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

Abstract

The effect of sequential extraction of trace metals on sulfur (S) speciation in anoxic sludge samples from two lab-scale biogas reactors augmented with Fe was investigated. Analyses of sulfur K-edge X-ray absorption near edge structure (S XANES) spectroscopy and acid volatile sulfide (AVS) were conducted on the residues from each step of the sequential extraction. The S speciation in sludge samples after AVS analysis was also determined by S XANES. Sulfur was mainly present as FeS (~60% of total S) and reduced organic S (~30% of total S), such as organic sulfide and thiol groups, in the anoxic solid phase. Sulfur XANES and AVS analyses showed that during first step of the extraction procedure (the removal of exchangeable cations), a part of the FeS fraction corresponding to 20% of total S was transformed to zero-valent S, whereas Fe was not released into the solution during this transformation. After the last extraction step (organic/sulfide fraction) a secondary Fe phase was formed. The change in chemical speciation of S and Fe occurring during sequential extraction procedure suggests indirect effects on trace metals associated to the FeS fraction 2 that may lead to incorrect results. Furthermore, by S XANES it was verified that the AVS analysis effectively removed the FeS fraction. The present results identified critical limitations for the application of sequential extraction for trace metal speciation analysis outside the framework for which the methods were developed.

Organic matter influences transformation products of ferrihydrite exposed to sulfide

“…Data were processed and normalized in Athena as described in ref. 8 and deconvolution of S XANES was performed using WinXAS 3.09, 60 following a modified version of the fitting approaches detailed in Manceau and Nagy 59 and Shakeri Yetka et al 61 Additional details are presented in the ESI. †…”

Effects of trace element addition on process stability during anaerobic co-digestion of OFMSW and slaughterhouse waste

“…During the degradation of protein-rich materials, high amounts of sulfides are produced resulting in precipitation of trace elements, why addition of iron in combination with trace elements in ionic form often is needed to reach profitable loading rates. (Takashima et al, 1990;Nordell et al, 2012;Shakeri Yekta et al, 2012;Moestedt et al, 2013).…”

Biogeochemistry of trace elements in anaerobic digesters

“…Shakeri Yekta et al (2012) investigated the effect of SE of TE on S speciation in anoxic sludge samples from two lab-scale biogas reactors augmented with Fe. Analyses of S K-edge XANES spectroscopy and Acid Volatile Sulfides (AVS) were conducted on the residues from each SE step.…”