The overall objective of this study is to model and optimize the elimination of lead ions from aqueous solutions by inactive brewer's yeast in a batch reactor. Optimization of the most important factors directly affecting the adsorption of lead onto the biosorbent was carried out by using a 2 k factorial experiment. This later is performed to ascertain the effect of solution pH, initial concentration of lead ions, inactive brewer's yeast dose, temperature, and their cross-influence on the lead adsorption yield. The results suggest that the most influential factor is the solution pH followed by the initial concentration of lead ions, inactive brewer's yeast dose, and temperature. The results have shown also the interaction between solution pH/initial lead concentration and initial lead concentration/inactive brewer's yeast dose with different degrees of importance. The optimal values of solution pH, initial concentration of lead ions, biosorbent dose, and temperature are 4, 53.75 mg·L–1, 2.3 ≤ m ads ≤ 2.5 g·L–1, and 305 ≤ T ≤ 308 K, respectively. Adsorption parameters for the Langmuir and Freundlich isotherm models were determined at different temperatures between (298 and 308) K. According to the biosorption isotherm plots, the Freundlich model describes perfectly the sorption of lead onto inactive brewer's yeast.

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In this paper, the degradation of sulfamethazine (SMT) was performed using of photocatalytic process in the presence of ZnO catalyst immobilized on glass plate (on ZnO/glass plate) under UV light. The ZnO/glass plate was characterized by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectra; the results of the characterization demonstrated that the properties of ZnO/glass plate were maintained unmodified. The adsorption and the photolysis tests revealed the absence of adsorption of SMT onto ZnO/glass plate and the absence of direct photolysis of SMT. The effect of the initial solution pH, the flow rate and the initial concentration of SMT on the photocatalytic process was studied and optimized by using central composite design (CCD). The model equation obtained led to a classification of these parameters based on their level of significance. The results suggested that the most influential factor was the initial concentration of SMT (x 2 ), which had the strongest effect on the response (-11.6) and the negative sign of the coefficient suggested that the degradation of SMT decreased for increasing initial SMT concentration. It was followed by the flow rate with positive effect on the yield of SMT degradation (+2.06). The model also demonstrated the absence of pH effect in the studied interval and that the strongest interaction was between the pH and the flow rate. The kinetic of degradation of the SMT can be described by a pseudo A c c e p t e d M a n u s c r i p t 2first order kinetic model for 10 and 50 mg/L of SMT; while the kinetic of degradation was described by a pseudo-second-order kinetic model for the highest initial amount, [SMT] 0 =100 mg/L. The optimal values of the solution pH, the flow rate and the initial concentration of SMT were 6, 0.56 L/min and 11 mg/L respectively. Under these conditions the removal efficiency of SMT was 96 % and the BOD 5 /COD ratio increased from 0 to 0.20 after 5h of irradiation time.

In this study, peroxydisulfate (PDS) was successfully activated by UV-irradiation for the degradation of paracetamol (PCT) frequently detected in the environment. Results showed that, increasing the initial PDS concentration from 5 to 20 mM promote the removal of PCT from 49.3% to 97.5% after 240 min of reaction time. As the initial PCT concentration increased from 0.066 to 0.132 mM, the degradation efficiency of PCT decreased from 98 to 73% after 240 min of reaction time, while the optimal pH was found to be 6. It is apparent that the degradation rate of PCT was favored by the lamp power regardless of the initial PCT concentration, for 0.132 mM of PCT, the degradation efficiency increased from 73 to 95% when the lamp power increased from 9 to 30 W, respectively. The kinetic of degradation of the PCT was described by a second order kinetic model. The model obtained by central composite design led to the following optimal conditions for PCT degradation: 0.132 mM initial PCT concentration, 20 mM PDS dose, pH solution 6 and lamp power 30 W led to the removal of 92% of PCT at 25 °C within 240 min of reaction time.

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