Biodegradation during contaminant transport in porous media: 4. Impact of microbial lag and bacterial cell growth

Miscible-displacement experiments were conducted to examine the impact of microbial lag and bacterial cell growth on the transport of salicylate, a model hydrocarbon compound. The impacts of these processes were examined separately, as well as jointly, to determine their relative effects on biodegradation dynamics. For each experiment, a column was packed with porous medium that was first inoculated with bacteria that contained the NAH plasmid encoding genes for the degradation of naphthalene and salicylate, and then subjected to a step input of salicylate solution. The transport behavior of salicylate was non-steady for all cases examined, and was clearly influenced by a delay (lag) in the onset of biodegradation. This microbial lag, which was consistent with the results of batch experiments, is attributed to the induction and synthesis of the enzymes required for biodegradation of salicylate. The effect of microbial lag on salicylate transport was eliminated by exposing the column to two successive pulses of salicylate, thereby allowing the cells to acclimate to the carbon source during the first pulse. Elimination of microbial lag effects allowed the impact of bacterial growth on salicylate transport to be quantified, which was accomplished by determining a cell mass balance. Conversely, the impact of microbial lag was further investigated by performing a similar double-pulse experiment under no-growth conditions. Significant cell elution was observed and quantified for all conditions/systems. The results of these experiments allowed us to differentiate the effects associated with microbial lag and growth, two coupled processes whose impacts on the biodegradation and transport of contaminants can be difficult to distinguish.     

Consolidation of degraded ornamental porous limestone stone by calcium carbonate precipitation induced by the microbiota inhabiting the stone

Although it has already been shown that calcareous stone can be consolidated by using a bacterially inoculated culture medium, a more user-friendly method is the in situ application of a sterile culture medium that is able to activate, among the microbial community of the stone, those bacteria with a potential for calcium carbonate precipitation. In order to test this new method for stone consolidation, non-sterilized decayed porous limestone was immersed in sterile nutritional media. Results were compared to those of the runs in which stone sterilized prior to the treatment was used. The effects of the microbial community on stone consolidation were determined by recording the evolution of the culture media chemistry. The treated stone was tested for mechanical resistance and porosity. Results demonstrate that the tested media were able to activate bacteria from the microbial community of the stone. As a consequence of the growth of these bacteria, an alkalinization occurred that resulted in calcium carbonate precipitation. The new precipitate was compatible with the substrate and consolidated the stone without pore plugging. Therefore, a good candidate to in situ consolidate decayed porous limestone is the application of a sterile culture medium with the characteristics specified in the present study.     

The effect of triclosan on microbial community structure in three soils

The application of sewage sludge to land can expose soils to a range of associated chemical toxicants. In this paper we explore the effects of the broad spectrum anti-microbial compound triclosan on the phenotypic composition of the microbial communities of three soils of contrasting texture (loamy sand, sandy loam and clay) using phospholipid fatty-acid (PLFA) analysis. Each soil type was dosed and subsequently re-dosed 6 weeks later with triclosan at five nominal concentrations in microcosms (10, 100, 500, 1000 mg kg⁻¹ and a zero-dose control). PLFA profiles were analysed using multivariate statistics focussing on changes in the soil phenotypic community structure. Additionally, ratios of fungal:bacterial PLFA indicators and cyclo:mono-unsaturated PLFAs (a common stress indicator) were calculated. It was hypothesised that triclosan addition would alter the community structure in each soil with a particular effect on the fungal:bacterial ratio, since bacteria are likely to be more susceptible to triclosan than fungi. It was also hypothesised that the PLFA response to re-dosing would be suppressed due to acclimation. Although the microbial community structure changed over the course of the experiment, the response was complex. Soil type and time emerged as the most important explanatory factors. Principal component analysis was used to detect phenotypic responses to different doses of triclosan in each soil. As expected, there was a significant increase in the fungal:bacterial ratio with triclosan dose especially in treatments with the highest nominal concentrations. Furthermore, the PLFA response to re-dosing was negligible in all soils confirming the acclimation hypothesis.     

