organic matter in the coastal surface waters of Qingdao, China

The composition and characterization of dissolved organic matter (DOM) and colloid organic matter (COM) in the coastal surface waters of Qingdao, China were examined. Water samples were collected in Spring 2008 from the Jiaozhou Bay and its adjacent area and fractionated into total dissolved (< 0.45 μm), colloidal (10 kDa–0.45 μm) and cutoff (< 10 kDa) fractions with the cross-flow ultrafiltration (CFF) system. The excitation–emission-matrix (EEM) spectral properties, the absorbance values at 254 nm ( A 254) and dissolved organic carbon (DOC) of the DOM were observed having the colloidal ratios of 8.7%, 6.2%, and 2.2%, respectively, and exhibiting a decreasing trend. Total dissolved carbohydrates (TCHO) and total hydrolysable amino acids (THAA) comprised 24% of the bulk DOC. Among them, the free monosaccharides (MCHO) and dissolved combined amino acids (DCAA）were the major fractions, followed by polysaccharides (PCHO) and dissolved free amino acids (DFAA). Colloidal TCHO and THAA concentrations were 3.2 µM C and 0.3 µM, respectively. They comprised ∼ 35% of the colloid organic carbon (COC), among which PCHO and DCAA were the dominating fractions. The dissolved carbohydrates and amino acids are mostly concentrated in the cutoff fraction. The A 254 values and DOC concentrations inside the Jiaozhou Bay were apparently higher than those outside, while pH and salinity were slightly lower, which might be due to the influence of terrestrial input and the semi-enclosed bay. The distribution pattern of TCHO was found having basically the same as the distributions of A 254 and DOC.

Assessment of the Interaction between Aquatic Colloids and Pharmaceuticals Facilitated by Cross-Flow Ultrafiltration

Interactions between pharmaceuticals and aquatic colloids are a key process regulating their environmental fate, but poorly understood. A validated cross-flow ultrafiltration (CFUF) system was used to isolate river colloids and to determine the partition of selected pharmaceuticals between colloidal (>1 kDa but <0.7 microm) and dissolved phases (<1 kDa) by liquid chromatography-tandem mass spectrometry (LC-MS-MS). The kinetics of pharmaceutical binding to colloids was rapid, reaching equilibrium within 5 min. The mass balance of chosen pharmaceuticals through CFUF system was satisfactory for propranolol, sulfamethoxazole, meberverine, carbamazepine, indomethacine, diclofenac, and meclofenamic acid. The partition coefficient normalized to colloidal organic carbon content (Kcoc) varied from 5.45 x 10(4) to 7.54 x 10(5) mL/g for the chosen pharmaceuticals, which are greater than those for endocrine disrupting chemicals (EDCs), suggesting substantially stronger colloidal interactions with pharmaceuticals than with EDCs. Linear relationships were demonstrated between log-Kcoc, and pharmaceutical properties such as log Kow (octanol-water partition coefficient), highlighting the importance of compound hydrophobicity in controlling their binding with colloids. Such a finding is in contrast to that for EDCs whose Kcoc values were independent of their Kow values. The CFUF-LCMS technique has the potential to become a widely applicable tool for quantifying the distribution of emerging organic pollutants between nanoparticles and the dissolved phase.

Application of cross-flow ultrafiltration for the determination of colloidal abundances in suboxic ferrous-rich ground waters

A suboxic groundwater from a sandy coastal aquifer was sampled using a new air free, large volume sampling method. Subsequent processing for size fractionation was completed with a modified cross-flow ultrafiltration (CFF) system equipped with a 1 kDa CFF membrane. By purging the CFF system with nitrogen, no oxygen was able to reach the sample. With this optimization, the sample was processed with higher than 90% recovery in terms of both iron and phosphate. Only about 4% of iron and 20% of phosphate in the filtered (0.2 microm) groundwater sample was found to be in colloidal form in the groundwater. In contrast, if no care was taken to maintain the suboxic environment of the original sample, iron was rapidly and completely oxidized and subsequently adsorbed to the CFF membrane. Other elements, such as phosphorus, were also lost to the CFF membrane to a substantial degree, and the mechanism is most likely coprecipitation with iron oxides. This study thus strongly supports the importance of maintaining ambient redox conditions during sampling and fractionation, especially for the determinations of colloid abundances in groundwater.

Partial Validation of Cross Flow Ultrafiltration by Atomic Force Microscopy

Atomic force microscopy was used to evaluate a cross flow ultrafiltration (CFUF) system. The CFUF system was used for the size fractionation of natural colloidal material from freshwaters. Analysis of the images of bulk water, permeates, and retentates shows the primary materials observed were near-spherical structures with height dimensions up to approximately 12 nm. The number of colloidal particles (per unit area) on the mica surfaces derived from the retentates increased by a factor of 2 between a concentration factor (cf) of 1 and of 20. Colloidal densities of nanoparticles were approximately 2 orders of magnitude lower in the permeate compared to the retentate, indicating a good size fractionation. As the cf value increased from 1 to 20, the percentage of <1-nm material decreased substantially and the percentage of >1-nm material increased substantially in the retentates. Line transects along a surface and surface roughness values show good agreement with the above results. Results suggest the size fractionation is good but not perfect and high cf values produce a better size fractionation, although some retention of small material is always observed. High cf values are recommended.

