Volatile fatty acids recovery and antibiotic degradation from erythromycin fermentation residues by combined thermal pretreatment and anaerobic fermentation: Insights into microbial communities and metabolic pathways

Evaluation of initial pH and urea hydrogen peroxide (UHP) co-pretreatment on waste-activated sludge

Wastewater treatment and conversion into renewable energy sources have been of great interest in recent times due to growing environmental pollution concerns and need for sustainable energy sources. Sewage sludge treatment can convert sludge into renewable energy. In this study, the impact of initial pH and urea hydrogen peroxide (UHP) co-pretreatment on sludge hydrolysis and anaerobic digestion was investigated. The pH of sludge was initially adjusted to 7, 9, and 11 before the addition of 8 mmol/g VS UHP. Under 24 h pretreatment, alkaline medium and UHP effectively enhanced sludge solubilization and hydrolysis. The combination of chemical, sonication, and centrifugation improved the extraction of extracellular polymerase substances released in soluble state. Secondly, anaerobic digestion was performed for 11 days to determine the influence of a lower mesophilic temperature (20 °C) and retention time on the pretreated sludge. The highest NH4+-N concentration of 5.32 g/L was recorded in pH 7+UHP. The most significant total VFA concentration of 13.1 g COD/L was observed in pH 7+UHP on day 9. Acetic acid, isovaleric acid and propionic acid accounted for 80%-83% of the total VFA composition in all pretreated reactors. Lower mesophilic temperature efficiently optimized UHP and VFA production in the pretreated reactors. Microbial metabolism was stabilized under a longer retention time. Alkaline pH and longer retention time elevated NH4+-N and VFA concentration. The results showed that initial pH and UHP co-pretreatment of waste activated sludge offer an alternative pathway for enhancing sludge hydrolysis and VFA production applicable in sludge treatment.

Effect of high corn straw loads on short-chain fatty acid production in semi-continuous rumen reactor

Ruminal microorganisms can efficiently hydrolyze biomass waste for short-chain fatty acid (SCFA) production. However, the continuous SCFA production by ruminal microorganisms at high loads is unclear. In this study, the effectiveness of a rumen semi-continuous reactor at high load for SCFA production was explored. Results showed that SCFA concentration reached 13.3 g/L at 8 % (w/v) corn straw load. The higher the corn straw load, the lower the volatile solid removal. Rumen microbial community composition changed significantly with increasing corn straw load. A significant decrease in bacterial diversity and abundance was observed at 8 % corn straw load. Some core genera such as Prevotella, Saccharofermentans, and Ruminococcus significantly increased. As corn straw loads increased, the expression of functional genes related to hydrolysis and acidogenesis gradually increased. Thus, the 8.0 % load is suitable for SCFA production. These findings provide new insights into high load fermentation of ruminal microorganisms.