Study of pyrene biodegradation capacity in two types of solid media

Removal of pyrene, a representative PAH, was studied using laboratory tests in two different types of solid media: an organic matter collected on the surface of a vertical flow constructed wetland (VFCW) and a formulated clay silicate sand (inorganic matter). The aim of this study was to evaluate the capacity of pyrene biodegradation in these media in order to use them for treating run-off water. The sorption process, the kinetics of pyrene biodegradation and the influence of selected bacteria were also investigated. The sorption process was evaluated by adsorption isotherms and desorption kinetics using a batch equilibration method. The adsorption coefficient values of 28.8 and 2.1 for the organic and the inorganic matter respectively, confirmed the relationship of adsorption with organic carbon content. A small proportion of the sorbed pyrene was available for desorption (8% and 15% for the organic and the inorganic matter, respectively), indicating that sorption was partially irreversible, with the presence of hysteresis. For the formulated clay silicate sand inoculated with a specific bacteria (Mycobacterium sp.6PY1), selected for its ability to degrade PAHs, pyrene removal was complete in 32 days. With the organic matter, these values ranged from 40% to 95% for the different experiments, following a lag time of 3 weeks before observation of a significant degradation. Indigenous bacterial species in the organic medium had the metabolic capacity to degrade pyrene, and microbial populations pre-exposed to the PAH degraded pyrene faster than similar unexposed populations. Three metabolites of pyrene degradation by Mycobacterium were found. They accumulated in both organic and inorganic matter, indicating that the enzymes catalyzing them have slow kinetics.     

考虑降解时变扩散系数污染物迁移模型解析解

降解作用是污染物在介质中运移的主要控制进程之一。假设扩散系数为深度的线性函数,建立了污染物在多孔介质中的一维扩散模型,同时考虑降解作用的影响,针对零浓度的下边界条件,推求了模型的解析解。将常扩散系数模型解与相关文献进行了对比,说明了本文所提方法的正确性及可靠性。基于变系数计算模型,讨论了降解作用对污染物运移规律的影响,并分析了相关参数的敏感性。结果表明,扩散系数对计算结果存在较大影响,降解作用能够有效降低污染物的浓度,且降解越强,污染物浓度达到稳定状态需要的时间越短。     

Mobilization of adsorbed copper and lead from naturally aged soil by bacterial extracellular polymers

Sorption of pollutants is a dominant phase transfer process affecting the fate and transport of metals through the subsurface. The movement of contaminants is retarded by sorption to the stationary subsurface porous media and can seriously hinder remediation efforts. Research has shown that the binding of adsorbed metals becomes more pronounced the longer the contaminant is in the subsurface and the release rates of aged metal contaminants have not received the research attention given to freshly added metals in laboratory studies. Metal release rates are also influenced by the presence of dissolved ligands that compete with mineral soil surfaces by providing binding sites. Dissolved organic matter such as bacterial extracellular polymers are common in natural soil solutions and the metal binding properties of bacterial polymers are well established. Therefore, binding of metals to dissolved biopolymers may result in mobilization of an adsorbed metal. This is important for cases where the metals are assumed to be relatively immobile such as in the case of land applied biosolids. In addition, naturally occurring adherent bacteria commonly produce extracellular polymers and thus may modify the bioavailability of meal contaminants at the point of their attachment. In this study samples from three sites, one a land applied sludge test site, were used to investigate the ability of bacterial extracellular polymers to release metals from soils with long-term exposures. The presence of ?200mg/L bacterial extracellular polymer was found to increase the short-term (less than 350h) release of Cu and Pb by a factor of 2-4-fold.     

