Roughness and hydrophobicity studies of nanofiltration membranes using different modes of AFM

Determination of the surface roughness by AFM is crucial to the study of particle fouling in nanofiltration. It is, however, very difficult to compare the different roughness values reported in the literature because of a lack in uniformity in the methods applied to determine surface roughness. AFM is used in both noncontact mode and tapping mode; moreover, the size of the scan area is highly variable. This study compares, for six different nanofiltration membranes (UTC-20, N30F, Desal 51HL, Desal 5DL, NTR7450, NF-PES-10), noncontact mode AFM with tapping mode AFM for several sizes of the scan area. Although the absolute roughness values are different for noncontact AFM and tapping mode AFM, no difference is found between the two modes of AFM in ranking the nanofiltration membranes with respect to their surface roughness. NTR 7450 and NF-PES-10 are the smoothest membranes, while the roughest surface can be found with Desal 51HL and Desal 5DL. UTC-20 and N30F are characterized by an intermediate roughness value. An increase in roughness with increasing scan area is observed for both AFM modes. Larger differences between the roughnesses of the membranes are obtained with tapping mode AFM because of the tapping of the tip on the surface. Phase imaging is an extension of tapping mode AFM, measuring the phase shift between the cantilever oscillation and the oscillation of the piezo driver. This phase shift reflects the interaction between the cantilever and the membrane surface. A comparison with contact angle measurements proves that a small phase shift corresponds to a large contact angle, representing a hydrophobic membrane surface.

Achievements, difficulties and future challenges for the FARMING network

The EC FARMING network (Food and Agriculture Restoration Management Involving Networked Groups) was set up to bring together the many and diverse stakeholders who would be involved in intervention following wide scale radioactive contamination of the food chain, so that acceptable strategies can be developed for maintaining agricultural production and safe food supply. The network comprises stakeholder panels in the UK, Finland, Belgium, France and Greece that have met regularly since 2001 to debate, discuss and exchange opinion on the acceptability, constraints and impact of various countermeasure options and strategies. The objectives of this paper are to consolidate the main achievements of the FARMING project over the period 2000-2004, to highlight the various difficulties that were encountered and to discuss the challenges for engaging stakeholders in off-site emergency management and long-term rehabilitation in the future.

Management of incinerator residues in Flanders (Belgium) and in neighbouring countries. A comparison

This paper covers the Flemish legislative tools concerning the management of bottom ash, fly ash and APC residue from municipal waste incinerators, with respect to their contamination with heavy metals. The situation in Flanders is compared to the one in the Walloon region, The Netherlands, Germany and France. Waste management in the countries considered differs on the level of available management options, of leaching tests and of limit values. To make an indicative comparison of leaching tests and limit values in the different countries, leaching tests were carried out on bottom ash and fly ash, and the results are compared to the relevant limit values for recycling and landfilling of the different countries. The comparison of legislations as well as the leaching results show that discrepancies in waste management between the different regions and countries exist. Recently, European limit values for landfilling became available. European legislation on recycling, however, has not been developed and urgently needs to be considered and drafted as the market for recycling can be expanding rapidly.

Variation in stakeholder opinion on countermeasures across Europe

A compendium of agricultural countermeasures and rural waste disposal options has been compiled as part of the EC STRATEGY (Sustainable Restoration and Long-Term Management of Contaminated Rural, Urban and Industrial Ecosystems) project. The compendium was discussed by the FARMING (Food and Agriculture Restoration Management Involving Networked Groups) network of stakeholders during meetings of national panels in the UK, Finland, Belgium, Greece and France in 2002. Their preliminary feedback has been summarised in terms of whether an option is generally acceptable, unacceptable or only acceptable under specific circumstances. A considerable divergence of opinion between national panels was apparent for many of the options considered. This could be attributed to differences in geomorphology, climate, land management, infrastructure, consumer confidence, sociopolitical context and culture. Where consensus was reached between stakeholders it was generally for those countermeasures that provide public reassurance, sustain farming practices and minimise environmental impact. Furthermore, whilst there was general agreement that contaminated food should not enter the food chain, many of the options proposed for its subsequent management were not generally acceptable to stakeholders.

