Adsorptive removal of Drimarine Red HF-3D dye from aqueous solution using low-cost agricultural waste: batch and column study

This study involves the utilisation of peanut husk for the removal of Drimarine Red HF-3D dye from aqueous solutions. Batch study experiments were conducted with native, HNO₃-treated and Na-alginate-immobilised peanut husk biomass. Maximum dye removal (95.24 mg/g) was obtained with HNO₃-treated biomass. The experimental data were successfully explained with a pseudo-second-order kinetic model for all types of biosorbents. The equilibrium data fitted well to the Freundlich adsorption isotherm model. A thermodynamic study was also carried out to check the nature of the adsorption process. A fixed-bed column study for Drimarine Red HF-3D was carried out to optimise the effect of bed height, flow rate and initial dye concentration using peanut husk biomass. The column study showed that biosorption capacity increased with the increase in initial dye concentration and bed height, but decreased with increased flow rate. Data for Drimarine Red HF-3D were in very good agreement with the bed depth service time model. Fourier transform infrared analysis demonstrated the involvement of different functional groups in dye biosorption. These results showed that peanut husk biomass possessed good potential for the removal of Drimarine Red HF-3D from aqueous solution.     

Removal,adsorption and desorption of pentachlorophenol (PCP) by filamentous fungi: Rhizopusarrhizus and Cunninghamella elegans in batch system

PCP was, and in some countries still is, one of the most frequently used fungicides and pesticides, specially in wood preservation. The extensive use is correlated with contamination of water and soil and it is detected in several compartments of the food chain.

Some Micromycetes are able to adsorb and degrade PCP, with two mechanisms involved: biosorption (including both adsorption and absorption) and biodegradation.

Our work is focused on the biosorption alone and biodegradation‐biosorption of PCP by respectively denatured and living R.arrhizus and C.elegans fungi.

Living fungi are cultivated in batch system and denaturation is obtained by drying (70°C) and grinding the fungi to a calibrated powder (200–400 μm). Kinetic studies are performed with 10 mg/1 PCP initial concentration. Adsorption capacity is measured at equilibrium concentration as high as about 400 mg/1 PCP.

The results show that: PCP adsorption, for the two fungi, follows a two steps process. R. arrhizus dead and living biomasses are able to bind respectively, 75 and 55% of a 10 mg/1 PCP initial concentration in 1 hour contact time and then 75 and 100% in 96 hours. For C.elegans, 70 and 28% in 1 hour and in 96 hours 70 and 90%, respectively.

The PCP binding by living fungi is higher than non living ones, but with a slower rate.

The maximum PCP adsorption capacity is about 24 mg/g of R.arrhizus dried biomasses and 16 mg/g for C.elegans ones, in 48 hours contact time. Isotherm curves follow the Langmuir model.

Desorption studies with methanol (to reuse biomasses) shows that it is a rapid phenomenon (about 100% in 24 hours for the two fungi).

An industrial and economical process to depollute contaminated water by PCP is possible by using cheap fungal by‐products from fermentation industries.     

Biosorption of Cr(III) from aqueous solution by freeze-dried activated sludge: Equilibrium,kinetic and thermodynamic studies

Batch biosorption experiments were conducted to remove Cr(III) from aqueous solutions using activated sludge from a sewage treatment plant. An investigation was conducted on the effects of the initial pH, contact time, temperature, and initial Cr(III) concentration in the biosorption process. The results revealed that the activated sludge exhibited the highest Cr(III) uptake capacity (120 mg·g⁻¹) at 45°C, initial pH of 4, and initial Cr(III) concentration of 100 mg·L⁻¹. The biosorption results obtained at various temperatures showed that the biosorption pattern accurately followed the Langmuir model. The calculated thermodynamic parameters, ΔG^o (−0.8– −4.58 kJ·mol⁻¹), ΔH^o (15.6–44.4 kJ·mol⁻¹), and ΔS^o (0.06–0.15 kJ·mol⁻¹·K⁻¹) clearly indicated that the biosorption process was feasible, spontaneous, endothermic, and physical. The pseudo first-order and second-order kinetic models were adopted to describe the experimental data, which revealed that the Cr(III) biosorption process conformed to the second-order rate expression and the biosorption rate constants decreased with increasing Cr(III) concentration. The analysis of the values of biosorption activation energy (E_a = −7 kJ·mol⁻¹) and the intra-particle diffusion model demonstrated that Cr(III) biosorption was film-diffusion-controlled.