The influence of substrate and electron acceptor availability on bioactive zone dynamics in porous media

Two approaches were used to investigate the influence of dissolved oxygen (DO) and substrate availability on the formation and dynamics of "bioactive zones" in a water-saturated porous medium. A bioactive zone is defined as a region where a microbial community is sufficiently active to metabolize bioavailable substrates. In the first approach, microbial activity was characterized by monitoring the spatial and temporal variability of DO and aqueous substrate (salicylate and naphthalene) concentrations during miscible-displacement experiments. In the second approach, microbial activity was monitored using multiple fiber optics emplaced in the porous medium to detect luminescence produced by Pseudomonas putida RB1353, a bioluminescent reporter organism that produces light when salicylate (an intermediate of naphthalene degradation) is present. The results of both approaches show that the location and size of the bioactive zones were influenced by in situ DO and substrate availability. When DO was not a limiting factor (i.e., lower substrate input concentrations), the bioactive zone encompassed the entire column, with the majority of the microbial activity occurring between the inlet and midpoint. However, as the availability of DO became limiting for the higher substrate input experiments, the size of the bioactive zone shrank and was ultimately limited to the proximity of the column inlet.     

The reactive transport of trichloroethene is influenced by residence time and microbial numbers

The dechlorination rate in a flow-through porous matrix can be described by the species specific dechlorination rate observed in a liquid batch unless mass transport limitations prevail. This hypothesis was examined by comparing dechlorination rates in liquid batch with that in column experiments at various flow rates (3-9-12 cm day(-1)). Columns were loaded with an inoculated sand and eluted with a medium containing 1mM trichloroethene (TCE) for 247 days. Dechlorination in the column treatments increased with decreasing flow rate, illustrating the effect of the longer residence time. Zeroth order TCE or cis-DCE degradation rates were 4-7 folds larger in columns than in corresponding batch systems which could be explained by the higher measured Geobacter and Dehalococcoides numbers per unit pore volume in the columns. The microbial numbers also explained the variability in dechlorination rate among flow rate treatments marked by a large elution of the dechlorinating species' yield as flow increased. Stop flow events did not reveal mass transport limitations for dechlorination. We conclude that flow rate effects on reactive transport of TCE in this coarse sand are explained by residence time and by microbial transport and that mass transport limitations in this porous matrix are limited.     

Biodegradation of Kupferschiefer black shale organic matter (Fore-Sudetic Monocline, Poland) by indigenous microorganisms

This study provides the first evidence for the direct biodegradation of persistent organic matter extracted from the organic-rich polymetallic black shale ore Kupferschiefer, one of the most important sources of metals in the world. It was demonstrated that an enriched community of indigenous heterotrophic microorganisms isolated from black shale grown under aerobic conditions could utilize shale organic matter as the sole carbon and energy source. Colonization of shale organic matter was observed. The main biodegradation intermediates and products such as phosphonic acid dioctadecyl ester and isoindole-1,3 were detected in the aqueous phase of cultures. The bacterial community showed the ability to PAH biodegradation, assimilation of organic acids and esters as well as lipase activity. The intracellular accumulation of phosphorus by bacteria during growth on organic matter was confirmed. Strains within the genus Pseudomonas were found to dominate the bacterial population at the end of the experiment. The results of this study confirm that indigenous bacteria are likely to play a role in the biotransformation of black shale and can influence the geochemical cycles of ancient organic carbon in the deep terrestrial subsurface. This process may also occur in tailings ponds containing black shale, and cause the mobilization of potentially toxic compounds to the soil and groundwater.     

Biodegradation during contaminant transport in porous media: 3. Apparent condition-dependency of growth-related coefficients

