Long-term performance on volatile fatty acids production improved in a kitchen wastewater fermenter by co-fermentation of sludge and membrane separation.

Kitchen wastewater can be transformed into a valuable resource through anaerobic fermentation. However, the efficiency of this process is hindered by various factors including salt inhibition and nutrient imbalance. In this study, we examined the effects of co-fermentation with sludge and membrane filtration on the anaerobic fermentation of kitchen wastewater. Our findings indicate that co-fermentation with sludge resulted in a 4-fold increase in fermentation rate and a 2-fold increase in short-chain fatty acids (SCFAs) production. This suggests that the addition of sludge helped to alleviate salt and acid inhibition through ammonia buffering and elemental balancing. The membrane filtration retained 60% of soluble carbohydrates and 15% of proteins in the reactor for further fermentation and recovered nearly 100% of NH4+ and SCFAs in the filtrate, which helped to alleviate acid and ammonia inhibition. The combined fermentation system significantly increased the richness and diversity of microorganisms, particularly caproiciproducens and Clostridium_sensu_stricto_12. The membrane flux remained stable and at a relatively high level, indicating that the combined process may be economically feasible. However, scaling up the co-anaerobic fermentation of kitchen wastewater and sludge in a membrane reactor is necessary for further economic evaluation in the future.

Long-term rumen microorganism fermentation of corn stover in vitro for volatile fatty acid production.

Rumen microorganisms have the ability to efficiently hydrolyze and acidify lignocellulosic biomass. The effectiveness of long-term rumen microorganism fermentation of lignocellulose in vitro for producing volatile fatty acids (VFAs) is unclear. The feasibility of long-term rumen microorganism fermentation of lignocelluose was evaluated in this study, and a stable VFA production was successfully realized for 120 d. Results showed that VFA concentration reached to 5.32-8.48 g/L during long-term fermentation. Hydrolysis efficiency of hemicellulose and cellulose reached 36.5%-52.2% and 29.4%-38.4%, respectively. A stable bacterial community was mainly composed of Prevotella, Rikenellaceae_RC9_gut_group, Ruminococcus, and Succiniclasticum. VFA accumulation led to a pH decrease, which caused the change of bacterial community structure. Functional prediction showed that the functional genes related to hydrolysis and acidogenesis of corn stover were highly expressed during long-term fermentation. The successful long-term rumen fermentation to produce VFAs is of great significance for the practical application of rumen microorganisms.

High salinity slowed organic acid production from acidogenic fermentation of kitchen wastewater by shaping functional bacterial community.

The high salinity of kitchen wastewater might have adverse effects on the production of short-chain fatty acids (SCFAs) in anaerobic fermentation. The effects and mechanisms of salinity on SCFA production in the anaerobic fermentation of kitchen wastewater were studied by varying the salt concentration, as follows: 0 g/L (S0), 2 g/L (S2), 6 g/L (S6), 10 g/L (S10), 15 g/L (S15), and 20 g/L (S20). Experimental results showed that hypersaline conditions (>10 g NaCl/L) accelerated the release of soluble proteins at the initial stage of anaerobic fermentation. They also significantly prohibited the hydrolysis and degradation of soluble proteins and carbohydrates. Compared with low salinity tests, the SCFA concentrations under hypersaline conditions (>10 g NaCl/L) only reached approximately 43% of the highest concentration on day 10, although the SCFA concentrations in all tests were very close on day 10 (14 g COD/L). High salinity delayed the production of n-butyric acid but did not change the composition of the total SCFAs. High salinity enriched Enterococcus and Bifidobacterium, the relative abundance levels of which reached 27.57% and 49.71%, respectively, before the depletion of substrate. High salinity showed a negative correlation with the relative abundance of the genera Clostridium_sensu_stricto_1, Prevotella and unclassified_f_Oscillospiraceae which are responsible for SCFA production. This study provided a theoretical basis for the fficient utilization of kitchen wastewater.

Preparation, characterization, and functional evaluation of proanthocyanidin-chitosan conjugate.

In this study, chitosan (CS) was conjugated with proanthocyanidin (PA) by a free radical grafting reaction. The successful synthesis of PA-CS conjugate was confirmed by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance. The optimal molar ratio of PA to CS repeat unit for the preparation of PA-CS was 0.13:1, which led to a high PA content of 381.76 mg PAE/g in PA-CS. The antioxidant assays demonstrated that PA-CS had much stronger radical scavenging activity and reducing power than the native CS. Especially, the half-inhibition concentrations of PA-CS against DPPH and ABTS radicals were only 6.2 µg/mL and 5.9 µg/mL, respectively. In addition, PA-CS showed an alteration in antibacterial activity compared with CS, and the alteration varied with bacterial strain.