Experimental optimization of enzymatic and thermochemical pretreatments of bread waste by central composite design study for bioethanol production.

The present study aimed at optimizing the combined effect of enzymatic and thermo-chemical pretreatment hydrolysis of bread waste (BW) for enhancing the yield of reducing sugars (RS). Statistical optimization of enzymatic and thermochemical pretreatment processes was performed using the central composite design (CCD) tool of response surface methodology (RSM) using four process parameters (waste bread ratio, alpha-amylase concentration, temperature and pH) on total sugars yield as response variable. It was found that the optimal conditions for maximally RS yield were at bread ratio of 0.03 g/mL, alpha-amylase concentration of 0.2 mL/L, temperature of 100 °C and pH 5.3. Under these conditions, the yield of RS reached 90%, with bioethanol concentration of about 85.8 g/L after 72 h of batch fermentation. The modified Gompertz equation was used to describe the cumulative bioethanol production. A good agreement was found between simulated and experimental data.

Enhanced biogas production from anaerobic digestion of wastewater from the fruit juice industry by sonolysis: experiments and modelling.

The aim of this study is to investigate the use of ultrasound pretreatment as potential technique to solubilize organic matter and fermentation of fruit juice effluents in anaerobic batch reactor. The efficacy of ultrasound pretreatment has been assessed at low frequency of 20 kHz and at different sonication times (20, 40 and 60 min). Compared with control, the amount of biogas produced increased by 47, 57 and 60% for sonication times of 20, 40 and 60 min, respectively. Methane content of the produced biogas was about 59% in the control and 64% in the case of effluent subjected to ultrasonication for 60 min. After 20 days of anaerobic digestion of the fruit juice effluents, the efficiency of chemical oxygen demand (COD) increased by 9, 31 and 35% with respect to control for sonication times of 20, 40 and 60 min, respectively, corresponding to total sugars uptake efficiency of about 35, 51 and 54%, respectively. The modified Gompertz equation was used to describe the cumulative biogas production. A good agreement was found between simulated and experimental data.

Anaerobic digestion of wastewater from the fruit juice industry: experiments and modeling.

Anaerobic digestion of wastewater from the fruit juice industry was carried out in a batch digester. To study the effect of the pH values as well as the nutrient medium on the fermentation process, different parameters were monitored under mesophilic temperature, such as cumulative biogas volume, chemical oxygen demand (COD), total sugar, and biomass growth. It was found that for all cases, the COD concentration decreased with time. The lowest value reached was obtained when the nutrient medium was added; it was about 110 g/L after 480 h. In such cases, the COD removal reached about 80%; the highest cumulative biogas volume of about 5,515.8 NmL was reached after 480 h testing; and the lowest value reached was about 2,862.3 NmL in the case of peach-substrate containing sodium sulfite. The addition of nutrient medium improved the cumulative biogas production as well as the COD abatement. Measurement of the biogas composition highlighted three gaseous components, namely, methane (56.52%), carbon dioxide (20.14%), and hydrogen sulfide (23.34%). The modified Gompertz equation and the first-order kinetic model were used to describe the cumulative biogas production and the organic matter removal, respectively. A good agreement was found between simulated and experimental data.