Craig Criddle - Academia.edu (original) (raw)

Papers by Craig Criddle

trichloroethylene. community structure and cometabolism of Effects of phenol feeding pattern on m... more trichloroethylene. community structure and cometabolism of Effects of phenol feeding pattern on microbial

Author(s): Wu, L.Y.; Huang, Z.J.; Gentry, T.J.; Wu, W-M; Nostrand, J.D. Van; Schadt, C.W.; Watson... more Author(s): Wu, L.Y.; Huang, Z.J.; Gentry, T.J.; Wu, W-M; Nostrand, J.D. Van; Schadt, C.W.; Watson, D.; He, Z.; Criddle, C. S.; Tiedje, J.; Hazen, T.C.; Zhou, J.; Matthew, F.W. | Abstract: A pilot-scale system was established to examine the feasibility of in situ bioremediation and immobilization of U(VI) at a highly contaminated aquifer at the U. S. DOE's Field Research Center, Oak Ridge, TN. An above-ground treatment system, including a denitrifying fluidized bed reactor, was used to pre-condition the groundwater to optimize subsurface U immobilization. Ethanol to stimulate microbial reduction of soluble U(VI) to insoluble U(IV). Three monitoring wells (FW101-2, 102-2, and 102-3) were analyzed using a functional gene array containing g24,000 probes covering 10,000 genes to examine the effect of geochemistry on the functional microbial community dynamics. Microarray results indicate that, during the U (VI) reduction period, both FeRB and SRB populations reached their highest lev...

Applied and Environmental Microbiology, 1996

Cometabolism of trichloroethylene (TCE) by phenol-fed enrichments was evaluated in four reactors ... more Cometabolism of trichloroethylene (TCE) by phenol-fed enrichments was evaluated in four reactors with distinct phenol feeding patterns. The reactors were inoculated from the same source, operated at the same average dilution rate, and received the same mass of phenol over time. Only the timing of phenol addition differed. Reactor C received phenol continuously; reactor SC5 received phenol semicontinuously--alternating between 5 h of feed and 3 h without feed; reactor SC2 alternated between 2 h of feed and 6 h without feed; and reactor P received a single pulse every 24 h. The structure of the enrichments and their capacity for TCE transformation were analyzed. In long-term operation, reactors C and SC5 were dominated by fungi, had higher levels of predators, were more susceptible to biomass fluctuations, and exhibited reduced capacity for TCE transformation. Reactors P and SC2 were characterized by lower levels of fungi, higher bacterial biomass, higher concentrations of TCE-degradi...

Environmental Science: Processes & Impacts, 2020

Prior to the 1960s, knowledge of biological transformations of highly halogenated aliphatic compo... more Prior to the 1960s, knowledge of biological transformations of highly halogenated aliphatic compounds was limited, except in mammalian organisms where enzymatic transformations occurred to rid the body of ingested harmful chemicals.

Applied and Environmental Microbiology, 1995

Previous research has established that Pseudomonas sp. strain KC rapidly transforms carbon tetrac... more Previous research has established that Pseudomonas sp. strain KC rapidly transforms carbon tetrachloride (CT) to carbon dioxide (45 to 55%), a nonvolatile fraction (45 to 55%), and a cell-associated fraction ((equiv)5%) under denitrifying, iron-limited conditions. The present study provides additional characterization of the nonvolatile fraction, demonstrates that electron transfer plays a role in the transformation, and establishes the importance of both extracellular and intracellular factors. Experiments with (sup14)C-labeled CT indicate that more than one nonvolatile product is produced during CT transformation by strain KC. One of these products, accounting for about 20% of the [(sup14)C]CT transformed, was identified as formate on the basis of its elution time from an ion-exchange column, its boiling point, and its conversion to (sup14)CO(inf2) when incubated with formate dehydrogenase. Production of formate requires transfer of two electrons to the CT molecule. The role of el...

