Finite difference simulation of biological chromium (VI) reduction in aquifer media columns

Abstract

A mechanistic mathematical model was developed that successfully traced the Cr(VI) concentration profiles inside porous aquifer media columns. The model was thereafter used to calculate Cr(VI) removal rate for a range of Cr(VI) loadings. Internal concentration profiles were modelled against data collected from intermediate sample ports along the length of the test columns. For the first time, the performance of a simulated barrier was evaluated internally in porous media using a finite difference approach. Parameters in the model were optimised at transient-state and under near steady-state conditions with respect to biomass and effluent Cr(VI) concentration respectively. The best fitting model from this study followed non-competitive inhibition kinetics for Cr(VI) removal with the best fitting steady-state parameters: Cr(VI) reduction rate coefficient, k = 5.2×10 ; and a semi-empirical reaction order, n = 2. The model results showed that post-barrier infusion of biomass into the clean aquifer downstream of the barrier could be limited by depletion of the substrates within the barrier. The model when fully developed will be used in desktop evaluation of proposed in situ biological barrier systems before implementation in actual aquifer systems.

Tolerance and reduction of Cr(VI) by Bacillus amyloliquefaciens, B. thuringiensis and Paenibacillus sp., isolated from Pasto River

“…and Bacillus amyloliquefaciens (E4M3). Other studies report that bacteria isolated from environments contaminated with heavy metals such as chromium showed the ability to tolerate and even reduce chromium (VI), among the microorganisms described, the bacteria identified in this study (Dhal, et al, 2013;Mtimunye & Chirwa, 2014;Das, et al, 2014;Joutey, et al, 2015;Zhao, et al, 2016;Benson, et al, 2018). In Figure 2 we can observe the phylogenetic tree, where Methanothermobacter marburgensis represents the outgroup or external root (purple rhombus) and Bacillus sp.…”

Bacterial Reduction of Cr(VI): Operational Challenges and Feasibility

“…Even though a number of successful reports are available on the success of using the pumpand-treat technique to remediate Cr-contaminated groundwater, the issue in removing residual Cr persists until the present day [66]. Both chemical and biological processes have recently been used to treat Cr(VI) in groundwater using the pump and treat methodology [67,68]. Chemical treatment processes employed in the remediation of Cr(VI) are efficient but at the same time produce unwanted chemical by-products which result in the production of toxic sludge [69].…”

“…Therefore, the chemical processes are viewed as costly and environmentally intrusive. Alternative biological treatment methods using aquatic biomass and/or Cr(VI)-reducing bacteria have long been investigated and proposed by a number of researchers [64,68]. These methods may be applied ex situ [70] or in situ in biological barriers [71].…”

Eficiencia en la reducción de Cromo por una bacteria silvestre en un tratamiento tipo Batch utilizando como sustrato agua residual del municipio de Pasto, Colombia

“…Recientemente, se estimó el porcentaje de reducción de un consorcio microbiano conformado en su mayoría por bacterias del genero Bacillus, el proceso se observó aproximadamente durante siete semanas, trascurrido este tiempo, las únicas especies bacterianas que persistieron fueron, Enterobacter sp., B. cereus y B. thuringiensis, demostrando la gran capacidad de adaptación al medio de las bacterias y su eficiencia en la reducción del metal (100%) 38 .…”