Pretreatment before filtration on GAC

Though GAG can accommodate clarified water that is still colloidal and whose fine particles may not be retained by the granular medium, its adsorption activity is nevertheless curtailed. It is often preferable to carry out a complete tertiary flocculation treatment upstream from GAC. 

Flocculation of petrochemical and pharmaceutical industry effluents may entail the use of up CO 500 mg l of commercial inorganic coagulant and an intermediate settler with considerable hydroxide sludge production. In contrast, the reduction in COD achieved in this way may go up to 80 or 100, even 130 mg-l  

Two types of compounds are eliminated that ceui be biodegraded only slightly or not at all  

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