Tamarind fruit shell was used as a low-cost biosorbent for the removal of methylene blue from aqueous solution. The various factors affecting adsorption, such as agitation, pH, initial dye concentration, contact time, and temperature, were investigated. The dye adsorption capacity was strongly dependent on solution pH as well as temperature. The Langmuir isotherm model showed good fit to the equilibrium adsorption data, and the maximum adsorption capacity obtained was 1.72 mg g⁻¹ at 303 K. The kinetics of adsorption followed the pseudo-second-order model and the rate constant increased with increase in temperature, indicating endothermic nature of adsorption. The Arrhenius equation was used to obtain the activation energy (E a) for the adsorption system. The activation energy was estimated to be 19.65 kJ mol⁻¹. Thermodynamic parameters such as Gibbs free energy (ΔG ⁰), enthalpy (ΔH ⁰), and entropy (ΔS ⁰) were also investigated. Results suggested that adsorption of methylene blue onto tamarind fruit shell was a spontaneous and endothermic process. The present investigation suggests that tamarind fruit shell may be utilized as a low-cost adsorbent for methylene blue removal from aqueous solution.

Background, aim, and scope Two new high phenol-degrading strains, Micrococcus sp. and Alcaligenes faecalis JH 1013, were isolated. The two isolates could grow aerobically in mineral salts medium containing phenol as a sole carbon source at concentration of 3,000 mg L⁻¹. It was found that the binary mixed culture of the two isolates possessed good potential for phenol removal. Material and methods Phenol biodegradation using the binary mixed culture of the two isolates was studied. The optimal conditions were determined to be temperature 32°C, pH 7.0, inoculum size 10.0%, and agitation rate 150 rpm in the synthetic wastewater. In addition, the kinetics of the cell growth and phenol degradation by the binary mixed culture were also investigated using Haldane model over a wide range of initial phenol concentrations from 20 to 2,400 mg L⁻¹. Results The experimental data indicated that the binary mixed culture had pretty high phenol degradation potential, which could thoroughly degrade the phenol in the synthetic wastewater containing phenol 2,400 mg L⁻¹ within 72 h under aerobic condition. Under the optimal conditions, the phenol concentration was reduced speedily from 1,000 to below 0.28 mg L⁻¹ in the presence of the binary mixed culture, and the phenol degradation rate reached 99.97% after 16 h. It was well below the standard value 0.28 mg L⁻¹ as described by Chinese Environmental Protection Agency. It was clear that the Haldane kinetic model adequately described the dynamic behavior of phenol degradation by the binary mixed culture with kinetic constants of q max = 0.45 h⁻¹, K sq = 64.28 mg L⁻¹, and K iq = 992.79 mg L⁻¹. The phenol concentration to avoid substrate inhibition had been inferred theoretically to be 252.62 mg L⁻¹. Conclusions Phenol, as the only carbon source, could be degraded by the binary mixed culture at high initial phenol concentrations. Phenol exhibited inhibitory behavior, and the growth kinetics of the binary mixed culture could be correlated well by the simple Haldane's inhibitory model. The kinetics parameters were invariably required for the design and simulation of batch and continuous bioreactor treating phenolic wastewaters.