The biodegradation of organic contaminants in the subsurface has become a major focus of attention, in part, due to the tremendous interest in applying in situ biodegradation and natural attenuation approaches for site remediation. The biodegradation and transport of contaminants is influenced by a combination of microbial and physicochemical properties and processes. The purpose of this paper is to investigate the impact of hydrodynamic residence time, substrate concentration, and growth-related factors on the simulation of contaminant biodegradation and transport, with a specific focus on potentially condition-dependent growth coefficients. Two sets of data from miscible-displacement experiments, performed with different residence times and initial solute concentrations, were simulated using a transport model that includes biodegradation described by the Monod nonlinear equations and which incorporates microbial growth and oxygen limitation. Two variations of the model were used, one wherein metabolic lag and cell transport are explicitly accounted for, and one wherein they are not. The magnitude of the maximum specific growth rates obtained from calibration of the column-experiment results using the simpler model exhibits dependency on pore-water velocity and initial substrate concentration (C0) for most cases. Specifically, the magnitude of micron generally increases with increasing pore-water velocity for a specific C0, and increases with decreasing C0 for a specific pore-water velocity. Conversely, use of the model wherein observed lag and cell elution are explicitly accounted for produces growth coefficients that are similar, both to each other and to the batch-measured value. These results illustrate the potential condition-dependency of calibrated coefficients obtained from the use of models that do not account explicitly for all pertinent processes influencing transport of reactive solutes.     

Lead pollution in a large, prairie-pothole lake (Rush Lake, WI, USA): effects on abundance and community structure of indigenous sediment bacteria

Rush Lake (WI, USA), the largest prairie-pothole lake east of the Mississippi River, has been contaminated with lead pollution as a result of over 140 years of waterfowl hunting. We examined: (1) the extent of lead pollution in Rush Lake sediments and (2) whether lead pollution in Rush Lake is affecting the abundance and community structure of indigenous sediment bacteria. Sediment lead concentrations did not exceed 59 mg Pb kg(-1) dry sediment. No relationship was observed between sediment lead concentration and the abundance of aerobic (P=0.498) or anaerobic (P=0.416) heterotrophic bacteria. Similarly, lead did not appear to affect bacterial community structure when considering both culturable and nonculturable community members. In contrast, the culturable fraction of sediment bacteria in samples containing 59 mg Pb kg(-1) exhibited a unique community structure. While factors other than lead content likely play roles in determining bacterial community structure in the sediments of Rush Lake, these data suggest that the culturable fraction of sediment bacterial communities is affected by elevated lead levels.     

Metal (Cu, Cd and Zn) removal and stabilization during multiple soil washing by saponin

The influence of multiple saponin washing on copper, cadmium and zinc removal and stability in three types of soils (loamy sand, loam, silty clay) was investigated. Distribution of metals and their mobility measured as the ratio of exchangeable form to the sum of all fractions in soils was differential. After single washing the highest efficiency of metal removal was obtained in loamy sand (82-90%) and loam (67-88%), whereas the lowest in silty clay (39-62%). In loamy sand and loam metals had higher mobility factors (44-61% Cu, 60-76% Cd, and 68-84% Zn) compared to silty clay (9% Cu, 28% Cd and 36% Zn). Triplicate washing led to increase both efficiency of metal removal and percentage content of their stable forms.In consequence, fractional patterns for metals before and after treatment changed visibly as a result of their redistribution. Based on the redistribution index, the most stable metal (mainly in residual and organic fractions) after triplicate washing was Cu in loamy sand and loam. For silty clay contaminated with Cd, effective metal removal and its stabilization required a higher number of washings.     

Effects of in-situ ozonation on indigenous microorganisms in diesel contaminated soil: survival and regrowth

Soil column experiments were conducted to investigate the effects of chemical oxidation on the survival of indigenous microbes (i.e., heterotrophic microbes, phenanthrene-degrading microbes, and alkane-degrading microbes) for field soil contaminated with diesel fuel. Rapid decreases of total petroleum hydrocarbons (TPH) and aromatics of diesel fuel were observed within the first 60 min of ozone injection; after 60 min, TPH and aromatics decreased asymptotically with ozonation time. The three types of indigenous microbes treated were very sensitive to ozone in the soil column experiment, hence the microbial population decreased exponentially with ozonation time. The numbers of heterotrophic, alkane-degrading, and phenanthrene-degrading bacteria were reduced from 10(8) to 10(4), 10(7) to 10(3), and 10(6) CFU g soil(-1) to below detection limit after 900 min of ozonation, respectively. Except for the soil sample ozonated for 900 min, incubation of ozone-treated soil samples that were not limited by oxygen diffusion showed further removal of TPH. The soil samples that were ozonated for 180 min exhibited the lowest concentration of TPH and the highest regrowth rate of the heterotrophic and alkane-degrading populations after the 9 weeks of incubation.     

