Dark fermentation, anaerobic digestion and microbial fuel cells: An integrated system to valorize swine manure and rice bran

• Integrated systems treating agricultural wastes need to diversified products.
• We propose dark fermentation, anaerobic digestion and microbial fuel cells as integrated system.
• These processes produce methane, hydrogen, electricity and fertilizers.
• Waste produces 27.3 ± 7.2 LH2 kg−1COD, 154 ± 14 LCH4 kg−1COD and 39.8 W h kg−1COD to 54.2 W h kg−1COD.
• Waste gave 0.3 kg of bio-fertilizers kgwaste1.

This work describes how dark fermentation (DF), anaerobic digestion (AD) and microbial fuel cells (MFC) and solid-liquid separation can be integrated to co-produce valuable biochemicals (hydrogen and methane), bioelectricity and biofertilizers. Two integrated systems (System 1: AD + MFC, and System 2: DF + AD + MFC) are described and compared to a traditional one-stage AD system in converting a mixture (COD = 124 ± 8.1 gO2 kg−1Fresh Matter) of swine manure and rice bran. System 1 gave a biomethane yield of 182 LCH4 kg−1COD-added, while System 2 gave L yields of bio-hydrogen and bio-methane of 27.3 ± 7.2 LH2 kg−1COD-added and 154 ± 14 LCH4 kg−1COD-added, respectively. A solid-liquid separation (SLS) step was applied to the digested slurry, giving solid and liquid fractions. The liquid fraction was treated via the MFC-steps, showing power densities of 12–13 W m−3 (500 Ω) and average bioelectricity yields of 39.8 W h kg−1COD to 54.2 W h kg−1COD.

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