Preparation And Dye Adsorption Of Activated Carbon From Sewage Sludge

The activated carbon was prepared from sewage sludge of municipal wastewater treatment plant by chemical activation (activation reagent is ZnCl₂), meanwhile, the preparation condition and mechanism were discussed. Based on characterizition of the activated carbon from sewage sludge (ACs), the adsorption kinetics and thermodynamics of three dyes (Reactive Brilliant Red K-2BP, Acid Scarlet GR, and Direct Violet N) on the ACs were studied by batch adsorption tests. Further, the disposal effect of actual dye wastewater by the ACs was investigated.It was found that, based on the iodine value, the best preparation condition was ascertained: the activation temperature was 550℃, the concentration of activation reagent was 25%, the activation time was 15min and the ratio of sludge to activation reagent was 1:2. On this condition, the iodine value of the ACs was 326mg·g^-1 , the BET surface area was 289m²Â·g^-1 , the rate of achievement was 51.31%. Compared with the commercial activated carbon which was mainly microporous. the ACs was mesoporous and had more opened porous structure, and it was more suitable for the adsorption of large molecular compounds such as dyes. The contents of metal elements in the lixivium of the ACs didn't exceed the content limit.The ACs possessed high adsorption capability for three dyes, and the order of adsorption capability of the ACs for three dyes was as follows: Acid Scarlet GR> Reactive Brilliant Red K-2BP> Direct Violet N. The adsorption of three dyes on the ACs followed the pseudo second-order kinetic model. For Reactive Brilliant Red K-2BP and Direct Violet N, the intra-particle diffusion is one of the rate-controlling steps, whereas for Acid Scarlet GR, the intra-particle diffusion is not the rate-controlling step. Both Langmuir and Freundlich isotherm equation showed reasonable applicability for the adsorption of three dyes on the ACs The adsorption of three dyes on the ACs which was favorable and mainly physical adsorption possessed low activation energy (E_a), moreover, it was endothermic (enthalpy â–³H>0), spontaneous (free energy â–³G<0) and accompanied by an increase in entropy (â–³S>0). For actual dye wastewater, the AC_s possessed excellent decoloration effect.The above results indicate that The AC_s can be employed as an effective, safe and economically feasible substitute for commercial activated carbon in treatment of wastewater that contains large molecular pollutant such as dye.