Determination of bromacil transport as a function of water and carbon content in soils

This study was conducted to determine the significance of bromacil transport as a function of water and carbon content in soils and to explore the implications of neglecting sorption when making assessments of travel time of bromacil through the vadose zone. Equilibrium batch sorption tests were performed for loamy sand and sandy soil added with four different levels of powdered activated carbon (PAC) content (0, 0.01, 0.05, and 0.1%). Column experiments were also conducted at various water and carbon contents under steady-state flow conditions. The first set of column experiments was conducted in loamy sand containing 1.5% organic carbon under three different water contents (0.23, 0.32, and 0.41) to measure breakthrough curves (BTCs) of bromide and bromacil injected as a square pulse. In the second set of column experiments, BTCs of bromide and bromacil injected as a front were measured in saturated sandy columns at the four different PAC levels given above. Column breakthrough data were analyzed with both equilibrium and nonequilibrium (two-site) convection-dispersion equation (CDE) models to determine transport and sorption parameters under various water and carbon contents. Analysis with batch data indicated that neglect of the partition-related term in the calculation of solute velocity may lead to erroneous estimation of travel time of bromacil, i.e. an overestimation of the solute velocity by a factor of R. The column experiments showed that arrival time of the bromacil peak was larger than that of the bromide peak in soils, indicating that transport of bromacil was retarded relative to bromide in the observed conditions. Extent of bromacil retardation (R) increased with decreasing water content and increasing PAC content, supporting the importance of retardation in the estimation of travel time of bromacil even at small amounts of organic carbon for soils with lower water content.     

Effects of sewage sludge amendments on pesticide sorption and leaching through undisturbed Mediterranean soils

The Gharb region in Morocco is an important agricultural zone where soils receive pesticide treatments and organic amendments to increase yields. The groundwater aquifer in the Gharb region is relatively shallow and thus vulnerable. The objective of this work was to study the influence of organic amendments on diuron, cyhalofop-butyl and procymidone leaching through undisturbed soil columns. Two soils were sampled from the Gharb region, a Dehs (sandy soil) and a R’mel (loamy clay soil). Following elution (124.5 mm), the amount of pesticide residues in the leachates of the sandy soil (0.06–0.21 %) was lower than in those of the loamy clay soil (0.20–0.36 %), which was probably due to preferential flow through the loamy clay soil. The amount of procymidone leached through the amended soil columns was greater than the control for the sandy soil only. The organic amendments did not significantly influence diuron and cyhalofop-butyl leaching in either of the soils. The application of organic amendments affected the amounts of dissolved organic matter (DOM) eluted and thus pesticide leaching as a function of soil-type. Nevertheless, in some case, the formation of pesticide-DOM complexes appeared to promote pesticide leaching, thus increasing groundwater contamination risks.     

Effects of sewage sludge amendments on pesticide sorption and leaching through undisturbed Mediterranean soils

The Gharb region in Morocco is an important agricultural zone where soils receive pesticide treatments and organic amendments to increase yields. The groundwater aquifer in the Gharb region is relatively shallow and thus vulnerable. The objective of this work was to study the influence of organic amendments on diuron, cyhalofop-butyl and procymidone leaching through undisturbed soil columns. Two soils were sampled from the Gharb region, a Dehs (sandy soil) and a R'mel (loamy clay soil). Following elution (124.5 mm), the amount of pesticide residues in the leachates of the sandy soil (0.06-0.21 %) was lower than in those of the loamy clay soil (0.20-0.36 %), which was probably due to preferential flow through the loamy clay soil. The amount of procymidone leached through the amended soil columns was greater than the control for the sandy soil only. The organic amendments did not significantly influence diuron and cyhalofop-butyl leaching in either of the soils. The application of organic amendments affected the amounts of dissolved organic matter (DOM) eluted and thus pesticide leaching as a function of soil-type. Nevertheless, in some case, the formation of pesticide-DOM complexes appeared to promote pesticide leaching, thus increasing groundwater contamination risks.     

