A fluid treatment apparatus for the treatment of a fluid substance, comprising: a reactor chamber defined by a perimeter wall; a fluid inlet, having an inlet port, adapted to provide fluid communication from an external supply of a fluid substance to be treated to said reactor chamber whereby said fluid substance passes into and through said reactor chamber; a fluid outlet, having an outlet port, adapted to provide a fluid communication from said reactor chamber whereby said fluid substance passes from said reactor chamber; at least one electromagnetic radiation waveguide (120, 122), having an optical interface comprising a first interface member operably coupled to a waveguide input port and a second interface member operably coupled to a waveguide output port, said waveguide input port and said waveguide output port are operably coupled to diametrically opposed spaced apart locations on said perimeter wall of said reactor chamber and adapted to couple electromagnetic radiation of a predetermined first wavelength to a fluid substance passing through said reactor chamber, and wherein said perimeter wall of said reactor chamber, said fluid inlet and said fluid outlet are shaped so that said fluid substance received from said fluid inlet is forced into a continuous swirling flow when passing through said reactor chamber towards said fluid outlet, and wherein said inlet port is adapted change an initial fluid pressure of said fluid substance to a predetermined first fluid pressure when passing through said fluid inlet port into said reactor chamber, and wherein said outlet port is adapted to change a chamber fluid pressure of said fluid substance to a predetermined second fluid pressure when passing through said fluid outlet port into said fluid outlet. a reactor chamber defined by a perimeter wall; a fluid inlet, having an inlet port, adapted to provide fluid communication from an external supply of a fluid substance to be treated to said reactor chamber whereby said fluid substance passes into and through said reactor chamber; a fluid outlet, having an outlet port, adapted to provide a fluid communication from said reactor chamber whereby said fluid substance passes from said reactor chamber; at least one electromagnetic radiation waveguide (120, 122), having an optical interface comprising a first interface member operably coupled to a waveguide input port and a second interface member operably coupled to a waveguide output port, said waveguide input port and said waveguide output port are operably coupled to diametrically opposed spaced apart locations on said perimeter wall of said reactor chamber and adapted to couple electromagnetic radiation of a predetermined first wavelength to a fluid substance passing through said reactor chamber, and wherein said perimeter wall of said reactor chamber, said fluid inlet and said fluid outlet are shaped so that said fluid substance received from said fluid inlet is forced into a continuous swirling flow when passing through said reactor chamber towards said fluid outlet, and wherein said inlet port is adapted change an initial fluid pressure of said fluid substance to a predetermined first fluid pressure when passing through said fluid inlet port into said reactor chamber, and wherein said outlet port is adapted to change a chamber fluid pressure of said fluid substance to a predetermined second fluid pressure when passing through said fluid outlet port into said fluid outlet.