Applied and Environmental Microbiology, 1993

Under denitrifying conditions, Pseudomonas sp. strain KC transforms carbon tetrachloride (CT) to ... more Under denitrifying conditions, Pseudomonas sp. strain KC transforms carbon tetrachloride (CT) to carbon dioxide via a complex but as yet undetermined mechanism. Transformation rates were first order with respect to CT concentration over the CT concentration range examined (0 to 100 micrograms/liter) and proportional to protein concentration, giving pseudo-second-order kinetics overall. Addition of ferric iron (1 to 20 microM) to an actively transforming culture inhibited CT transformation, and the degree of inhibition increased with increasing iron concentration. By removing iron from the trace metals solution or by removing iron-containing precipitate from the growth medium, higher second-order rate coefficients were obtained. Copper also plays a role in CT transformation. Copper was toxic at neutral pH. By adjusting the medium pH to 8.2, soluble iron and copper levels decreased as a precipitate formed, and CT transformation rates increased. However, cultures grown at high pH witho...

IOP Conference Series: Earth and Environmental Science, 2018

Petroleum-based plastic pollution has been a global environmental concern for decades. The obviou... more Petroleum-based plastic pollution has been a global environmental concern for decades. The obvious contrast between the remarkable durability of the plastics and their short service time leads to the increasing accumulation of plastic wastes in the environment. A costeffective, sustainable strategy to solve the problem should focus on source control and clean up. Polystyrene (PS) wastes, a recalcitrant plastic polymer, are among the wide spread man-made plastic pollutants. Destruction of PS wastes can be achieved using various abiotic methods such as incineration but such methods release potential air pollution and generation of hazardous by-products. Biodegradation and bioremediation has been proposed for years. Since the 1970's, the microbial biodegradation of plastics, including PS, has been evaluated with mixed and isolated cultures from different sources such as activated sludge, trash, soil, and manure. To date, PS biodegradation by these microbial cultures is still quite slow. Recently, the larvae of yellow mealworms (Tenebrio molitor Linnaeus) have demonstrated promising PS biodegradation performance. Mealworms have demonstrated the ability to chew and ingest PS foam as food and are capable of degrading and mineralizing PS into CO 2 via microbedependent activities within the gut in less than the 12-15 hrs gut retention time. These research results have revealed a potential for microbial biodegradation and bioremediation of plastic pollutants.

Advances in Water and Wastewater Treatment Technology, 2001

Our ability to incorporate data that is obtained by using high throughput molecular techniques su... more Our ability to incorporate data that is obtained by using high throughput molecular techniques such as DNA based community fingerprinting, whole genome expression analysis, and protein spectrum analysis, into mathematical models is extremely limited. These techniques generate thousands of data points but only few and the most obvious relationships can be established, often only qualitatively. For the information to be useful for the control and management of a biological system, we must be able to quantify and establish the underlying relationships between community structure and function, preferably by mathematical tools. Currently, such mathematical tools do not exist since the underlying relationships between molecular data and function are too complex to be formulated. It is expected that approaches such as artificial _neural networks (ANN) that do not require a priori knowledge of such relationships may be able to fill this gap. This study presents data on the application of ANN to link the function and community structure of two quadruplicate sets of laboratory-scale methanogenic microbial communities under shock load conditions. The community structure was characterized using terminal restriction fragment length polymorphisms, amplified ribosomal DNA restriction analysis, sequencing, and phase contrast and fluorescent microscopic techniques with image analysis. The results of this study indicate that ANN is a powerful tool to establish links between function and community structure provided sufficient data sets are available for training and testing of the network. In addition, it may also be useful to identify important microbial populations that correspond to various functions, which is not generally possible by other means. The limitations of neural networks to analyze data pertaining to complex microbial systems is also elucidated.

