Enhancing pharmaceutical crystallization in a flow crystallizer with ultrasound: Anti-solvent crystallization.

Continuous crystallization is a fast growing application domain in the pharmaceutical industry. Application of ultrasound has been proven to have positive effects like reduction in induction time and Metastable Zone Width (MSZW) in both batch and flow systems. Further understanding of flow-based sonocrystallization is required to achieve industrial level scale up. This work investigates the sonocrystallization of pharmaceutical compounds in a tubular flow crystallizer. Acetyl Salicylic Acid (ASA-Aspirin) is used as a model compound with ethanol and water as solvent and anti-solvent, respectively. Experiments were conducted in silent and sonicated conditions to study the MSZW. Ultrasound made it possible to achieve crystallization within the crystallizer which was not possible in silent conditions, under the tested conditions. Continuous crystallization was achieved at as low as 48 wt% of anti-solvent and crystallization was already seen at a supersaturation of 1.02. In some experiments, temperature rise with ultrasound caused the crystals to re-dissolve within the channels. Better crystallization - no re-dissolution - was achieved by using low ultrasonic power without any loss in the yield. Particle sizes of product crystals were in the range of 4-46 µm. In conclusion, ultrasound was highly effective in enabling anti-solvent crystallization of a pharmaceutical compound in a tubular flow crystallizer.

Influence of dissolved gases on sonochemistry and sonoluminescence in a flow reactor.

In the present work, the influence of gas addition is investigated on both sonoluminescence (SL) and radical formation at 47 and 248 kHz. The frequencies chosen in this study generate two distinct bubble types, allowing to generalize the conclusions for other ultrasonic reactors. In this case, 47 kHz provides transient bubbles, while stable ones dominate at 248 kHz. For both bubble types, the hydroxyl radical and SL yield under gas addition followed the sequence: Ar>Air>N2>>CO2. A comprehensive interpretation is given for these results, based on a combination of thermal gas properties, chemical reactions occurring within the cavitation bubble, and the amount of bubbles. Furthermore, in the cases where argon, air and nitrogen were bubbled, a reasonable correlation existed between the OH-radical yield and the SL signal, being most pronounced under stable cavitation at 248 kHz. Presuming that SL and OH originate from different bubble populations, the results indicate that both populations respond similarly to a change in acoustic power and dissolved gas. Consequently, in the presence of non-volatile pollutants that do not quench SL, sonoluminescence can be used as an online tool to qualitatively monitor radical formation.

Characterization of stable and transient cavitation bubbles in a milliflow reactor using a multibubble sonoluminescence quenching technique.

The bubble type, generated by an ultrasonic field, was studied in a batch and flow reactor using a multibubble sonoluminescence (MBSL) quenching technique with propanol and acetone. The influence of frequency and transducer configuration was evaluated using the same piezoelectric element in both setups. Results show that the bubble type not only depends on the frequency, but also on the input power or transducer configuration. Additionally, the effect of flow on sonoluminescence yield and bubble type was studied in the continuous setup at various frequencies. As the flow becomes turbulent, the sonoluminescence signal reaches a plateau for three out of four frequencies, and a transition from transient to stable cavitation occurs for frequencies below 200 kHz.

Photovoltaics: reviewing the European Feed-in-Tariffs and changing PV efficiencies and costs.

Feed-in-Tariff (FiT) mechanisms have been important in boosting renewable energy, by providing a long-term guaranteed subsidy of the kWh-price, thus mitigating investment risks and enhancing the contribution of sustainable electricity. By ongoing PV development, the contribution of solar power increases exponentially. Within this significant potential, it is important for investors, operators, and scientists alike to provide answers to different questions related to subsidies, PV efficiencies and costs. The present paper therefore (i) briefly reviews the mechanisms, advantages, and evolution of FiT; (ii) describes the developments of PV, (iii) applies a comprehensive literature-based model for the solar irradiation to predict the PV solar energy potential in some target European countries, whilst comparing output predictions with the monthly measured electricity generation of a 57 m² photovoltaic system (Belgium); and finally (iv) predicts the levelized cost of energy (LCOE) in terms of investment and efficiency, providing LCOE values between 0.149 and 0.313 €/kWh, as function of the overall process efficiency and cost. The findings clearly demonstrate the potential of PV energy in Europe, where FiT can be considerably reduced or even be eliminated in the near future.

