Innovative and scalable photocatalytic reactors have been developed for the degradation of pesticides in agro-industry and the disinfection of effluents from municipal waste water treatment plants. The reactors (slurry batch reactor, or membrane reactor) are working under continuous flow conditions, can incorporate novel, environmentally friendly photocatalytic materials and be powered by solar light, a key factor for the reduction of energy requirements for water treatment. They represent a cost-effective cutting-edge application of nanotechnology for enhancing water quality.