Proceedings of the National Academy of Sciences, 2013

Significance This work introduces a microbial battery for recovery of energy from reservoirs of o... more Significance This work introduces a microbial battery for recovery of energy from reservoirs of organic matter, such as wastewater. Microorganisms at an anode oxidize dissolved organic substances, releasing electrons to an external circuit, where power can be extracted. The electrons then enter a solid-state electrode that remains solid as electrons accumulate within it. The solid-state electrode is periodically removed from the battery, oxidized, and reinstalled for sustained power production. Molecular oxygen is not introduced into the battery, and ion-exchange membranes are avoided, enabling high efficiencies of energy recovery.

Microbial Ecology, 2006

This study evaluates changes in the microbial community structure and function of a pilot-scale d... more This study evaluates changes in the microbial community structure and function of a pilot-scale denitrifying fluidized bed reactor during periods of constant operating conditions and periods of perturbation. The perturbations consisted of a shutdown period without feed, two disturbances in which biofilms were mechanically sheared from carrier particles, and a twofold step increase in feed nitrate concentration. In the absence of perturbations, nitrate removal was stable and consistently greater than 99%. The structure and dynamics of the microbial community were studied using cloning and sequencing techniques and terminal restriction fragment length polymorphism (T-RFLP) of the SSU rRNA gene. Under unperturbed operating conditions, stable function was accompanied by high constancy and low variability of community structure with the majority of terminal restriction fragments (T-RFs) appearing throughout operation at consistent relative abundances. Several of the consistently present T-RFs correlated with clone sequences closely related to Acidovorax (98% similarity), Dechloromonas (99% similarity), and Zoogloea (98% similarity), genera recently identified by molecular analyses of similar systems. Significant changes in community structure and function were not observed after the shutdown period. In contrast, following the increase in loading rate and the mechanical disturbances, new T-RFs appeared. After both mechanical disturbances, function and community structure recovered. However, function was much more resilient than community structure. The similarity of response to the mechanical disturbances despite differences in community structure and operating conditions suggests that flexible community structure and potentially the activity of minor members under nonperturbation conditions promotes system recovery.

Journal of Contaminant Hydrology, 2010

Flow-interruption tracer test is an effective approach to identify kinetic mass transfer processe... more Flow-interruption tracer test is an effective approach to identify kinetic mass transfer processes for solute transport in subsurface media. By switching well pumping and resting, one may alter the dominant transport mechanism and generate special concentration patterns for identifying kinetic mass transfer processes. In the present research, we conducted three-phase (i.e., pumping, resting, and pumping) field-scale flow-interruption tracer tests using a conservative tracer bromide in a multiple-well system installed at the US Department of Energy Site, Oak Ridge, TN. A novel modeling approach based on the resting-period measurements was developed to estimate the mass transfer parameters. This approach completely relied on the measured breakthrough curves without requiring detailed aquifer characterization and solving transport equations in nonuniform, transient flow fields. Additional measurements, including hydraulic heads and tracer concentrations in large pumping wells, were taken to justify the assumption that mass transfer processes dominated concentration change during resting periods. The developed approach can be conveniently applied to any linear mass transfer model. Both first-order and multirate mass transfer models were applied to analyze the breakthrough curves at various monitoring wells. The multirate mass transfer model was capable of jointly fitting breakthrough curve behavior, showing the effectiveness and flexibility for incorporating aquifer heterogeneity and scale effects in upscaling effective mass transfer models.

Journal of Contaminant Hydrology, 2008

A travel-time based approach is developed for estimating first-order reaction rate coefficients f... more A travel-time based approach is developed for estimating first-order reaction rate coefficients for transport with nonequilibrium linear mass transfer in heterogeneous media. Tracer transport in the mobile domain is characterized by a travel-time distribution, and mass transfer rates are described by a convolution product of concentrations in the mobile domain and a memory function rather than predefining the mass transfer model. A constant first-order reaction is assumed to occur only in the mobile domain. Analytical solutions in Laplace domain can be derived for both conservative and reactive breakthrough curves (BTCs). Temporal-moment analyses are presented by using the first and second moments of conservative and reactive BTCs and the mass consumption of the reactant for an inverse Gaussian travel-time distribution. In terms of moment matching, there is no need for one to specify the mass transfer model. With the same capacity ratio and the mean retention time, all mass transfer models will lead to the same moment-derived reaction rate coefficients. In addition, the consideration of mass transfer generally yields larger estimations of the reaction rate coefficient than models ignoring mass transfer. Furthermore, the capacity ratio and the mean retention time have opposite influences on the estimation of the reaction rate coefficient: the first-order reaction rate coefficient is positively linearly proportional to the capacity ratio, but negatively linearly proportional to the mean retention time.

