Correlation of wood-based components and dewatering properties of waste activated sludge from pulp and paper industry.

Large amounts of wet sludge are produced annually in municipal and industrial wastewater treatment. Already in pulp and paper industry, more than ten million tons of primary sludge, waste activated sludge, and de-inking sludge is generated. Waste activated sludge contains large quantities of bound water, which is difficult to dewater. Low water content would be a matter of high calorific value in incineration but it also has effects on the volume and the quality of the matter to be handled in sludge disposal. In this research waste activated sludges from different pulp and paper mills were chemically characterised and dewatered. Correlations of chemical composition and dewatering properties were determined using multivariate analysis. Chemical characterisation included basic sludge analysis, elementary analysis and analysis of wood-based components, such as hemicelluloses and lignin-derived material. Dewatering properties were determined using measurements of dry solids content, flux and flocculant dosage. The effects of different variables varied according to the response concerned. The variables which were significant regarding cake DS increase in filtration or centrifugation and flocculant dosage needed in filtration were different from those which were significant regarding flux.

Ultrasound assisted cleaning of ceramic capillary filter.

Research in the fields of filtration and dewatering connected with the use of ultrasound (US) has been carried out mainly with small laboratory-scale batch or continuously operating devices. So far the only large scale industrial cake filtration applications have been developed and manufactured by Larox Oyj for mining industry. These applications apply ultrasound for cleaning of ceramic capillary action elements having at maximum total filtration area of approximately 150 m(2). Several hundreds of filter units have been delivered worldwide during the past two decades.

New processing technique for viscous amorphous materials and characterisation of their stickiness and deformability.

This paper reports on a technique using ultrasound-assisted equipment to characterise and handle stickiness of viscous amorphous blends of citric acid and paracetamol after melt mixing and during processing. Deformability and stickiness were studied using a specially designed sample measurement compartment. An ultrasound-assisted nozzle and knife for pharmaceutical applications were studied. The application of ultrasound was found to increase the mass flow through a nozzle connected to a pressurized tank. This effect was found to be separate from the increased mass transport resulting from the reduced viscosity as the temperature was increased. Ultrasound was also found to have a favourable influence on cutting through melt extrudates. The stickiness and resistance to deformation of samples were observed to be dependent on the amount of paracetamol in the blend and temperature that was in agreement with the glass transition temperature and viscosity. Other influencing factors, such as time-dependent wetting and surface energetics, are discussed. We conclude that it is possible to characterise stickiness and resistance to deformation of viscous amorphous materials with a specially designed probe test, and the stickiness of amorphous material can be handled during processing with ultrasound-assisted equipment.

Ultrasonic depolymerization of aqueous carboxymethylcellulose.

Prolonged exposure of solutions of macromolecules to high-energy ultrasonic waves produces a permanent reduction in viscosity. However, the exact mechanism by which degradation occurs is still open to discussion. According to this study hydrodynamic forces played the primary role in degradation process. This study showed that there is an optimal carboxymethylcellulose (CMC) concentration to the most efficient degradation. Ultrasound degraded preferentially large CMC molecules and cleavage took place roughly at the centre of the CMC molecules. Degradation of CMC did not proceed below a certain molecular mass. During ultrasonic degradation the molecular mass distribution narrowed. For any polymer degradation process to become acceptable to industry, it is important to be able to specify the sonication conditions to produce a particular relative molecular mass distribution.

Ultrasonic depolymerization of aqueous polyvinyl alcohol.

Ultrasonication has proved to be a highly advantageous method for depolymerizing macromolecules because it reduces their molecular weight simply by splitting the most susceptible chemical bond without causing any changes in the chemical nature of the polymer. Most of the effects involved in controlling molecular weight can be attributed to the large shear gradients and shock waves generated around collapsing cavitation bubbles. In general, for any polymer degradation process to become acceptable to industry, it is necessary to be able to specify the sonication conditions which lead to a particular relative molar mass distribution. This necessitates the identification of the appropriate irradiation power, temperature, concentration and irradiation time. According to the results of this study the reactors constructed worked well in depolymerization and it was possible to degrade aqueous polyvinyl alcohol (PVA) polymer with ultrasound. The most extensive degradation took place at the lowest frequency used in this study, i.e. 23 kHz, when the input power was above the cavitation threshold and at the lowest test concentration of PVA, i.e. 1% (w/w). Thus this study confirms the general assumption that the shear forces generated by the rapid motion of the solvent following cavitational collapse are responsible for the breakage of the chemical bonds within the polymer. The effect of polymer concentration can be interpreted in terms of the increase in viscosity with concentration, causing the molecules to become less mobile in solution and the velocity gradients around the collapsing bubbles to therefore become smaller.