Review of photochemical reaction constants of organic micropollutants required for UV advanced oxidation processes in water

Emerging organic contaminants (pharmaceutical compounds, personal care products, pesticides, hormones, surfactants, fire retardants, fuel additives etc.) are increasingly found in water sources and therefore need to be controlled by water treatment technology. UV advanced oxidation technologies are often used as an effective barrier against organic contaminants. The combined operation of direct photolysis and reaction with hydroxyl radicals ensures good results for a wide range of contaminants. In this review, an overview is provided of the photochemical reaction parameters (quantum yield, molar absorption, OH radical reaction rate constant) of more than 100 organic micropollutants. These parameters allow for a prediction of organic contaminant removal by UV advanced oxidation systems. An example of contaminant degradation is elaborated for a simplified UV/H₂O₂ system.     

Subsurface multiphase flow of organic contaminants: Model development and validation

A numerical model has been developed to predict the migration of organic contaminants in the subsurface. The formulations take a multiphase approach in describing the flow of organic contaminants in saturated and unsaturated porous media. In a three-phase fluid system of contaminant, gas, and water, simultaneous flow of the water and the contaminant phases is formulated by applying mass conservation principles to each of the phases under the condition of no interphase mass exchange. For each phase, the formulations incorporate the spatial variability of the relative permeability and its direction dependency. The complex formulations are solved numerically using an implicit finite difference scheme. The accuracy of the numerical model is determined against experimental data from the literature. The predicted migration pattern in both homogeneous and stratified media agrees well with the experimental data. Numerical simulations illustrate the strong effects of the medium permeability and the water distribution profiles on the flow pattern and the pressure distribution of the contaminant.     

Simultaneous uptake of anionic surfactants and micellar-solubilized contaminants using anion-exchange resins

This research studied simultaneous uptake of anionic surfactants and micellar-solubilized organic contaminants by anion-exchange resins. Anionic surfactant molecules adsorbed onto the positively charged resin mainly through electrostatic attraction, while the micellar-solubilized contaminants were excluded from aqueous solutions once the remaining micelles could no longer solubilize them. Data suggest that the excess contaminants adsorbed onto the resin skeleton and admicelle layer formed on the resin surface through hydrophobic interactions and eventually partitioned into the resin gel phase matrix. In batch adsorption, the contaminant solubilization capacity did not decrease linearly with respect to surfactant concentration decrease due to the increased solution counterion activity during anion exchange, and caused "delayed" contaminant uptake relative to that of the surfactant. No such effect occurred in continuous column adsorption, where the surfactant and contaminant breakthrough occurred simultaneously. Surfactant head and tail group properties, along with resin structure and particle size significantly affected surfactant and contaminant uptake rates. Relative to recovering the surfactant, the high exchange potential of the anionic surfactant prevented effective surfactant desorption, even at high electrolyte concentration and in the presence of a cosolvent. The resin matrix also had high affinity for the partitioned contaminant, and the contaminant elution from the resin seemed to be controlled by equilibrium partitioning.     

Biofiltration of airborne VOCs with green wall systems—Microbial and chemical dynamics

Botanical air filtration is a promising technology for reducing indoor air contaminants, but the underlying mechanisms need better understanding. Here, we made a set of chamber fumigation experiments of up to 16 weeks of duration, to study the filtration efficiencies for seven volatile organic compounds (VOCs; decane, toluene, 2‐ethylhexanol, α‐pinene, octane, benzene, and xylene) and to monitor microbial dynamics in simulated green wall systems. Biofiltration functioned on sub‐ppm VOC levels without concentration‐dependence. Airflow through the growth medium was needed for efficient removal of chemically diverse VOCs, and the use of optimized commercial growth medium further improved the efficiency compared with soil and Leca granules. Experimental green wall simulations using these components were immediately effective, indicating that initial VOC removal was largely abiotic. Golden pothos plants had a small additional positive impact on VOC filtration and bacterial diversity in the green wall system. Proteobacteria dominated the microbiota of rhizosphere and irrigation water. Airborne VOCs shaped the microbial communities, enriching potential VOC‐utilizing bacteria (especially Nevskiaceae and Patulibacteraceae) in the irrigation water, where much of the VOC degradation capacity of the biofiltration systems resided. These results clearly show the benefits of active air circulation and optimized growth media in modern green wall systems.     

