Ultrasonic Energy Effect on Dark Fermentation by Ultrasound Application Alone and in Combination with Heat Shock

In the present work, the ultrasonic specific energy (USE) effect on anaerobic sludge in methane inhibition and hydrogen production capability by dark fermentation in pretreatments with ultrasound (US) and combined ultrasound with heat shock (US?+?HS) was evaluated. The non-pretreated anaerobic sludge was used as a control, and the sludge pretreated with heat shock (HS) at 85 C for 45 min was a comparison system. HS inhibited methane production by 96.4??0.6%, while pretreatments with US and US?+?HS in a USE interval between 20.5 and 102.5 kJ L?1 showed inhibition of 77.9??0.37 to 88.9??0.17% and 89.8??0.17 to 95.7??0.10%, respectively. Nevertheless, from the statistical analysis, it was determined that the HS and US?+?HS in all of the USE levels have the same inhibition effect. US at 41.0 kJ L?1 reached an accumulated hydrogen value that was 3.2-fold higher than the control and 79.5% greater than HS, while for US?+?HS at 82.0 kJ L?1, it was 2.3-fold higher than the control and 19.6% greater than HS. A comparative analysis from adimensionalized kinetic parameters showed that hydrogen production potential (Pmax) and maximum hydrogen rate (Rmax) on the anaerobic sludge pretreated with US and US?+?HS at 40 kHz are higher than or similar to that reported. The higher efficiencies of anaerobic sludge in hydrogen production from sucrose were seen in USE levels of 41.0 and 61.5 kJ L?1 for US, and of 61.5 and 82.0 kJ L?1 for US?+?HS. The HAc/HBut molar ratio from 0.255 to 0.410 showed that hydrogen was produced via the butyrate route. The ultrasonic specific energy applied to the anaerobic sludge of 41.0?61.5 kJ L?1 by ultrasound and 61.5?82.0 kJ L?1 by combined ultrasound with heat shock is a highly feasible method with which to inhibit methane production and improve hydrogen production in dark fermentation.