Buffering action of acetate on hydrogen production by Ethanoligenens harbinense B49

The buffering effect of acetate on hydrogen production during glucose fermentation by Ethanoligenens harbinense B49 was investigated compared to phosphate, a widely used fermentative hydrogen production buffer. Specific concentrations of sodium acetate or phosphate were added to batch cultures, and the effects on hydrogen production were comparatively analyzed using a modified Gompertz model. Adding 50 mM acetate or phosphate suppressed the hydrogen production peak and slightly extended the lag phase. However, the overall hydrogen yields were 113.5 and 108.5 mmol/L, respectively, and the final pH was effectively controlled. Acetate buffered against hydrogen production more effectively than did phosphate, promoting cell growth and preventing decreased pH. At buffer concentrations 100-250 mM, the maximum hydrogen production was barely suppressed, and the lag phase extended past 7 h. Therefore, although acetate inhibits hydrogen production, using acetate as a buffer (like phosphate) effectively prevented pH drops and increased substrate consumption, enhancing hydrogen production.

Improving the short-chain fatty acids production of waste activated sludge stimulated by a bi-frequency ultrasonic pretreatment.

Short-chain fatty acids (SCFAs) are the most important intermediate in the waste activated sludge (WAS) fermentation process. This work explored a novel approach to improve the SCFAs production from WAS. Experimental results showed that the disintegration and acidification of WAS were enhanced markedly by using bi-frequency (28+40 kHz) ultrasonic pretreatment compared with mono-frequency (28 kHz and 40 kHz) ultrasonic pretreatments. After 28+40 kHz ultrasonic pretreatment, the SCOD concentration increased from original 363 mg COD l-1 to 10810 mg COD l-1 which was 1.53-fold and 1.44-fold of the values obtained with 28kHz and 40kHz ultrasonic pretreatments, respectively. The maximum SCFAs production reached 7587 mg COD l-1 in the 28+40 kHz test which was respectively 1.25-fold and 1.31-fold of that in the 28kHz (6053 mg COD l-1) and 40 kHz (5809 mg COD l-1) tests. This was the highest SCFAs production obtained so far using WAS, pretreated by ultrasonic technology, as the renewable carbon source. SCFAs composition analysis revealed there was more acetic acid (3992 mg COD l-1, accounted for 52.6% of the total SCFAs) for the 28+40 kHz ultrasonic pretreatment which was beneficial to many subsequent bioprocesses.