Activated carbon base for water treatment

Hello everybody

As we know activated carbon filters shall be backwashed. So it seems that the granules should have a minimum resistance against erosion might happens through granules contacting each other during backwash. I see coal based activated carbon, with proper level of hardness, is recommended for potable and process water filtration services. I think that it is for meeting the erosion resistance. On the other hand, activated carbon with other bases, have lower hardness and higher iodine index than coal based one.

Please share your idea and experiences. If hardness is important as a factor for being erosion resistant?