Design, fabrication and optimization of a novel integrated UV-microwave assisted catalytic reactor for the continuous flow treatment of wastewater
This work has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie Grant Agreement No. .
We developed an environmentally-friendly, totally innovative method for the treatment of toxic and recalcitrant contaminants in wastewater by enhancing the rate of a novel heterogeneous catalytic treatment process using microwave energy and ultraviolet radiation. It provides a solution to the, as yet, unmet challenge of using microwaves to treat large wastewater flows with an innovative reactor design, which is scalable to meet the demands of industry. To this day, many wastewater streams containing toxic and recalcitrant pollutants in developed as well as developing countries are treated only by dilution. Individual treatment technologies are not effective in removing these recalcitrant pollutants owing to their toxicity, shock loads, selectivity and slow reaction rates. The effective integration of various treatment technologies, such as advanced oxidation processes, microwave and UV irradiation, is therefore the way forward.In recent years, several reports have demonstrated the use of microwave and ultraviolet radiation to promote the oxidative degradation of bio-refractory wastes. The radiation increases the reaction rate; providing high-efficiency with no pollution to the environment. Nevertheless, the use of microwaves in catalysis and in the water and wastewater industry remains at laboratory scale. The major challenges in the water/wastewater industries are centered on the poor penetration depth of microwaves, which restricts the dimensions of reactors.The overall objectives of the action were as follows:
- to develop a principle of scaling of a microwave and UV assisted reactor up to the dimensions required by industry, and;
- to build a reactor which proves this principle.
In the project, we proposed a principle of scaling, we numerically simulated different designs of reactors based on this principle, and we built a novel UV and microwave assisted reactor with 3 microwave ports (sections) and a variable UV flux.
Conclusion of the action: The proposed, designed and developed microwave and UV assisted reactor can be used for treatment of wide range of wastewaters: pharmaceutical, agricultural, wastewater from fracking, etc. Scaling-up the reactor would essentially broaden the number of potential users of this promising wastewater treatment technology.
Main Results Achieved So Far
We measured dielectric permittivity and loss tangent of the catalyst in dry and wet conditions. Measurements showed that the main factor affecting the levels of permittivity and loss tangent was the content of water trapped on the surface of the catalyst. The results of the measurements were used for choosing the designs of UV and microwave assisted reactors, as well as in numerical simulations of the reactors.
We have developed a principle of scaling of microwave and UV assisted reactors, and designed and numerically simulated different reactors based on this principle. In collaboration with Societe Pour L'Application Industrielle de la Recherche en Electronique et Microondes (SAIREM) and Industrial Microwave Systems Ltd (IMS) we adapted the chosen reactor design to industry standards. Some of technical solutions were simplified without reduction of basic characteristics of the system: effectiveness of microwave heating of wastewater and catalyst, UV light distribution, heat transfer and mixing in fluid streams. We determined appropriate type and frequency band of microwave sources and the type, power and quantity of UV lamps as well as all dimensions of the reactor. Finally we built the system with 3 microwave ports, 3 transmission lines and 3 magnetrons operating at 2.45 GHz (see Fig. 1). The output power of each magnetron could vary from 200 W to 2 kW so that the maximum level of microwave power of the system was 6 kW. The reactor was equipped with 10 UV low pressure lamps emitting the light at 254 nm wavelength.
The results of numerical simulations of reactor were reported on Frontiers International Conference on Wastewater Treatment, 21-24 May 2017, Palermo, Italy. The developed reactor is now being tested for the treatment of pharmaceutical and agricultural wastewaters; the results of testing as well as the final scalable design of the reactor will be published in peer reviewed journal(s). We are expecting that the reactor will be further tested towards the treatment of a wide range of pharmaceutical wastewaters, and fracking and produced water from petroleum drilling.
Progress Beyond the State of the Art, Results and Potential Impacts
The reactor system integrating UV and microwave radiations can be very effective for the degradation of wide range of recalcitrant pollutants. For instance, in preliminary experiments we found that at least a tenfold increase in the rate of degradation of clotrimazole was achieved with the UV and microwave enhanced treatment system compared to the unassisted reaction. The most important result of the project is a principle of scaling of the reactors up to dimensions required by industry. The proposed novel design of the rector is based on a layered structure of catalyst, which is formed by rotating discs partially immersed in wastewater. Our design, unlike all others reported in the literature, is highly appropriate for scaling by increasing the discs diameter as well as by a quantity of the discs.Microwave and UV radiations can propagate in gaps between the catalyst discs and accordingly deliver UV light and microwave power to inner regions of each disc.
Growing population and industrial activities mean that fresh and potable water resources are declining at an alarming rate with the generation of vast amounts of wastewater and subsequent release of contaminants in to water courses. The ever-increasing volume and diversity of pollutants offer a significant challenge to conventional wastewater treatment systems. As a result of increasing environmental awareness and more stringent legislation, most conventional wastewater treatment cannot meet discharge standards, especially those of emerging organic contaminants e.g. pharmaceuticals. In the project, we developed a method of treatment, the reactor design and the principle of scaling of UV and microwave assisted reactors, which can be successfully implemented in water and wastewater industry for treatment of streams containing toxic and recalcitrant pollutants.