Cadmium (Cd) is a highly toxic heavy metal considered carcinogenic to humans. The adsorption behavior of cadmium adsorption using untreated and chemically modified rice husk was investigated. Experimental tests were carried out to evaluate the influence of the variables pH, initial concentration of cadmium, and dosage of adsorbent in the adsorption process. In optimal experimental conditions, the maximum adsorption efficiency was 92.65%. Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM) were used allowing the identification of the main functional groups and morphology of rice husk and treated rice husk, and the results showed an improvement of adsorption characteristics after rice husk treatment with NaOH. The optimum adsorption pH for both types of rice husk was 7. The maximum adsorption capacities of RH and treated RH fitted by the Langmuir model were 5.13 mg/g and 11.06 mg/g, respectively. The pseudosecond order kinetics has the best coefficients of determination for untreated ( ) and treated ( ) rice husk. The adsorption process was found to be endothermic in nature with enthalpy of 14.08 kJ/mol and entropy of 170.98 J/mol.K. The calculated activation energy was 24 kJ/mol. The results showed the potential of rice husk as a low-cost, easily managed, and efficient biosorbent for Cd removal from waters.

In the present work, the equilibrium, thermodynamics, and kinetics of boron removal from aqueous solutions by the adsorption on commercial magnesium oxide powder were studied in a batch reactor. The adsorption efficiency of boron removal increases with temperature from 25°C to 50°C. The experimental results were fitted to the Langmuir, Freundlich, and Dubinin–Radushkevich (DR) adsorption isotherm models. The Freundlich model provided the best fitting, and the maximum monolayer adsorption capacity of MgO was 36.11 mg·g⁻¹. In addition, experimental kinetic data interpretations were attempted for the pseudo-first-order kinetic model and pseudo-second-order kinetic model. The results show that the pseudo-second-order kinetic model provides the best fit. Such result suggests that the adsorption process seems to occur in two stages due to the two straight slopes obtained through the application of the pseudo-first-order kinetic model, which is confirmed by the adjustment of the results to the pseudo-second-order model. The calculated activation energy (Ea) was 45.5 kJ·mol⁻¹, and the values calculated for ∆G°, ∆H°, and ∆S° were −4.16 kJ·mol⁻¹, 21.7 kJ·mol⁻¹, and 87.3 kJ·mol⁻¹, respectively. These values confirm the spontaneous and endothermic nature of the adsorption process and indicated that the disorder increased at the solid-liquid interface. The results indicate that the controlling step of boron adsorption process on MgO is of a physical nature.

This study investigates the potential of a synergistic co-culture of microalgae (M) and activated sludge (AS) for the bioremediation of agro-industrial wastewater and the valorization of resulting biomass for biofertilizer production. Co-cultures were established with inoculation ratios of 1:1, 1:3, 1:0, and 0:1 (M:AS) and cultivated under two photoperiod regimes (24L:0D and 16L:8D) for 14 days. The highest removal efficiencies were observed in the 1:1 and 1:3 treatments under the 24L:0D regime, achieving up to 90.61% COD, 100% nitrogen, and 99.8% phosphorus removal. Biomass analysis revealed substantial macromolecular content, including lipids (24.2% and 16.2%), proteins (39.5% and 43.2%), and carbohydrates (70.8% and 53.7%) under 24L:0D and 16L:8D, respectively. The biofertilizer potential of the biomass was assessed using Cucumis sativus seeds, showing improved germination and growth, particularly at 25% dilution, with a 90% germination index, an average of 4 ± 0 leaves, and shoot length of 5.05 ± 2.07 cm. These findings highlight the dual benefit of pollutant removal and biomass valorization in integrated wastewater management.