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

ABSTRACTThe 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.

Enhanced degradation of quinoline by coupling microbial electrolysis cell with anaerobic digestion simultaneous.

In this study, the feasibility of quinoline-wastewater treatment was investigated in a coupled microbial electrolysis cell and anaerobic digestion system (MEC-AD). Improved degradation and enhanced mineralization of quinoline were obtained, and the optimal voltage was determined to be 1.0 V. Effective removal of quinoline at relative high concentration, and a 1.5-fold increase in methane production were achieved. The results indicated that the MEC-AD could simultaneously remove carbon and nitrogen from quinoline. Gas chromatography-mass spectrometry analysis identified 2-hydroxyquinoline and 8-hydroxycoumarin as the intermediates of quinoline. The formation and degradation of metabolites were rapid, and they did not accumulate in the MEC-AD. The results of microbial community structure analysis demonstrated that the functional species were enriched and coexisted, and that the dominant bacterial genera were SM1A02, Comamonas, Desulfovibrio, Geobacter, and Actinomarinales_norank; the dominant archaeal genera were Methanocorpusculum and Nitrosoarchaeum. Furthermore, the applied current played a selective role in the enrichment of microorganisms.