Food waste valorization by purple phototrophic bacteria and anaerobic digestion after thermal hydrolysis

Abstract

Increased demand for effective waste management strategies, along with the need for a transition from a fossil fuel-based economy to a bio-based economy sharpens the need for synergies and scientific innovations. Food waste (FW) is an essential component of municipal solid waste, and its accumulation has become a global concern. This work discusses a closed-loop integrated biorefinery. It couples thermal hydrolysis with anaerobic digestion and photofermentation for the recovery of bioenergy resources and the production of value-added products. Thermal hydrolysis yielded up to 40.4% solids solubilization, allowing the separation of an organic-rich hydrolysate. This pre-treatment also improves anaerobic digestibility of the solid fraction, thus increasing biogas production, which can feed a combined heat and power plant. This approach makes the process sustainable and energy-efficient while decreasing the total volume of the disposal waste by 78.6%. Phototrophic treatment of the hydrolysate through a purple phototrophic bacteria-based mixed culture resulted in biomass growth with high protein content (65% wt.). The system also produced polyhydroxyalkanoates (PHA) and hydrogen, accounting for a total valorization of 16.9% of the initial total solids of the raw food waste. This variety of possible products allows setting a seasonal production in a biorefinery, depending on the composition of the debris and the market demand. Modulation of the nitrogen composition of the food waste can help to choose the best option, where low Nitrogen drives PHA and hydrogen production. In contrast, high Nitrogen leads to increased protein production.