Aerobic composting of digested residue eluted from dry methane fermentation to develop a zero-emission process

Area of Science:

• Environmental Science
• Waste Management
• Soil Science

Background:

• Digested residue from fuel ethanol and methane production using kitchen garbage presents a waste management challenge.
• Developing a zero-emission process requires valorizing this residue into a usable product, such as fertilizer.

Purpose of the Study:

• To assess the compostability of digested kitchen garbage residue.
• To determine if the residue can be transformed into an added-value fertilizer.
• To optimize the composting process for waste valorization.

Main Methods:

• Laboratory-scale composting reactor used to process the digested residue.
• Addition of mature compost and a bulking agent to facilitate composting.
• Analysis of volatile total solid (VTS) degradation, physicochemical properties, and germination index (GI).
• Real-time quantitative PCR (qPCR) used to identify ammonia-oxidizing bacteria (AOB).

Main Results:

• Volatile total solid (VTS) degradation reached approximately 27% within 13 days.
• Initial residue was unsuitable as fertilizer due to high ammonium (NH4+) and volatile fatty acids (VFAs).
• After 62 days, a highly matured compost was achieved with 16.4 g/kg-TS nitrogen, 9.7 g/kg-TS nitrate (NO3-), and a germination index (GI) of 151%.

Conclusions:

• Composting effectively transforms digested kitchen garbage residue into a valuable fertilizer.
• Nitrification, driven by ammonia-oxidizing bacteria (AOB), occurs during the composting process.
• The zero-emission process is feasible, converting waste into a high-quality soil amendment.