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The Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) project will test the overarching hypothesis that an active hydrological system exists beneath a West Antarctic ice stream that exerts a major control on ice dynamics, and the metabolic and phylogenetic diversity of the microbial community in subglacial water and sediment. WISSARD will explore Subglacial Lake Whillans (SLW, unofficial name) and its outflow toward the grounding line where it is thought to enter the Ross Ice Shelf seawater cavity. Introducing microbial contamination to the subglacial environment during drilling operations could compromise environmental stewardship and the science objectives of the project, consequently we developed a set of tools and procedures to directly address these issues. WISSARD hot water drilling efforts will include a custom water treatment system designed to remove micron and sub-micron sized particles (biotic and abiotic), irradiate the drilling water with germicidal ultraviolet (UV) radiation, and pasteurize the water to reduce the viability of persisting microbial contamination. Our clean access protocols also include methods to reduce microbial contamination on the surfaces of cables/hoses and down-borehole equipment using germicidal UV exposure and chemical disinfection. This paper presents experimental data showing that our protocols will meet expectations established by international agreement between participating Antarctic nations.

Chemical constituents trapped within glacial ice provide a unique record of climate, as well as repositories for biological material such as pollen grains, fungal spores, viruses, bacteria and dissolved organic carbon. Past research suggests that the veins of polycrystalline ice may provide a liquid microenvironment for active microbial metabolism fueled by concentrated impurities in the veins. Despite these claims, no direct measurements of impurity concentration in ice veins have been made. Using micro-Raman spectroscopy, we show that sulfate and nitrate concentrations in the veins of glacial ice from Greenland (Greenland Ice Sheet Project 2) and Antarctic (Newall Glacier and a Dominion Range glacier) core samples were 104 and 105 times greater than the concentrations measured in melted (bulk) core water. Methanesulfonate was not found in the veins, consistent with its presence as particulate matter within the ice. The measured vein concentration of molecular anions implies a highly acidic (pH < 3) vein environment with high ionic strength (mM-M). We estimate that the vein volume provides 16.7 and 576 km3 of habitable space within the Greenland and Antarctic ice sheets, respectively, which could support the metabolism of organisms that are capable of growing in cold, high ionic strength solutions with low pH.

To quantify the effect of dynamic particle size changes and degradation and accumulation of suspended solids (SS) in influents to reactors on membrane fouling frequency in hybrid powder-activated carbon (PAC)–microfiltration (MF) reactors, we operated a PAC–MF system (hollow-fiber module) for more than five months to purify river water before and after pretreatment by a biofilter. The transmembrane pressure, backwashing pressure, resistance to filtration, and SS accumulation and degradation during these dynamic changes were evaluated. The initial dose of PAC was 40 g/L of the reactor and no additional PAC was added during this continuous operational period. The presence of PAC reduced the membrane resistance to filtration even at the end of filtration period when the number of particles in the smallest range (>1.0–3.6 μm) was the highest measured by the flow cytometer and microscopy image analysis. This resistance was reduced further when the river water was biofiltered prior to membrane filtration. This real-time study demonstrates that over time PAC and other particles coming into the reactors through the influents degrade and/or become smaller because of the turbulence caused by continuous aeration below the MF membrane fibers. The number of particles in the reactors with diameters less than 10 μm increased with time, increasing the fouling frequency; however, the presence of PAC further reduced the particle enhanced fouling. The presence of PAC also increased SS degradation by up to 10%. The increased number of bacteria inside the PAC–MF systems did not contribute to the number of membrane fouling. Even though the particle sizes inside the reactors became smaller with time, the gradual increase in net accumulation of SS was also an important factor controlling the performance of the PAC–MF system.

Changes in the viscoelastic material properties of bacterial biofilms resulting from chemical and antimicrobial treatments were measured by rheometry. Colony biofilms of Staphylococcus epidermidis or a mucoid Pseudomonas aeruginosa were subjected to a classical creep test performed using a parallel plate rheometer. Data were fit to the 4-parameter Burger model to quantify the material properties. Biofilms were exposed to the chloride salts of several common mono-, di-, and tri- valent cations, and to urea, industrial biocides, and antibiotics. Many of these treatments resulted in statistically significant alterations in the material properties of the biofilm. Multivalent cations stiffened the P. aeruginosa biofilm, while ciprofloxacin and glutaraldehyde weakened it. Urea, rifampin, and a quaternary ammonium biocide weakened the S. epidermidis biofilm. In general, there was no correspondence between the responses of the two different types of biofilms to a particular treatment. These results underscore the distinction between the killing power of an antimicrobial agent and its ability to alter biofilm mechanical properties and thereby influence biofilm removal. Understanding biofilm rheology and how it is affected by chemical treatment could lead to improvements in biofilm control.

