Effect of salinity on anaerobic fermentation gas production behaviors of the thermal pretreated fruit waste

Abstract

The impact of salinity levels (0 g/L,5 g/L,10 g/L,15 g/L,20 g/L, and 25 g/L) on the production of combustible gases from anaerobic fermentation of fruit pomace waste with thermal pretreatment. The underlying mechanisms behind this effect are also be analyzed. The experimental findings reveal that the production of gas from anaerobic fermentation of fruit pomace waste is significantly inhibited under high salt conditions (NaCl ≥ 5 g/L). Specifically, the gas production of the experimental groups with salinity ranging from 15 g/L to 25 g/L is about 79% of that observed in the blank group (without adding NaCl). In addition, high salinity also delays the start of fermentation. Consistent with the experimental data, the Gompertz model simulations reveal that increasing the salt concentration prolongs the fermentation period. Notably, the experimental group with salt concentration of 20–25 g/L is subjected to an 11-h delay, yet this prolongation does not disrupt the 24-h fermentation completion cycle. The high salinity inhibits the total amount of hydrogen in the fruit pomace waste gas production, but it has little effect on the proportion of hydrogen in the gas production. Salinity affects the production of various volatile fatty acids, including acetic, propionic, and butyric acids, without altering the overall composition of short-chain fatty acids. The study shows that high salinity inhibits the consumption of organic matter during the fermentation process of fruit waste, reduce the production of H₂, and notably delays in the onset of fermentation.