[Organization of the nuclear emergency plan]

The first Belgian nuclear emergency plan was drawn up in the aftermath of the Chernobyl accident and was primarily aimed at dealing with the consequences of major accidents happening in large nuclear facilities like nuclear power plants. Both the experience during a decade of nuclear emergency exercises and a changing environment with increased menace of malevolent actions by terrorists urged the modification and extension of the initial plan; The latest "Nuclear and radiological emergency plan for the Belgian territory" was published as the Royal Decree of October 17th, 2003. In contrast to what happened in other emergency situations, nuclear and radiological emergencies are, from the moment they are recognised as such and regardless of their (potential) impact, coordinated at the level of the federal authorities. They will gather at the Coordination and Crisis Centre in Brussels. Political decision making will be based both on radiological and socio-economical considerations. The radiological evaluation will take into account on-site observations such as the state and evolution of some crucial technical parameters, meteorological data (observations and forecast) and measured radiological data, where available. Protective measures may be proposed by the radiological experts, but will probably be modified in the light of socio-economical considerations such as the social and/or economical disruption that might arise from fully deploying these proposed measures. The final decision will be taken by political authorities, more particularly the Minister of the Interior. The execution of the decided protective measures will be the responsibility of one or more provinces, who can further delegate to the municipal level and/or to particular services such as the police force, fire department, civil protection, health services and communication experts. The nuclear and radiological emergency plan also deals with some common protective measures such as the installation of a dissuasion perimeter or exclusion zone, the evacuation, sheltering, protection of the food chain, the use of stable iodine and the decontamination from radioactive substances. At least some of the countermeasures ask for -often extensive- preparation in advance, which is generally done in adefined geographical area in the vicinity of a nuclear facility, referred to as "emergency planning zone" for that particular countermeasure and facility. However, the existence of these zones does in no way exclude the application of this countermeasure outside of them. The radiological evaluation is being prepared by introducing "emergency reference levels", for which the Federal Agency for Nuclear Control is responsible. This consists in pre-defining radiation doses which "generally" to "almost invariably" call for the adoption of a given countermeasure. Finally, the nuclear and radiological emergency plan includes stipulations on the required information to the population, on the education and training of (potentially) intervening parties as well as on the minimum requirements for running nuclear emergency exercises.

Carbonation of MSWI-bottom ash to decrease heavy metal leaching, in view of recycling

The 0.1-2 mm fraction of a MSWI-bottom ash cannot be used as granular construction material because leaching of Cu exceeds Flemish limit values. In addition, leaching of Ba, Mo and Sb exceeds informal limit values. Leaching characteristics thus need to be improved. Carbonation was the chosen treatment method and this was performed by placing samples in a CO2 chamber. The CO2 percentage and the temperature of the chamber atmosphere, as well as the initial humidity of the samples, were varied to optimize carbonation parameters. Metal leaching was tested with the EN 12457 extraction test. Carbonation decreased Cu leaching from 3.3 to 1.0 mg/kg, but not yet to below the official limit value of 0.5 mg/kg. Leaching of Mo and Sb remained fairly constant or even increased after carbonation, but their limit values are only informal. Ba leaching decreased to below the informal limit value. Carbonation also caused Cr leaching to increase, in some cases to above the official limit value. Of the tested parameters, a CO2 percentage of 10% and a carbonation temperature of 50 degrees C in the atmosphere, together with ash humidity between 13% and 25% appeared to give the best leaching results. The main carbonation reactions took place within the first 24 h.

Regeneration of brewery waste water using nanofiltration

The brewing industry is a large consumer of groundwater for brewing, rinsing and cooling purposes. As regulations become more and more stringent and the cost of water increases, water recycling gains interest. This paper investigates the possibilities of nanofiltration for the treatment of brewery waste water streams in view of recycling. Four different water streams (waste water after biological treatment, bottle rinsing water, rinsing water of the brewing room and rinsing water of the bright beer reservoir) were filtered with four different nanofiltration membranes (UTC-20, UTC-60, Desal-HL-51 and Desal-5-DK). The results for the biologically treated waste water were the most promising. For the other streams, rejection of organics was insufficient to obtain the required quality, mainly due to the high concentrations of organics such as ethanol in the feed water. Over the periods considered (3 h) only moderate flux decline (10-40%) was observed for most membranes and feed solutions. For Desal-5-DK at high pH, an increase of the flux was observed.