The inadvertent or the deliberate introduction of pathogens into drinking water can lead to public health consequences. Distribution system sampling strategies are needed to provide information on the identity, source and fate of the introduced pathogens. Porous media biofilm reactors conditioned with undefined drinking water biofilms were tested for their ability to immobilize Escherichia coli 0157:H7. Biofilms were established by applying continuous flow of biologically activated carbon treated water with natural microflora and supplemented nutrient solution (0.5 mg l(-1) C) for 2 or 3 weeks. Control reactors were clean and were not colonized with biofilm. All reactors were injected with slug doses of approximately 1 x 10(9) cfu E. coli O157:H7. On the basis of the plate count enumeration of the introduced pathogen, reactors pre-colonized for 2 or 3 weeks retained significantly more cells (0.75 and 9.37% of the introduced spike dose, respectively) compared with uncolonized control reactors (0.22%). Compared with cultivation, microscopic direct counts and quantitative PCR suggested significantly higher and lower numbers of pathogens, respectively. Plate counts were thus considered as the method of choice for pathogen enumeration in this study. In addition to providing general insights into interactions between pathogens and drinking water biofilms, the study concluded that engineered biofilm systems may be considered as a device to capture pathogens from the bulk flow for monitoring purposes.

This article shows how the use of high-dose powdered activated carbon and biofiltration are able to improve the performance of membrane-based microfiltration systems. The first part of this feature, which was published in the May 2007 issue of Membrane Technology , provides an overview of the study, materials and methods, and experimental design and operational conditions of the reactors. The second instalment, which appears here, discusses the results of this study.

The goal of the work was to determine if biological treatment of water containing soil-derived humic substances has the potential for reducing the fouling of membranes used in water treatment. Laboratory scale biological filters containing biologically active carbon or iron oxide coated sand were fed humic-laden water with or without prechlorination. This stream was split, with half being further treated by microfiltration. Treated water was assessed for total organic carbon removal and biofouling potential using a glass bead assay and membrane assay for total cell counts, fouling layer thickness, and flux reduction. A combination of these assays provided more insight than any single measurement. Compared to untreated control water, biological treatment was capable of reducing downstream fouling of membrane systems. For example, fouling layer thickness was reduced by half after biological treatment, and cell counts were reduced four- to five-fold. Biological treatment coupled with microfiltration provided the best reduction of fouling, while prechlorination did not appear to impact the process. These results suggest that biological treatment may be valuable in reducing membrane fouling while reducing the amount of disinfectants used in pretreatment.

To investigate growth of heterotrophic biofilm bacteria, a model biofilm reactor was developed to simulate a drinking water distribution system. Controlled addition of three different carbon sources (amino acids, carbohydrates, and humics) at three different concentrations (500, 1,000, and 2,000 ppb carbon) in the presence and absence of chlorine were used in separate experiments. An additional experiment was run with a 1:1:2 mixture of the above carbon sources. Biofilm and effluent total and culturable cells in addition to total and dissolved organic carbon were measured in order to estimate specific growth rates (SGRs), observed yields, population densities, and bacterial carbon production rates. Bacterial carbon production rates (µg C/L day) were extremely high in the control biofilm communities (range = 295-1,738). Both growth rate and yield decreased with increasing carbon concentrations. Therefore, biofilm growth rates were zero-order with respect to the carbon concentrations used in these experiments. There was no correlation between growth rate and carbon concentration, but there was a significant negative correlation between growth rate and biofilm cell density (r = -0.637, p = 0.001 control and r = -0.57, p = 0.021 chlorinated biofilms). Growth efficiency was highest at the lowest carbon concentration (range = 12-4.5%, amino acids and humics respectively). Doubling times ranged from 2.3-15.4 days in the control biofilms and 1-12.3 days in the chlorinated biofilms. Growth rates were significantly higher in the presence of chlorine for the carbohydrates, humics, and mixed carbon sources (p = 0.004, < 0.0005, 0.013, respectively). The concept of r/K selection theory was used to explain the results with respect to specific growth rates and yields. Humic removal by the biofilm bacteria (78% and 56% for the control and chlorinated biofilms, respectively) was higher than previously reported literature values for planktonic bacteria. A number of control experiments indicated that filtration of drinking water was as effective as chlorination in controlling bacterial biofilm growth.

