Dry anaerobic digestion of food waste and cardboard at different substrate loads, solid contents and co-digestion proportions

Abstract

The increasing food waste production calls for developing efficient technologies for its treatment. Anaerobic processes provide an effective waste valorization. The influence of the initial substrate load on the performance of batch dry anaerobic co-digestion reactors treating food waste and cardboard was investigated. The load was varied by modifying the substrate to inoculum ratio (S/X), the total solids content and the co-digestion proportions. The results showed that the S/X was a crucial parameter. Within the tested values (0.25, 1 and 4gVS·gVS), only the reactors working at 0.25 produced methane. Methanosarcina was the main archaea, indicating its importance for efficient methanogenesis. Acidogenic fermentation was predominant at higher S/X, producing hydrogen and other metabolites. Higher substrate conversions (≤48%) and hydrogen yields (≤62mL·gVS) were achieved at low loads. This study suggests that different value-added compounds can be produced in dry conditions, with the initial substrate load as easy-to-control operational parameter.

Poultry Litter Solid State Anaerobic Digestion: Effect of Digestate Recirculation Intervals and Substrate/Inoculum Ratios on Process Efficiency

“…Other SSAD studies also concluded that with a low substrate:inoculum ratio (1:3 or up to 25% TS), they obtained a higher methane yield, and low methane yields were observed at higher TS concentrations (Abbassi-Guendouz et al, 2012;Di Maria et al, 2012;Sun et al, 2016;Capson-Tojo et al, 2017). The TS content affects the mass transfer among gasliquid-solid phases and, consequently, the substrate degradation rate.…”

“…The low generation of biogas is a consequence of the complex phenomena occurring at high TS concentrations (Capson-Tojo et al, 2017). Abbassi-Guendouz et al (2012) Xu et al (2014) reported a two-sided effect of TS concentration during AD, with an increase of up to 10%(TS) stimulated microbial growth and a consequent increase in methane generation.…”

Addition of biochar and trace elements in the form of industrial FeCl3 to stabilize anaerobic digestion of food waste: dosage optimization and long‐term study

“…One of the alternatives that has been applied to favor the consumption of VFAs in FW AD is the supplementation of trace elements (TEs) . TEs have been found to favor VFA consumption in both mesophilic and thermophilic AD of FW, mainly due to a favored synthesis of critical enzymes in the process of syntrophic hydrogenotrophic methanogenesis (HM), which is known to be the predominant methane‐producing pathway during FW AD . TEs addition has been successfully applied to avoid accumulation of VFAs at high organic loading rates (OLRs) and to recover acidified reactors …”

“…to be the predominant methane-producing pathway during FW AD. 2,11,[15][16][17] TEs addition has been successfully applied to avoid accumulation of VFAs at high organic loading rates (OLRs) 10,18,19 and to recover acidified reactors. 20,21 Another strategy to favor VFA consumption during AD that has gained attention in the last few years is the addition of conductive materials.…”

“…The first complication occurring during FW AD is related to the fast biodegradability of this substrate, which is mainly composed of easily degradable carbohydrates. Therefore, the reactors can be easily overloaded, especially in batch systems, causing an imbalance between the acidogenesis/acetogenesis and the methanogenesis steps, which results in an initial accumulation of volatile fatty acids (VFAs) and a consequent pH drop. The second issue to be dealt with is related to the high protein content of this substrate and its low water content (∼20% total solids; TS).…”