Biomedical subjects

B E Rittmann

Publications and source records attributed to B E Rittmann.

At least 19 recordsLinked to original sources

PubMed2006

The membrane biofilm reactor: the natural partnership of membranes and biofilm.

Many exciting new technologies for water-quality control combine microbiological processes with adsorption, advanced oxidation, a membrane or an electrode to improve performance, address emerging contaminants or capture renewable energy. An excellent example is the H2-based membrane biofilm reactor (MBfR), which delivers H2 gas to a biofilm that naturally accumulates on the outer surface of a bubbleless membrane. Autotrophic bacteria in the biofilm oxidise the H2 and use the electrons to reduce NO3-, CIO4- and other oxidised contaminants. This natural partnership of membranes and biofilm makes it possible to gain many cost, performance and simplicity advantages from using H2 as the electron donor for microbially catalysed reductions. The MBfR has been demonstrated for denitrification in drinking water; reduction of perchlorate in groundwater; reduction of selenate, chromate, trichloroethene and other emerging contaminants; advanced N removal in wastewater treatment and autotrophic total-N removal.

Biofilms↗

PubMed2004

Comparing biofilm models for a single species biofilm system.

A benchmark problem was defined to evaluate the performance of different mathematical biofilm models. The biofilm consisted of heterotrophic bacteria degrading organic substrate and oxygen. Mathematical models tested ranged from simple analytical to multidimensional numerical models. For simple and more or less flat biofilms it was shown that analytical biofilm models provide very similar results compared to more complex numerical solutions. When considering a heterogeneous biofilm morphology it was shown that the effect of an increased external mass transfer resistance was much more significant compared to the effect of an increased surface area inside the biofilm.

Bacteria↗

PubMed2004

Modelling a spatially heterogeneous biofilm and the bulk fluid: selected results from benchmark problem 2 (BM2).

The numerical simulation of mass transfer and conversion in spatially heterogeneous biofilms on the meso-scale requires an accurate description of the hydrodynamics in the biofilm systems and of spatial effects. This leads to systems of three-dimensional nonlinear partial differential equations that are numerically very expensive to solve and to data requirements that are not easy to meet. In this paper several modeling approaches to reduce the physical complexity and, hence, accelerate the computation are compared. They range from a mere reduction of dimensionality by lumping the problem along a secondary flow direction to global mass balances or empirical correlations, at the core of which a one-dimensional boundary value problem must be solved. It is found that even strongly simplified models can describe the qualitative behaviour of the model with regard to variations in the geometrical and hydrodynamic model parameters quite well. In order to obtain also quantitatively reliable results the hydrodynamics must be considered in an appropriate manner.

Bacteria↗

PubMed2004

Results from the multi-species benchmark problem (BM3) using one-dimensional models.

The IWA's Biofilm Modeling Task Group created a multi-species benchmark problem in which heterotrophic bacteria, nitrifying bacteria, and inert biomass coexist in a biofilm. Members of the Task Group submitted solutions from nine different one-dimensional models. The most important distinctions among the models were (1) whether the model required a full numerical solution or was solved with a spreadsheet, and (2) the way the biomass types were distributed in the biofilm. The models that protected the slow-growing species by having them accumulate away from the outer surface always had the largest surface coverage by nitrifiers and inerts, but the heterotroph coverage declined to compensate. Coverage by heterotrophs and removal of substrate COD were most strongly affected by dilution from nitrifiers and inerts near the outer surface. Models that did not allow the nitrifiers and inerts to dilute the heterotrophs significantly in the outer layer predicted more removal of COD than did the other models. The choice of the model to use depends on the user's needs and the relative importance of including protection of slow-growing species and/or dilution of fast-growing species.

Bacteria↗

PubMed2004

Hydrogen-based, hollow-fiber membrane biofilm reactor for reduction of perchlorate and other oxidized contaminants.

Many oxidized pollutants, such as nitrate, perchlorate, bromate, and chlorinated solvents, can be microbially reduced to less toxic or less soluble forms. For drinking water treatment, an electron donor must be added. Hydrogen is an ideal electron donor, as it is non-toxic, inexpensive, and sparsely soluble. We tested a hydrogen-based, hollow-fiber membrane biofilm reactor (MBfR) for reduction of perchlorate, bromate, chlorate, chlorite, chromate, selenate, selenite, and dichloromethane. The influent included 5 mg/L nitrate or 8 mg/L oxygen as a primary electron accepting substrate, plus 1 mg/L of the contaminant. The mixed-culture reactor was operated at a pH of 7 and with a 25 minute hydraulic detention time. High recirculation rates provided completely mixed conditions. The objective was to screen for the reduction of each contaminant. The tests were short-term, without allowing time for the reactor to adapt to the contaminants. Nitrate and oxygen were reduced by over 99 percent for all tests. Removals for the contaminants ranged from a minimum of 29% for chlorate to over 95% for bromate. Results show that the tested contaminants can be removed as secondary substrates in an MBfR, and that the MBfR may be suitable for treating these and other oxidized contaminants in drinking water.

