Abstract
Volatile fatty acids (VFAs) and trace elements (TEs) interactions (VFAs*TEs) during biomethanization have effects that could be exploited to enhance anaerobic digestion (AD) of biomass. The goal of this study was to validate biocatalytic effects of specialized VFAs*TEs identified from a batch-derived Optimum TEs Configuration (or simply ‘Optimum’) on high organic loading rate (OLR) involving mixed fruit residue (MFR) fed in semi-continuous AD operation. The specialized VFAs*TEs were formulated as Variants of the Optimum and included Optimum –Cobalt (Co) for specialized VFAs*Co effects, and Optimum +Selenium (Se) for specialized VFAs*Se effects. Four duplicate AD reactors were treated with formulations reflecting the Optimum and the Variants. Each duplicate reactor was semi-continuously fed with MFR at varying OLR until instability occurred. Methane production, total volatile organic acidity (FOS) / total alkalinity (TAC) and VFAs fingerprints were measured as main responses. The results showed that reactors of the Optimum and its Variants were unstable at OLR of 8g oDM/L/d, but stability was restored in the Optimum –Co (FOS/TAC values of 0.6 compared to 1.51 and 1.67 for Optimum and Optimum +Se respectively). The average specific CH4 production (Nml/g oDM) of the Optimum and its Variants were Control: 431±36; Optimum: 553±16; Optimum –Co: 580±12; and Optimum +Se: 545±13. Optimum –Co also had the lowest acetic acid and butyric acid accumulation, but had higher propionic acid concentration (0.7 g/L) compared to the Optimum (0.3 g/L) and Optimum +Se (0.4 g/L).
Highlights
Biomethanization involves biochemical processes and pathways that favor methane production during biomass degradation
The goal of this study was to validate biocatalytic effects of specialized Volatile fatty acids (VFAs)*trace elements (TEs) identified from a batch-derived Optimum TEs Configuration on high organic loading rate (OLR) involving mixed fruit residue (MFR) fed in semicontinuous anaerobic digestion (AD) operation
The results showed that reactors of the Optimum and its Variants were unstable at OLR of 8g oDM/L/d, but stability was restored in the Optimum – Co (FOS/TAC values of 0.6 compared to 1.51 and 1.67 for Optimum and Optimum +Se respectively)
Summary
Biomethanization involves biochemical processes and pathways that favor methane production during biomass degradation. Anaerobic digestion (AD) reactors are supplemented with trace elements (TEs) during biomethanization to maximize the processes of methane (CH4) production, volatile fatty acids (VFAs) degradation and process stability (Braga et al, 2018; Mancini et al, 2018; Yazdanpanah et al, 2018). TEs improve biomethanization by enhancing the biocatalytic potentials of metalloenzymes (MEs) that are associated with AD, reduce digester acid accumulation and improve CH4 production (Ezebuiro and Koerner, 2017; Ezebuiro et al, 2018; Da Silva et al, 2021). Managing digester acidification is important because VFAs accumulation beyond critical levels of 200 mmol/L may lead to biomethanization failure (Zhang et al, 2010; Bardi and Aminirad, 2020).
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