Recovery of medium-chain-length polyhydroxyalkanoates (PHAs) through enzymatic digestion treatments and ultrafiltration

Medium-chain-length (mcl) polyhydroxyalkanoates (PHAs) are biodegradable polyesters accumulated intracellularly as energy resources by bacterial species such as Pseudomonas putida. The most popular method for PHA recovery in the downstream processing is solvent extraction using chloroform and methanol. An alternate method is bioseparation using enzymatic digestion process which eliminates the need for hazardous solvents. This research focuses on an attempt to optimize the recovery of PHAs by solubilisation of non-PHA granules through enzymatic treatments such as; Alcalase (to digest the denatured proteins), sodium dodecyl sulfate (SDS) to assist solubilisation, ethylene diamine tetra acetic acid (EDTA) to complex divalent cations and lysozyme to digest the peptidoglycan wall enveloping the cell. The experiment was designed through Taguchi's design of experiment (DOE) using Qualitek-4 software. The results show that Alcalase enzyme used had the most significant effect on the treatment process and contributed to about 71.5% in terms of process factor importance among the different factors on treatment performance for PHA recovery. It is desired to recover the PHA granules in water suspension after the enzymatic treatment by removing the solubilised non-PHA cell material through crossflow ultrafiltration system and purified through continuous diafiltration process. Final purity of PHA in water suspension obtained using GC analysis is 92.6%, with a nearly 90% recovery, thus concluding that this method is indeed a suitable alternative.

Ultrasonic control of ceramic membrane fouling caused by natural organic matter and silica particles

The ultrasonic control of membrane fouling caused by natural organic matter (NOM) and silica particles was investigated under various solution conditions. Twenty kilohertz ultrasound was applied to a cross-flow ultrafiltration system with γ-alumina membranes. Experimental results indicated that solution chemistry affected the ability of ultrasound to control membrane fouling. More effective control of membrane fouling occurred at high pH, low ionic strength, and in the absence of divalent cations, consistent with the expectation of stronger electrostatic repulsion between foulant–foulant and foulant–membrane components. Fourier transform infrared spectra of the NOM foulant showed the presence of aliphatic carbon and carboxylate functional groups, both of which decreased in magnitude with increasing pH, in the absence of Ca 2+, or the presence of ultrasound. A decrease in the NOM rejection rate during ultrasound was observed. This likely occurred due to decreased steric exclusion of NOM through the fouled membrane, as scanning electron microscope images indicated that ultrasound partially removed the foulant layer from the membrane surface allowing larger NOM molecules to pass through the membrane. No damage to the membrane by ultrasound was observed.

Ultrasonic control of ceramic membrane fouling by particles: Effect of ultrasonic factors

Ultrasound at 20 kHz was applied to a cross-flow ultrafiltration system with γ-alumina membranes in the presence of colloidal silica particles to systematically investigate how ultrasonic factors affect membrane cleaning. Based on imaging of the ultrasonic cavitation region, optimal cleaning occurred when the membrane was outside but close to the cavitation region. Increasing the filtration pressure increased the compressive forces driving cavitation collapse and resulted in fewer cavitation bubbles absorbing and scattering sound waves and increasing sound wave penetration. However, an increased filtration pressure also resulted in greater permeation drag, and subsequently less improvement in permeate flux compared to low filtration pressure. Finally, pulsed ultrasound with short pulse intervals resulted in permeate flux improvement close to that of continuous sonication.

Dynamic behaviour of river colloidal and dissolved organic matter through cross-flow ultrafiltration system

Through cross-flow filtration (CFF) with a 1-kDa regenerated cellulose Pellicon 2 module, the ultrafiltration characteristics of river organic matter from Longford Stream, UK, were investigated. The concentration of organic carbon (OC) in the retentate in the Longford Stream samples increased substantially with the concentration factor ( cf), reaching approximately 40 mg/L at cf 15. The results of dissolved organic carbon (DOC) and colloidal organic carbon (COC) analysis, tracking the isolation of colloids from river waters, show that 2 mg/L of COC was present in those samples and good OC mass balance (77–101%) was achieved. Fluorescence measurements were carried out for the investigation of retentate and permeate behaviour of coloured dissolved organic materials (CDOM). The concentrations of CDOM in both the retentate and permeate increased with increasing cf, although CDOM were significantly more concentrated in the retentate. The permeation model expressing the correlation between log [CDOM] in the permeate and log cf was able to describe the permeation behaviour of CDOM in the river water with regression coefficients ( r 2 ) of 0.94 and 0.98. Dry weight analysis indicated that the levels of organic colloidal particles were from 49 to 71%, and between 29 and 51% of colloidal particles present were inorganic. COC as a percentage of DOC was found to be 10–16% for Longford Stream samples.

