Efficiency of Ultrasonic Pretreatment on Improving Biodegradability of Tomato Wastes and Increasing Biohydrogen Production

The effects of ultrasonic factors (acoustic power and sonication time) and substrate mixture (tomato waste and cow manure) on the lignocellulosic structure degradability, elimination of feedstock pollutants and solids, and bio-H 2 fermentation improvement were studied using the integration of multiple regression modeling and structural equation modeling. Analyses indicated that (i) a mixture of substrates is needed for improving the feedstock quality and bio-H 2 fermentation, (ii) highest feedstock solid removal was attained in 0.42 W/mL acoustic power at 15-min sonication time with mixture 75%:25% cow manure/tomato waste, (iii) highest feedstock pollutant removal was obtained in ultrasonic power of 0.34 W/mL at 15 min with higher amounts of tomato waste in the mixtures, (iv) highest lignin removal was achieved for ultrasonic power of 0.42 W/mL at 15 min with higher amounts of cow manure in the mixtures, and (v) highest amount of bio-H 2 was produced in ultrasonic power of 0.1 W/mL at 25 min with mixtures 0–25%:75–100% or 75–100%:0–25% cow manure/tomato waste. In proper conditions of pretreatment and substrate mixture, the removal of solid, volatile solid, lignin, cellulose, and hemicellulose contents increased respectively by 3.58%, 17.95%, 57.67%, 24.38%, and 38.7% compared to the control system, leading to a 6% increase in bio-H 2 production.