Model predictions of fate and transport of organic solutes in soils and groundwater are sensitive to assumptions concerning rates of microbial degradation. We studied the independent effects of residence time (RT) and pore water velocity (ν) on the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) by employing a series of unsaturated soil column experiments (continuous pulse concentration = 1 mg L-1) with varying column lengths and ν. While 2,4-D degradation under batch conditions was best described by a logistic rate expression, analysis of the 2,4-D breakthrough curves (BTCs) showed that (i) observed 2,4-D degradation rates were consistent with a first-order kinetic model and (ii) a single set of independently determined rate parameters from batch experiments could not describe 2,4-D degradation for all transport conditions. Apparent first-order degradation rate constants obtained from column data were found to be independent of column RT, but increased with decreasing ν, especially at ν < 1 cm h-1....

A predictive model has been developed to describe degradation of toluene in a flat-plate vapor phase bioreactor (VPBR). The VPBR model incorporates kinetic, stoichiometric, injury, and irreversible loss coefficients from suspended culture studies for toluene degradation by \iP. \Iputida\N 54G and measured values of Henry’s law constant and boundary layer thickness at the gas-liquid and liquid-biofilm interface. The model is used to estimate the performance of the reactor with respect to toluene degradation and to predict profiles of toluene concentration and bacterial physiological state within the biofilm. These results have been compared with experimentally determined values from a flat plate VPBR under electron acceptor and electron donor limiting conditions. The model accurately predicts toluene concentrations in the vapor phase and toluene degradation rate by adjusting only three parameters: biomass density and rates of death and endogenous decay. Qualitatively, the model also predicts gradients in the physiological state of cells in the biofilm. This model provides a rational design for predicting an upper limit of toluene degradation capability in a VPBR and is currently being tested to assess applications for predicting performance of bench and pilot-scale column reactors.

Toluene degradation kinetics by biofilm and planktonic cells of Pseudomonas putida 54G were compared in this study. Batch degradation of (14)C toluene was used to evaluate kinetic parameters for planktonic cells. The kinetic parameters determined for toluene degradation were: specific growth rate, micro(max) = 10.08 +/- 1.2/day; half-saturation constant, K(S) = 3.98 +/- 1.28 mg/L; substrate inhibition constant, K(I) = 42.78 +/- 3.87 mg/L. Biofilm cells, grown on ceramic rings in vapor phase bioreactors, were removed and suspended in batch cultures to calculate (14)C toluene degradation rates. Specific activities measured for planktonic and biofilm cells were similar based on toluene degrading cells and total biomass. Long-term toluene exposure reduced specific activities that were based on total biomass for both biofilm and planktonic cells. These results suggest that long-term toluene exposure caused a large portion of the biomass to become inactive, even though the biofilm was not substrate limited. Conversely, specific activities based on numbers of toluene-culturable cells were comparable for both biofilm and planktonically grown cultures. Planktonic cell kinetics are often used in bioreactor models to model substrate degradation and growth of bacteria in biofilms, a procedure we found to be appropriate for this organism. For superior bioreactor design, however, changes in cellular activity that occur during biofilm development should be investigated under conditions relevant to reactor operation before predictive models for bioreactor systems are developed.

Sulfide product inhibition kinetics for growth and activity of Desulfovibrio desulfuricans was investigated in batch and continuous cultures at pH = 7.0. A non-competitive inhibition model adequately described sulfide product inhibition kinetics. Inhibition coefficient (Ki) for maximum specific growth rate (μinhmax) was 251 mg l−1 S in a batch experiment. Cell yield determined in a chemostat was reduced in half by a sulfide concentration of about 250 mg l−1 S, which was very close to the Ki value for the batch growth. Maximum specific growth rate (μinhmax) and cell yield (YcLac) were strongly inhibited by high levels of sulfide concentrations, whereas specific lactate utilization rate increased with increasing sulfide concentrations. The results indicated an increase in the relative energy needed for maintenance to overcome sulfide inhibition and uncoupling growth from energy production. However, D. desulfuricans to some extent could recover from the shock of high sulfide concentrations. Stoichiometry for catabolic reactions (energy producing) did not change at high sulfide concentrations, while anabolic reactions (cellular synthesis) were strongly inhibited by high sulfide concentrations. These results suggested that separation of sulfide product inhibition into growth (cell yield) and activity (substrate utilization rate) was important to incorporate the sulfide product inhibition kinetics in a variety of applications.

