Anwendung von Mikrowellen zur Reaktivierung von granulierter Aktivkohle aus der Abwasserbehandlung

Activated carbon is a common media for removing micropollutants out of wastewater. It presents plenty advantages such as no treatment by-products, no increase of sewage sludge. Most importantly, activated carbon can be produced from renewable raw materials. Disadvantages of activated carbon, however, include its high costs and the disposal of loaded activated carbon. Loaded granular activated carbon (GAC) can be thermally reactivated for reuse, which, however, usually causes high energy consumption.Microwave irradiation can be used for the reactivation of GAC saturated with one substance, as proved in plenty researches. This research found that microwave irradiation can reactivate the GAC used in the fourth purification stage of a municipal wastewater treatment plant for treating micropollutants. Loaded GAC could be reactivated with microwave irradiation and reused several times without loss of its adsorption capacity. The burn-off of the GAC during the reactivation was approximately 5%. The optimum GAC reactivation parameters were determined at 500 °C, 100 min operation time, 23% water content of the GAC, and 0.1 g/min steam furnace atmosphere. The mean pore size turned bigger after the reactivation at the optimum operation. The ash content of GAC decreased slightly after microwave reactivation. The content of volatile components dropped as well. The lab-scale experiments of this study showed approximately the same energy consumption for GAC reactivation as that from the conventional reactivation plants. Comparative studies with an industrial waste water treatment plant showed that the optimum reactivation conditions of the same GAC can vary at different loads.Although the microwave technology has not yet been applied to GAC reactivation industry, the laboratory study shows its suitability. But exhaust gases out of the reactivation must be purified in a large-scale microwave plant. Yet, technical implementation must take account of the small penetration depth of the microwaves into the GAC, the "hot spots" and the "thermal runaway" issues.Once these technical challenges get solved, microwave technology can be applied for an on-site reactivation of the GAC on the waste water treatment plants, especially thanks to the easy control and flexibility of the microwave facilities. In this way, wastewater treatment plant can improve its Life Cycle Assessments for the GAC usage, via largely avoiding the transport of the GAC from and to the central reactivation plants. Furthermore, another technical solution for environmental protection and sustainable development could be to develop a mobile GAC microwave reactivation system to flexibly serve plenty waste water treatment plants with GAC filtration