Clogging of a limestone fracture by stimulating groundwater microbes

Evaluating the efficacy of slow-releasing carbon source tablets for in situ biological heterotrophic denitrification of groundwater

Slow-releasing precipitating tablets (SRPTs) and slow-releasing floating tablets (SRFTs) were formulated to release fumarate as a carbon source (CS) and/or electron donor (ED) in an in situ biological heterotrophic denitrification system. These tablets were prepared using pharmaceutical manufacturing. Soil column tests were conducted to evaluate nitrate denitrification efficacy, microbial population changes, and mass balance of fumarate and potential electron acceptors. Significant and simultaneous consumption of both fumarate and nitrate, and the production and consumption of nitrite were observed in both SRPT-treated and SRFT-treated soil columns. These results suggest that SRPT and SRFT releasing fumarate, induce heterotrophic biological denitrification. In the SRPT- and SRFT-treated columns, 65% and 73% of fumarate were associated with heterotrophic denitrification, respectively. Particularly, surplus citric acid, originally designed to serve as a floating agent, was utilized for 36% and 28% for SRFT flotation and denitrification, respectively. The results of 16s RNA analyses revealed that a bacterium that shared 99% 16s rRNA sequence similarity with those of Azoarcus sp. AN9, and Pseudogulbenkiania sp. NH8B, a facultative heterotrophic denitrifier, was detected in the column effluent. This study confirms that SRPT and SRFT can effectively operate long-term in situ biological denitrification processes, because it is possible to supply detailed CS and/or ED uniformly by applying both SRPT and SRFT in the well.

Microbial Community Composition in Thermal Waters from the Lindian Geothermal Field (Songliao Basin, North-Eastern China)

Geothermal systems represent discrete and relatively homogenous habitats for extremophiles; investigation into the microbial community is key to revealing the geochemical environment and the geochemical evolution of fluids in geothermal reservoirs. The reservoir of the Lindian geothermal field in Northeast China, is highly reducing and rich in methane, but the pathways of methane generation and the related microbial community structure are still unclear. In this research, five thermal water samples were collected and tested, and the microbial community structure and diversity were analyzed. The results show that in the sandstone reservoir belonging to the low-temperature (reservoir temperature < 90°C) brackish water (total dissolved solids concentration between 1000 and 10,000 mg/L) environment, the richness of the microbial community is relatively high. The microbial community structure is different from other geothermal systems reported but similar to that of oilfields, which may be related to the highly reducing geochemical environment with abundant organic matter. According to the analysis of archaeal function, the biogas production in the Lindian geothermal field is dominated by hydrogen nutrition type methane production, while the H2 reducing methylamine type methane production is secondary, and results of Pearson correlation show that the archaeal communities are more strongly correlated to physicochemical factors than the bacterial communities.

Co-occurrence of microplastics and triclosan inhibited nitrification function and enriched antibiotic resistance genes in nitrifying sludge

As more and more microplastics (MPs) and triclosan (TCS), which are added in consumer products, enter wastewater treatment plants with sewage, there are concerns about the impacts of the co-occurrence of MPs and TCS on biological wastewater treatment. In this study, the co-effects of four 1 mg/L MPs (polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC) and polyamide (PA)) and 0.5 mg/L TCS on nitrification were investigated in lab-scale nitrifying sequencing batch reactors (SBRs) (SBR-PE, SBR-PS, SBR-PVC and SBR-PA) relative to control which received no MPs (SBR-CK). The removal rates of NH₄⁺-N and TCS in SBR-CK were around 100% and 92%, respectively. Compared with SBR-CK, no measurable inhibition was observed on nitrification in SBR-PE and SBR-PS, however, SBR-PVC and SBR-PA rapidly lost nitrification function during 14 days, which might be due to the reducing of MLSS caused by PVC, PA and TCS co-loading. Furthermore, PS, PVC and PA decreased the removal of TCS. The co-occurrence of TCS and PS, PVC, PA increased extracellular polymeric substances, reduced microbial diversity and shifted microbial communities. Notably, the acrA-03, mexF, fabI, intI1, intI3 and IS613 genes were enriched by MPs and TCS co-loading. Therefore, the removal of MPs and TCS from wastewater should be prioritized.