Measurement of cellular and extracellular carbon contents of sulfate-reducing bacteria (SRB) is essential and important in studies of the role of SRB in corrosion and biofouling. An epifluorescence (EPI) microscopic technique and a lipopolysaccharide (LPS) assay were used to quantify cellular and extracellular carbon contents in Desulfovibrio desulfuricans biofilms. The average contents of lipopolysaccharide (LPS) and cellular carbon were 7.3 ± 2.8 (fg LPS) cell −1 and 39.9 ± 9.9 (fg cellular-C) cell −1 , respectively, in a D. desulfuricans chemostat culture. A ratio of cellular carbon content to LPS content was 6.5 ± 2.8, and was used to estimate cellular carbon contents in a D. desulfuricans biofilm. The LPS and EPI methods gave comparable results for suspended samples, but not for biofilm samples.

Packed-bed bioreactors filled with diatomaceous earth (D.E.) pellets were used to evaluate the effects of competition between inoculated and invading microbial species on the spatial and temporal distribution of microorganisms within an individual pellet. The (D.E.) pellets were cylinders 6 mm in diameter and 5–10 mm long with a mean pore diameter of 20 μm. Bench-scale experiments evaluated competition between two distinct microbial species: Pseudomonas aeruginosa , a motile, obligate aerobe ( μ max = 0.4 h −1 ) and Klebsiella pneumoniae , a non-motile, facultative organism ( μ max = 2.0 h −1 ). Organism growth rate appeared to be more important than motility or order of introduction in determining organism spatial and temporal distribution within the pellets. Pilot-scale experiments used pellets colonized with a pseudomonad growing on chlorobenzene as the sole carbon and energy source. Organic-rich ground water containing benzene, chlorobenzene and a population of indigenous microorganisms was used as feed. Pellet concentrations of the inoculated pseudomonad dropped from 10 9 to 10 6 colony forming units (cfu) ml −1 pellet volume over 15 days. These experiments demonstrate that inoculated organisms within porous packing media may undergo significant loss in colonization numbers when faced with competition from faster growing organisms.

A phenomenological model has been developed to describe biomass distribution and substrate depletion in porous diatomaceous earth (DE) pellets colonized by Pseudomonas aeruginosa. The essential features of the model are diffusion, attachment and detachment to/from pore walls of the biomass, diffusion of substrate within the pellet, and external mass transfer of both substrate and biomass in the bulk fluid of a packed bed containing the pellets. A bench-scale reactor filled with DE pellets was inoculated with P. aeruginosa and operated in plug flow without recycle using a feed containing glucose as the limiting nutrient. Steady-state effluent glucose concentrations were measured at various residence times, and biomass distribution within the pellet was measured at the lowest residence time. In the model, microorganism/substrate kinetics and mass transfer characteristics were predicted from the literature. Only the attachment and detachment parameters were treated as unknowns, and were determined by fitting biomass distribution data within the pellets to the mathematical model. The rate-limiting step in substrate conversion was determined to be internal mass transfer resistance; external mass transfer resistance and microbial kinetic limitations were found to be nearly negligible. Only the outer 5% of the pellets contributed to substrate conversion. © 1993 Wiley & Sons, Inc.