Nonideal transport of reactive contaminants in heterogeneous porous media: 7. distributed-domain model incorporating immiscible-liquid dissolution and rate-limited sorption/desorption

The purpose of this work is to present a distributed-domain mathematical model incorporating the primary mass-transfer processes that mediate the transport of immiscible organic liquid constituents in water-saturated, locally heterogeneous porous media. Specifically, the impact of grain/pore-scale heterogeneity on immiscible-liquid dissolution and sorption/desorption is represented in the model by describing the system as comprising a continuous distribution of mass-transfer domains. With this conceptualization, the distributions of the initial dissolution rate coefficient and the sorption/desorption rate coefficient are represented as probability density functions. Several sets of numerical experiments are conducted to examine the effects of heterogeneous dissolution and sorption/desorption on contaminant transport and elution. Four scenarios with different combinations of uniform/heterogeneous rate-limited dissolution and uniform/heterogeneous rate-limited sorption/desorption are evaluated. The results show that both heterogeneous rate-limited sorption/desorption and heterogeneous rate-limited dissolution can significantly increase the time or pore volumes required to elute immiscible-liquid constituents from a contaminated porous medium. However, sorption/desorption has minimal influence on elution behavior until essentially all of the immiscible liquid has been removed. For typical immiscible-liquid constituents that have relatively low sorption, the asymptotic elution tailing produced by heterogeneous rate-limited sorption/desorption begins at effluent concentrations that are several orders of magnitude below the initial steady-state concentrations associated with dissolution of the immiscible liquid. Conversely, the enhanced elution tailing associated with heterogeneous rate-limited dissolution begins at concentrations that are approximately one-tenth of the initial steady-state concentrations. Hence, dissolution may generally control elution behavior of immiscible-liquid constituents in cases wherein grain/pore-scale heterogeneity significantly influences both dissolution and sorption/desorption.     

Alkylphenol polyethoxylate removal in a pilot-scale reed bed and phenotypic characterization of the aerobic heterotrophic community.

The removal of the non-ionic surfactant Triton X-100, dosed at 30 and 300 mg/L in a pilot-scale subsurface horizontal flow reed bed, and the aerobic heterotrophic cultivable community associated with the roots and with the substrate gravel in both absence and presence of Triton X-100 were investigated. t-Octylphenol (OP) and its mono-, di- and tri-ethoxyl derivatives, among others, were found in the outlet. A mass balance allowed us to calculate that approximately 40% of the Triton X-100 metabolites OP and octylphenol polyethoxylate derivatives flowed out of the reed bed during the dosage and postdosage experiments. More aerobic heterotrophic microorganisms adhered to the roots than to the gravel. The appearance of new strains (Aeromonas, Flavobacterium, and Aquaspirillum) and the increased presence of others (Pseudomonas) during the dosage of Triton may be linked to the capacity of these bacteria to adapt to the presence of the surfactant or to use it as a nourishment.     

脉冲磁场对电厂循环冷却水中异养菌的灭活

为了控制微生物繁殖对电厂循环冷却水系统造成的危害，研究了脉冲电源发生器与线圈绕组相连产生的脉冲磁场对循环水中异养菌的灭活影响，并对灭活关键因素进行了分析。实验结果表明，脉冲磁场对电厂循环冷却水中的异养菌有灭活作用；灭活率对频率和输出电压有选择性，并且随着作用时间和温度的升高而升高；在扫频范围100～1000 Hz、输出电压3 V、单次作用时间为15 s，温度45℃时，异养菌灭活率达到78.8%。     

Aliphatic hydrocarbons in an oil-contaminated soil

Microbial decontamination of hydrocarbon-polluted soil was paralleled with soil respiration measurements. About 1,500 tons of a loamy top soil were found to be contaminated with approximately 2000 mg/kg of aliphatic hydrocarbons, mainly oleic (C18:1) and linoleic acid (C18:2) found in the vicinity of a linoleum manufacturing and then a car dewaxing plant. The contaminated soil was analysed for dry matter, pH, dehydrogenase activity, electrical conductivity and nutrient content viz. nitrate, phosphorus and potassium, as well as a number of indigenous microbes. The soil was low in salt and nutrients. This paper describes the procedure and measures to decontaminate this bulk soil on site from approx. 2,000 to 500 mg of aliphatic hydrocarbons/kg dry matter by use of a nutrient emulsion, indigenous micro-organisms and aeration over 13 months. This 75% reduction in aliphatic hydrocarbons resulted in a concomitant carbon efflux, measured as soil respiration, and was used to calculate carbon fluxes.     

