A process for treating contaminated water has the steps of filtering the contaminated water through a filter so as to produce a filtrate therefrom, introducing nutrients and a biomass into an interior volume of the of a light reactor, passing the filtrate into the light reactor, reacting light with the nutrients and the biomass so as to produce a light-reacted biomass, transferring the light-reacted biomass to a dark reactor, reacting the transferred light-reacted biomass with carbon dioxide in the dark reactor, and filtering the reacted biomass from the dark reactor so as to remove the biomass therefrom. The nutrients in the biomass are continuously stirred within the light reactor in a toroidal circulation pattern.