Sulfur K-edge XANES and acid volatile sulfide analyses of changes in chemical speciation of S and Fe during sequential extraction of trace metals in anoxic sludge from biogas reactors

► Changes in speciation of S and Fe during sequential extraction of trace metals. ► Sulfur is mainly present as FeS, organic sulfide and thiols in biogas reactors. ► Sulfur XANES verified that FeS is effectively removed as AVS. ► During extraction of the exchangeable metals FeS was oxidized to zero-valent S.