To characterize the effects of season, temperature, plant species, and chemical oxygen demand (COD) loading on sulfate reduction and metals removal in treatment wetlands we measured pore water redox potentials and concentrations of sulfate, sulfide, zinc and COD in subsurface wetland microcosms. Two batch incubations of 20 day duration were conducted in each of four seasons defined by temperature and daylight duration. Four treatments were compared: unplanted controls, Typha latifolia (broadleaf cattail), and Schoenoplectus acutus (hardstem bulrush), all at low COD loading (267 mg/L), plus bulrush at high COD loading (534 mg/L). Initial SO4-S and zinc concentrations were 67 and 24 mg/L, respectively. For all treatments, sulfate removal was least in winter (4 degrees C, plant dormancy) greatest in summer (24 degrees C, active plant growth) and intermediate in spring and fall (14 degrees C), but seasonal variation was greater in cattail, and especially, bulrush treatments. Redox measurements indicated that, in winter, plant-mediated oxygen transfer inhibited activity of sulfate reducing bacteria, exacerbating the reduction in sulfate removal due to temperature. Doubling the COD load in bulrush treatments increased sulfate removal by only 20-30% when averaged over all seasons and did not alter the basic pattern of seasonal variation, despite tempering the wintertime increase in redox potential. Seasonal and treatment effects on zinc removal were broadly consistent with sulfate removal and presumably reflected zinc-sulfide precipitation. Results strongly suggest that interactive effects of COD loading rate, temperature, season, and plant species control not only sulfate reduction and zinc sequestration, but also the balance of competition between various microbial consortia responsible for water treatment in constructed wetlands.

Untreated sewage has been released from McMurdo Station, Antarctica, into McMurdo Sound for several years. In this study organic carbon degradation was compared in seawater from McMurdo Sound at −1.8°C and 20°C using the BOD test. The ultimate BOD was 3 times larger at 20°C than at −1.8°C following 25 days of incubation. On the basis of on these findings, sewage from McMurdo Station, Antarctica, should receive at least secondary treatment before release to lessen the impact of anthropogenic organic carbon on the polar marine environment of McMurdo Sound.

The influence of chlorine on biofilm in low organic carbon environments typical of drinking water or industrial process water was examined by comparing biomass and kinetic parameters for biofilm growth in a chlorinated reactor to those in a non-chlorinated control. Mixed-population heterotrophic biofilms were developed in rotating annular reactors under low concentration, carbon-limited conditions (< 2 mg/L as carbon) using three substrate groups (amino acids, carbohydrates and humic substances). Reactors were operated in parallel under identical conditions with the exception that chlorine was added to one reactor at a dose sufficient to maintain a free chlorine residual of 0.09-0.15 mg/L in the effluent. The presence of free chlorine resulted in development of less biofilm biomass compared to the control for all substrates investigated. However, specific growth and organic carbon removal rates were on the average five times greater for chlorinated biofilm compared to the control. Observed yield values were less for chlorinated biofilm. Although chlorinated biofilm's specific organic carbon removal rate was high, the low observed yield indicated organic carbon was being utilized for purposes other than creating new cell biomass. The impacts of free chlorine on mixed-population biofilms in low-nutrient environments were different depending upon the available substrate. Biofilms grown using amino acids exhibited the least difference between control and chlorinated kinetic parameters; biofilm grown using carbohydrates had the greatest differences. These findings are particularly relevant to the fundamental kinetic parameters used in models of biofilm growth in piping systems that distribute chlorinated, low-carbon-concentration water.

Physiological stress associated with toluene exposure in batch cultures of Pseudomonas putida 54G was investigated. P. putida 54G cells were grown using a continuous vapor phase feed stream containing 150 ppmv or 750 ppmv toluene as the sole carbon and energy source. Cells were enumerated on non-selective (R2A agar plates) and a selective minimal medium incubated in the presence of vapor phase toluene (HCMM2). Differential recovery on the two media was used to evaluate bacterial stress, culturability and loss of toluene-degrading capability. A majority of the bacteria were reversibly stressed and could resume active colony formation on selective medium after passage on non-selective medium. A small fraction of the bacterial cells suffered an irreversible loss of toluene degradation capability and were designated as Tol− variants. Numbers of stressed organisms increased with duration of toluene exposure and toluene concentration and coincided with accumulation of metabolic intermediates from incomplete toluene degradation. Respiring cell numbers in the batch cultures decreased as injury increased, indicating a possible relationship between respiring and injured cells. Rate expressions for injury, for formation of Tol− variants and for growth of Tol− variants were determined by calibrating a theoretical model to the results obtained. These rate expressions can be used to calibrate bioreactor models, and provide a basis for better design and control of bioremediation systems.

