Harvesting zero waste from co-digested fruit and vegetable peels via integrated fermentation and pyrolysis processes

Area of Science:

• Biotechnology and Bioengineering
• Waste Management and Valorization
• Renewable Energy Production

Background:

• Fruit and vegetable peels (FVPs) represent a significant waste stream with potential for resource recovery.
• Current waste management strategies often overlook the economic potential of FVPs for energy and material production.
• Developing integrated processes for waste valorization is crucial for a circular economy.

Purpose of the Study:

• To assess an innovative economic approach for producing fermentative hydrogen and biochar from FVPs.
• To optimize the multi-fermentation process for maximizing hydrogen yield and chemical oxygen demand (COD) reduction.
• To evaluate the biochar production potential and economic viability from fermented digestates.

Main Methods:

• Multi-fermentation of various combinations of FVPs (pea, tomato, banana, orange) to produce hydrogen.
• Pyrolysis of fermentation digestates at 500°C to produce biochar.
• Characterization of biochar properties including specific surface area, density, and pore volume.
• Economic analysis of both fermentation and pyrolysis stages to determine overall profitability.

Main Results:

• Multi-fermentation of 25% pea + 25% tomato + 25% banana + 25% orange (M4) achieved maximal hydrogen yield (3.9 ± 0.6 mmol/gCOD) and COD reduction (56.2 ± 4.6%).
• Biochar from spinach (S1) exhibited the highest specific surface area (28.43 ± 3.95 m²/g), density (1.93 ± 0.18 g/cm³), pore volume (0.59 ± 0.08 cm³/g), and biochar yield (59.04 ± 2.36%).
• The maximum overall profit from integrated fermentation and pyrolysis was $5.21/kgfeedstock, achieved with the M4 fermentation batch.

Conclusions:

• The integrated fermentation/pyrolysis process offers an economically viable route for valorizing FVPs into hydrogen and biochar.
• Optimized multi-fermentation significantly enhances hydrogen production efficiency.
• Biochar derived from specific FVP digestates possesses favorable characteristics for potential applications, contributing to the overall economic feasibility.