Comparative study of adsorption capacity of various adsorbents for treating dye wastewaters

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Abstract
The objective of this laboratory study was to determine the effect of dosage, contact time and type of adsorbents on the color and COD (chemical oxygen demand) removal for dye wastewaters. The adsorption parameters for Langmuir and Freundlich isotherms and mass transfer coefficients from bulk solution to particle surfaces for disperse dye were also determined. The adsorbents used in this study included powdered activated carbon (PAC), granular activated carbon (GAC), activated alumina, molecular sieves, diatomite, and sawdust. For an initial dye concentration of 150 ppm and adsorbent dosage of 15 g/1 and a contact time of 2 hours, the COD removal efficiency was 98%, 60–65%, and 24–30%, for PAC, activated alumina, and molecular sieves, respectively. The order of adsorbent efficiency was found to be: PAC > activated alumina > molecular sieves > GAC > diatomite. The adsorption capacity of diatomite and GAC was very poor. The color removal (color difference or AE∗ab) varied from 45 to 55 for most adsorbents studied. Sawdust increased in COD values and showed poor color removal. Mass transfer coefficients, KKcm/hr) for disperse‐red‐60 on various adsorbents were determined to be; 14.79 × 10"6 for PAC, 3.98 × 10"6 for activated alumina, 1.65 × 10‐6 for molecular sieves, and 0.62 × 10‐6 for GAC.