Granular Activated Carbon or "GAC" filters are often used as "polishing filters" in the RO process. GAC filters can remove VOCs, pesticides, nitrates, hydrogen sulfide, and much more.
2) Carbon Block Filters
A variety of contaminants can be effectively reduced or removed by carbon block filters, including VOCs, THMs, mercury, chlorine, and more. A carbon block filter's ability to remove contaminants depends upon the filter micron rating. Some carbon block filters rated at one micron or less (meaning they have a very small pore size) are certified to remove lead, iron, arsenic, cysts, and coliform bacteria.