Assessing the potential for rhizoremediation of PCB contaminated soils in northern regions using native tree species

Rhizosphere bioremediation of polychlorinated biphenyls (PCBs) offers a potentially inexpensive approach to remediating contaminated soils that is particularly attractive in remote regions including the Arctic. We assessed the abilities of two tree species native to Alaska, Salix alaxensis (felt-leaf willow) and Picea glauca (white spruce), to promote microbial biodegradation of PCBs via the release of phytochemicals upon fine root death. Crushed fine roots, biphenyl (PCB analogue) or salicylate (willow secondary compound) were added to microcosms containing soil spiked with PCBs and resultant PCB disappearance, soil toxicity and microbial community changes were examined. After 180 d, soil treated with willow root crushates showed a significantly greater PCB loss than untreated soils for some PCB congeners, including the toxic congeners, PCB 77, 105 and 169, and showed a similar PCB loss pattern (in both extent of degradation and congeners degraded) to biphenyl-treated microcosms. Neither P. glauca (white spruce) roots nor salicylate enhanced PCB loss, indicating that biostimulation is plant species specific and was not mediated by salicylate. Soil toxicity assessed using the Microtox bioassay indicated that the willow treatment resulted in a less toxic soil environment. Molecular microbial community analyses indicated that biphenyl and salicylate promoted shifts in microbial community structure and composition that differed distinctly from each other and from the crushed root treatments. The biphenyl utilizing bacterium, Cupriavidus spp. was isolated from the soil. The findings suggest that S. alaxensis may be an effective plant for rhizoremediation by altering microbial community structure, enhancing the loss of some PCB congeners and reducing the toxicity of the soil environment.     

生物强化对MBR系统生物特性及群落结构的影响

采用高效菌强化膜生物反应器对溴氨酸废水进行处理,考察了生物强化前后系统对溴氨酸的降解能力及其内部微生物生理状态变化.并采用核糖体基因间隔序列分析技术(RISA)解析了高效菌投加前后污泥系统的群落变化.实验表明,投菌后在进水负荷增加的条件下,上清液和膜出水的溴氨酸脱色率分别约为50%和65%,相应的COD去除率分别约为25%和50%,和投菌前基本保持一致;TTC-脱氢酶活性和胞外聚合物(EPS)浓度略有波动,但是运行一段时间后即恢复到投菌前水平.群落分析表明高效菌可以在系统中稳定存在,并且不对原菌群结构造成较大影响.     

Microbial removal of uranium in uranium-bearing black shale

The effects of several conditional factors on efficiency of U bioleaching using an iron-oxidizer, Acidithiobacillus ferrooxidans, from U-bearing black shale (349 mg kg-1 of U) were investigated. When batch-type reactors containing black shale were initially inoculated with the cells, lower pH, higher redox potential and higher amount of aqueous Fe3+ than those of non-inoculated reactor were observed until 200 h. Such development of condition, which was facilitated by microbial activity, can enhance the rate and extent of U leaching from the solid substrate. However, under the condition of enough nutrients and energy source (Fe2+) supplied, indigenous Fe-oxidizers in the non-inoculated black shale were activated over time. They exerted almost same influence on the leaching efficiency with the inoculated samples after 250 h. Low initial Fe2+ supply (5 g l-1) and no addition of inorganic nutrients resulted in nearly identical extent of U leaching with that of 9 g l-1 of initial Fe2+ and nutrients supply. The results indicate that, in a practical process of bioleaching, the expenses for Fe2+ and nutrients addition can be reduced.