Ground Water, 2011

A generalized, efficient, and practical approach based on the travel-time modeling framework is d... more A generalized, efficient, and practical approach based on the travel-time modeling framework is developed to estimate in situ reaction rate coefficients for groundwater remediation in heterogeneous aquifers. The required information for this approach can be obtained by conducting tracer tests with injection of a mixture of conservative and reactive tracers and measurements of both breakthrough curves (BTCs). The conservative BTC is used to infer the travel-time distribution from the injection point to the observation point. For advection-dominant reactive transport with well-mixed reactive species and a constant travel-time distribution, the reactive BTC is obtained by integrating the solutions to advective-reactive transport over the entire travel-time distribution, and then is used in optimization to determine the in situ reaction rate coefficients. By directly working on the conservative and reactive BTCs, this approach avoids costly aquifer characterization and improves the estimation for transport in heterogeneous aquifers which may not be sufficiently described by traditional mechanistic transport models with constant transport parameters. Simplified schemes are proposed for reactive transport with zero-, first-, nthorder, and Michaelis-Menten reactions. The proposed approach is validated by a reactive transport case in a two-dimensional synthetic heterogeneous aquifer and a field-scale bioremediation experiment conducted at Oak Ridge, Tennessee. The field application indicates that ethanol degradation for U(VI)-bioremediation is better approximated by zero-order reaction kinetics than first-order reaction kinetics.

Ground Water, 2000

This paper describes the design and hydraulic characterization of a cost-effective biocurtain tha... more This paper describes the design and hydraulic characterization of a cost-effective biocurtain that is currently being used to remove carbon tetrachloride from an aquifer in Schoolcraft, Michigan. Novel aspects of the design are the use of closely spaced wells to recirculate solutes through a biocurtain, well screens spanning the vertical extent of contamination, and a semipassive mode of operation, with only six hours of low-level pumping per week. This design was developed by coupling flow and transport simulations with a cost optimization algorithm, based on initial hydraulic conductivity data and system design constraints from a previous pilot-scale experiment adjacent to the current site. The hydraulic conductivity of the site was characterized using permeameter analysis on more than 200 samples from continuous well cores that were collected during well installation. The subset of available conductivity data was used to predict tracer transport through the biocurtain during system operation. Observed tracer concentration arrival histories during initial system operation confirmed model predictions. Modeling also established that closely spaced wells operated for brief periods each week could effectively deliver the agents needed for remediation across the biocurtain. This was confirmed during long-term operation of the system, which has resulted in highly efficient contamination degradation. The delivery well design methodology is expected to be broadly applicable at other sites where flow can be recirculated between a series of delivery wells.