Biofilms↗

PubMed2004

IAL-CHS (internal airlift loop--ceramic honeycomb supports) reactor used for biodegradation of 2,4-dichlorophenol and phenol.

The internal airlift loop reactor with ceramic honeycomb supports (IAL-CHS) was applied for biodegradation of 2,4-dichlorophenol (2,4-DCP) and phenol. A strain of DCP-degrading bacteria isolated from activated sludge, Achromobacter sp., was rapidly immobilized onto the ceramic honeycomb supports. The immobilized cells effectively biodegraded 2,4-DCP alone and together with phenol in batch and continuous-flow experiments. For example, 2,4-DCP was biodegraded from an influent concentration of 50 mg/L to less than 1 mg/L with a 6-h hydraulic retention time (HRT) in continuous flow tests. The immobilized biomass grew and accumulated through 2,4-DCP biodegradation, and the rate of degradation increased accordingly.

Anthelmintics↗

PubMed2003

The trade-offs and effect of carrier size and oxygen-loading on gaseous toluene removal performance of a three-phase circulating-bed biofilm reactor.

We conducted a series of steady-state and short-term experiments on a three-phase circulating-bed biofilm reactor (CBBR) for removing toluene from gas streams. The goal was to investigate the effect of macroporous-carrier size (1-mm cubes versus 4-mm cubes) on CBBR performance over a wide range of oxygen loading. We hypothesized that the smaller biomass accumulation with 1-mm carriers would minimize dissolved-oxygen (DO) limitation and improve toluene removal, particularly when the DO loading is constrained. The CBBR with 1-mm carriers overcame the performance limitation observed with the CBBR with 4-mm carriers: i.e., oxygen depletion inside the biofilm. The 1-mm carriers consistently gave superior removal of toluene and chemical oxygen-demand, and the advantage was greatest for the lowest oxygen loading and the greatest toluene loading. The 1-mm carriers achieved superior performance because they minimized the negative effects of oxygen depletion, while continuing to provide protection from excess biomass detachment and inhibition from toluene.

Air Pollutants↗

PubMed2002

Measuring and modelling VOC biotransformation rates.

A new protocol was used to determine biotransformation rate coefficients for volatile organic compounds in activated sludge systems. The values obtained from the protocol were compared to biotransformation rates obtained from a pilot plant. It was seen that biotransformation rates were easier to obtain from the protocol. Observations also showed that acclimation of the microorganisms to the volatile organic compounds did not change the biotransformation rates. The experimental conditions were then modelled using TOXCHEM+, a mechanistic model to predict volatile organic compound behaviour. The TOXCHEM+ predictions, using system default biotransformation rates, compared favourably with the low biotransformation rates measured by the protocol for bromoform and the chlorinated compounds, while under predicting the biotransformation rates for the non-chlorinated volatile organic compounds.

Biotransformation↗

PubMed2001

Evaluation of the interaction between biodegradation and sorption of phenanthrene in soil-slurry systems.

This work develops and utilizes a non-steady-state model for evaluating the interactions between sorption and biodegradation of hydrophobic organic compounds in soil-slurry systems. The model includes sorption/desorption of a target compound, its utilization by microorganisms as a primary substrate existing in the dissolved phase, and/or the sorbed phase in biomass and soil, oxygen transfer, and oxygen utilization as an electron acceptor. Biodegradation tests with phenanthrene were conducted in liquid and soil-slurry systems. The soil-slurry tests were performed with very different mass transfer rates: fast mass transfer in a flask test at 150 rpm, and slow mass transfer in a roller-bottle test at 2 rpm. The results of liquid tests indicate that biodegradation of the soil-soluble organic fraction did not significantly enhance the biodegradation rate. In the slurry tests, phenanthrene was degraded more rapidly than in liquid tests, but at a similar rate in both slurry systems. Modeling analyses with several hypotheses indicate that a model without biodegradation of compound sorbed to the soil was not able to account for the rapid degradation of phenanthrene, particularly in the roller-bottle slurry test. The model with sorbed-phase biodegradation and the same biokinetic parameters, but unique mass transfer coefficients, simulated the experimental data in both slurry tests most successfully. Reduced mass transfer resistance to bacteria attached to the soil is the most likely phenomenon accounting for rapid sorbed-phase biodegradation.

