Granular activated carbon (GAC) adsorption-photocatalysis hybrid system in the removal of herbicide from water

The performance of the granular activated carbon (GAC) fixed bed adsorption, the continuous photocatalysis systems and a combination of the two were studied to evaluate their capabilities in removing the herbicide of metsulfuron-methyl (MM) from waste water. Columns packed with GAC at different bed depths were operated at different filtration rates over a period of several weeks. Removal of MM via adsorption using GAC fixed beds of 5, 10 and 15 cm depths (operated at meter per hour) achieved a removal of 35, 55 and 65% of MM respectively. In the continuous photocatalysis system, heterogeneous photocatalysis with TiO2 was used to degrade MM. The system achieved removal rates between 40 and 60%. GAC photocatalysis hybrid system is a coupling of GAC fixed bed adsorption and the continuous photocatalysis system where the effluent from the former was fed to the later. TiO2 and small amount of powder activated carbon (PAC) were used as the catalyst in the photocatalysis system. The system had a high removal rate of over 90%. The retention time of the photocatalysis system was less than 10 min. This system allows a greater degree of flexibility in the manner the system can be operated.