Environmental Science & Technology, 2006

Few studies have demonstrated changes in community structure along a contaminant plume in terms o... more Few studies have demonstrated changes in community structure along a contaminant plume in terms of phylogenetic, functional, and geochemical changes, and such studies are essential to understand how a microbial ecosystem responds to perturbations. Clonal libraries of multiple genes (SSU rDNA, nirK, nirS, amoA, pmoA, and dsrAB) were analyzed from groundwater samples (n) 6) that varied in contaminant levels, and 107 geochemical parameters were measured. Principal components analyses (PCA) were used to compare the relationships among the sites with respect to the biomarker (n) 785 for all sequences) distributions and the geochemical variables. A major portion of the geochemical variance measured among the samples could be accounted for by tetrachloroethene, 99 Tc, NO 3 , SO 4 , Al, and Th. The PCA based on the distribution of unique biomarkers resulted in different groupings compared to the geochemical analysis, but when the SSU rRNA gene libraries were directly compared (∆C xy values) the sites were clustered in a similar fashion compared to geochemical measures. The PCA based upon functional gene distributions each predicted different relationships among the sites, and comparisons of Euclidean distances based upon diversity indices for all functional genes (n) 432) grouped the sites by extreme or intermediate contaminant levels. The data suggested that the sites with low and high perturbations were functionally more similar than sites with intermediate conditions, and perhaps captured the overall community structure better than a single phylogenetic biomarker. Moreover, even though the background site was phylogenetically and geochemically distinct from the acidic sites, the extreme conditions of the acidic samples might be more analogous to the limiting nutrient conditions of the background site. An understanding of microbial community-level responses within an ecological framework would provide better insight for restoration strategies at contaminated field sites.

Environmental Science & Technology, 1987

Bansformations of halwenated aliphatic cornpun& oxidation. r e d d o n , substitulion, and akhydr... more Bansformations of halwenated aliphatic cornpun& oxidation. r e d d o n , substitulion, and akhydrohalogerdon reactions occur abwtidly or in m i d i a l and mammalian systems otic and biotic chemistry of halogenated aliphatic compounds. Knowledge of cxmcqld tiamavo& for understand-abiotic aansformatloos ' canprovidea tiolls. Mast abiotic transformations are slow, but t&ey urn stiU be significaa withinthetimescalescommonly associated with groundwater m o v m. In contrast, biotic transformations typid y proceed much faster, provided that there are sufficient substrate and nutrients and a microbial poprlation that canldiate SUChtransformations. Recent studies, which describe transformations of halogenated aliphatic canpounds in mi&i and lIwnmal i a n s y m , are akodiscussedinthis systemingeneral. ing bidogicalhl mediated t r a n s f~marticle. These studies reveal broad patterns of transformalion in biological All three systems (abiotic, mammalian, and microbial) have similarities in r r-TABLE 1 Production, proposed maximum contaminant levels, ratings of comnlon halogenated aliphatic compounda Compound Trihalomethanes Vinyl chloride 1 .l-Dichlorcethylene trans-I ,2-Dichloroethylene Trichloroethylene Tetrachloroethylene 1,l-Dichloroethane 1.2-Dichloroethane 1 ,1, 1-Trichloroelhane 1 ,BDibromoelhane .Reference 4. 'Maximum mntaminenl level. Reference 5. <Carcinogenicity: 1 = chemical is carcinr^^^'^' chemical cannot be classified. bReference 6. reaction mechanism and transforma-I ences. For each, the transformation of halogenated aliphatic compounds can that q* ~~~~yydrohalogenation-elimina-lonizatbn potential-thi dil-fer (oxidations and reductions) and tion of HX to form an alkene, ence between the energy of ultra Dlhalo-elimination-reductive let radiation used to bombard a mc+ those that do not (substitutions and deh y~' % e M t i m)~ External elimination of two halide substi-ecule and the energy of the ejected transfer i s as the transfer Of tuents to form an alkene. electron. e1-m to and from some agent other Electwhi16e reacting specie Yonooxygenase-an enzyme than the that accepts an electron pair. that catalyzes reactions in which one Eiiiinatlon-a reaction in which atom of O2 appears in the product Processesin this article and terms that frequently appear = detwo groups, such as hydrogen and and the other in H a. f i in the side E-1-Of trans-Nudeophila-a reacting specie chlorine, are lost from adjacent car-f0nnatiOm are listed in Figure 1. COmbon atoms so that a double bond is that brings an electron pair. mon abbreviations for the various Sohrolysls-a reaction in which for&. halogenated aliphatic Compounds are Epoxldation-a reaction in which the solvent serves as the nulisted in Table 2. an epoxide is generated. cleophiie. Substitutiin-a reaction in wh ~ ~ Hydro@%noly&i-a reduction in substitution which a carbon-halogen bond is one substituent on a molecule is Halogenated aliphatic compounds ken and hydrogen replaces the placed by an0t'-undergo substitution and dehydmhalo-PERMISSUN m USE PICMAN WAS GIVEN BY A T A R I GAMES. tion products. They also have differbe divided into classes: re-Definitions of terms Coupling-a reaction in which halogensubstituent. Hydroxylation-addition alkyl or aryl groups connect tcdroxyl gmP. ' systems (Table 4) (22-29). Glutathione reacts with halogenafur-containing compounds. Under turic acids (28). Some chlorinated alkanes are transformed into alcohols in 724 Envimn. Sei. TBchnol., W. 21. No. 8. Igs7 strength may inrrease the L i l i o o d of creased stability of charged imermedicompounds more readily than is chloted aliphatic compounds to produce sulproper conditions, these compounds are further trrmsformed into mercap