Characterization, performance modeling, and design of an active capping remediation project in a heavily polluted urban channel

Collateral Channel is a heavily polluted former navigation slip to the Chicago Sanitary and Ship Canal (Illinois, USA). Characterization of sediment cores taken in the channel show high levels of heavy metals, polycyclic aromatic hydrocarbons (PAHs) and other contaminants in deposited sediment dating back to the 1800's. Of these, PAHs were the contaminants of greatest concern based upon exceedance of sediment contamination criteria (Σ₁₆ PAHs up to 1500 mg/kg). Benthic animal counts revealed a lack of biodiversity, with relatively low levels of small tubificid oligochaetes (generally < 3000/m²) in surficial sediments. Comparison of surficial sediment contaminant levels between 1995 and 2005 showed few decreases in contaminant levels, indicating a lack of “natural recovery” processes occurring in the channel. These results led to an analysis of sediment amendments for an active capping demonstration project in the channel using transport models developed in our previous work (Viana et al., 2008). Based on the sediment characterization and modeling results, the active capping design will be focused on organic contaminant sequestration through the use of organoclay. A site-specific difficulty is the substantial rates of gas ebullition from anaerobic organic matter biodegradation in the sediments, particularly in the summer months. These gases can open advective channels that may result in substantial pollution release and compromise cap effectiveness, and thus the capping scenario must control for such releases. The active capping layer will underlay a sloped sand layer and a high permeability gas venting system to allow biogenically-produced gas migration to shoreline collectors through an innovative support grid. The cap will include an overlaying wetland to remove nutrients from the adjoining Chicago River and provide a public recreational space.     

The use of isotopic and lipid analysis techniques linking toluene degradation to specific microorganisms: applications and limitations

Phospholipid fatty acid (PLFA) analysis combined with (13)C-labeled tracers has been used recently as an environmental forensics tool to demonstrate microbial degradation of pollutants. This study investigated the effectiveness and limitations of this approach, applied to the biodegradation of toluene by five reference strains that express different aerobic toluene degradation pathways: Pseudomonas putida mt-2, P. putida F1, Burkholderia cepacia G4, B. pickettii PKO1, and P. mendocina KR1. The five strains were grown on mineral salts base medium amended with either 10 mM natural or [(13)C-ring]-labeled toluene. PLFA analysis showed that all five strains incorporated the toluene carbon into membrane fatty acids, as demonstrated by increases in the mass of fatty acids and their mass-spectrometry fragments for cells grown on (13)C-labeled toluene. Because of its ubiquitous presence and high abundance in bacteria, C16:0 fatty acid might be a useful biomarker for tracking contaminant degradation and (13)C flow. On the other hand, the (13)C-label (which was supplied at relatively high concentrations) generally exerted an inhibitory effect on fatty acid biosynthesis. Differences in fatty acid concentrations between cells grown on natural versus (13)C-labeled toluene would affect the interpretation of lipid profiles for microbial community analysis as indicated by principal component analysis of fatty acids. Therefore, caution should be exercised in linking lipid data with microbial population shifts in biodegradation experiments with (13)C-labeled tracers.     

Composition of bacterial and archaeal communities in freshwater sediments with different contamination levels (Lake Geneva, Switzerland)

The aim of this study was to compare the composition of bacterial and archaeal communities in contaminated sediments (Vidy Bay) with uncontaminated sediments (Ouchy area) of Lake Geneva using 16S rRNA clone libraries. Sediments of both sites were analysed for physicochemical characteristics including porewater composition, organic carbon, and heavy metals. Results show high concentrations of contaminants in sediments from Vidy. Particularly, high contents of fresh organic matter and nutrients led to intense mineralisation, which was dominated by sulphate-reduction and methanogenesis. The bacterial diversity in Vidy sediments was significantly different from the communities in the uncontaminated sediments. Phylogenetic analysis revealed a large proportion of Betaproteobacteria clones in Vidy sediments related to Dechloromonas sp., a group of dechlorinating and contaminant degrading bacteria. Deltaproteobacteria, including clones related to sulphate-reducing bacteria and Fe(III)-reducing bacteria (Geobacter sp.) were also more abundant in the contaminated sediments. The archaeal communities consisted essentially of methanogenic Euryarchaeota, mainly found in the contaminated sediments rich in organic matter. Multiple factor analysis revealed that the microbial community composition and the environmental variables were correlated at the two sites, which suggests that in addition to environmental parameters, pollution may be one of the factors affecting microbial community structure.     

