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

Abstract

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.

Enhanced Biogas Production through Anaerobic Co-Digestion of Agricultural Wastes and Wastewater: A Case Study in South Africa

“…The AWs consisted of different fruit and vegetables; hence the collected samples were subjected into manual separation to separate targeted waste i.e., potatoes, apples, butternuts, carrots, and bananas from the mixed AW. The selection of the AWs was based on the availability of the waste stock from the market during the experimental study, these AWs were in abundance at the dumping site and also the majority have been demonstrated by different studies to have been viable for biogas production [13,22,[29][30][31][32][33]. The amount of each AWs that were taken from the site were about ± 3 kg in weight.…”

“…The current study of Co-AD apples at 2.5 kgVS/L.d produced a methane composition of 63%. Coalla et al [32] conducted a study using apple waste with OLR 1.5 kg/m 3 .d and HRT of 52 days that produced methane composition of 77-80%, and Gonzá lez-Garcí a et al [31] conducted a study using apple pomace pulp (7.5% w/w) co-digested with swine manure with an HRT of 33 days and produced a methane composition of 61.96%. The difference in methane composition can be attributed to the longer HRT and the type of substrate (apple waste) [49,64].…”