An Exploratory Study on the Pathways of Cr (VI) Reduction in Sulfate-reducing Up-flow Anaerobic Sludge Bed (UASB) Reactor

Abstract

Electroplating wastewater contains both Cr (VI) and sulfate. So Cr (VI) removal under sulfate-rich condition is quite complicated. This study mainly investigates the pathways for Cr (VI) removal under biological sulfate-reducing condition in the up-flow anaerobic sludge bed (UASB) reactor. Two potential pathways are found for the removal of Cr (VI). The first one is the sulfidogenesis-induced Cr (VI) reduction pathway (for 90% Cr (VI) removal), in which Cr (VI) is reduced by sulfide generated from biological reduction of sulfate. The second one leads to direct reduction of Cr (VI) which is utilized by bacteria as the electron acceptor (for 10% Cr (VI) removal). Batch test results confirmed that sulfide was oxidized to elemental sulfur instead of sulfate during Cr (VI) reduction. The produced extracellular polymeric substances (EPS) provided protection to the microbes, resulting in effective removal of Cr (VI). Sulfate-reducing bacteria (SRB) genera accounted for 11.1% of the total bacterial community; thus they could be the major organisms mediating the sulfidogenesis-induced reduction of Cr (VI). In addition, chromate-utilizing genera (e.g. Microbacterium) were also detected, which were possibly responsible for the direct reduction of Cr (VI) using organics as the electron donor and Cr (VI) as the electron acceptor.

Enhancement of Chromium (VI) Reduction in Microcosms Amended with Lactate or Yeast Extract: A Laboratory-Scale Study

“…This result was in line with previous studies, in which Shewanella oneidensis was highly susceptible to growth inhibition by Cr(VI), even at 15 µg/L [35,36]. In this work, the process of Cr(VI) reduction in all of the experimental conditions (BIO, LATT, and YE) of laboratory microcosms occurred in the absence of oxygen, as confirmed by the resazurin control tests, and according to Cheung and Gu [37], and Qian et al [38].…”

Direct Cr (VI) bio-reduction with organics as electron donor by anaerobic sludge

“…It has been proved that the indirect Cr (VI) reduction rate was mainly dependent on the biological sulfate reduction rate [15]. As a result, the indirect Cr (VI) reduction rate is almost five times of the direct Cr (VI) reduction rate according to our results.…”

Chromium in Environment, Its Toxic Effect from Chromite-Mining and Ferrochrome Industries, and Its Possible Bioremediation

“…These bacteria can cope with the higher concentration of Cr(VI) (Fude et al 1994). Many researchers have reported the reduction of Cr(VI)to Cr(III) by sulphate-and iron-reducing bacteria through indirect mechanism via their anaerobic metabolic end products (Arias and Tebo 2003;Qian et al 2016;Michel et al 2003;Zhu et al 2008). Sulphate-reducing bacteria produce sulphide during reduction of sulphate that further reduces Cr(VI).…”