Semi-solid anaerobic co-digestion of source-separated fecal slag and food waste: focusing on methane production, ecological risk assessment, and quality evaluation as fertilizer

Toilet revolution is driven by the urgent need for solutions to improve sanitation and access to high-quality organic fertilizer for rural areas, which is tagged resource recovery from human waste. This study provides a possible solution via semisolid anaerobic co-digestion (Aco-D) of source-separated fecal slag (SFS) and food waste (FW) (3:1). A comprehensive investigation of Aco-D at different inoculum/substrate ratios (ISR) was conducted. Results revealed that the reactor with ISR of 1:4 reached the highest methane yield (255.05 mL/gVS), which enhanced Methanosaetaceae, Methanomicrobiales, and Syntrophomonas. Additionally, the reactor with low feedstock (ISR of 1:2) showed higher removal efficiency of antibiotics (74.75%). The ecological risk of digestate decreased to an insignificant hazard quotient level, and the contents of nutrients and heavy metals were in line with the standard requirement for fertilizer. This study could serve as an alternative technology to support further research in SFS management and digestate utilization as fertilizer.

Automated summary

The toilet revolution is driven by the urgent need for improving sanitation and access to high-quality organic fertilizer in rural areas. This study offers a potential solution through the semi-solid anaerobic co-digestion of source-separated fecal slag and food waste. It provides insights into the optimal inoculum/substrate ratio and highlights the benefits of this technology in terms of methane yield, removal efficiency of antibiotics, and ecological risk reduction.