Comparison of filtering models for milk substitutes.

Membrane-based methods of filtering are becoming increasingly popular in the food industry, but membrane fouling significantly affects filtration performance, making the characterisation of fouling mechanisms critical. This study examined the applicability of three mathematical models. The resistance-in-series model divides the total resistance into membrane resistance, reversible resistance and irreversible resistance. The Hermia models distinguish four basic blocking mechanisms, namely complete blocking, standard blocking, intermediate blocking and cake filtration. The Makardij model analyses the flux-reducing or -enhancing effects. In the experiments, different models were investigated and compared. The feed solution was two milk substitute drinks (soy and oat) that were ultrafiltered under different operating parameters (transmembrane pressures: 0.05-0.1 MPa, stirring rate: 100-400 min-1). By fitting the data to the models, the most characteristic blocking mechanism and the rate constant that most influenced flux could be determined.

Application of dielectric constant measurement in microwave sludge disintegration and wastewater purification processes.

It has been numerously verified that microwave radiation could be advantageous as a pre-treatment for enhanced disintegration of sludge. Very few data related to the dielectric parameters of wastewater of different origins are available; therefore, the objective of our work was to measure the dielectric constant of municipal and meat industrial wastewater during a continuous flow operating microwave process. Determination of the dielectric constant and its change during wastewater and sludge processing make it possible to decide on the applicability of dielectric measurements for detecting the organic matter removal efficiency of wastewater purification process or disintegration degree of sludge. With the measurement of dielectric constant as a function of temperature, total solids (TS) content and microwave specific process parameters regression models were developed. Our results verified that in the case of municipal wastewater sludge, the TS content has a significant effect on the dielectric constant and disintegration degree (DD), as does the temperature. The dielectric constant has a decreasing tendency with increasing temperature for wastewater sludge of low TS content, but an adverse effect was found for samples with high TS and organic matter contents. DD of meat processing wastewater sludge was influenced significantly by the volumetric flow rate and power level, as process parameters of continuously flow microwave pre-treatments. It can be concluded that the disintegration process of food industry sludge can be detected by dielectric constant measurements. From technical purposes the applicability of dielectric measurements was tested in the purification process of municipal wastewater, as well. Determination of dielectric behaviour was a sensitive method to detect the purification degree of municipal wastewater.