Sulfate-reducing Environments Research Articles

Factors affecting linear alkylbenzene sulfonates removal in subsurface flow constructed wetlands.

The behavior of linear alkylbenzene sulfonate (LAS) and sulfophenyl carboxylate (SPC) biointermediates in a pilot subsurface flow constructed wetland (SFCW) is reported for the first time. The effects of wetland configuration and operation on their treatment efficiency were investigated. The pilot SFCW constituted by eight beds of 55 m2 with different aspect ratios (1 x 1; 1.5 x 1; 2 x 1; 2.5 x 1), two water depths (i.e., 0.47 and 0.27 cm) at 5 cm below surface and two medium sizes (i.e., D60 = 10 mm and 3.5 mm) planted with Phragmites sp. That SFCW pilottreats urban wastewater (i.e., 200 inhabitants) and was operated at four hydraulic loading rates (HLRs) (20, 27, 36, and 45 mm d(-1)). Influent and effluent sampling was carried out from May 2001 to January 2002 with a weekly pattern. Main results were as follows: (i) water depth has a major influence on the performance of SFCW for the LAS removal, and HLR shows significant effect on SPC evolution; (ii) water temperature has a significant effect on the LAS evolution; (iii) biodegradation of LAS and SPC can occur under sulfate-reducing environment and mixed conditions (i.e., sulfate-reducing and denitrification), but aerobic respiration cannot be excluded; and (iv) C13 LAS homologues were generally removed in higher extent than the shorter alkyl chain counterparts. In the most appropriate conditions, LAS and SPC can be biodegraded up to 71% and 11%, respectively, in the pilot SFCW evaluated.

Speciation of arsenic in sulfidic waters.

Formation constants for thioarsenite species have been determined in dilute solutions at 25°C, ΣH2S from 10-7.5 to 10-3.0 M, ΣAs from 10-5.6 to 10-4.8 M, and pH 7 and 10. The principal inorganic arsenic species in anoxic aquatic systems are arsenite, As(OH)30, and a mononuclear thioarsenite with an S/As ratio of 3:1. Thioarsenic species with S/As ratios of 1 : 1,2 : 1, and 4 : 1 are lesser components in sulfidic solutions that might be encountered in natural aquatic environments. Thioarsenites dominate arsenic speciation at sulfide concentrations > 10-4.3 M at neutral pH. Conversion from neutral As(OH)30 to anionic thioarsenite species may regulate the transport and fate of arsenic in sulfate-reducing environments by governing sorption and mineral precipitation reactions.

Kinetics of chemical decolorization of the azo dye C.I. Reactive Orange 96 by sulfide

The mechanism of decolorization of azo dyes based on the extracellular chemical reduction with sulfide (H 2S, HS −, S 2−) was postulated for sulfate reducing environments. To design technical decolorization processes of textile wastewater treatment with sulfide produced by sulfate reducing bacteria (SRB), kinetics is of great significance. Batch experiments were made in order to investigate the kinetics of abiotic decolorization of the reactive mono-azo dye C.I. Reactive Orange 96 (RO 96) with sulfide, with varying pH. The decolorization of RO 96 by sulfide under the exclusion of O 2 corresponded to first-order kinetics with respect to both dye and sulfide concentration. The decolorization of RO 96 with sulfide at neutral pH (7.1) was advantageous compared with that at pH for 4.1, 6.3, and 6.5. This is attributed to an increase in the fraction of HS − of total sulfide species at neutral pH. The rate constants k for the decolorization at 37 °C were obtained as 0.01 for pH=4.1, 0.06 for pH=6.3, 0.08 for pH=6.5, and 0.09 for pH=7.1 in mM −1 min −1. The high rate constants for sulfide at pH 6.5–7.1 support that the decolorization through SRB (i.e. by bio-sulfide) can be effective in anaerobic bacterial systems with sulfate.

Field and Laboratory Studies of Carbon Tetrachloride Transformation in a Sandy Aquifer under Sulfate Reducing Conditions

A field experiment was conducted in which carbon tetrachloride (CT) was found to transform to chloroform (CF) and carbon disulfide (CS2) in a ratio of about 2:1. Subsequent laboratory work was undertaken to better define the conditions required for this product ratio and to investigate its use as a means of distinguishing biologically driven and abiotic transformations in aquifers. The field experiment was conducted to assess the efficacy of a bioremediation scheme for treating CT in groundwater. The test section of the aquifer was taken to sulfate reducing conditions by the periodic addition of acetate from a nutrient injection wall (NIW). Under these conditions, CT was observed to transform completely producing primarily CF and CS2 at a ratio of approximately 2:1. In laboratory columns designed to mimic the field conditions, low-input concentrations of CT (<70 μg/L) resulted in complete dechlorination of the molecule, while higher input concentrations (>400 μg/L) led to the production of CF and CS2 in the same ratio as observed in the field. It was determined that amorphous iron sulfide had precipitated on the sand grains during the column experiments. Stertile laboratory batch experiments were conducted to test CT reactivity with various iron sulfide solids. A narrow ratio of 2:1 ± 0.4 CF to CS2 was only observed for CT reacting with freshly precipitated, amorphous FeS in near pH neutral solutions. The 2:1 ratio may be a useful tool for distinguishing abiotic transformations from biodegradation in sulfate reducing environments where FeS is actively precipitated.