Energy Environ. Sci., 2013

A new process for the removal of nitrogen from wastewater is introduced. The process involves thr... more A new process for the removal of nitrogen from wastewater is introduced. The process involves three steps: (1) partial nitrification of NH 4 + to NO 2 À ; (2) partial anoxic reduction of NO 2 À to N 2 O; and (3) N 2 O conversion to N 2 with energy recovery by either catalytic decomposition to N 2 and O 2 or use of N 2 O to oxidize biogas CH 4. Steps 1 and 3 have been previously established at full-scale. Accordingly, bench-scale experiments focused on step 2. Two strategies were evaluated and found to be effective: in the first, Fe(II) was used to abiotically reduce NO 2 À to N 2 O; in the second, COD stored as polyhydroxybutyrate (PHB) was used as the electron donor for partial heterotrophic reduction of NO 2 À to N 2 O. For abiotic reduction with Fe(II), the efficiency of conversion of NO 2 À to N 2 O was over 90% with 98% nitrogen removal from water. For partial heterotrophic denitrification, different selection conditions were imposed on acetate-and nitrite-fed communities initially derived from waste activated sludge. No N 2 O was detected when acetate and nitrite were supplied continuously, but N 2 O was produced when acetate and nitrite were added as pulses. N 2 O conversion efficiency was dependent upon the method of addition of acetate and nitrite. When acetate and nitrite were added together (coupled feeding), the N 2 O conversion efficiency was 9-12%, but when acetate and nitrite additions were decoupled, the N 2 O conversion efficiency was 60-65%. Decoupled substrate addition selected for a microbial community that accumulated polyhydroxybutyrate (PHB) during an anaerobic period after acetate addition then consumed PHB and reduced NO 2 À during the subsequent anoxic period. The biological N removal efficiency from the water was 98% over more than 200 cycles. This indicates that decoupled operation can sustain significant long-term N 2 O production. Compared to conventional nitrogen removal, the three-step process, referred to here as Coupled Aerobic-anoxic Nitrous Decomposition Operation (CANDO), is expected to decrease oxygen requirements, decrease biomass production, increase organic matter available for recovery as biogas methane, and enable energy recovery from nitrogen, but pilot-scale studies are needed. Broader context The release of reactive forms of nitrogen is a major environmental threat causing hypoxia and eutrophic zones in water bodies. Globally, rising energy costs and increasingly stringent discharge regulation are major drivers for efficient wastewater treatment processes that lower costs and increase recoverable energy from waste. While many processes recover energy from carbon waste as CH 4 , none recovers energy from waste nitrogen. This work introduces a new wastewater treatment process that removes and recovers energy from nitrogen waste by exploiting the thermodynamic properties of N 2 O for energy recovery. The proposed process, referred to here as Coupled Aerobic-anoxic Nitrous Decomposition Operation (CANDO), involves three steps: (1) partial aerobic nitrication of NH 4 + to NO 2 À , (2) partial anoxic denitrication of NO 2 À to N 2 O, and (3) N 2 O conversion to N 2 with energy recovery via catalytic decomposition of N 2 O or use of N 2 O as an oxidant in CH 4 combustion. If successfully scaled-up, this process has the potential to lower aeration and biosolid production (the two major operational costs), increase CH 4 recovery from "freed" organic matter, and introduces a new renewable energy source from CH 4 combustion with N 2 O.

