Energy and Nutrients from Apple Waste Using Anaerobic Digestion and Membrane Technology

The worldwide increment of food waste requires innovative management solutions, aligned with sustainability, energy, and food security. Anaerobic digestion (AD), followed by nutrient recovery, may be considered an interesting approach. This study proposed a co-digestion of apple pomace (AP) with swine manure (SM) to study the effect of different proportions of AP (0, 7.5, 15, and 30%, on a volatile solids (VS) basis) on the methane production and the stability of the process. Subsequently, the gas-permeable membrane (GPM) technology was applied to recover nitrogen (N) as ammonium sulfate (bio-based fertilizer) from the digestates produced after the AD of 7.5% of AP and SM, and SM alone. The results showed that the co-digestion of 7.5% and 15% of AP with SM presented a methane production similar to the AD of SM alone (with 412.3 +/- 62.6, 381.8 +/- 134.1, and 421.7 +/- 153.6 mL g VS-1 day(-1), respectively). The later application of the GPM technology on the resulting digestates, with SM alone and with 7.5% of AP with SM, showed total ammoniacal N recovery rates of 33 and 25.8 g N m(-2) d(-1), respectively. Therefore, the AP valorization through the AD process, followed by N recovery from the digestate, could be a good management strategy.

Automated summary

The increase in global food waste requires innovative management solutions that are sustainable, energy-efficient, and promote food security. This study examined the co-digestion of apple pomace and swine manure, as well as the recovery of nitrogen from the resulting digestate using gas-permeable membrane technology. The results showed that co-digestion of 7.5% and 15% apple pomace with swine manure yielded methane production similar to the digestion of swine manure alone.