An efficient process for improvement of biohydrogen and biomethane production from tomato waste: Inhibitory effects of ultrasonic pretreatment

Abstract

The present study was undertaken to determine the effect of ultrasonic pretreatment of tomato wastes on improving the production of bio-H2 and bio-CH4. Furthermore, inhibitory effects of phenolic and tannin compounds that may be produced during the breaking of complex structures using the ultrasonic irradiations were investigated. For this purpose, anaerobic digestion of different mixtures of tomato waste and cow manure, ultrasonically pretreated with different acoustic powers and sonication times, was studied based on a combined d-optimal experimental design. A two-stage optimization process was developed by integrating multivariate modeling and desirability analysis. The first stage of the optimization process showed that the ultrasonic pretreatment of 197.21 W (0.33 W/mL) at 21.47 min for the mixtures with high amounts of tomato wastes (>90 %) produced small amounts of the total phenolic compounds (2.03 mg equivalent gallic acid/g: mg/g) and tannin content (4.37 mg catechin equivalent/g: mg/g). These conditions produced high amounts of total solid (6.53 %), total volatile solid (77.84 %) and total carbohydrate (6.95 mg glucose equivalent/g: mg/g). These values led to producing Bio-H2 > 18 %vol and Bio-CH4 > 2 %vol. The second stage of the optimization process indicated that total phenolic compounds < 12.5 mg/g and tannin content < 25.5 mg/g were needed to maximize both bio-H2 and bio-CH4 production and optimize the desirability of biogas production.