Adsorption↗

PubMed2001

How adaptation and mass transfer control the biodegradation of linear alkylbenzene sulfonate by activated sludge.

We use a nonsteady-state model to evaluate the effects of community adaptation and sorption kinetics on the fate of linear alkylbenzene sulfonate (LAS) in batch experiments conducted with activated sludge that was continuously fed different concentrations of LAS. We observed a sharp decrease in the biodegradation rate between 30 and 60 minutes and the presence of an LAS residual at the end of the batch experiments. The modeling analysis indicates that these phenomena were caused by relatively slow inter-phase mass transport of LAS. The modeling analyses also showed that the amount of LAS-degrading biomass increased when the continuous activated sludge was fed a higher LAS concentration. Although community adaptation to LAS involved accumulation of more LAS degraders, the increase was not proportional to the feed concentration of LAS, which supports the concept that LAS degraders also utilized portions of the general biochemical oxygen demand (BOD) fed to the continuous activated sludge systems.

Alkanesulfonic Acids↗

PubMed2001

The roles of intermediates in biodegradation of benzene, toluene, and p-xylene by Pseudomonas putida F1.

Several types of biodegradation experiments with benzene, toluene, or p-xylene show accumulation of intermediates by Pseudomonas putida F1. Under aerobic conditions, the major intermediates identified for benzene, toluene, and p-xylene are catechol, 3-methylcatechol, and 3,6-dimethylcatechol, respectively. Oxidations of catechol and 3-methylcatechol are linked to biomass synthesis. When oxygen is limited in the system, phenol (from benzene) and m-cresol and o-cresol (from toluene) accumulate.

Benzene↗

PubMed2001

A two-step model for the kinetics of BTX degradation and intermediate formation by Pseudomonas putida F1.

A two-step model is developed for the aerobic biodegradation of benzene, toluene, and p-xylene (BTX) by Pseudomonas putida F1. The model contains three unique features. First, an initial dioxygenation step transforms BTX into their catechol intermediates, but does not support biomass growth. Second, the benzene or toluene intermediates are mineralized, which supports biomass synthesis. Third, BTX exhibit competitive inhibition on each other's transformation, while toluene and benzene noncompetitively inhibit the mineralization of their catechol intermediate. A suite of batch and chemostat experiments is used to systematically measure the kinetic parameters for the two-step transformations and the substrate interactions.

Benzene↗

PubMed2001

Successional changes in an evolving anaerobic chlorophenol-degrading community used to infer relationships between population structure and system-level processes.

The response of a complex methanogenic sediment community to 2-chlorophenol (2-CP) was evaluated by monitoring the concentrations of this model contaminant and important metabolic intermediates and products and by using rRNA-targeted probes to track several microbial populations. Key relationships between the evolving population structure, formation of metabolic intermediates, and contaminant mineralization were identified. The nature of these relationships was intrinsically linked to the metabolism of benzoate, an intermediate that transiently accumulated during the mineralization of 2-CP. Before the onset of benzoate fermentation, reductive dehalogenation of 2-CP competed with methanogenesis for endogenous reducing equivalents. This suppressed H(2) levels, methane production, and archaeal small-subunit (SSU)-rRNA concentrations in the sediment community. The concentrations of bacterial SSU rRNA, including SSU rRNA derived from "Desulfovibrionaceae" populations, tracked with 2-CP levels, presumably reflecting changes in the activity of dehalogenating organisms. After the onset of benzoate fermentation, the abundance of Syntrophus-like SSU rRNA increased, presumably because these syntrophic organisms fermented benzoate to methanogenic substrates. Consequently, although the parent substrate 2-CP served as an electron acceptor, cleavage of its aromatic nucleus also influenced the sediment community by releasing the electron donors H(2) and acetate. Increased methane production and archaeal SSU-rRNA levels, which tracked with the Syntrophus-like SSU-rRNA concentrations, revealed that methanogenic populations in particular benefited from the input of reducing equivalents derived from 2-CP.

Acetates↗

PubMed2001

Contributions of biofilm versus suspended bacteria in an aerobic circulating-bed biofilm reactor.

This study demonstrated that, during the two-step biodegradation of toluene in an aerobic circulating-bed biofilm reactor, biofilm and suspended bacteria played critical roles. Although the suspended bacteria were less than 1% of the total amount of biomass in the system, they transformed up to 30% of the toluene into its intermediate in the bulk liquid phase. On the other hand, most of the toluene intermediate was removed inside the biofilm, where diffusion resistance reduced the toluene concentration, thereby relieving inhibition to the degradation reaction of the intermediate. The suspended bacteria are most important for rapidly biodegraded substrates, for which diffusion limitation controls the kinetics in the biofilm. They lose importance when the effects of an inhibiting substrate must be overcome.

