Effect of operating conditions on speciation and bioavailability of trace metals in submerged anaerobic membrane bioreactors

This study investigated the effect of changes in pH (7, 6.5 and 6), hydraulic retention time (HRT) (6 h, 4 h, and 2 h), solids retention time (SRT) (100 d and 25 d) on the speciation of trace metals (TMs) in submerged anaerobic membrane bioreactors (SAMBRs). The results showed that the metal retention capacity of SAMBRs reduced when the pH, HRT and SRT were reduced i.e. up to 21.9%, 39.1%, and 17.1%, respectively, but it was also found that the speciation of these TMs generally shifted towards highly bioavailable fractions i.e. Soluble and Exchangeable. The degree of shifting in speciation depended on the affinity of the TMs for anaerobic sludge and their sensitivity to the changes. TMs with the most and the least significant changes in speciation were Fe and Mn, respectively.