Strategic selection of an optimal sorbent mixture for in-situ remediation of heavy metal contaminated sediments: framework and case study.

Aquatic sediments contaminated with heavy metals originating from mining and metallurgical activities pose significant risk to the environment and human health. These sediments not only act as a sink for heavy metals, but can also constitute a secondary source of heavy metal contamination. A variety of sorbent materials has demonstrated the potential to immobilize heavy metals. However, the complexity of multi-element contamination makes choosing the appropriate sorbent mixture and application dosage highly challenging. In this paper, a strategic framework is designed to systematically address the development of an in-situ sediment remediation solution through Assessment, Feasibility and Performance studies. The decision making tools and the experimental procedures needed to identify optimum sorbent mixtures are detailed. Particular emphasis is given to the utilization and combination of commercially available and waste-derived sorbents to enhance the sustainability of the solution. A specific case study for a contaminated sediment site in Northern Belgium with high levels of As, Cd, Pb and Zn originating from historical non-ferrous smelting is presented. The proposed framework is utilized to achieve the required remediation targets and to meet the imposed regulations on material application in natural environments.

Synthesis of inorganic polymers using fly ash and primary lead slag.

The present work reports on the synthesis and properties of inorganic polymers ("geopolymers") made of 100% fly ash from lignite's combustion, 100% primary lead slag and mixtures of the two. In the inorganic polymers with both fly ash and lead slag the main crystalline phases detected are wüstite, magnetite, sodium zinc silicate, quartz, anorthite, and gehlenite; litharge partially dissolves. FTIR analysis in these samples revealed that the main peaks and bands of end members also exist, along with a new amorphous reaction product. In terms of microstructure, both fly ash and lead slag dissolve and contribute in the binding phase whereas the larger particles act as aggregates. For an increasing lead slag in the composition, the binding phase is changing in chemistry and reaches PbO values higher than 50 wt.% for the 100% lead slag inorganic polymer. Regarding the properties of fly ash and lead slag inorganic polymers, compressive strength is higher than 35 MPa in all cases and water absorption diminishes as the lead slag content increases. A comparison of leaching results before and after polymerisation reveals that pH is an important factor as Pb is immobilised in the binding phase, unlike Zn and As.

Municipal solid waste generation in growing urban areas in Africa: current practices and relation to socioeconomic factors in Jimma, Ethiopia.

As one of cities in the developing countries, a rapid population growth and industrial activities pose many environmental challenges for Jimma city, Ethiopia. One aspect of urban growth posing a threat on sustainable development is poor solid waste management, which results in environmental pollution. The purpose of this study is to evaluate the quantity, composition, sources of waste generated, their current disposal practices, and to recommend appropriate management technologies. The total waste generated daily in Jimma city was ca. 88,000 kg, and the average per capita generation rate was 0.55 ± 0.17 kg/capita/day. Eighty-seven percent of the waste was produced by households and 13% by institutions, and a negligible fraction (0.1%) was generated by street sweepings. During the rainy season, 40% more waste was generated than in the dry season because of the increased availability of agricultural food product. Further analysis showed that biodegradable organic waste constitutes 54% by weight with an average moisture content of 60% that falls within the required limits for composting. The nonbiodegradable components constitute 46% of which 30% of it was nonrecyclable material. Only 25% of the community uses municipal containers for disposal at the selected landfill site. Fifty-one percent of the households disposed their waste in individually chosen spots, whereas 22% burned their waste. Finally 2% of households use private waste collectors. The socioeconomic analysis showed that higher family income and educational status is associated more with private or municipal waste collection and less with the application of backyard or open dumping. These insights into generated waste and management practice in Jimma city allow making suggestions for improved collection, treatment, and disposal methods. A primary conclusion is that the biodegradable waste is a major fraction having suitable properties for recycling. As such an economic benefit can be obtained from this waste while avoiding the need for disposal.

Energetic valorization of wood waste: estimation of the reduction in CO2 emissions.

