Abstract:
Trace metals are essential for the growth of anaerobic microorganisms, however, in practice they are often added
to anaerobic digesters in excessive amounts,which can lead to inhibition. The concept of bioavailability of metals
in anaerobic digestion has been poorly understood in the past, and a lack of deep understanding of the relationship
between trace metal speciation and bioavailability can result in ineffective metal dosing strategies for
anaerobic digesters. Sequential extraction schemes are useful for fractionating trace metals into their different
forms, and metal sulfides can serve as a store and source for trace metals during anaerobic digestion, while
natural/synthetic chelating agents (soluble microbial products-SMPs, extracellular polysaccharides-EPS, and
EDTA/NTA) are capable of controlling trace metal bioavailability. Nevertheless, more work is needed to: investigate
the speciation and bioavailability of Ca, Mg,Mn, W, and Se; compare the bioavailability of different forms of
trace metals e.g. carbonates, sulfides, phosphates to different anaerobic trophic groups; determine what factors
influence metal sulfide dissolution; investigate whether chelating agents can increase trace metal bioavailability;
develop and adapt specialized analytical techniques, and; determine how trace metal dynamics change in an
anaerobic membrane bioreactor (AnMBR).