Evaluating a new injection method of liquid/gas mixture spray injection via performing long-term in situ bioremediation tests

During in situ bioremediation, continuous injection of growth substrates such as carbon sources, electron donors, or electron acceptors inevitably results in microbial growth, resulting in biological clogging in an aquifer. Therefore, for successful bioremediation, development of a new injection method is needed to reduce or alleviate this clogging problem. In this study, we carried out field tracer tests using single-well push-pull tests (SWPPTs), single-well natural gradient drift tests (SWNGDTs), and long-term in situ well-to-well tests to develop and evaluate a new method of liquid/gas mixture spray injection. The effectiveness of the new method was evaluated by estimating the factors as follow: longitudinal dispersivity (α_L), radius of influence (RI), shear stress on the surface of aquifer particles (σ), biofilm-shear-loss rate (R_s), and the ratio of volume occupied by cells grown to the original pore volume. At the tested site, the liquid/gas mixture spray injection method turned out to have several advantages compared to the traditional solution injection method: 1) transport of solute to a larger proportion of an aquifer by a factor of 1.3-1.7, 2) application of higher shear stress onto the surface of soil particles by a factor of 4.2-5.0, 3) faster biofilm sloughing rates by a factor of 2.3-2.6, 4) reduction in the ratio of the volume occupied by microorganisms to total pore volume (Vol_microbes/Vol_pore), and 5) efficient trichloroethylene (TCE) dechlorination for a period of 550 days without any injection problems. This new injection method showed positive effects on the hydrogeological and physical characteristics of the system, thus alleviating the biological clogging problem.

Vibrio and Bacterial Communities Across a Pollution Gradient in the Bay of Bengal: Unraveling Their Biogeochemical Drivers

The highly populated coasts of the Bay of Bengal are particularly vulnerable to water-borne diseases, pollution and climatic extremes. The environmental factors behind bacterial community composition and Vibrio distribution were investigated in an estuarine system of a cholera-endemic region in the coastline of Bangladesh. Higher temperatures and sewage pollution were important drivers of the abundance of toxigenic Vibrio cholerae. A closer relation between non-culturable Vibrio and particulate organic matter (POM) was inferred during the post-monsoon. The distribution of operational taxonomic units (OTUs) of Vibrio genus was likely driven by salinity and temperature. The resuspension of sediments increased Vibrio abundance and organic nutrient concentrations. The δ¹³C dynamic in POM followed an increasing gradient from freshwater to marine stations; nevertheless, it was not a marker of sewage pollution. Bacteroidales and culturable coliforms were reliable indicators of untreated wastewater during pre and post-monsoon seasons. The presumptive incorporation of depleted-ammonium derived from ammonification processes under the hypoxic conditions, by some microorganisms such as Cloacibacterium and particularly by Arcobacter nearby the sewage discharge, contributed to the drastic ¹⁵N depletion in the POM. The likely capacity of extracellular polymeric substances production of these taxa may facilitate the colonization of POM from anthropogenic origin and may signify important properties for wastewater bioremediation. Genera of potential pathogens other than Vibrio associated with sewage pollution were Acinetobacter, Aeromonas, Arcobacter, and Bergeyella. The changing environmental conditions of the estuary favored the abundance of early colonizers and the island biogeography theory explained the distribution of some bacterial groups. This multidisciplinary study evidenced clearly the eutrophic conditions of the Karnaphuli estuary and assessed comprehensively its current bacterial baseline and potential risks. The prevailing conditions together with human overpopulation and frequent natural disasters, transform the region in one of the most vulnerable to climate change. Adaptive management strategies are urgently needed to enhance ecosystem health.

Shifts in bacterial community composition and abundance of nitrifiers during aerobic granulation in two nitrifying sequencing batch reactors

Shifts in bacterial community composition and abundance of nitrifiers during aerobic granulation, and the effects of wastewater composition on them were investigated using Illumina sequencing and quantitative PCR. The bacterial diversity decreased sharply during the post-granulation period. Although cultivated with different wastewater types, aerobic granular sludge (AGS) formed with similar bacterial structure. The bacterial structure in AGS was completely different from that of seed sludge. The minor genera in seed sludge, e.g., Arcobacter, Aeromonas, Flavobacterium and Acinetobacter, became the dominant genera in AGS. These genera have the potential to secrete excess extracellular polymer substances. Whereas, the dominant genera in seed sludge were found in less amount or even disappeared in AGS. During aerobic granulation, ammonia-oxidizing archaea were gradually washed-out. While, ammonia-oxidizing bacteria, complete ammonia oxidizers and nitrite-oxidizing bacteria were retained. Overall, in this study, the bacterial genera with low relative abundance in seed sludge are important for aerobic granulation.

