6.2 Adsorption treatments.
Adsorption is a physicochemical effluent treatment in which effluent is mixed with the porous material (powder or granules), such as activated carbon and clay, or let the effluent pass through a filter bed composed of granular materials. In this way, pollutants in the effluent are adsorbed and removed on the surface of the porous materials or filter. Commonly used adsorbents are activated carbon, silicon polymers and kaolin. Different adsorbents have selective adsorption of dyes. The activated carbon has been regarded as the best adsorbent for dyeing effluent so far. However, the adsorption on activated carbon without pretreatment is impossible because the suspended solids repidly clog the filter. Therefore, this procedure is only feasible in combination with flocculation decantation treatment or a biological treatment. The combination permits a reduction of suspended solids and organic substances, as well as a slight reduction in the colour. Moreover, the cost of activated carbon is high.