Photocatalysis has been a widely studied technology since the 1970s. Many investigations have
been carried out with the aim of understanding the fundamental processes and enhancing
photocatalytic efficiencies especially for water, air, and soil pollution control. In this comprehensive paper, studies focused on the treatment of hazardous wastewater (bearing heavy metals
and organic compounds) by photocatalysis and the effects of various parameters such as pH,
light intensity, dissolved oxygen, etc., are reviewed. In addition, the design features and
efficiencies of various photoreactors used for this process are discussed. Some studies on the
economic analysis of photocatalytic systems are also included. It can be concluded that the
photocatalysis process is suitable for the treatment of drinking water and industrial wastewater.
Also, harvesting the energy of the sun for photoreactions would make it a cleaner and more
cost-effective treatment method.