Plutonium in groundwater at the 100K-Area of the U.S. DOE Hanford Site

We examined the concentration, size distribution, redox state and isotopic composition of plutonium (Pu) in groundwater at the 100K-Area at the U.S. Department of Energy's (DOE) Hanford Site. Total concentrations of Pu isotopes were extremely low (10 −4 to 10 −6 pCi/kg, ≈10 4 to 10 6 atoms/kg) but measurable for the first time in the 100K-Area wells using mass spectrometric analyses that are much more sensitive than alpha spectroscopy methods used previously. Size fractionation data from two wells suggest that 7–29% of the Pu is associated with colloids, operationally defined here as particles between 1 kDa–0.2 μm in size. These colloids were collected using a 1 kDa cross-flow ultrafiltration (CFF) system developed specifically for groundwater actinide studies to include careful controls both in the field and during processing to ensure in situ geochemical conditions are maintained and size separations can be well characterized. Pu in this colloidal fraction was exclusively in the more reduced Pu(III/IV) form, consistent with the higher affinity of Pu in the lower oxidation states for particle surfaces. While the overall concentrations of Pu were low, the Pu isotopic composition suggests at least two local sources of groundwater Pu, namely, local Hanford reactor operations at the 100K-Area and spent nuclear fuel from the N-reactor, which was stored in concrete pools at this site. Differences between this site and the Savannah River Site (SRS) are noted, since groundwater Pu at the F-Area seepage basin at SRS has been found using these same methods, to be characterized by lower colloidal abundances and higher oxidation states. This difference is not directly attributable to groundwater redox potential or geochemical conditions, but rather the physical–chemical difference in Pu sources, which at SRS appear to be dominated downstream from the seepage basins by decay of 244Cm, resulting in more oxidized forms of 240Pu. There is no clear evidence for colloid facilitated transport of Pu in groundwater at the Hanford Site, since downstream wells have both an order of magnitude lower concentrations of Pu and a lower fractional colloidal distribution.

Validation of cross-flow ultrafiltration for sampling of colloidal particles from aquatic systems.

The use of cross-flow ultrafiltration (CFF) for the isolation of colloids from the bulk aquatic matrices has been increasing over the last decade; however, a thorough validation of each CFF system is needed before its application to natural samples. Laboratory experiments have been conducted to validate a 1-kDa Millipore Pellicon 2 cartridge type CFF system, using a range of molecular probes spiked in natural waters. Using the separation data of these probes, key validation parameters have been calculated, including retention coefficient (RC), concentration factor (cf), colloid concentration, recovery, and mass balance. The permeation behaviour of these molecules has also been studied using a simple permeation model. Results show that good retention (>80%) of high molecular weight (HMW, >1 kDa) molecules and low retention (<20%) of low molecular weight (LMW, <1 kDa) molecules can be achieved at high cf values or over long timescales. In addition, permeation modelling and the calculation of colloid concentration demonstrate the same findings, again recommending high cf values or long timescales for ultrafiltration to minimise the retention of LMW molecules. The retention characteristics of 3-kDa dextran change slightly with salinity. Mass balance calculations show good recoveries for all of the molecules tested. The apparent membrane molecular cut-off of the CFF system has been estimated to be between 2.1 and 2.5 kDa, which is slightly greater than the manufacturer's nominal MW cut-off of 1 kDa.

SIGNIFICANCE OF MEMBRANE TYPE AND FEED STREAM IN THE ULTRAFILTRATION OF SUGARCANE JUICE

This work examines the purification of sugarcane juice in a cross-flow ultrafiltration (UF) system. Experiments were conducted on-site at a sugar mill using fresh feed drawn from the appropriate stage in the sugar manufacturing process. Different polymeric membranes with a nominal molecular weight cutoff rating in the 10–50 kD range were evaluated. The 20 kD polyethersulphone membrane was identified to be the most effective in terms of acceptable flux coupled with significant removal of nonsugar impurities. Subsequent trials were performed on four feed streams viz. mixed juice, raw juice, rotary vacuum filtrate, and clarified juice. It was observed that with the exception of the clarified juice, the fine suspended particles (bagacillo) in all the other streams formed a secondary filtration layer on the membrane surface during the course of filtration. The permeate displayed a 1.5–3 unit rise in juice purity, which is a remarkable improvement over the 0.5–1 unit rise obtained in the liming-sulphitation process. In addition, the UF permeate was typically over three times as clear with a fivefold color reduction when compared to the clarified juice produced by the conventional process.