The idea is that the strontium-90, carbon-14, etc can be filtered out, leaving just the tritiated water to be discharged.
> Greenpeace said it had confirmed with Tepco that the system was not designed to remove carbon-14
Maybe there are updates on this matter but I couldn't find anything online.
"C-14 also cannot be removed by ALPS, but its concentration is far lower than its regulatory standard for discharge."
Source: https://www.meti.go.jp/english/earthquake/nuclear/decommissi...