Bioprecipitation of Arsenic Sulphide at Low pH

Abstract

A process for the precipitation of trivalent arsenic sulphide in sulphate-reducing condition at low pH would be very attractive due to the high arsenic content (60%) in the final precipitate. A bacterial consortium able to reduce sulphate at pH 4.5 served to inoculate a column bioreactor that was continuously fed with As(V) or As(III), glycerol as energy source, at pH values between 2 and 5. The best efficiency, in terms of residual As concentration in the outlet, was obtained with the lowest feed pH, i.e. pH 2. However, in these conditions, the bacterial activity inside the bioreactor was isolated in higher pH zones. The diversity, functionality and evolution of the consortium colonizing the bioreactor were characterized by means of biomolecular tools, in relation with operating parameters (pH, As, sulphide). Fermentative and sulphate-reducing bacteria were present both in the liquid phase and onto the filling material. All sulphate-reducers that were detected belonged to the Desulfosporosinus genus. Spectroscopic analyses of the solid phases that precipitated into the bioreactor revealed the presence of amorphous precursors of orpiment of nano-size.

How prokaryotes deal with arsenic†

“…Depending on the As oxidation state, which varies according to the local physicochemical conditions (mainly the redox potential Eh and the pH), sulfate reducers and iron oxidizers could maintain this metalloid outside of the cell by reaction with the product of their energy metabolism. Indeed, the final product of sulfur and sulfate reduction is H 2 S which precipitates with As(V) to form insoluble sulfide complexes (Rittle et al ., 1995; Newman et al ., 1997; Keimowitz et al ., 2007; Battaglia‐Brunet et al ., 2009). Bacteria mediating Fe(II) oxidation through nitrate reduction to get energy for growth in anoxic conditions have been shown to play a key role in arsenic cycling by forming solid hydrous ferric oxide on which As(V) (Senn and Hemond, 2002; Hohmann et al ., 2010) or As(III) (Gibney and Nusslein, 2007; Hohmann et al ., 2010) sorbs.…”

Complete removal of arsenic and zinc from a heavily contaminated acid mine drainage via an indigenous SRB consortium

“…Enrichment of an indigenous SRB consortium. A SRB consortium reducing sulfate at pH 4.5 was enriched from surface sediments of the Carnoulès AMD sampled 30 m downstream the tailing impoundment, using a basal medium described in [30], but with 100 mg/L As III (1.33 mM) instead of As V (Table SI- 1). After one month of sub-culturing in this medium (once a week), the enrichment was inoculated in penicillin flasks containing a synthetic AMD medium (Table SI-2), mimicking the Carnoulès AMD composition.…”

Observing signals of the bulk matter Randall-Sundrum model through rare decays of supersymmetric particles

“…It is thus required to produce only specific mass eigenstates at a collider. This is achieved by lepton colliders, such as the ILC [16] and the CLIC [17], where the center-of-mass energy of a process is fixed. For example, the flavor-mixing ratios in "almost SU(2) doublet smuon mass eigenstate" and in "almost SU(2) singlet smuon mass eigenstate" are predicted to be different.…”