The activated carbon stage is combined with immersed membrane filtration.
Pesticides and organic matter are adsorbed on the activated carbon.
Colloids contained within the raw water and flocculated solids from the first pre-treatment stage are separated by the membranes, which act as a physical barrier.
In addition, the membranes separate activated carbon from the filtered water, therefore keeping the same level of PAC in the system. The combined PAC, colloids and flocculated solids gradually form a deposit around the membranes.
Back-washing is then employed to avoid clogging and allows for recirculation of the PAC to the contact tank. The saturated PAC is removed through blow-off.