Challenges of a feasible route towards sustainability in environmental protection

Anaerobic processes for treatment of low and high strength wastewaters and solid wastes constitute the core method in the natural biological mineralization (NBM) treatment concept. When adequately combined with the complementary NBM-systems and modern clean water saving practices in wastewater collection and transport, they represent a feasible route to sustainable environmental protection (EPsus), in essence even towards a more sustainable society. Despite the development and implementation of modern high rate Anaerobic Wastewater Treatment (AnWT-) systems and complementary innovative NBM-processes, the considerable progress made since the seventies in fundamental insights in microbiology, biochemistry and process technology, still numerous challenging improvements in the NBM-field can be realized. This contribution is mainly based on the insights attained from wide ranging literature evaluations and the results of experimental research conducted by numerous PhD students who participated in our group over the last four decades. An attempt is made here to identify major facets on which an improved insight can, and consequently should, be obtained in order to accomplish more optimal operation and design of various types of Anaerobic Degradation (AnDeg-) processes

Crystallization Kinetics of Colloidal Spheres under Stationary Shear Flow

A systematic experimental study of dispersions of charged colloidal spheres is presented on the effect of steady shear flow on nucleation and crystal-growth rates. In addition, the non-equilibrium phase diagram as far as the melting line is concerned is measured. Shear flow is found to strongly affect induction times, crystal growth rates and the location of the melting line. The main findings are that (i) the crystal growth rate for a given concentration exhibits a maximum as a function of the shear rate, (ii) contrary to the monotonous increase of the growth rate with increasing concentration in the absence of flow, a maximum of the crystal growth rate as a function of concentration is observed for sheared systems, and (iii) the induction time for a given concentration exhibits a maximum as a function of the shear rate. These findings will be partly explained on a qualitative level.Comment: 17 pages, 10 figures, accepted in Langmui

Trains, tails and loops of partially adsorbed semi-flexible filaments

Polymer adsorption is a fundamental problem in statistical mechanics that has direct relevance to diverse disciplines ranging from biological lubrication to stability of colloidal suspensions. We combine experiments with computer simulations to investigate depletion induced adsorption of semi-flexible polymers onto a hard-wall. Three dimensional filament configurations of partially adsorbed F-actin polymers are visualized with total internal reflection fluorescence microscopy. This information is used to determine the location of the adsorption/desorption transition and extract the statistics of trains, tails and loops of partially adsorbed filament configurations. In contrast to long flexible filaments which primarily desorb by the formation of loops, the desorption of stiff, finite-sized filaments is largely driven by fluctuating filament tails. Simulations quantitatively reproduce our experimental data and allow us to extract universal laws that explain scaling of the adsorption-desorption transition with relevant microscopic parameters. Our results demonstrate how the adhesion strength, filament stiffness, length, as well as the configurational space accessible to the desorbed filament can be used to design the characteristics of filament adsorption and thus engineer properties of composite biopolymeric materials

Dynamic Response of Block Copolymer Wormlike Micelles to Shear Flow

The linear and non-linear dynamic response to an oscillatory shear flow of giant wormlike micelles consisting of Pb-Peo block copolymers is studied by means of Fourier transform rheology. Experiments are performed in the vicinity of the isotropic-nematic phase transition concentration, where the location of isotropic-nematic phase transition lines is determined independently. Strong shear-thinning behaviour is observed due to critical slowing down of orientational diffusion as a result of the vicinity of the isotropic- nematic spinodal. This severe shear-thinning behaviour is shown to result in gradient shear banding. Time-resolved Small angle neutron scattering experiments are used to obtain insight in the microscopic phenomena that underly the observed rheological response. An equation of motion for the order-parameter tensor and an expression of the stress tensor in terms of the order-parameter tensor are used to interpret the experimental data, both in the linear and non-linear regime. Scaling of the dynamic behaviour of the orientational order parameter and the stress is found when critical slowing down due to the vicinity of the isotropic-nematic spinodal is accounted for.Comment: Accepted by J. Phys.: Condens. Matter, CODEF II Special Issue. 20 pages, 9 figure

Dynamic Response of Block Copolymer Wormlike Micelles to Shear Flow

The linear and non-linear dynamic response to an oscillatory shear flow of giant wormlike micelles consisting of Pb-Peo block copolymers is studied by means of Fourier transform rheology. Experiments are performed in the vicinity of the isotropic-nematic phase transition concentration, where the location of isotropic-nematic phase transition lines is determined independently. Strong shear-thinning behaviour is observed due to critical slowing down of orientational diffusion as a result of the vicinity of the isotropic- nematic spinodal. This severe shear-thinning behaviour is shown to result in gradient shear banding. Time-resolved Small angle neutron scattering experiments are used to obtain insight in the microscopic phenomena that underly the observed rheological response. An equation of motion for the order-parameter tensor and an expression of the stress tensor in terms of the order-parameter tensor are used to interpret the experimental data, both in the linear and non-linear regime. Scaling of the dynamic behaviour of the orientational order parameter and the stress is found when critical slowing down due to the vicinity of the isotropic-nematic spinodal is accounted for.Comment: Accepted by J. Phys.: Condens. Matter, CODEF II Special Issue. 20 pages, 9 figure

Self-diffusion of Rod-like Viruses Through Smectic Layer

We report the direct visualization at the scale of single particles of mass transport between smectic layers, also called permeation, in a suspension of rod-like viruses. Self-diffusion takes place preferentially in the direction normal to the smectic layers, and occurs by quasi-quantized steps of one rod length. The diffusion rate corresponds with the rate calculated from the diffusion in the nematic state with a lamellar periodic ordering potential that is obtained experimentally.Comment: latex, 4 pages, 4 figures, accepted in Phys. Rev. Let

Supersaturated dispersions of rod-like viruses with added attraction

The kinetics of isotropic-nematic (I-N) and nematic-isotropic (N-I) phase transitions in dispersions of rod-like {\it fd}-viruses are studied. Concentration quenches were applied using pressure jumps in combination with polarization microscopy, birefringence and turbidity measurements. The full biphasic region could be accessed, resulting in the construction of a first experimental analogue of the bifurcation diagram. The N-I spinodal points for dispersions of rods with varying concentrations of depletion agents (dextran) were obtained from orientation quenches, using cessation of shear flow in combination with small angle light scattering. We found that the location of the N-I spinodal point is independent of the attraction, which was confirmed by theoretical calculations. Surprisingly, the experiments showed that also the absolute induction time, the critical nucleus and the growth rate are insensitive of the attraction, when the concentration is scaled to the distance to the phase boundaries.Comment: 13 pages, 14 figures. accepted in Phsical Review

Kinetic pathways of the Nematic-Isotropic phase transition as studied by confocal microscopy on rod-like viruses

We investigate the kinetics of phase separation for a mixture of rodlike viruses (fd) and polymer (dextran), which effectively constitutes a system of attractive rods. This dispersion is quenched from a flow-induced fully nematic state into the region where the nematic and the isotropic phase coexist. We show experimental evidence that the kinetic pathway depends on the overall concentration. When the quench is made at high concentrations, the system is meta-stable and we observe typical nucleation-and-growth. For quenches at low concentration the system is unstable and the system undergoes a spinodal decomposition. At intermediate concentrations we see the transition between both demixing processes, where we locate the spinodal point.Comment: 11 pages, 6 figures, accepted in J. Phys.: Condens. Matter as symposium paper for the 6th Liquid Matter Conference in Utrech

Annual Report of the Municipal Officers of the Town of Columbia Falls For The Municipal Year 1935-1936

status: publishe