Biosorption Kinetices of Nitrate onto Tamrind Fruit Shells

The biosorption of nitrate (NO₃⁻) onto the surface of tamarind fruit shells (TFS) is first time explored in this study, through the continuously stirred batch reactors (CMBR). The removal kinetics of NO₃⁻ was assessed based on different initial concentrations of NO₃⁻, biosorbent sizes, and agitation speeds. pH played a major role in the uptake of NO₃⁻ by TFS and about 92.6% removal was noticed at a pH of 5. An optimum dose of 10 g/l of 0.13 mm size (geometric mean size) TFS was assessed, at NO₃⁻ level of 60 mg/l. Irrespective of the initial NO₃⁻ concentrations adopted in the kinetics study (10, 40, 70, and 100 mg/l), two distinct zones such as rapid and slow biosorptions were identified. Further, within 30 min of contact time, more than 50% of initial NO₃⁻ was sorbed onto TFS and;an equilibrium was attained at 3 h. Although the overall biosorption kinetics of NO₃⁻ by TFS was well described by pseudo first-order kinetics (Lagergren's model), but the applicability of the integrated rate model (second order) was also revealed for rapid stage zone. The biosorption rate limiting step was assessed by the dependence of removal rates (mg/g/h1/2) with respect to different initial concentrations of NO₃⁻, TFS sizes, and agitation speeds. From this, it was concluded that the pore diffusion is the rate limiting step in rapid biosorptionwhere as, film diffusion is the rate limiting in slow sorption zone.