## 1 Introduction  
A general goal of drinking water treatment is to reduce health hazards due to pathogenic microorganisms in water using minimal concentrations of disinfectants. Chlorination at high doses of water, which includes organic molecules at concentrations of the order of mg/L, results in production of trihalomethanes (THMs) and haloacetic acids (HAAS), whereas reduced efficiency in eliminating some epidemic microorganisms occurred at low doses [1]. Disinfection by chloramines results in formation of nitrosamines [2]. Ozone is powerful in removal of microorganisms, but its application results in formation of nitrosamines [3] and cyanogen halides [4].  
Filtration by means of a granulated micelle-clay complex has been proposed as one possible solution for reducing harmful disinfection byproducts (DBP). Two types of granulated complexes were employed. The micelle-clay complexes were synthesized by interacting micelles of an organic cation with a clay, which has a relatively large surface area. The two organic cations chosen were octadecyltrimethylammonium (ODTMA), and benzyldimethylhexadecylammonium (BDMHDA), whose critical micelle concentrations were relatively small. They include large hydrophobic fractions and are positively charged to about half of the cation exchange capacity (CEC) of the clay, which is useful in the removal of microorganisms whose external surfaces are net negatively charged. [PERSON] et al. [5] employed micelle-clay complexes in powdered form, and demonstrated in batch and filtration experiments the removal from water of several types of Gram-negative and Gram-positive bacteria and _Cryptosporidium parvum_. [PERSON] et al. [6] demonstrated efficient removal of Escherichia coli (_E. Coli_) by a polymer-clay powdered complex. However, in a filter the powdered complex had to be mixed with an excess of a granulated material, such as sand, whereas the granulated complex can be included exclusively in filters, which enables upscaling. Recent studies demonstrated efficient removal of (i) pathogenic and indicator bacteria [7, 8], and (ii) cyanobacteria [9], by filling filters with granulated micelle-clay complexes.  
In removing pollutants from drinking water or wastewater, it is important to reduce the processing time and costs. Regeneration of the used filter after removal of bacteria was accomplished by passing dilute solutions of NaOCl or HCl, [5, 6, 7, 8], or by heating in an oven for 2 h at 105 \({}^{\circ}\)C [7, 8].  
Microwaves are in the 300 MHz to 300 GHz frequency range of the electromagnetic spectrum. When microwaves interact with dielectric materials, the materials are heated as a result of the high frequency oscillations of the electric dipoles in the polar molecules. Due to penetration capability of microwaves, microwave (MW) heating is volumetric heating with advantages such as easy start-up and stopping, rapid heating, and non-contact heating. [PERSON] and [PERSON] [10] reviewed microbial inactivation by MW. A major aim of the current study was to explore the use of MW radiation for the regeneration of granulated micelle-clay complexes after being used in filtration of drinking water. This is the first study of the application of MW radiation to the regeneration and reuse of clay-composites in removal of bacteria from water by filtration. As will be shown, the MW procedure proved to be optimal in terms of removal of bacteria and saving of energy and time. The regeneration, which enables a low cost reuse of the purification complex, has an environmental advantage.