The paper describes the toluene degradation process in a flat plate vapor phase bioreactor (VPBR) by a Pseudomonas putida 54G biofilm. Oxygen microelectrodes were used to measure oxygen concentration profiles through the gas, liquid, and biofilm phases. The linear shape of the dissolved oxygen concentration profile in the outer 87% of the biofilm thickness suggested an absence of reaction in this layer. Oxygen consumption in the remaining basal 13 % (0.3 mm) followed zero order kinetics with a rate constant of 102.2 g m−3 h−1, for toluene gas concentration of 1.5 g m−3. The increase in respiratory activity near the substratum was confirmed by microscopic study of cryogenic biofilm sections, and the lack of activity in the surface film was interpreted as a consequence of injury exerted by the toxic substrate. The accumulation of dead cells on the top of the biofilm contributed a resistance to the transport of substrates to deeper layers of the biofilm suggesting a protective role of the outer layer against the harmful effect of the toxic. These results highlight a new conceptual biofilm model in which both microbial growth and inactivation are controlled by substrate transport, leading to a structure that itself controls substrate availability.

The effects of prolonged toluene exposure and degradation on bacterial cultures of Pseudomonas putida 54G were investigated in three reactor systems: a batch suspended culture system, a bench-scale flat plate biofilm reactor, and a bench-scale packed column reactor. Humidified air containing 150 ppmv (toluene limiting) to 750 ppmv (oxygen limiting) toluene vapor was the sole source of carbon and energy supplied to these systems. Results from the suspended batch culture experiments were used to develop rate expressions and kinetic parameters for loss of culturability and of toluene degradative capacity. Experiments in the flat plate reactor were carried out to examine the effects of injury on biofilm structure and function. The packed column studies were performed under conditions relevant to field application, and confirmed results from the other two studies - that decreased culturability on toluene media correlated with decreased specific toluene degradation rate, particularly at higher toluene concentration.

The documented release of carbon fines from granular activated carbon filters is a concern for drinking water utilities, since these particles may carry coliform and even pathogenic bacteria through the disinfection barrier. Such a breakthrough could have an impact on distribution system biofilms. Using total cell counts, specific monoclonal antibody staining, and computerized image analysis, we monitored the colonization of introduced Klebsiella pneumoniae associated with carbon fines in mixed-population biofilms. The particles transported the coliforms to the biofilms and allowed successful colonization. Chlorine (0.5 mg/liter) was then applied as a disinfectant. Most K. pneumoniae along with the carbon fines left the biofilm under these conditions. The impact of chlorine was greater on the coliform bacteria and carbon fines than on the general fixed bacterial population. However, 10% of the introduced coliforms and 20% of the fines remained in the biofilm. The possibility that this represents a mechanism for bacteria of public health concern to be involved in regrowth events is discussed.

Laboratory reactors operated under oligotrophic conditions were used to evaluate the importance of initial growth rate and substratum composition on the long-term persistence of coliforms in mixed-population biofilms. The inoculum growth rate had a dramatic effect on the ability of coliforms to remain on surfaces. The most slowly grown coliforms (mu = 0.05/h) survived at the highest cell concentration. Antibody staining revealed that Klebsiella pneumoniae existed primarily as discrete microcolonies on the surface. Both coliforms and heterotrophic plate count bacteria were supported in larger numbers on a reactive substratum, mild steel, than on polycarbonate.

Three strains of Pseudomonas fluorescens with different motility rates and adsorption rate coefficients were injected into porous-medium reactors packed with l-mm-diameter glass spheres. Cell breakthrough, time to peak concentration, tailing, and cell recovery were measured at three interstitial pore velocities (higher than, lower than, and much lower than the maximal bacterial motility rate). All experiments were done with distilled water to reduce the effects of growth and chemotaxis. Contrary to expectations, motility did not result in either early breakthrough or early time to peak concentration at flow velocities below the motility rate. Bacterial size exclusion effects were shown to affect breakthrough curve shape at the very low flow velocity, but no such effect was seen at the higher flow velocity. The tendency of bacteria to adsorb to porous-medium surfaces, as measured by adsorption rate coefficients, profoundly influenced transport characteristics. Cell recoveries were shown to be correlated with the ratio of advective to adsorptive transport in the reactors. Adsorption rate coefficients were found to be better predictors of microbial transport phenomena than individual characteristics, such as size, motility, or porous-medium hydrodynamics.