Biotechnology and Bioengineering, 1995

Liquid film and diffusional resistances of brewery granules during acetate, propionate, and ethan... more Liquid film and diffusional resistances of brewery granules during acetate, propionate, and ethanol utilization were investigated. Substrate utilization rate increased with decreased granule size. Effectiveness factors for acetate, propionate, and ethanol were calculated by comparing the maximum rates of substrate utilization of whole granules (1.8 to 3.0 mm) and fine flocs (20 to 75 mum) derived by disrupting whole granules. For acetate, propionate, and ethanol, maximum specific substrate utilization rates (k(m') g/g VS . d) for the flocs, were 5.11, 6.25, and 5.49, respectively, and half-velocity coefficients (K(g') mM) were 0.45, 0.40, and 3.37, respectively. Calculated effectiveness factors were 0.32, 0.41, and 0.75 for acetate, propionate, and ethanol, respectively. The effect of temperature on substrate utilization was examined at 26 degrees C, 31 degrees C, and 37 degrees C using acetate as sole carbon source. Utilization rates increased with temperature. Flocs were most sensitive to temperature, and whole granules were least affected. The behavior of flocs was well described by the Van't Hoff-Arrhenius equation. Effectiveness factors for acetate utilization by the granules were 0.36, 0.35, and 0.32 at 26 degrees C, 31 degrees C, and 37 degrees C, respectively, indicating little effect of temperature. Based on these results, we conclude that both liquid film and diffusional resistances influenced the rate of substrate utilization in a UASB reactor with granular sludge. Temperature effects were much less important than diffusional limitations within the granules. (c) 1995 John Wiley & Sons, Inc.

Biotechnology and Bioengineering, 1997

A model for cometabolism is verified experimentally for a defined methanotrophic mixed culture. T... more A model for cometabolism is verified experimentally for a defined methanotrophic mixed culture. The model includes the effects of cell growth, endogenous cell decay, product toxicity, and competitive inhibition with the assumption that cometabolic transformation rates are enhanced by reducing power obtained from oxidation of growth substrates. A theoretical transformation yield is used to quantify the enhancement resulting from growth substrate oxidation. A systematic method for evaluating model parameters independently is described. The applicability of the model is evaluated by comparing experimental data for methanotrophic cometabolism of TCE with model predictions from independently measured model parameters. Propagation of errors is used to quantify errors in parameter estimates and in the final prediction. The model successfully predicts TCE transformation and methane utilization for a wide range of concentrations of TCE (0.5 to 9 mg/L) and methane (0.05 to 6 mg/L).

Biotechnology and Bioengineering, 1993

Experimental observations indicate that the rates of cometabolic transformation are linked to the... more Experimental observations indicate that the rates of cometabolic transformation are linked to the consumption of growth substrate during growth and to the consumption of cell mass and/or energy substrate in the absence of growth substrate. Three previously proposed models (models 1 through 3) describing the kinetics of cometabolism by resting cells are compared, and the interrelationships and underlying assumptions for these models are explored. Models 1 to 3 are shown to converge at high concentrations of the nongrowth substrate. An expression describing nongrowth substrate transformation in the presence of growth substrate is proposed, and this expression is integrated with an expression for cell growth to give a single unstructured model (model 4) that encompasses models 1 to 3 and describes cometabolism by both resting and growing cells. Model 4 couples transformation of nongrowth substrate to consumption of growth substrate and biomass, and predicts that cometabolism will result, and decreased specific growth rates for a cometabolizing population. Competitive inhibition can also be incorporated in the model. Experimental aspects of model calibration and verification are discussed. The need for models that distinguish between the exhaustion of cell activity and cell death is emphasized.