Applications of Microbial Processes in Geotechnical Engineering

Over the last 10-15 years, a new field of "biogeotechnics" has emerged as geotechnical engineers seek to find ground improvement technologies which have the potential to be lower carbon, more ecologically friendly, and more cost-effective than existing practices. This review summarizes the developments which have occurred in this new field, outlining in particular the microbial processes which have been shown to be most promising for altering the hydraulic and mechanical responses of soils and rocks. Much of the research effort in this new field has been focused on microbially induced carbonate precipitation (MICP) via ureolysis, while a comprehensive review of MICP is presented here, the developments which have been made regarding other microbial processes, including MICP via denitrification and biogenic gas generation are also presented. Furthermore, this review outlines a new area of study: the potential deployment of fungi in geotechnical applications which has until now been unexplored.

Extracellular polymeric substances of bacteria and their potential environmental applications

Biopolymers are considered a potential alternative to conventional chemical polymers because of their ease of biodegradability, high efficiency, non-toxicity and non-secondary pollution. Recently, extracellular polymeric substances (EPS, biopolymers produced by the microorganisms) have been recognised by many researchers as a potential flocculent for their applications in various water, wastewater and sludge treatment processes. In this context, literature information on EPS is widely dispersed and is very scarce. Thus, this review marginalizes various studies conducted so far about EPS nature-production-recovery, properties, environmental applications and moreover, critically examines future research needs and advanced application prospective of the EPS. One of the most important aspect of chemical composition and structural details of different moieties of EPS in terms of carbohydrates, proteins, extracellular DNA, lipid and surfactants and humic substances are described. These chemical characteristics of EPS in relation to formation and properties of microbial aggregates as well as degradation of EPS in the matrix (biomass, flocs etc) are analyzed. The important engineering properties (based on structural characteristics) such as adsorption, biodegradability, hydrophilicity/hydrophobicity of EPS matrix are also discussed in details. Different aspects of EPS production process such as bacterial strain maintenance; inoculum and factors affecting EPS production were presented. The important factors affecting EPS production include growth phase, carbon and nitrogen sources and their ratio, role of other nutrients (phosphorus, micronutrients/trace elements, and vitamins), impact of pH, temperature, metals, aerobic versus anaerobic conditions and pure and mixed culture. The production of EPS in high concentration with high productivity is essential due to economic reasons. Therefore, the knowledge about all the aspects of EPS production (listed above) is highly essential to formulate a logical and scientific basis for the research and industrial activities. One of the very important issues in the production/application/biodegradation of EPS is how the EPS is extracted from the matrix or a culture broth. Moreover, EPS matrix available in different forms (crude, loosely bound, tightly bound, slime, capsular and purified) can be used as a bioflocculant material. Several chemical and physical methods for the extraction of EPS (crude form or purified form) from different sources have been analyzed and reported. There is ample information available in the literature about various EPS extraction methods. Flocculability, dewaterability and biosorption ability are the very attractive engineering properties of the EPS matrix. Recent information on important aspects of these properties qualitatively as well as quantitatively has been described. Recent information on the mechanism of flocculation mediated by EPS is presented. Potential role of EPS in sludge dewatering and biosorption phenomenon has been discussed in details. Different factors influencing the EPS ability to flocculate and dewaterability of different suspensions have been included. The factors considered for the discussion are cations, different forms of EPS, concentration of EPS, protein and carbohydrate content of EPS, molecular weight of EPS, pH of the suspension, temperature etc. These factors were selected for the study based upon their role in the flocculation and dewatering mechanism as well the most recent available literature findings on these factors. For example, only recently it has been demonstrated that there is an optimum EPS concentration for sludge flocculation/dewatering. High or low concentration of EPS can lead to destabilization of flocs. Role of EPS in environmental applications such as water treatment, wastewater flocculation and settling, colour removal from wastewater, sludge dewatering, metal removal and recovery, removal of toxic organic compounds, landfill leachate treatment, soil remediation and reclamation has been presented based on the most recent available information. However, data available on environmental application of EPS are very limited. Investigations are required for exploring the potential of field applications of EPS. Finally, the limitations in the knowledge gap are outlined and the research needs as well as future perspectives are highlighted.