Adsorption and desorption of trace organic contaminants from granular activated carbon adsorbers after intermittent loading and throughout backwash cycles

A granular activated carbon (GAC) adsorption simulation methodology using the observed trace organic contaminant mid-point breakthrough and the pore diffusion model is presented, validated, and used to model adsorption and concentration gradient driven desorption. Trace organic contaminant adsorption was well-simulated by this approach; however, desorption from GAC adsorbers was found to occur at lower concentrations than predicted by either pore or surface diffusion model calculations. The observed concentration profiles during desorption yielded a lower peak concentration and more elongated attenuation of contaminants after intermittent loading conditions than predicted by the models. Hindered back diffusion caused by irreversibly adsorbed dissolved organic matter on the GAC surface is hypothesized to be responsible for slowing the desorption kinetics. In addition, laboratory test results indicate a negligible impact of simulated backwashing the GAC media on trace organic contaminant breakthrough.     

Geochemical Landscape Analysis: Development and Application to the Risk Assessment of Acid Mine Drainage. A Case Study in Central Sweden

Acid mine drainage containing toxic contaminants is a major cause of landscape degradation at numerous historic mine sites in Europe. Risk assessment of acid mine drainage and related polluted lands requires an approach that is able to study the complexity of pollution emissions and impacted landscapes. The objective of this paper is to link geochemical contaminant fate modelling and landscape analysis for the risk assessment of acid mine drainage along the source–pathway–receptor chain. A simple geochemical landscape analysis tool is developed using landscape ecology spatial analysis and geochemical modelling methods. A case study is presented for the analysis of geochemical landscapes in central Sweden. Results show that the method can be used efficiently for the risk assessment of toxic mine contaminants in the complex wetland landscape in the study area.     

多孔介质中化学–热–水力–力学耦合过程本构模型和数值模拟

本文发展了一个多孔介质中的化学–热–水力–力学(CTHM)耦合本构模型。该模型基于文献[1]中多孔介质热–水力–力学(THM)本构模型、文献[2,3]中的污染物传输本构模型和文献[4]提出的化学–力学本构模型。在本构模型中引入化学软化函数以模拟孔隙水中有机污染物对多孔介质力学性质的影响。考虑了温度对污染物传输机制的影响。本文CTHM耦合本构模型已在多孔介质的热–水力–力学–污染物传输数学模型中建立。在CTHM本构模拟框架中对计及化学塑性效应、描述在热–水力–污染物传输耦合作用下多孔介质力学行为、在应力–吸力–温度四维空间中包含了五重屈服面的耦合本构模型发展了一致性切线模量矩阵。数值结果突出显示了污染物浓度在多孔介质化学–热–水力–力学(CTHM)耦合系统中的影响。     

Contaminants removal by bentonite amended slow sand filter

Earlier studies have indicated that variability in size, surface texture and charge greatly influence the contaminant removal process in granular media. Based on surface characteristics of montmorillonite, it is anticipated that small addition of this clay would increase adhesion sites for bacterial growth and extracellular polymer production in the slow sand filter and thereby enhance its contaminant removal ability. Experiments were performed by permeating groundwater contaminated with pathogens (total coliform and E. Coli) and inorganic contaminants through the bentonite amended slow sand filter (BASSF). Surprisingly, the BASSF retained inorganic contaminants besides pathogens. Water-leach tests (pH of water leachate ranged from 2 to 9) with spent BASSF specimen indicated that the inorganic contaminants are irreversibly adsorbed to a large extent. It is considered that the combined effects of enhanced-organic matter mediated adhesion sites and increased hydraulic retention time enables the BASSF specimen to retain inorganic contaminants. It is envisaged that BASSF filters could find use in treating contaminated groundwater for potable needs at household and community level.     