Comparison of immobilisation of air pollution control residues with cement and with silica

Cement as agent for immobilising Pb from air pollution control residues is compared with the use of different silica-containing materials. The DIN 38414-S4 leaching test was used to control Pb leachability and to compare obtained Pb leachate concentrations with the landfill limit of 2 mg/l for Pb. Firstly, one scrubber residues was treated with cement and micro-silica. With cement, the Pb leachability could be reduced with a factor ranging from 3 to 50 depending on the type and amount of cement used and depending on the curing time. The landfill limit of 2 mg/l was, however, never attained. From all tested silica-containing additives, aerosil could reduce the initial Pb leaching (101.3mg/l) to below the detection limit at a dosage of 0.13 g aerosil/g residue. Second best and an economically preferable silica-containing additive was micro-silica: a reduction from 101.3 to 0.7 mg/l was observed at a dosage of 0.4 g micro-silica/g residue. The formation of Ca-silicates was found to be responsible for the decreased Pb leachability. To generalise the findings, the Pb leachability of five cement-treated and five micro-silica-treated air pollution control residues were compared. For three scrubber residues, 2-20 times lower Pb leachate concentrations were measured for micro-silica-treated samples (cured for 5 weeks) than cement-treated samples. For a fly ash and a boiler ash the difference was, respectively, 48 and 17 times. pH-dependent leaching tests showed that at pH=2.5, Pb leaching is 250 times lower for the micro-silica-treated residue than for the cement-treated residue and almost seven times lower at pH 12.4.

Separation of monovalent and divalent ions from aqueous solution by electrodialysis and nanofiltration

The possibilities of separating monovalent and multivalent ions by electrodialysis (ED) and nanofiltration (NF) are explored. Five synthetic single salt solutions were applied to ED and NF: NaCl, Na(2)SO(4), MgCl(2), MgSO(4) and NaNO(3). Two combinations of anionic and cationic exchange membranes were evaluated for ED (AMV/CMV Selemion membranes and ACS/CMS Tokuyama membranes), and two membranes were evaluated for NF (NTR 7450 and UTC-60). The separation was evaluated using an alternative parameter, the separation efficiency, in order to compare ED and NF. The separation efficiency ranges from 0% (no separation) to 100% (perfect separation). Both NF membranes had a good separation efficiency for the separation of monovalent and divalent anions (ca. 60%); the ED membranes performed worse. For the separation of monovalent and divalent cations, the UTC-60 membrane was the best for the considered separation because of size exclusion effects for the larger divalent ion. The ACS/CMS membranes had a similar separation efficiency (ca. 60%); the NTR 7540 membrane and AMV/CMV ED membranes showed only a small separation.

Immobilization of lead and zinc in scrubber residues from MSW combustion using soluble phosphates

The immobilization of MSWI-scrubber residues with soluble PO4(3-) was studied and compared to the immobilization using cement. The DIN 38414-S4 leaching protocol and pH dependent leaching were used to evaluate the leaching of Pb and Zn. Four different scrubber residues from MSW combustion (Pb concentration: 2.8-4.8 mg/g; Zn concentration: 3.0-12.3 mg/g) were mixed with water and cement or Na2HPO4 as source of soluble PO4(3-) at dosages of at least 0, 0.1, 0.2, 0.3 and 0.4 g per g residue. With cement as well as with PO4(3-) a reduction in Pb and Zn leaching was observed. With 0.4 g cement per g residue, the Pb leaching was reduced by a factor ranging from 70 to 100, but still exceeded the Pb landfill limit of 2 mg/l. With PO4(3-) the Pb leaching was reduced with a factor of 100-300 to below 2 mg/l. The Zn landfill limit (10 mg/l) was only exceeded by one untreated residue. Adding 0.2 g cement or 0.1 g PO4(3-) per g of that residue was enough to reduce leaching below 10 mg/l. However, when 0.6 g Na2HPO4 per g residue was added to a lime based scrubber residue, an increase in Zn leaching up to 12.5 mg/l was observed due to an increase in pH of up to 13.0. When using NaH2PO4 and H3PO4 no such increase in Zn leaching was observed. pH dependent leaching performed on one of the four residues showed that in the pH range of 2.5-6, Pb leaching was 100-50 times lower with Na2HPO4 treatment than with cement. In the pH range from 7-11, almost equal results were obtained for cement treated and Na2HPO4 treated residue. Above a pH of 12, Pb leaching was three times lower for the PO(4)(3-)-treated residue than for the cement treated residue. With soluble PO4(3-), Pb leaching below 2 mg/l could be attained at a dosage of 0.27 g PO4(3-)/g residue. With cement, Pb leaching was never below 2 mg/l.