Bacteria, Aerobic↗

PubMed2000

Analysis of oxygenation reactions in a multi-substrate system-A new approach for estimating substrate-specific true yields.

A series of experiments was performed in an aerobic chemostat reactor using a multi-substrate system consisting of acetate, phenol, and 2,4-dichlorophenol (DCP). The phenolic compounds require initial oxygenation reactions, while acetate is oxidized without oxygenations. The biomass completely dechlorinated DCP and utilized all of the substrates simultaneously as electron donors and carbon sources. However, DCP removal was less than for phenol and depended on the solids retention time. A novel substrate-specific yield analysis indicated that true yield values were approximated well by the number of electrons removed in non-oxygenation reactions. Experiments for estimating the kinetic parameters for utilization of the phenolic compounds were designed to eliminate the effects of the key cosubstrates of oxygenation reactions, O2, and the reduced intracellular electron carrier, NADH + H+. The maximum specific rate of substrate utilization, qmax, and the half-maximum rate concentration, K, for phenol and DCP were estimated. The kinetics for DCP were much slower than those for phenol, and the largest effect was a half-maximum rate concentration, which was 19 times larger for DCP. The larger K for DCP explains why DCP removal was low and sensitive to the solids retention time.

Acetates↗

PubMed2000

Mathematical description of microbiological reactions involving intermediates.

Stoichiometric relationships for biological reactions involving intermediate formation are developed from microbial reaction fundamentals and thermodynamic principles. Biological reactions proceed through intermediates, which sequester carbon and electrons whenever their degradation is relatively slow. Modeling intermediate formation and subsequent utilization requires evaluation of the distribution of electrons, energy, and macronutrients (C and N) between energy-generating pathways and cell-synthesis pathways for each step in the mineralization of the primary electron-donor substrate. We describe how energy and electron balances are utilized to predict the stoichiometry for each step of a multi-step degradation process. Each stoichiometric relationship developed predicts substrate utilization, cell growth, and the formation of other products (e.g., H(2)CO(3) or H(+)) for one step in the pathway to full mineralization. A modeling example demonstrates how different kinetics for each step in the degradation of nitrilotriacetic acid (NTA) leads to observed patterns in experimental results, such as a delay in the release of H(2)CO(3) after NTA is removed from solution.

Bicarbonates↗

PubMed2000

Microbial energetics and stoichiometry for biodegradation of aromatic compounds involving oxygenation reactions.

Oxygenation reactions significantly alter the energy and electron flows and, consequently, the overall stoichiometry for the microbial utilization of aromatic compounds. Oxygenation reactions do not yield a net release of electrons, but require an input of electrons to reduce oxygen molecules. The biodegradation pathway of phenanthrene as a model compound was analyzed to determine the impact of oxygenation reactions on overall stoichiometry using the half-reaction method. For individual oxygenation reactions, the half-reaction method for analyzing the electron and energy flows must be modified, because the reactions do not release electrons for synthesis or energy generation. Coupling the oxygenation reaction to subsequent reaction steps provides a net electron release for the coupled reactions. Modeling results indicate that oxygenation reactions increase the oxygen requirement and reduce the cell yield, compared to the conventional mineralization represented by hydroxylation reactions in place of oxygenations. The computed yields considering oxygenation reactions conform better to empirical yields reported in the literature than do yields computed by the hydroxylation single-step methods. The coupled-reaction model also is consistent with information about the ways in which micro-organisms that degrade aromatics accumulate intermediates, regulate degradation genes, and organize enzyme clusters.

Bacteria↗

PubMed1999

Unexpected population distribution in a microbial mat community: sulfate-reducing bacteria localized to the highly oxic chemocline in contrast to a eukaryotic preference for anoxia.

The distribution and abundance of sulfate-reducing bacteria (SRB) and eukaryotes within the upper 4 mm of a hypersaline cyanobacterial mat community were characterized at high resolution with group-specific hybridization probes to quantify 16S rRNA extracted from 100-microm depth intervals. This revealed a preferential localization of SRB within the region defined by the oxygen chemocline. Among the different groups of SRB quantified, including members of the provisional families "Desulfovibrionaceae" and "Desulfobacteriaceae," Desulfonema-like populations dominated and accounted for up to 30% of total rRNA extracted from certain depth intervals of the chemocline. These data suggest that recognized genera of SRB are not necessarily restricted by high levels of oxygen in this mat community and the possibility of significant sulfur cycling within the chemocline. In marked contrast, eukaryotic populations in this community demonstrated a preference for regions of anoxia.

Anaerobiosis↗