To improve the organics removal efficiency of surface water treatment technologies, powdered activated carbon (PAC) has often been added. Some of the PAC particles with the dissolved organics already adsorbed are present in the form of a colloidal quasi-colloidal dispersion and can be removed most efficiently by coagulating and flocculating them together with the natural suspended solids. This, however, cannot be accomplished unless the PAC is added 3-5 minutes ahead under violent stirring of the water to be treated. Laboratory data demonstrated that the PAC and the Al-hydroxides formed of the coagulant (Al-salt) added remove different types of organics from the water and consequently do not compete with each other.

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