3. Experimental Methods and Measurements
Bioadsorption experiments were carried out in a rotary shaker at 150 rpm using 250 mL-shaking flasks containing 50 mL of dye solutions at different concentrations and initial pH values of dye solutions. The initial pH values of the solutions were previous adjusted with 0.1 M HCl or 0.1 M NaOH using a DEEP VERSION model (EI) pH meter. The adsorbent (0.2 g) was added to each flask, and then the flasks were sealed up to prevent any change of volume of the solution during the experiments. After shaking the flasks for a predetermined time intervals, the samples were withdrawn from the flasks and the dye solutions were separated from the adsorbent by filtration after centrifugation. The pH values of the separated dye solutions were again measured for examining their change. Dye concentrations in the supernatant solutions were estimated by measuring absorbance at maximum wavelengths of dye with a Systronic Spectrophotometer104. The amounts of dyes adsorbed by the biomass were calculated using the following equation:
Where q (mg g) is the amount of dye adsorbed e -1by the biomass, C and C (mg L ) are the initial and equilibrium liquid-phase concentration of dye, respectively, V (L) the initial volume of dye solution, and W (g) the weight of the biomass. The effect of each parameter was studied by fixing the values of other parameters. The experiments were conducted with duplicate and the negative controls (with no adsorbent) to ensure that adsorption was by the prawn waste biomass and not by the container. All the experiments were duplicated and only the mean values are reported. The maximum deviation observed was less than ± 4%.