Abstract: The method for marine sewage treatment comprises the steps of (a) dispensing with each toilet flush a controlled amount of heterotrophic bacteria culture into the boat's holding tank in order to substantially denitrify the sewage and liquefy the solids, (b) pumping raw sewage from said holding tank to fill a radiation loop, (c) applying microwave energy for a predetermined duration to the raw sewage contained within said radiation loop in order to disinfect said sewage, and (d) passing the disinfected hot sewage through a phosphate filter to substantially reduce the phosphate level.