For use in an apparatus for the treatment of organic waste wherein said apparatus comprises at least one chamber, a magnetron assembly for the application of microwave energy to said waste to treat, reduce or sterilize said waste by means of reverse polymerization in said chamber, said magnetron assembly comprising a magnetron mounted on and with its anode projecting into a waveguide, means for isolating said magnetron from said chamber, and tuning means in said waveguide for optimizing coupling of said magnetron to said chamber wherein an end part of said waveguide adjacent to said chamber comprises a truncated cone.
