Methodological approaches for fractionation and speciation to estimate trace element bioavailability in engineered anaerobic digestion ecosystems: An overview

Abstract

Optimal supply of trace elements (TE) is a prerequisite for microbial growth and activity in anaerobic digestion (AD) bioprocesses. However, the required concentrations and ratios of essential TE for AD biotechnologies strongly depend on prevailing operating conditions as well as feedstock composition. Furthermore, TE in AD bioreactors undergo complex physicochemical reactions and may be present as free ions, complex bound or as precipitates depending on pH, or on the presence of sulfur compounds or organic macromolecules. To overcome TE deficiency, various commercial mineral products are typically applied to AD processes. The addition of heavy metals poses the risk of overdosing operating systems, which may be toxic to microbial consortia and ultimately the environment. Adequate supplementation, therefore, requires appropriate knowledge not only about the composition, but also on the speciation and bioavailability of TE. However, very little is yet fully understood on this specific issue. Evaluations of TE typically only include the measurement of total TE concentrations but do not consider the chemical forms in which TE exist. Thus detailed information on bioavailability and potential toxicity cannot be provided. This review provides an overview of the state of the art in approaches to determine bioavailable TE in anaerobic bioprocesses, including sequential fractionation and speciation techniques. Critical aspects and considerations, including with respect to sampling and analytical procedures, as well as mathematical modeling, are examined. The approaches discussed in this review are based on our experiences and on previously published studies in the context of the “COST Action 1302: European Network on Ecological Roles of Trace Metals in Anaerobic Biotechnologies.

Anaerobic digestion of chicken manure: Influence of trace element supplementation

“…Therefore, some portion of the TEs supplemented to batch bottles might not be bioavailable for anaerobic consortia. Since maintaining anaerobic conditions during the sampling is not easy and may fail to determine the bioavailable fraction of TEs [16], in this study only fractions in the sludge liquid phase and pellet were determined. For this purpose, at the end of BMP test, mixed liquor samples were taken from one-fold TE supplemented set and analyzed for the portion in the liquid and solid phases.…”

“…Moreover, the bioavailability of TEs in AD is another concern that must be considered when reporting the required concentrations. By applying chemical sequential extraction techniques, bioavailability might be investigated . For instance, Fuentes et al.…”

“…Moreover, the bioavailability of TEs in AD is another concern that must be considered when reporting the required concentrations. By applying chemical sequential extraction techniques, bioavailability might be investigated [16]. For instance, Fuentes et al [17] have reported that in addition to water-soluble fraction, exchangeable fraction of TEs is also bioavailable for metabolic activity.…”

The Minimum Requirements for Nickel and Cobalt as Trace Metals in Thermophilic Biogas Fermentation of Palm Oil Mill Effluents

“…High TS values indicate that the performance of microorganisms is less optimal so that the biogas produced will also decrease. The amount of biogas produced is a function of the concentration of TS in the digester 12 .…”

Trace element supplementation as a management tool for anaerobic digester operation: benefits and risks

“…Determining the total TE concentrations is, of course, a good start in quantifying key TE in a digester, but it is not sufficient to allow a determination of the 'bioavailable fraction'. The bioavailable fraction is defined as the degree to which elements are available for interaction with microbial community but, in reality, is complicated to measure and quantify (van Hullebusch et al 2016).…”