Transition metals and alkyl earth metals enhance the resilience of methane producing archaea in anaerobic bioreactors

Wilson, Ciarán J.
Transition elements (TEs) are a group of metallic elements in the periodic table that occupy the central block, specifically elements found in the "d-block" or groups 3 to 12. TEs are so-named because they are characterised by having partially filled d orbitals in their electron configuration. In anaerobic digestion (AD), TEs are supplemented to enhance the process performance. However, the complex dynamics associated with the treatment process and the inherent entanglement of chemical and biological interactions within the treatment process aren’t understood well and are under investigation in this study. Furthermore, TEs can be considered essential micro-nutrients or toxins depending on their concentration or valency. Transition element supplementation showed increased bio-methane potential in anaerobic bioreactors. Additionally, TEs contributed to stress resilience resulting from increasing concentrations of SO4/COD through the continued generation of biogas and methane. An increased rate of methanogenic activity coincided with greater efficiency in COD removal, consequently relatively high COD removal in bioreactors with minimal methane production can be attributed to high concentrations of sulphide. The presence of sulphate in the wastewater correlated with hydrogen sulphide production. The augmentation of TEs has a crucial role in decoupling solid retention times from hydraulic retention times. It can facilitate the recovery of value-added co-products from these systems. ICP-OES analysis detected low levels of TEs & alkaline earth metals from the untreated biomass. However, when exposed to TE supplementation, the concentrations of both groups of metals increased exponentially. The reduction of sulphate to sulphide appears to affect the incorporation of TEs into the biomass of the anaerobic granular sludge. Overall, the expression of the Methyl coenzyme A reductase gene was elevated in samples exposed to transition metal dosing. Moreover, compared to the control group, the expression of the (mcrA) gene was heightened at an optimal SO4/COD ratio of (1.49-2.98). In summary, the supplementation of TEs has positively impacted biologically produced methane from anaerobic bioreactors.
NUI Galway
Publisher DOI
Attribution-NonCommercial-NoDerivs 3.0 Ireland