Bioclogging in porous media: influence in reduction of hydraulic conductivity and organic contaminants during synthetic leachate permeation

In this study the concept of biofilm accumulation in the sand column was promoted to assess the changes in hydraulic conductivity and concentration of organic contaminants of the synthetic leachate. Four different combinations of column study were carried out using synthetic leachate as a substrate solution. Mixed and stratified mode of experiments with two different sizes (0.3 mm and 0.6 mm) of sand grains were used for column filling. Two columns were acting as a blank, the remaining two columns amended with mixed microbial cultures which were isolated from leachate. The column was operated with continuous synthetic leachate supply for 45 days. The results indicated that the highest hydraulic conductivity reduction occurred in the mixed sand microbial column with 98.8% when compared to stratified sand microbial column. The analysis of organic contaminants of the effluent leachate was also clearly shown that the mixed sand amended with microbes poses a suitable remedial measure when compared to natural and synthetic liners for controlling the leachate migration in the subsurface environment.

Impact of hydraulic well restoration on native bacterial communities in drinking water wells

The microbial monitoring of drinking water production systems is essential to assure water quality and minimize possible risks. However, the comparative impact of microbes from the surrounding aquifer and of those established within drinking water wells on water parameters remains poorly understood. High pressure jetting is a routine method to impede well clogging by fine sediments and also biofilms. In the present study, bacterial communities were investigated in a drinking water production system before, during, and after hydraulic purging. Variations were observed in bacterial communities between different wells of the same production system before maintenance, despite them having practically identical water chemistries. This may have reflected the distinct usage practices of the different wells, and also local aquifer heterogeneity. Hydraulic jetting of one well preferentially purged a subset of the dominating taxa, including lineages related to Diaphorobacter, Nitrospira, Sphingobium, Ralstonia, Alkanindiges, Janthinobacterium, and Pseudomonas spp, suggesting their tendency for growth in well-associated biofilms. Lineages of potential drinking water concern (i.e. Legionellaceae, Pseudomonadaceae, and Acinetobacter spp.) reacted distinctly to hydraulic jetting. Bacterial diversity was markedly reduced in drinking water 2 weeks after the cleaning procedure. The results of the present study provide a better understanding of drinking water wells as a microbial habitat, as well as their role in the microbiology of drinking water systems.

Microbes in Beach Sands: Integrating Environment, Ecology and Public Health

Beach sand is a habitat that supports many microbes, including viruses, bacteria, fungi and protozoa (micropsammon). The apparently inhospitable conditions of beach sand environments belie the thriving communities found there. Physical factors, such as water availability and protection from insolation; biological factors, such as competition, predation, and biofilm formation; and nutrient availability all contribute to the characteristics of the micropsammon. Sand microbial communities include autochthonous species/phylotypes indigenous to the environment. Allochthonous microbes, including fecal indicator bacteria (FIB) and waterborne pathogens, are deposited via waves, runoff, air, or animals. The fate of these microbes ranges from death, to transient persistence and/or replication, to establishment of thriving populations (naturalization) and integration in the autochthonous community. Transport of the micropsammon within the habitat occurs both horizontally across the beach, and vertically from the sand surface and ground water table, as well as at various scales including interstitial flow within sand pores, sediment transport for particle-associated microbes, and the large-scale processes of wave action and terrestrial runoff. The concept of beach sand as a microbial habitat and reservoir of FIB and pathogens has begun to influence our thinking about human health effects associated with sand exposure and recreational water use. A variety of pathogens have been reported from beach sands, and recent epidemiology studies have found some evidence of health risks associated with sand exposure. Persistent or replicating populations of FIB and enteric pathogens have consequences for watershed/beach management strategies and regulatory standards for safe beaches. This review summarizes our understanding of the community structure, ecology, fate, transport, and public health implications of microbes in beach sand. It concludes with recommendations for future work in this vastly under-studied area.

Removal of biocolloids suspended in reclaimed wastewater by injection into a fractured aquifer model

Two pilot-scale fractured aquifer models (FAMs) consisting of horizontal limestone slabs were employed to investigate the removal of biocolloids suspended in reclaimed wastewater. To better understand the behavior of real fractured aquifers, these FAMs intentionally were not "clean". The fracture apertures were randomly spread with soil deposits, and both FAMs were preflooded with reclaimed wastewater to simulate the field conditions of the Nardo fractured aquifer in the Salento area, Italy, where fractures are not clean due to artificial groundwater recharge. One of the FAMs was injected with secondary effluent from a wastewater treatment plant collected prior to the chlorination step and the other with exactly the same effluent, which was further treated in a commercial membrane reactor. Consequently, the organic and pathogen concentrations were considerably higher in the secondary effluent than in the membrane reactor effluent. Injected wastewater was continuously recirculated. Pathogen removal was greater for the secondary wastewater than the cleaner membrane reactor effluent. A simple mathematical model was developed to describe fracture clogging. The results suggest that the hydraulic conductivity of FAMs can be significantly degraded due to retention of viable and inactivated biocolloids suspended in reclaimed wastewater.