This paper investigates the potential CO(2) emission reductions related to a partial switch from fossil fuel-based heat and electricity generation to renewable wood waste-based systems in Flanders. The results show that valorization in large-scale CHP (combined heat and power) systems and co-firing in coal plants have the largest CO(2) reduction per TJ wood waste. However, at current co-firing rates of 10%, the CO(2) reduction per GWh of electricity that can be achieved by co-firing in coal plants is five times lower than the CO(2) reduction per GWh of large-scale CHP. Moreover, analysis of the effect of government support for co-firing of wood waste in coal-fired power plants on the marginal costs of electricity generation plants reveals that the effect of the European Emission Trading Scheme (EU ETS) is effectively counterbalanced. This is due to the fact that biomass integrated gasification combined cycles (BIGCC) are not yet commercially available. An increase of the fraction of coal-based electricity in the total electricity generation from 8 to 10% at the expense of the fraction of gas-based electricity due to the government support for co-firing wood waste, would compensate entirely for the CO(2) reduction by substitution of coal by wood waste. This clearly illustrates the possibility of a 'rebound' effect on the CO(2) reduction due to government support for co-combustion of wood waste in an electricity generation system with large installed capacity of coal- and gas-based power plants, such as the Belgian one.

Effect of carbonation on the leaching of organic carbon and of copper from MSWI bottom ash.

In Flanders, the northern part of Belgium, about 31% of the produced amount of MSWI bottom ash is recycled as secondary raw material. In view of recycling a higher percentage of bottom ash, a particular bottom ash fraction (Ø 0.1-2mm) was studied. As the leaching of this bottom ash fraction exceeds some of the Flemish limit values for heavy metals (with Cu being the most critical), treatment is required. Natural weathering and accelerated carbonation resulted in a significant decrease of the Cu leaching. Natural weathering during 3 months caused a decrease of Cu leaching to <50% of its original value, whereas accelerated carbonation resulted in an even larger decrease (to ca. 13% of its initial value) after 2 weeks, with the main decrease taking place within the first 48 h. Total organic carbon decreased to ca. 70% and 55% of the initial concentration in the solid phase, and to 40% and 25% in the leachate after natural weathering and after accelerated carbonation, respectively. In the solid material the decrease of the Hy fraction was the largest, the FA concentration remained essentially constant. The decrease of FA in the leachate can be attributed partly to an enhanced adsorption of FA to Fe/Al (hydr)oxides, due to the combined effect of a pH decrease and the neoformation of Al (hydr)oxides (both due to carbonation). A detailed study of adsorption of FA to Fe/Al (hydr)oxides showed that significant adsorption of FA occurs, that it increases with decreasing pH and started above pH 12 for Fe (hydr)oxides and around 10 for Al (hydr)oxides. Depending whether FA or Hy are considered the controlling factor in enhanced Cu leaching, the decreasing FA or Hy in the leachate explains the decrease in the Cu leaching during carbonation.

Influence of treatment techniques on Cu leaching and different organic fractions in MSWI bottom ash leachate.

The leaching of heavy metals, such as copper, from municipal solid waste incinerator (MSWI) bottom ash is of concern in many countries and may inhibit the beneficial reuse of this secondary material. Previous studies have focused on the role of dissolved organic carbon (DOC) on the leaching of copper. Recently, a study of the Energy Research Centre of The Netherlands (ECN) showed fulvic acid-type components to exist in the MSWI bottom ash leachates and to be likely responsible for the generally observed enhanced copper leaching. These findings were verified for a MSWI bottom ash (slashed circle 0.1-2 mm) fraction from an incinerator in Flanders. The filtered leachates were subjected to the IHSS fractionation procedure to identify and quantify the fractions of humic acid (HA), fulvic acid (FA) and hydrophilic organic carbon (Hi). The possible complexation of fulvic acid with other heavy metals (e.g., lead) was also investigated. The identified role of fulvic acids in the leaching of copper and other heavy metals can be used in the development of techniques to improve the environmental quality of MSWI bottom ash. Thermal treatment and extraction with a 0.2 M ammonium-citrate solution were optimized to reduce the leaching of copper and other heavy metals. The effect of these techniques on the different fractions of organic matter (HA, FA, Hi) was studied. However, due to the obvious drawbacks of the two techniques, research is focused on finding other (new) techniques to treat MSWI bottom ash. In view of this, particle size-based separation was performed to evaluate its effect on heavy metal leaching and on HA, FA and Hi in MSWI bottom ash leachates.

Effects of carbonation and leaching on porosity in cement-bound waste.

