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.

No abstract

a b s t r a c tAn increasing number of studies has been focused on the investigation of sludge treatment by microwave irradiation alone or combined with chemical methods. Besides the promising results for municipal sludge processing, the applicability of microwave pre-treatment methods is less evaluated and verified for food industry sludge, especially in continuous-flow operations. Therefore, our work is aimed at the investigation of microwave-alkaline treatment for meat processing sludge using disintegration degree (DD) and aerobic biodegradation index (BDI) as control parameters. Our results verified that irradiated microwave energy (E s ), calculated from microwave power and flow rate applied during continuous flow microwave process, and alkaline dosage also have a significant effect on disintegration degree and aerobic biodegradability. With microwave-alkaline treatment the DD was improved to over 45% from the initial value of 12%. The change of BDI cannot be described by the same tendency that obtained for DD. Due to the combined treatment, the BDI was improved from 7.8% to 25%, but over a certain value of E s and alkaline dosage, the aerobic biodegradability starts to worsen. Measurement of dielectric constant has been proved suitable to detect the physicochemical changes in sludge structure due to microwave-alkaline treatment, and behaviour of dielectric constant as a function of E s and alkaline dosage show a tendency similar to that which obtained for DD. These preliminary results enable the further and deeper analysis of dielectric parameters of sludge in order to find suitable real-time and/or in-line method to estimate the disintegration efficiency during sludge treatment processes.

Considering the rapid, volumetric and selective heating effects of microwaves the microwave assisted chemical methods could provide appropriate alternatives for conventional thermal methods in sludge processing. Microwave irradiation alone is suitable to accelerate the hydrolysis stage of anaerobic decomposition of sludge resulted in accelerated biogas production rate and in higher biogas yield. Alkaline pre-treatments increase the organic matter solubility and suitable for disintegration of sludge particles. In some study are concluded that acidic conditions help the disintegration of waste activated sludge and assist in the solubilisation of carbohydrates and proteins which led to increased higher biogas production, as well. Beside the promising results related to effects of microwave pre-treatments on anaerobic digestion of sludge there are very few reports on the investigation of combined acidic/alkali-microwave pre-treatment method for food industry originated sludge. Hence, our study focused on the examination of the effects of combined microwave-alkali and microwave-acidic pre-treatment on aerobic and anaerobic biodegradability of sludge produced in dairy industry Our experimental results verified, that microwave irradiation with alkaline dosage improve the solubility of organic matters in the pH range of 8-12. But enhancement of disintegration was not correlated linearly with biodegradability. During pre-treatment stage, applying pH over 10, the aerobic biodegradability show decreasing tendency. Applying of acidic condition during microwave irradiation resulted in lower disintegration degree than obtained for microwave-alkaline sludge pre-treatment method. But with microwave assisted acidic pre-treatments a higher aerobic biodegradability could be achieved than with alkaline dosage. In microwave pre-treatments acidic condition was preferable to increase the shorter aerobic biodegradability; the alkaline condition was favourable to intensify the anaerobic digestion process.

The amount of waste activated sludge (WAS) is increasing annually, and since it presents potential environmental and health-related risks, an appropriate treatment and stabilization process is needed. It has been shown in numerous studies in the past few decades that amongst the advanced treatment methods of sludge, microwave and ultrasound-based processes offer promising and effective alternatives. The main advantage of these physical methods is that they are energy-efficient, easy to implement and can be combined with other types of treatment procedures without major difficulties. In this review article we would like to present the recent scientific results of the microwave, ultrasound and combined (microwave-alkaline, microwave-H2O2, ultrasound-alkaline and ultrasound-H2O2) treatment of wastewater sludge, in terms of different process-efficiency indicators. Although the obtained results somewhat vary between the different scientific papers, it can be undoubtedly stated that both MW and US—either individually or in combination with chemical treatments—can enhance several aspects of sludge processing, like increasing the SCOD/TCOD rate, disintegration degree (DD), or the anaerobic digestibility (AD), but the extent of these increments clearly depends on the treatment conditions or parameters.

Enzymes are biological catalysts that generally are designed to do one job well, but to do one job only. Therefore, the enzymes that catalyze the hydrolysis of cellulose to sugar do not break down the sugars. Enzymatic hydrolysis processes have been under development for only 10 years. The important research issues include understanding the processes necessary to render the crystalline cellulose easily digestible, understanding and improving the basic mechanisms in the hydrolysis step, and developing better and less expensive enzymes. The other way to make a process less expensive may be the recycling of enzymes. The essential unit operation in the bioethanol production is the cellulose enzymatic degradation, so the question of recycling is very important. In our work the sonication assisted ultrafiltration was investigated as a potential method for enzyme recycling. The results showed the ultrasound effects the permeate flux since the resistance is reduced by the sonication. The sonicated enzyme keeps its activity so the recycling mechanism might be used for bioethanol production.

In our work the efficiency of enzymatic degradation of cellulosic biomass was investigated by conventional analytical methods and dielectric measurements. Our results show, that the dielectric measurements proved to be efficient and rapid method to detect the chemical and physicochemical change of biomass during the enzymatic hydrolysis of cellulose. Because of molecular weight decreasing, and the increasing of the concentration of polar and ionic components, the polarization ability of the system has been changed, what manifested in the change of dielectric parameters. Furthermore, dielectric measurements were suitable to detect the efficiency of biomass pre-treatment, as well.

Abstract-