No person or corporation shall, within the town of Waterford, East Lyme, Old Lyme or Stonington, or in any waters adjacent thereto, engage in the business of manufacturing from fish or garbage any oil, guano, fertilizer or phosphate, or in the business of rendering or treating garbage or other filthy or noxious matter, or in the town of Stonington, engage in the business of processing of fish for animal consumption. This section shall not apply to the continuance of any such business of any person or corporation whose plant within any of said towns had been erected prior to May 1, 1909, and was actively employed in the same specific business during the year 1908, while such business continued to be confined to the property owned by such person or corporation on said May 1, 1909, or to the treatment and disposal within any of said towns of garbage or other filthy or noxious matter originating within such town, or to the filleting and freezing of fish into food for human consumption within the town of Stonington.