Environmental stress and recovery: the geochemical record of human disturbance in New Bedford Harbor and Apponagansett Bay,Massachusetts (USA)

Sediments record the history of contamination to estuaries. Analysis of the concentrations of toxic organic compounds, contaminant and crustal metals, organic carbon content and isotopic composition in sediment cores from two estuarine systems in Buzzards Bay allowed reconstruction of human impacts over 350 years. Vertical distributions of the contaminants correlate with changes in the nature of watershed/estuarine activities. All contaminants were highly enriched (tens to hundreds times background) in modern New Bedford Harbor sediments. Enrichment began around the turn of the 20th century for all but PCBs, which were first synthesized in the 1930s. An increase in organic carbon content and a shift of carbon isotopes toward a more terrestrial signature illustrates increasing anthropogenic impact in New Bedford as population grew along with the industrial base. Institution of environmental protection measures in the late 20th century was reflected in decreased, although still substantially elevated, concentrations of contaminants. A lack of industrial development in Apponagansett Bay resulted in much lower concentrations of the same indicators, although specific contaminants related to the early whaling industry increased significantly above background as early as the late 18th century. The similarity of indicators in older portions of cores from NBH and unimpacted Apponagansett Bay demonstrates that cores can be used to establish reference conditions as successfully as using separate sites judged a priori to represent the reference state. The historical reconstruction approach provides the basis for establishing relationships between environmental stressors and factors that drive the stressors, as well as a framework for the assessment of ecological response(s) to environmental stressors over a range of time and/or exposure scales.     

A fugacity based continuous and dynamic fate and transport model for river networks and its application to Altamaha River

In this paper, a continuous and dynamic fugacity-based contaminant fate and transport model is developed. The dynamic interactions among all phases in the physical domain are addressed through the use of the fugacity approach instead of the use of concentration as the unknown variable. The full form of Saint Venant equations is used in order to solve for the hydrodynamic conditions in the river network. Then a fugacity-based advection-dispersion equation is modeled to examine the fate and transport of contaminants in the river network for all phases.The fugacity-based, dynamic and continuous contaminant fate and transport model developed here is applied to Altamaha River in Georgia, USA to demonstrate its use in environmental exposure analysis. Altamaha River is the largest river system east of Mississippi which offers habitat for many species, including about 100 rare endangered species, along its 140 mile course. Polychlorinated biphenyls (PCBs), a highly hydrophobic and toxic chemical ubiquitous in nature, and atrazine, the most commonly-used agricultural pesticide are modeled as contaminants in this demonstration. Through this approach the concentration distribution of PCBs and atrazine in the water column of Altamaha River as well as the sediments can be obtained with relative ease, which is an improvement over concentration based analysis of phase distribution of contaminants.     

Removal of contaminants released from room surfaces by displacement and mixing ventilation: modeling and validation

This paper presents the experimental and numerical modeling of contaminant dispersion in a full-scale environmental chamber with different room air distribution systems. For the experimental modeling, an area source with uniform emissions of a hypothetical contaminant (SF6) from the entire floor surface is designed and constructed. Two different types of ventilation are studied: displacement and mixing ventilation. A computer model for predicting the contaminant dispersion in indoor spaces was validated with experimental data. The validated model is used to study the effects of airflow and the area-source location on contaminant dispersion. Results show that the global airflow pattern has a strong impact on the distribution of the contaminants. In general, the personal exposure could be estimated by analyzing the relative source positions in the airflow pattern. Accordingly, the location of an exhaust diffuser may not greatly affect the airflow pattern, but can significantly affect the exposure level in the room. PRACTICAL IMPLICATIONS: When designing ventilation in addition to bringing fresh air to occupants, it is important to consider the removal of contaminants released in the off-gassing of building materials. Typical indoor off-gassing examples are emissions of volatile organic compounds from building enclosure surfaces such as flooring and painted walls. In this study, we conducted experimental and numerical modeling of different area sources in a mock-up office setup, with displacement or mixing ventilation. Displacement ventilation was as successful as mixing ventilation in removing the contaminant source from the floor area. Actually, the most important consideration in the removal of these contaminants is the relative position of the area source to the main airflow pattern and the occupied zone.     