Bacterial diversity in the active stage of a bioremediation system for mineral oil hydrocarbon-contaminated soils

Soils contaminated with mineral oil hydrocarbons are often cleaned in off-site bioremediation systems. In order to find out which bacteria are active during the degradation phase in such systems, the diversity of the active microflora in a degrading soil remediation system was investigated by small-subunit (SSU) rRNA analysis. Two sequential RNA extracts from one soil sample were generated by a procedure incorporating bead beating. Both extracts were analysed separately by generating individual SSU rDNA clone libraries from cDNA of the two extracts. The sequencing results showed moderate diversity. The two clone libraries were dominated by Gammaproteobacteria, especially Pseudomonas spp. Alphaproteobacteria and Betaproteobacteria were two other large groups in the clone libraries. Actinobacteria, Firmicutes, Bacteroidetes and Epsilonproteobacteria were detected in lower numbers. The obtained sequences were predominantly related to genera for which cultivated representatives have been described, but were often clustered together in the phylogenetic tree, and the sequences that were most similar were originally obtained from soils and not from pure cultures. Most of the dominant genera in the clone libraries, e.g. Pseudomonas, Acinetobacter, Sphingomonas, Acidovorax and Thiobacillus, had already been detected in (mineral oil hydrocarbon) contaminated environmental samples. The occurrence of the genera Zymomonas and Rhodoferax was novel in mineral oil hydrocarbon-contaminated soil.

Biodegradation of 2,4,6-trichlorophenol and associated hydraulic conductivity reduction in sand-bed columns

The aim of this research was to investigate the long-term hydraulic conductivity changes in sand-bed columns exposed to 2,4,6-trichlorophenol (TCP). Continuous flow laboratory studies were conducted using sand-bed columns (15 cm i.d.; 200 cm length) at 20+/-1 degrees C during 365 d. The influence of (i) initial loads of 2,4,6-TCP (15, 30, 45 and 60 mg kg(-1) of 2,4,6-TCP), and (ii) recirculating water velocity (0.09, 0.56 and 1.18 cm min(-1)) on the biodegradation of 2,4,6-TCP and hydraulic conductivity changes in the sand-bed columns were investigated. The experimental results indicated that biodegradation of 2,4,6-TCP followed pseudo-first-order kinetics in the range of k(1)=0.01-1.64 d(-1), and it was influenced by initial load (p<0.01) and recirculating water velocity (p<0.01). Indigenous microbial biomass growth and changes resulted in a spatial (180 cm) and temporal (365 d) reduction of hydraulic conductivity in the sand-bed columns by up to two orders of magnitude during biodegradation of 2,4,6-TCP. The fastest hydraulic conductivity reductions were observed in the sand-bed column operated at the highest recirculating water velocity and highest cumulative load of 2,4,6-TCP following 365 d of continuous treatment (p<0.05).

The effect of a biofilm on solute diffusion in fractured porous media

At sites in fractured rock where contamination has been exposed to the rock matrix for extended periods of time, the amount of contaminant mass residing in the matrix can be considerable. Even though it may be possible to diminish concentrations by the advection of clean water through the fracture features, back diffusion from mass held in the matrix will lead to a continuing source of contamination. In such an event, the development of a biofilm (a thin film of microbial mass) on the wall of the fractures may act to limit or prevent the back diffusion process. The objective of this preliminary study is to explore the influence imparted by the presence of a biofilm on the process of matrix diffusion. The investigation was conducted using radial diffusion cells constructed from rock core in which biofilm growth was stimulated in a central reservoir. Once biofilms were developed, forward diffusion experiments were conducted in which a conservative solute migrated from the central reservoir into the intact rock sample. Diffusion experiments were performed in a total of 11 diffusion cell pairs where biofilm growth was stimulated in one member of the pair and inhibited in the other. The effect of the presence of a biofilm on tracer diffusion was determined by comparison of the diffusion curves produced by each cell pair. A semi-analytical model that accounts for the presence of a biofilm was used to investigate the effect of the biofilm on mass transfer due to changes in the effective porosity, effective diffusion coefficient, and the depth of penetration of the biofilm into the intact rock. The results show that the biofilm acted to plug the rock matrix, rather than forming a discrete layer on the reservoir surface. The reduction in effective porosity due to the biofilm ranged from 6% to 52% with the majority of the samples in the 30% to 50% range. Based on the present results, with more efficient biofilm stimulation, it is reasonable to assume that a more complete plugging of the microcrack porosity might be possible, leaving a much thicker and efficient barrier than could be achieved via a surface biofilm.

