... do not contain any substances that harmful to people or environment. They are hard and rough in surface, ... specific surface area and porosity, When used in water treatment, they behave a activated surface property, a ... and efficient filter material to increase the water yield, upgrade the water quality, and save chemicals and energy. ... Φ10~12, Φ13~15, Φ16~20, Φ21~60. Waste Water Treatment Product