Performance of a fungal biofilter treating gas-phase solvent mixtures during intermittent loading

Biological treatment processes used to remove and degrade volatile organic compounds (VOCs) from contaminated gases emitted by industrial operations or waste treatment processes are almost always subjected to transient loading conditions because of the inherently unsteady-state nature of contaminant generating processes. In the study presented here, a laboratory-scale biofilter populated by a mixed culture of fungi was used to study the transient response to various periods of no contaminant loading in a system treating a model waste gas stream containing a mixture of commonly used solvents. The biofilter, packed with cubed polyurethane foam media and operated with an empty bed residence time of 15s, was supplied with a four-component mixture of n-butyl acetate, methyl ethyl ketone, methyl propyl ketone, and toluene at target influent concentrations of 124, 50.5, 174, and 44.6 mg/m(3), respectively. This corresponds to a total VOC loading rate of 94.3g/(m(3)h). Biofilter performance was evaluated over a 94-day period for three loading conditions intended to simulate processes generating contaminated gases only during daytime operation, daytime operation with weekend shutdown periods, and with long term (9-day) shutdown. Results indicate that fungal biofilters can be an effective alternative to conventional abatement technologies for treating solvent contaminated off-gases even under discontinuous loading conditions.     

The anoxic extractive membrane bioreactor

The extractive membrane bioreactor (EMB) employs a dense silicone rubber membrane to selectively extract hydrophobic organic compounds from industrial wastewaters into a bioreactor in order to biodegrade them. The major drawback of the EMB is excess biofilm growth on the membrane, which limits mass transfer and creates oxygen limitations. In this work, nitrate has been used as an electron acceptor instead of oxygen. Due to the high solubility of nitrate in water, it is hypothesised that nitrate penetrates the whole biofilm, preventing the formation of inactive zones of bacteria. Four experiments have been performed with toluene as a model substrate under anoxic conditions. The effect of nitrate concentrations on the biofilm and on the toluene flux have been investigated. In addition, the production of soluble microbial products (SMPs), and bacterial hydrophobicity were studied.Under high nitrate concentrations, the performance of the anoxic EMB was stable and no biofilm was formed. The bacteria metabolised toluene, and the toluene flux remained approximately constant. Conversely, at low nitrate concentration, a decrease in pollutant flux concomitant with biofilm growth was observed. The production of SMPs increased under limiting nitrate concentrations, but the hydrophobicity of the suspended bacteria remained constant. However, the bacterial hydrophobicity of the attached cells was significantly greater than that of the suspended cells.     

Retention and removal of pathogenic bacteria in wastewater percolating through porous media: a review

Properly designed biological filters or infiltration systems have the capacity to significantly reduce effluent concentrations of pathogenic microorganisms in wastewater. The retention and elimination of microbial cells in biological wastewater filter systems is influenced by several factors. In this review, these factors are discussed. Immobilization of microbial cells moving through a porous media is influenced by mechanisms such as physical straining as well as adsorption to porous media. The grain size of porous media and bacterial cell size are important factors affecting the straining of bacteria, as are the hydraulic loading rate or the extent of clogging layer development in the filter. Adsorption of cells to the porous media is influenced by the content of organic matter, degree of biofilm development, and electrostatic attraction due to ion strength of the solution or electrostatic charges of cell- and particle surfaces. The rate of inactivation of pathogenic microorganisms, in adsorbed or liquid phases, has been shown to be affected by abiotic and biotic factors such as moisture content, pH, temperature, organic matter, bacterial species, predation, and antagonistic symbiosis between microorganisms in the system.