Long-term persistence of a nutrient-starved biofilm in a limestone fracture

The persistence of biofilms is a key element of the biobarrier concept applied to fractured rock. After a 43-day biostimulation with molasses for the biofilm growth (phase I), the effects of a 179-day starvation on the persistence of the biofilm (phase II) were investigated in a single-fractured limestone apparatus equipped to detect small changes in hydraulic conductivity (K) (cm min(-1)). The K in the central fracture section (Kf) decreased by 4.6 logs between days 0 and 167 and increased by 1.3 logs between days 167 and 222, leading to an overall 3.3-logs reduction for the 222-day experiment. Accumulation of rod- and filamentous-shaped bacteria and deposition of minerals were thought to account for the decrease in Kf. Even though the filamentous bacterial cells possibly enhanced the stability of the developing biofilm, increases in Kf became more frequent after 100 days of operation. This decrease in stability was presumably related to sloughing events, which were in turn attributed to a combination of processes, including nutrient deprivation, the release of deposited minerals, decreasing fluid flowrate, and endogenous decay as part of biofilm ageing. This study indicates that biofilms developed in fractures can persist for extended periods at reduced K when exposed to a long-term starvation.

Two-dimensional distribution of microbial activity and flow patterns within naturally fractured chalk

The two-dimensional distribution of flow patterns and their dynamic change due to microbial activity were investigated in naturally fractured chalk cores. Long-term biodegradation experiments were conducted in two cores ( approximately 20 cm diameter, 31 and 44 cm long), intersected by a natural fracture. 2,4,6-tribromophenol (TBP) was used as a model contaminant and as the sole carbon source for aerobic microbial activity. The transmissivity of the fractures was continuously reduced due to biomass accumulation in the fracture concurrent with TBP biodegradation. From multi-tracer experiments conducted prior to and following the microbial activity, it was found that biomass accumulation causes redistribution of the preferential flow channels. Zones of slow flow near the fracture inlet were clogged, thus further diverting the flow through zones of fast flow, which were also partially clogged. Quantitative evaluation of biodegradation and bacterial counts supported the results of the multi-tracer tests, indicating that most of the bacterial activity occurs close to the inlet. The changing flow patterns, which control the nutrient supply, resulted in variations in the concentrations of the chemical constituents (TBP, bromide and oxygen), used as indicators of biodegradation.

Impact of microbial activity on the hydraulic properties of fractured chalk

The impact of microbial activity on fractured chalk transmissivity was investigated on a laboratory scale. Long-term experiments were conducted on six fractured chalk cores (20 cm diameter, 23-44 cm long) containing a single natural fracture embedded in a porous matrix. Biodegradation experiments were conducted under various conditions, including several substrate and oxygen concentrations and flow rates. 2,4,6-Tribromophenol (TBP) was used as a model contaminant (substrate). TBP biodegradation efficiency depended mainly on the amount of oxygen. However, under constant oxygen concentration at the core inlet, elevating the flow rates increased the removal rate of TBP. Transmissivity reduction was clearly related to TBP removal rate, following an initial slow decline and a further sharp decrease with time. The fracture's transmissivity was reduced by as much as 97% relative to the initial value, with no leveling off of the clogging process. For the most extreme cases, reductions of 262 and 157 microm in the equivalent hydraulic apertures were recorded for fractures with initial apertures of 495 and 207 microm, respectively. The reductions in fracture transmissivity occurred primarily because of clogging by bacterial cells and extracellular polymeric substances (EPS) produced by the bacteria. Most of the biodegradation activity was concentrated near the fracture inlet, where the most suitable biodegradation conditions (nutrients and oxygen) prevailed, suggesting that the clogging had occurred in that vicinity. The clogging must have changed the structure of the fracture void, thereby reducing the active volume participating in flow and transport processes. This phenomenon caused accelerated transport of non-reactive tracers and doubled the fracture's dispersivity under constant flow rates.

