Dual-fuel production from restaurant grease trap waste: Bio-fuel oil extraction and anaerobic methane production from the post-extracted residue

• Oil content was extracted from grease trap waste (GTW) by heat-treatment.
• A high purity oil equivalent to an A-grade fuel oil with 81–93 wt% of efficiency.
• Anaerobic digestion of post-extracted residue was inhibited by long-chain fatty acid.
• Ca-added digester achieved stable semi-continuous operation over one year.

An effective way for restaurant grease trap waste (GTW) treatment to generate fuel oil and methane by the combination of physiological and biological processes was investigated. The heat-driven extraction could provide a high purity oil equivalent to an A-grade fuel oil of Japanese industrial standard with 81–93 wt% of extraction efficiency. A post-extracted residue was treated as an anaerobic digestion feedstock, and however, an inhibitory effect of long chain fatty acid (LCFA) was still a barrier for high-rate digestion. From the semi-continuous experiment fed with the residual sludge as a single substrate, it can be concluded that the continuous addition of calcium into the reactor contributed to reducing LCFA inhibition, resulting in the long-term stable operation over one year. Furthermore, the anaerobic reactor performed well with 70–80% of COD reduction and methane productivity under an organic loading rate up to 5.3 g-COD/L/d.

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