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The feasibility of the removal of reactive dye from wastewater using a novel adsorbent, ECH cross-linked chitosan beads, as medium was examined. The effect of the pH and the initial concentration of the dye (RR222) solution on the adsorption capacity of the ECH cross-linked chitosan beads were also investigated. It was found that the initial dye concentration and the pH of the solution significantly affected the adsorption capacity. An increase in initial dye concentration results in the increase of adsorption capacity while an acidic pH was found to be favorable for the adsorption of dye. It was also found that the equilibrium adsorption of RR222 could be adequately described by using the Langmuir model (r2 > or = 0.999). Moreover, results showed that the adsorption rate of RR222 onto ECH cross-linked chitosan beads could be described by using the second-order kinetic model, suggesting that chemical sorption instead of mass transfer was the rate-limiting step for the adsorption process. The maximum monolayer adsorption capacity obtained from the Langmuir model was extremely high as compared to the data reported in literature; 2252 g/kg at 30 degrees C with a pH of 3.0. Therefore, ECH cross-linked chitosan beads could be a feasible medium for the removal of reactive dye from wastewater and potentially an alternative for the decolorization of wastewater.

Mushroom tyrosinase was immobilized on modified polystyrene- polyamino styrene (PSNH) and polymethylchloride styrene (PSCL)-to produce L-DOPA from L-tyrosine. Glutaraldehyde was used as an activating agent for the PSNH to immobilize the tyrosinase, and 10% (w/v) glutaraldehyde was optimal in conferring the highest specific activity (11.96 U/g) to the PSNH. Methylchloride on the PSCL was directly linked with the tyrosinase, and 1.5 mmol of Cl/g was optimal in attaining the specific activity of 17.0 U/g. The temperature and optimal acidity were, respectively, 60 degrees C and pH 5.5 for the PSNH, and 70 degrees C and pH 3.0 for the PSCL. In a 50-mL batch reactor working over 36 h, the L-DOPA production rate at 30 degrees C was 1.44 mg/(L x h) for the PSNH and 2.33 mg/(L x h) for the PSCL. The production rate over 36 h was 3.86 mg/(L x h) for the PSNH at 60 degrees C and 5.54 mg/(L x h) for the PSCL at 70 degrees C. Both of the immobilized enzymes showed a remarkable stability with almost no change in activity after being stored wet. The operational stability study indicated a 22.4% reduction in L-DOPA production for the PSNH and an 8.63% reduction for the PSCL over seven runs (each run was for 144 h at 30 degrees C) when the immobilized enzymes were used under turnover conditions. The immobilized tyrosinase was more stable on the PSCL than on the PSNH.