Biogeochemical cycling of heavy metals in lake sediments: impact of multispecies diffusion and electrostatic effects

Fate and transport of heavy metals is controlled by the biogeochemical processes in the environment. Reactive transport modeling is particularly important for capturing the complex interplay between the microbial community dynamics and redox-stratified environments. The focus of this study is to investigate the impacts of (i) multicomponent diffusion (MCD) and (ii) electrical double layer (EDL) on reactive diffusive transport of heavy metals at Lake Coeur d'Alene (LCdA) sediments. The solute benthic fluxes at LCdA sediments are controlled by diffusion, and therefore, the biogeochemical model is focused purely on diffusive transport. In diffusive transport-dominated multicomponent systems, species-specific multicomponent diffusion (i.e., Nernst-Planck representation of diffusion) and the explicit treatment of electrostatic effects can play an important role on the overall dynamics of biogeochemical cycling of metals in the system. The results of this study demonstrate that the use of single uniform diffusion coefficient for all species in purely diffusion-dominated sediments may underestimate the mobility of heavy metals undergoing complex reaction network. This outcome is further signified when explicit treatment of EDL effects is considered in addition to MCD. The simulation results also illustrate the importance of aqueous metal (bi)sulfide complexes, especially when MCD and EDL effects are implemented in reactive transport simulations, impacting the solubility and dynamics of heavy metals in diffusion-dominated systems. The competitive effects of Fe-reducing bacteria FRB and sulfate reducing bacteria SRB activities on pH and overall biogeochemical processes are also demonstrated with multispecies diffusion and explicit treatment of electrostatic effects in the system

Modeling contaminant transport and remediation at an acrylonitrile spill site in Turkey

The August 1999 earthquake in Turkey damaged three acrylonitrile (AN) storage tanks at a plant producing synthetic fiber by polymerization. A numerical modeling study was carried out to analyze the groundwater flow and contaminant (AN) transport at the spill site. This study presents the application of a numerical groundwater model to determine the hydrogeological parameters of the site, where such data were not available during the field surveys prior to the simulation studies. The two- and three-dimensional transient flow and transport models were first calibrated using the first 266 days of observed head and concentration data and then verified using the remaining 540-day observed data set. Off-site migration of the contaminant plume was kept under control within the site boundaries owing to the favorable geology of the site, the characteristics of the local groundwater flow regime and the pumping operations. As expected, the applied pump-and-treat system was effective at high-permeability zones, but not fully effective at low-permeability zones. The results of long-term simulations for unconfined aquifer showed that the size of the plume in the high permeability zone shrank significantly due to the dilution by natural recharge. However, in the low permeability zone, it was not significantly affected. The study showed that accurate and sufficient data regarding the, source characteristics, concentration and groundwater level measurements, groundwater pumping rates and their durations at each of the extraction points involved in the pump-and-treat system along with the hydrogeological site characterization are the key parameters for successful flow and transport model calibrations

Reactive diffusive transport of heavy metals in Lake Coeur d'Alene sediments

Lake Coeur d'Alene Basin, Idaho sediments have been heavily enriched with toxic metals, including Cd, Cu, Pb, and Zn, serving as a toxic, mutagenic and carcinogenic source of contaminants. Our focus is to develop a biotic/abiotic diffusive reactive transport model to evaluate the fate, transport, exposure and effects of zinc, lead, and copper in Lake Coeur d'Alene benthic sediments. The model is structured as a multicomponent reactive transport to simulate spatial and temporal distributions of metals in the benthic sediments and their effect on microbial consortia including multiple trophic groups and microbial populations in the benthic sediments. The 1-D inorganic diffusive transport model is coupled to a microbially-mediated redox reaction network which integrates syntrophic consortium biotransformation dynamics accounting for product and metal toxicity inhibition under a diffusive transport regime. The model simulates the mobilization of heavy metals initially sorbed onto hydrous ferric oxides through microbial reductive dissolution of Fe(III) minerals under redox disequilibrium conditions with simultaneous biogenic sulfide production, forming soluble metal (bi)sulfide complexes and insoluble metal sulfide minerals, and the effects of these metals on benthic microbial communities via accounting of dose, where dose is expressed in a novel fashion as a structural variable in the population dynamics of the microbial consortia

Influence of Heavy Metals on Microbial Growth Kinetics Including Lag Time: Mathematical Modeling and Experimental Verification

Heavy metals can significantly affect the kinetics of substrate biodegradation and microbial growth, including lag times and specific growth rates. A model to describe microbial metabolic lag as a function of the history of substrate concentration has been previously described by Wood et al. (Water Resour Res 31:553-563) and Ginn (Water Resour Res 35:1395-1408). In the present study, this model is extended by including the effect of heavy metals on metabolic lag by developing an inhibitor-dependent functional to account for the metabolic state of the microorganisms. The concentration of the inhibiting metal is explicitly incorporated into the functional. The validity of the model is tested against experimental data on the effects of zinc on Pseudomonas species isolated from Lake Coeur d\u27Alene sediments, Idaho, USA, as well as the effects of nickel or cobalt on a mixed microbial culture collected from the aeration tank of a wastewater treatment plant in Athens, Greece. The simulations demonstrate the ability to incorporate the effect of metals on metabolism through lag, yield coefficient, and specific growth rates. The model includes growth limitation due to insufficient transfer of oxygen into the growth medium

Single and joint effects of Zn and Cu to ATP pool and microbial recovery in continuous growth systems

Summarization: BACKGROUND Four parallel continuous stirred tank reactors were used to investigate the single and joint exposure of Zn and Cu to Arthrobacter sp. JM018, in terms of the impact on the adenosine triphosphate (ATP) pool and microbial tolerance. RESULTS ATP, optical density (OD), and substrate concentration measurements indicated that Cu was more toxic than Zn under all conditions studied. The results showed that although both OD and ATP measurements individually reflected a decrease in microbial growth rate after the addition of metals for the reactors exposed to Cu, specific ATP (i.e. ATP/OD) showed only a temporary reduction followed by a monotonic return to pre‐exposure levels within 100 h. The latter implied tolerance and recovery in the energy status of these cells, after the initial shock due to the exposure to Cu. CONCLUSION Specific ATP is an important quantity to be considered as a measure of the activity or energy status of microbial biomass surviving after exposure to toxic metals or other unfavorable conditions. The study provides insights for maintaining metal‐tolerant microbial communities and to explore both quantitatively and experimentally the dynamics of ATP pool and microbial tolerance in metal‐contaminated environments. © 2018 Society of Chemical IndustryΠαρουσιάστηκε στο: Journal of Chemical Technology and Biotechnolog