Effects of combined ultrasonic and grinding pre-treatments on anaerobic digestion of vinegar residue: organic solubilization, hydrolysis, and CH₄ production

ABSTRACT

The high lignocellulose content of vinegar residues (VR) limits their biochemical methane potential (BMP) in anaerobic digestion (AD). However, unlike reported high cellulosic materials such as straw and grass, single pre-treatment with ultrasonication or grinding only slightly improved VR AD, due to the high protein and carbohydrate contents of VR. This study used statistical analysis to show that the methane yield, protein and polysaccharide release, and hydrolysis performance during VR AD were significantly enhanced with a combined grinding-ultrasound pre-treatment. Specifically, at 60 min of ultrasonic, the group with the combined pre-treatment (60 min + RS) showed the highest VR BMP (∼307.1 mLCH₄/gVS), 68.7% greater than that in the control group. This group also exhibited optimal conditions for dissolution of polysaccharide and protein, with accumulated amounts of ∼500 and 1600 mg/L, respectively. The highest volatile fatty acid (VFA) concentration in the 60 min + RS group was 61.5% higher than that in the control group. Both dissolution and hydrolysis experiments suggested that ultrasound accelerated protein release from VR, particularly after the particle size was reduced, and that the grinding pre-treatment had a positive effect on polysaccharide release.

GRAPHICAL ABSTRACT

KEYWORDS:

• Vinegar residue (VR)
• anaerobic digestion
• ultrasonic pre-treatment
• grinding pre-treatment
• organic dissolution

Acknowledgements

This project is supported by the Natural Nature Science Foundation of China (NSFC, No. 51908396), by Science and Technology Innovation Major Project of Ningbo, Zhejiang Province (No. 2018B10023), and by the Natural Science Foundation of Shanxi Province, China (No. 201801D221338).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This project is supported by the Nature Science Foundation of China (NSFC, No. 51908396), by Project of Science and Technology Innovation, Ningbo Municipal Bureau of Science and Technology, Zhejiang Province (No. 2018B10023), and by the Natural Science Foundation of Shanxi Province, China (No. 201801D221338).