Characterization of biofilms occurred in seepage groundwater contaminated with petroleum within an urban subway tunnel

Biofilms occurring in seepage groundwater contaminated with petroleum in an urban subway drainage system were characterized. The development of biofilms was observed only in the sites where petroleum-contaminated groundwater had seeped or was seeping. Moreover, the conditions of the biofilms such as color and development extent were influenced by the amount of spilled petroleum: By increasing the amount of spilled petroleum, the amount of biofilms increased and its color whitened. It deteriorated and became dark-brown if the contaminated groundwater did not seep any more. These facts indicate that the biofilms can be used as a preliminary indicator to identify the locations of fuel contaminated sumps and seeps without a more detailed assessment such as instrumental analysis. The biofilms were capable of degrading petroleum at 15 degrees C, which is similar to the average temperature of the seepage groundwater. Filamentous bacteria, Sphaerotilus spp., were isolated from the biofilms. It is considered that these bacteria are responsible for the development of biofilms in the seepage groundwater contaminated with petroleum because they can secrete extracellular polymeric substances.

Conservation of ornamental stone by Myxococcus xanthus-induced carbonate biomineralization

Increasing environmental pollution in urban areas has been endangering the survival of carbonate stones in monuments and statuary for many decades. Numerous conservation treatments have been applied for the protection and consolidation of these works of art. Most of them, however, either release dangerous gases during curing or show very little efficacy. Bacterially induced carbonate mineralization has been proposed as a novel and environmentally friendly strategy for the conservation of deteriorated ornamental stone. However, the method appeared to display insufficient consolidation and plugging of pores. Here we report that Myxococcus xanthus-induced calcium carbonate precipitation efficiently protects and consolidates porous ornamental limestone. The newly formed carbonate cements calcite grains by depositing on the walls of the pores without plugging them. Sonication tests demonstrate that these new carbonate crystals are strongly attached to the substratum, mostly due to epitaxial growth on preexisting calcite grains. The new crystals are more stress resistant than the calcite grains of the original stone because they are organic-inorganic composites. Variations in the phosphate concentrations of the culture medium lead to changes in local pH and bacterial productivity. These affect the structure of the new cement and the type of precipitated CaCO(3) polymorph (vaterite or calcite). The manipulation of culture medium composition creates new ways of controlling bacterial biomineralization that in the future could be applied to the conservation of ornamental stone.

Competition for oxygen by iron and 2,4,6-trichlorophenol oxidizing bacteria in boreal groundwater

Kinetics of simultaneous iron and 2,4,6-trichlorophenol (TCP) oxidation by groundwater enriched cultures were studied in order to reveal the competition for oxygen in aerobic in situ bioremediation of boreal groundwater. Chemical iron oxidation at near neutral pH in synthetic groundwater depended by the first order on the concentrations of ferrous iron and dissolved oxygen and by the second order on pH. The chemical iron oxidation rate constant was on average 2.2 x 10(13)mol(-2)L(2)atm(-1)min(-1). Chemical iron oxidation was insignificantly affected by natural organic matter, 2,4,6-tri-, 2,3,4,6-tetra- or pentachlorophenol in groundwater. Biological oxidation of iron followed zero-order kinetics. At pH of 6.3 and dissolved oxygen (DO) concentration of 11.5 mgL(-1), the rate of biological iron oxidation was 3.8 x 10(-4)mmolL(-1)min(-1) and up to one order of magnitude higher than the chemical oxidation rate, 5.2 x 10(-6) mmolL(-1)min(-1). Biological oxidation of iron was completely inhibited by pentachlorophenol at 23 micro mol-1. With a groundwater enriched culture, oxygen was consumed at higher rates by 2,4,6-TCP oxidizers (2.5-7.6 x 10(-5)mmolDOL(-1)min(-1)) than the iron oxidizing bacteria (0.8-3.1 x 10(-5) mmolDOL(-1)min(-1)) at both low and saturated DO-concentrations. The results indicate that in situ iron oxidation is predominantly biogenic in the studied boreal aquifer. 2,4,6-TCP degrading bacteria consumed DO at higher rates than the iron oxidizing bacteria and thereby, favour bioremediation of the polychlorophenol contaminated groundwater.