Electrodialysis and nanofiltration of surface water for subsequent use as infiltration water

In order to achieve stable groundwater levels, an equilibrium between the use of groundwater for drinking water production and natural or artificial groundwater recharge by infiltration is needed. Local governments usually require that the composition of the water used for artificial recharge is similar to the surface water that is naturally present in the specific recharge area. In this paper, electrodialysis (ED) and nanofiltration were evaluated as possible treatment technologies for surface water from a canal in Flanders, the North of Belgium, in view of infiltration at critical places on heathlands. Both methods were evaluated on the basis of a comparison between the water composition after treatment and the composition of local surface waters. The treatment generally consists of a tuning of pH and the removal of contaminants originating from industrial and agricultural activity, e.g., nitrates and pesticides. Further evaluation of the influence of the composition of the water on the characteristics of the artificial recharge, however, was not envisaged. In a case study of water from the canal Schoten-Dessel, satisfactory concentration reductions of Cl(-), SO(4)(2-), NO(3)(-), HCO(3)(-), Na(+), Mg(2+), K(+) and Ca(2+) were obtained by ultrafiltration pretreatment followed by ED. Nanofiltration with UTC-20, N30F, Desal 51 HL, UTC-60 and Desal 5 DL membranes resulted in an insufficient removal level, especially for the monovalent ions.

Environmental assessment of waste matrices contaminated with arsenic

The use of equilibrium-based and mass transfer-based leaching tests has been proposed to provide an integrated assessment of leaching processes from solid wastes. The objectives of the research presented here are to (i) validate this assessment approach for contaminated soils and cement-based matrices, (ii) evaluate the use of diffusion and coupled dissolution-diffusion models for estimating constituent release, and (iii) evaluate model parameterization using results from batch equilibrium leaching tests and physical characterization. The test matrices consisted of (i) a soil contaminated with arsenic from a pesticide production facility, (ii) the same soil subsequently treated by a Portland cement stabilization/solidification (S/S) process, and (iii) a synthetic cement-based matrix spiked with arsenic(III) oxide. Results indicated that a good assessment of contaminant release from contaminated soils and cement-based S/S treated wastes can be obtained by the integrated use of equilibrium-based and mass transfer-based leaching tests in conjunction with the appropriate release model. During the time scale of laboratory testing, the release of arsenic from the contaminated soil matrix was governed by diffusion and the solubility of arsenic in the pore solution while the release of arsenic from the cement-based matrices was mainly controlled by solubilization at the interface between the matrix and the bulk leaching solution. In addition, results indicated that (i) estimation of the activity coefficient within the matrix pore water is necessary for accurate prediction of constituent release rates and (ii) inaccurate representation of the factors controlling release during laboratory testing can result in significant errors in release estimates.

Characterisation and treatment of roads covered with zinc ashes, muffle furnace fragments and lead slags from former non-ferrous metal industries in Belgium

Zinc ashes, muffle furnace fragments and lead slags from non-ferrous industries were applied to pave roads in the North of Belgium. From an inventory it appeared that there are at least 490 km of such roads. In our survey the materials on these roads were characterised. The total metal concentration, the availability and the leaching as a function of time were determined. It appeared that these materials contain high concentrations of heavy metals, some of which are readily available. The high leaching of some metals makes them as such unsuitable as secondary construction material. Methods for the application of these materials for road construction were examined where the materials replaced part of the sand and gravel fraction in lean concrete and in bituminous mixtures, or where they replaced the sand in sand-cement mixtures, all these to be used for road foundations, cycle tracks, etc. When lead slags were applied in lean concrete, a material was obtained complying with the standards for secondary construction materials and with sufficient compressive strength for road foundations. When zinc ashes or muffle fragments were used to replace sand in sand-cement mixtures, again a suitable construction material was obtained. The other combinations tried out were rather unsuccessful, because of high metal leaching and/or poor compressive strength.