Porosity is possibly an important parameter with respect to leaching of constituents from cement monoliths. During its lifetime, the pore structure of cementitious matrices changes due to carbonation and leaching. This paper discusses the effects of both accelerated carbonation and continuous leaching on the porosity, and, conversely, how porosity affects leaching properties. Two sample types are investigated: a mortar with MSWI-bottom ash substituting the sand fraction and a cement paste with 30 wt% of the cement substituted by a flue gas cleaning residue. The samples have been intensively carbonated in a 20% CO(2) atmosphere for up to 60 days and were subsequently leached. The porosity was investigated by mercury intrusion porosimetry. Accelerated carbonation decreases total porosity by 12% in the case of 60 days of treatment of bottom ash mortars, whereas continuous leaching during 225 days increases it by 16%. Both carbonation and leaching decrease the amount of smaller capillary pores. Carbonation decreases both porosity and pH. Decreasing porosity diminishes leaching of sodium and potassium, while the decrease in pH increases leaching. However, the former process dominates the latter, resulting in a net decreasing effect of carbonation on the release of sodium and potassium from these cement matrices.

Integrated municipal solid waste treatment using a grate furnace incinerator: the Indaver case.

An integrated installation for treatment of municipal solid waste and comparable waste from industrial origin is described. It consists of three grate furnace lines with flue gas treatment by half-wet scrubbing followed by wet scrubbing, and an installation for wet treatment of bottom ash. It is demonstrated that this integrated installation combines high recovery of energy (40.8% net) with high materials recovery. The following fractions were obtained after wet treatment of the bottom ash: ferrous metals, non-ferrous metals, three granulate fractions with different particle sizes, and sludge. The ferrous and non-ferrous metal fractions can both be recycled as high quality raw materials; the two larger particle size particle fractions can be applied as secondary raw materials in building applications; the sand fraction can be used for applications on a landfill; and the sludge is landfilled. For all components of interest, emissions to air are below the limit values. The integrated grate furnace installation is characterised by zero wastewater discharge and high occupational safety. Moreover, with the considered installation, major pollutants, such as PCDD/PCDF, Hg and iodine-136 are to a large extent removed from the environment and concentrated in a small residual waste stream (flue gas cleaning residue), which can be landfilled after stabilisation.

Extraction of heavy metals from municipal solid waste incinerator (MSWI) bottom ash with organic solutions.

Municipal solid waste incinerator (MSWI) bottom ash often cannot be recycled as construction material in Flanders, because leaching of Cu exceeds the limit value of 0.5mg/kg. Leaching of other components such as Mo and Sb is critical as well, but limit values for these elements are to date only informal. A treatment technique was investigated to lower pollutant leaching: extraction with solutions of organic complexants to remove Cu. Six different solutions were used, of which washing with citric acid and ammonium citrate decreases Cu leaching to below the limit value. Extraction was then performed with different concentrations of ammonium citrate. Subsequent washing of the extracted material with distilled water appears to be vital to remove all residual ammonium citrate. Extraction with a 0.2M solution of ammonium citrate followed by three washing steps decreases metal leaching to below the limit values.

Accelerated carbonation for treatment of MSWI bottom ash.

Leaching of heavy metals from MSWI bottom ash exceeds some of the Flemish limit values for recycling the material as granular construction application. In particular, leaching of Cu, Zn and Pb often exceeds the limit value, with Cu being the most critical. In order to recycle bottom ash, treatment is therefore required. The bottom ash studied was divided on-site into four fractions using a large-scale wet sieving installation: a sludge fraction (Ø 0-0.1mm), a sand fraction (Ø 0.1-2mm) and two gravel fractions (Ø 2-6 and 6-50mm). The two gravel fractions complied with the limit values after 3 months of natural ageing. The sand and sludge fraction did not reach the limit value for Cu. Four weeks of accelerated carbonation resulted in an important decrease of Cu leaching from these two fractions, although the limit value is still exceeded. In view of applying carbonation as one of the treatment methods in an integrated industrial application, two tests were additionally performed. The use of stack gas as carbonating medium was verified by setting up an accelerated carbonation experiment at the incineration plant. Also, the depth of carbonation was measured in a 10 cm thick sample of the sand fraction after different periods of treatment. After 3 months of natural ageing only the upper 4 cm underwent a significant carbonation, while after one week of accelerated carbonation the total sample was carbonated. A model was developed to predict these experimental results.

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.

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.

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.