Because Activated carbon can interact with many pollutants and Kien Vu said activated carbon is cheap, higher adsorption capacity, easy to prepare or buy, large surface area, oxygen containing functional groups.....
Apart from been cheap, high removal rate, large specific surface area, easy to buy and operate, etc., activated Carbon in RO is mainly used to protect RO membranes from oxidants such as chlorine, while in wastewater is for adsorption of organic compounds, removal of colour and odour.