Influence of Different Redox Conditions on the Biodegradation of the Pesticide Metabolites Phenol and Chlorophenols

Abstract The fate and behaviour of phenol and monochlorophenols during bankfiltration and underground passage with variable redox conditions were investigated. A model ecosystem was used consisting in laboratory filter columns filled with natural underground material and operated with natural aerobic and anaerobic groundwater to create different redox situations. The test substances (phenol, 2-chlorophenol, 3-chlorophenol, 4-chlorophenol) were added continuously to the infiltrating water and their concentration in the filter effluents determined. Beside the redox conditions other factors known to affect microbial degradation processes like the substrate concentration and the underground material were varied stepwise. Phenol was degraded under both, aerobic and anaerobic conditions. The presence of oxygen is more favourable to degradation; no lag phase was observed under aerobic conditions. In a sulfate reducing environment, phenol could only be degraded after microbial adaptation. The length of the lag ph...

Modeling kinetics of chloroform cometabolism in methanogenic and sulfate-reducing environments

The kinetics of chloroform cometabolism in methanogenic and sulfate-reducing environments were modeled. Chloroform inhibits acetate utilization in methanogenic environments and therefore the rate of chloroform cometabolism was modeled using two terms: cometabolism due to primary substrate utilization and cometabolism due to microbial cell decay (no primary substrate utilization). The modified Haldane equation was used to model chloroform cometabolism due to primary substrate utilization and the Monod equation was used for the cometabolism due to microbial cell decay. A commercial software, SigmaPlot (Jandel Scientific Software) was used to determine the optimum parameters for the model. The model agreed very well with the experimental results. The model parameters confirmed that the sulfate-reducing culture has a very high potential for chloroform cometabolism compared to the methanogenic cultures. Also, the methanogenic culture grown on acetate is very sensitive to chloroform compared to the methanogenic culture grown on methanol.

Modeling kinetics of chloroform cometabolism in methanogenic and sulfate-reducing environments

The kinetics of chloroform cometabolism in methanogenic and sulfate-reducing environments were modeled. Chloroform inhibits acetate utilization in methanogenic environments and therefore the rate of chloroform cometabolism was modeled using two terms: cometabolism due to primary substrate utilization and cometabolism due to microbial cell decay (no primary substrate utilization). The modified Haldane equation was used to model chloroform cometabolism due to primary substrate utilization and the Monod equation was used for the cometabolism due to microbial cell decay. A commercial software, SigmaPlot (Jandel Scientific Software) was used to determine the optimum parameters for the model. The model agreed very well with the experimental results. The model parameters confirmed that the sulfate-reducing culture has a very high potential for chloroform cometabolism compared to the methanogenic cultures. Also, the methanogenic culture grown on acetate is very sensitive to chloroform compared to the methanogenic culture grown on methanol.

Oxidation of Polycyclic Aromatic Hydrocarbons under Sulfate-Reducing Conditions

[(sup14)C]naphthalene and phenanthrene were oxidized to (sup14)CO(inf2) without a detectable lag under strict anaerobic conditions in sediments from San Diego Bay, San Diego, Calif., that were heavily contaminated with polycyclic aromatic hydrocarbons (PAHs) but not in less contaminated sediments. Sulfate reduction was necessary for PAH oxidation. These results suggest that the self-purification capacity of PAH-contaminated sulfate-reducing environments may be greater than previously recognized.

Metal-organic matter interactions in the formation of an oil shale deposit

An attempt was made to distinguish metal-organic matter interactions in two types of sulfate-reducing environments, mild (MR) and strong sulfate-reducing (SR), in the Aleksinac oil shale deposit (Oligocene-Miocene). Samples from the MR group show (all differences are statistically highly significant): lower organic matter content, compared with the SR group, higher O/C and N/C ratios (0.147 ± 0.054 and 0.041 ± 0.014, respectively, compared with 0.125 ± 0.031 and 0.035 ± 0.008, respectively, in the SR group), and higher Cu, Zn, Pb, Cr, Mo and Co contents than in the SR group. Statistically significant correlations between metals, the N/C and the SiO 2/Al 2O 3 ratio in the MR group only, represent a record of highly interdependent processes of organic-metal-silicate interactions which had been occurring in the mild sulfate-reducing conditions during oil shale formation.