Long-term semi-continuous acidogenic fermentation for food wastes treatment: Effect of high organic loading rates at low hydraulic retention times and uncontrolled pH conditions

The present study investigated the effect of high organic loading rates at low hydraulic retention times without pH control on food wastes fermentation. The acidogenic fermentation was robust to the hydraulic retention time drawdown. Hydraulic retention time variation led to compositional changes of fermentation product. Lactic acid and ethanol were always the dominant end-products and achieved the highest proportion (90.9%) at the 1-day hydraulic retention time. CO2 was the dominant biogas with the absence of H2 and CH4. The concentration of total fermentation product decreased with the lower hydraulic retention time, but the highest fermentation products rate was obtained at the lowest hydraulic retention time. The dominant bacteria was Lactobacillus at the genus level. This work demonstrated the feasibility of operating an acidogenic fermentation reactor at a high organic loading rate, low hydraulic retention time, and uncontrolled pH for improved reactor capacity, construction and operation cost-saving, and easy operation.

Automated summary

This study investigated the impact of high organic loading rates and low hydraulic retention times without pH control on food waste fermentation. The results showed that the acidogenic fermentation process remained stable even with a decrease in hydraulic retention time. The composition of fermentation products varied with different hydraulic retention times, with lactic acid and ethanol being the dominant end-products. CO2 was the main biogas produced, while H2 and CH4 were absent. The concentration of total fermentation products decreased with shorter hydraulic retention times, but the fermentation products rate was highest at the lowest hydraulic retention time. Lactobacillus was the predominant bacteria at the genus level. This research demonstrated the feasibility of operating an acidogenic fermentation reactor at high organic loading rates, low hydraulic retention times, and without pH control, which can improve reactor capacity, reduce construction and operation costs, and simplify operation.