In practice, trace metals are often supplemented in excessive amounts, which can lead to inhibitory effects on the biological treatment processes. This is due to the lack of an in-depth understanding of trace metal speciation and bioavailability. Initially, the bioavailability of trace metals was generally quantified based on the total rather than
‘free’ or bioavailable metal concentrations. However, it is now clear that chemical speciation is critical when predicting bioavailability. Although trace metal speciation has been studied extensively over the years to determine the fate of trace metals in an anaerobic environment, its relationship with trace metal bioavailability is still not clearly understood.