The processes leading to bacterial colonization on solid-water interfaces are adsorption, desorption, growth, and erosion. These processes have been measured individually in situ in a flowing system in real time using image analysis. Four different substrata (copper, silicon, 316 stainless-steel and glass) and 2 different bacterial species (Pseudomonas aeruginosa and Pseudomonas fluorescens) were used in the experiments. The flow was laminar (Re = 1.4) and the shear stress was kept constant during all experiments at 0.75 N m(-2). The surface roughness varied among the substrata from 0.002 microm (for silicon) to 0.015 microm (for copper). Surface free energies varied from 25.1 dynes cm(-1) for silicon to 31.2 dynes cm(-1) for copper. Cell curface hydrophobicity, reported as hydrocarbon partitioning values, ranged from 0.67 for Ps. fluorescens to 0.97 for Ps. aeruginosa.The adsorption rate coefficient varied by as much as a factor of 10 among the combinations of bacterial strain and substratum material, and was positively correlated with surface free energy, the surface roughness of the substratum, and the hydrophobicity of the cells. The probability of desorption decreased with increasing surface free energy and surface roughness of the substratum. Cell growth was inhibited on copper, but replication of cells overlying an initial cell layer was observed with increased exposure time to the cell-containing bulk water. A mathematical model describing cell accumulation on a substratum is presented.

The growth of environmental and clinical coliform bacteria under conditions typical of drinking water distribution systems was examined. Four coliforms (Klebsiella pneumoniae, Escherichia coli, Enterobacter aerogenes, and Enterobacter cloacae) were isolated from an operating drinking water system for study; an enterotoxigenic E. coli strain and clinical isolates of K. pneumoniae and E. coli were also used. All but one of the coliforms tested were capable of growth in unsupplemented mineral salts medium; the environmental isolates had greater specific growth rates than did the clinical isolates. This trend was maintained when the organisms were grown with low levels (less than 1 mg liter-1) of yeast extract. The environmental K. pneumoniae isolate had a greater yield, higher specific growth rates, and a lower Ks value than the other organisms. The environmental E. coli and the enterotoxigenic E. coli strains had comparable yield, growth rate, and Ks values to those of the environmental K. pneumoniae strain, and all three showed significantly more successful growth than the clinical isolates. The environmental coliforms also grew well at low temperatures on low concentrations of yeast extract. Unsupplemented distribution water from the collaborating utility supported the growth of the environmental isolates. Growth of the K. pneumoniae water isolate was stimulated by the addition of autoclaved biofilm but not by tubercle material. These findings indicate that growth of environmental coliforms is possible under the conditions found in operating municipal drinking water systems and that these bacteria could be used in tests to determine assimilable organic carbon in potable water.

The test of an individual's growth is his capacity to relate effectively and intimately to significant others. A challenge in adult life is to achieve a marriage that contains creative communication. It is necessary for an individual to be intact as a person in order for him to develop a capacity to relate empathically and knowingly with a mate. If this relating is mutual, a synergism of gratifying stimulation to each is the outcome. The psychiatrist's activity in conjoint therapy is to facilitate empathic communication and to assist with the working through of regressive, defensive investments within the marital relationship.

The author has found analytic group therapy of married couples to be a useful treatment technique. The couples discover themselves in each other and are challenged to the task of breaking the defensive tyranny of their neurotic relationships. Techniques and specific stages of progress are described.

THE RELATIONSHIP between accidental and suicidal death presents an insufficiently studied but fascinating problem. A good deal of research has been accomplished into suicidal modes and suicidal deaths, and there has been a moderate amount of writing and research on nonlethal accidents. However, up to this time there has been relatively little research done on psychological aspects of accidental death. Yet, the questions of how accidental deaths occur and how, if in any ways, these deaths relate to suicidal ones are, indeed, intriguing issues. To be sure, one opinion exists to the effect that accidents should be regarded as entirely "accidental"—that is, that in any given accident we are merely noting what must happen on occasion as a result of the unpredictable interplay of a number of forces. However, this point of view would not be entirely acceptable to observers of social situations who would wish to study the

(1968). The Technique and Practice of Psychoanalysis, Volume I by Ralph R. Greenson. International Journal of Group Psychotherapy: Vol. 18, No. 1, pp. 115-116.