Based on the main objectives of this research, as raw materials to produce activated carbon, rice husk was collected from the local market. Before processing the husk was dried in air. A low-cost furnace was used to produce activated carbon in the laboratory. The fabrication of the furnace is presented elsewhere (Rahman and Bari, 2010). yousuf2716@yahoo.com
2.1 Production of Activated Carbon About 3.5 kg of rice husk was placed in a container with a diameter of 25 cm and a height of 25 cm. The rice husk was placed in racks in the container for uniform activation. Then the container was closed and placed in the furnace for thermal activation at about 500 oC for 5 hours. A low-cost furnace was made in the laboratory for the production of activated carbon.
2.2 Experimental Sample Two types of samples were used in this study. The first one was methylene blue solution which was prepared in the laboratory and the second one was the effluent of textile dyeing and washing from Sharoj Washing & Dyeing Ltd. Bangladesh.
2.3 Adsorption Studies In all experiments 100 mL samples were taken in 250 mL conical flasks. Methylene blue solution was used to characterize compare the activity of the activated carbon. Finally, the efficiency of dye removal of real wastewater was done on collected effluent from the textile industry. All batch adsorption studies were conducted thrice and mean values were taken.
2.3.1 Kinetic Study In each conical flask, 100mL of each experimental sample was taken and activated carbon made from rice husk was added. Conical flasks were then subjected to mixing in a horizontal lab-made shaker at 200 rpm. At every 5 minutes, time interval samples were withdrawn and filtered. Percent transmittances of filtered samples were determined by a UV-Visible spectrophotometer (Model-DR/2500, HACH, USA) to determine the dye reduction. Each experiment was performed thrice and the mean value was taken.
2.3.2 Effect of Adsorbent Dose In each conical flask 100 mL sample was taken for each experiment. Different doses of activated carbon varying in the range of 0.05g to 2.25g at 0.05g interval were taken as an adsorbent in a conical flask. Conical flasks were subjected to having adsorption in a horizontal shaker 200 rpm for a maximum adsorption time 60 minutes. Adsorbents were removed by filtration in order to get clear samples. Percent transmittances of the filtered samples were measured. Each experiment was performed thrice and the mean value was taken as before.
2.3.3 Effect of Temperature on Adsorption For this experiment, 2.0 g of activated carbon and 100 mL samples are taken in each flask. Contact time was adjusted to 60 minutes for each experiment. Effect of temperature on adsorption was studied at different temperatures of 30 oC, 32.5 oC, 35 oC, 37.5 oC, 40 oC, 42.5 oC, 45 oC, 50 oC, 55 oC and 60 oC. At all temperatures, the conical flasks were mixed in a horizontal shaker at 200 rpm. Adsorbents were removed by filtration in order to get clear samples. Percent transmittances of the filtered samples were measured. Each experiment was performed ten times and the mean value was taken.
2.4 Adsorption by Different Activated Carbon and Prepared Activated Carbon In a conical flask, 100 mL of each textile wastewater sample was taken and 1.0 g, 3.0 g, 5.0 g, and 8.0 g of laboratory-grade activated carbon and 1.0 g, 3.0 g, 5.0 g, 8.0 g, 11.0 g and 14.0 g of prepared crushed activated carbon, prepared activated carbon and two types of commercial-grade activated carbon was added to conical flasks. Conical flasks were then subjected to mixing in a horizontal shaker at 200 rpm for predefined maximum adsorption time, 60 minutes, and at 40oC temperature. Adsorbents were removed by filtration in order to get clear samples. Percent transmittances of the filtered samples were measured. Experiments were repeated trice.
2.5 Method Used for Measuring Dye Spectrophotometer (DR/2500, HACH, USA) was used for measuring percent transmittance for measuring the dye. Percent transmittances of all experimental samples were measured at 369 nm. All other Physico-chemical parameters were measured as per Standard Methods (AWWA, 2005). The results are expressed as average values with standard deviation.