Modelling of the retention of uncharged molecules with nanofiltration

In this paper, a model is developed for the retention of organic molecules with a given nanofiltration membrane at different pressures as a function of the molecular weight. The Spiegler-Kedem transport equations were used to derive the reflection coefficient, the maximal retention that would theoretically be obtained at infinite transmembrane pressure, from experimental retention values for a large set of molecules with the effective diameter of the molecule as a size parameter. Secondly, the pore size distribution of the membrane is derived from the experimental reflection coefficients. This allows to calculate the reflection coefficient for a molecule with a given effective diameter. Since this parameter is not readily available, a correlation between the effective diameter and the molecular weight has been established and introduced in the model equations. Subsequently, the contribution of diffusion in the transport of molecules through the membrane was evaluated by introducing a membrane diffusion parameter, which was determined experimentally for the membranes NF70, NTR 7450 and UTC-20. Finally, the pore size distribution, the diffusion parameter and the experimental water flux through the membrane were used to calculate the retention as a function of the molecular weight and pressure for the same three membranes. This allows to determine retention curves at different pressures, and to calculate the variation of the MWC with pressure.

Flux decline during nanofiltration of organic components in aqueous solution

Flux decline due to interaction of the membrane with the feed solution is a major drawback for the use of nanofiltration in environmental applications. This paper studies different mechanisms of flux decline for the nanofiltration of aqueous solutions containing organic compounds. The resistance model for flux decline is used: different mechanisms contribute through an increase of the resistance of the membrane against mass transport. The focus in this research is on pore blocking and adsorption inside the membrane pores. Osmotic pressure is also taken into account as it decreases the driving force. The nanofiltration membranes used were NF70 (Dow), UTC-20 and UTC-60 (Toray Ind.), and NTR 7450 (Nitto-Denko). Experiments with different organic components in aqueous solution showed that adsorption resulted in a strong decrease of the water flux. The results of the flux decline as a function of the concentration could well be fitted with the Freundlich equation for adsorption. The components that showed the largest effect had the highest polarity (permanent dipole moment or polarizability), which indicates that adsorption is favored by the polarity of the components in solution. Moreover, the molecules with a size similar to the pore size had a stronger effect on the water flux than other molecules. This can be explained by blocking of the pores by adsorbed compounds.

Evaluation of the use of a sequential extraction procedure for the characterization and treatment of metal containing solid waste

Metal containing wastes like MSWI fly ashes and blast furnace sludge form a major environmental problem as they are polluted with heavy metals. The ash has to be landfilled or can be used as a construction material, but a pretreatment is in general necessary. Washing of the ashes with water in order to dissolve soluble salts or extracting the heavy metals with chemicals are possibilities. Blast furnace sludge contains large quantities of iron and carbon and could be recycled in the blast furnace, if the zinc content were not that high. Using a hydrometallurgical process the zinc can be removed from the sludge particles. In order to evaluate such treatment methods knowledge of the leaching behaviour of the studied material is very important. One of the factors influencing the leaching behaviour is the composition and mineralogy of the solids. A sequential extraction procedure, whereby the material is sequentially leached with different leaching solutions, can be used as an aid to characterize the material and to determine which chemical conditions are needed to obtain a sufficient extraction efficiency. To verify the accuracy of the sequential extraction procedure, a method is tested on MSWI fly ash and evaluated by comparing the results with those of leaching experiments whereby the final pH of the leaching solutions is varied over a wide range. Based upon this evaluation some suggestions for the use of the sequential extraction procedure are made and an adapted procedure is suggested, and applied to a blast furnace sludge.

Soil- and plant-based countermeasures to reduce 137Cs and 90Sr uptake by grasses in natural meadows: the REDUP project

The effectiveness of a set of soil- and plant-based countermeasures to reduce 137Cs and 90Sr transfer to plants was tested in natural meadows in the area affected by Chernobyl fallout. Countermeasures comprised the use of agricultural practices (disking + ploughing, liming and NPK fertilisation), addition of soil amendments and reseeding with a selection of grass species. Disking + ploughing was the most effective treatment, whereas the K fertiliser doses applied were insufficient to produce a significant increase in K concentration in soil solution. The application of some agricultural practices was economically justifiable for scenarios with a high initial transfer, such as 137Cs-contaminated organic soils. The use of soil amendments did not lead to a further decrease in transfer. Laboratory experiments demonstrated that this was because of their low radionuclide sorption properties. Finally, experiments examining the effect of plant species on radionuclide transfer showed that both transfer and biomass can depend on the plant species, indicating that those with high radionuclide root uptake should be avoided when reseeding after ploughing.