Extant Kinetic Parameters Research Articles

Research Digest: Field Validation of Biokinetic Coefficients for Predicting Degradation of Organic Compounds

This research was the first significant demonstration of an extant respirometric test to determine the biodegradation rate parameters (biokinetics) of select individual organic compounds at full scale wastewater treatment plants. Extant kinetics were measured at five different municipal and industrial activated sludge systems. The respirograms were well correlated with actual analytical measurements of compound disappearance for ethylene glycol and acetone. Furfural respirograms revealed differential rates of oxygen consumption, indicative of the formation of an intermediate compound which was identified as furoic acid in subsequent analysis. A calibration procedure was developed to assess the competent biomass concentration, since the COD fraction tended to underestimate the degrading fraction for two of the four test compounds. Acetone, for instance, had a measured influent COD fraction of 0.08%, and the actual competent fraction was estimated to be 2.3% based on the model calibration. Once the competent biomass concentration was determined, extant kinetic parameters were subsequently used to predict activated sludge system performance. Predicted effluent concentrations were within 2, 5, and 16% of the average measured concentrations for acetone, linear alkyl benzene sulfonate, and furfural, respectively. Day to day predictions for these compounds were less accurate, possibly due to the non-steady state nature of the activated sludge systems studied. Alkyl sulfate (AS) was not predicted well with respect to the percentage difference between predicted and measured concentrations. However, the overall mass difference was small (4.2 μgCOD/L predicted versus 0.82 μgCOD/L measured). The sub part per billion measured concentrations for AS were at least a magnitude of order lower than any of the other target compound concentrations. One of the surprising findings of the study was that the variability in kinetic parameter values was no more than typically observed in laboratory activated sludge reactors operated at steady-state. The dynamic operating nature and varying influent concentrations resulted in the maximum standard deviations for furfural at the Cedar Rapids Water Pollution Control Facility (standard deviations were 54 and 79% of the average values of and KS, respectively). From these results, a sampling and testing period of 8 to 10 tests over a three month period is recommended to accurately characterize the biodegradation performance of an activated sludge system with respect to specific organic compounds in the influent. This title belongs to WERF Research Report Series ISBN: 9781843396307 (eBook)

Measurement of biodegradability parameters for single unsubstituted and methylated polycyclic aromatic hydrocarbons in liquid bacterial suspensions

Substrate depletion experiments were conducted to characterize aerobic biodegradation of 20 single polycyclic aromatic hydrocarbons (PAHs) by induced Sphingomonas paucimobilis strain EPA505 in liquid suspensions. PAHs consisted of low molecular weight, unsubstituted, and methyl-substituted homologs. A material balance equation containing the Andrews kinetic model, an extension of the Monod model accounting for substrate inhibition, was numerically fitted to batch depletion data to estimate extant kinetic parameters including the maximal specific uptake rates, q(max), the affinity coefficients, K(S), and the substrate inhibition coefficients, K(I). Strain EPA505 degraded all PAHs tested. Applied kinetic models adequately simulated experimental data. A cell proliferation assay involving reduction of the tetrazolium dye WST-1 was used to evaluate the ability of strain EPA505 to utilize individual PAHs as sole energy and carbon sources. Of the 22 PAHs tested, 9 supported bacterial growth. Evaluation of the biokinetic data showed that q(max) correlated highly with transmembrane flux as theoretically estimated by a diffusion model, pointing to transmembrane transport as a potential rate-determining process. The biodegradability data generated in this study is essential for the development of quantitative structure-activity relationships (QSARs) for biodegradability and for modeling biodegradation of simple PAH mixtures.

Kinetics of biodegradation of binary and ternary mixtures of PAHs

The kinetics of biodegradation of mixtures of polycyclic aromatic hydrocarbons (PAHs) by Sphingomonas paucimobilis strain EPA505 were investigated. The investigation focused on three- and four-ring PAHs, specifically 2-methylphenanthrene, fluoranthene, and pyrene. Uptake rates in aerobic batch suspended cultivations were measured for the individual PAHs and their binary and ternary mixtures. It was observed that kinetics were influenced by the mixture composition and the kinetic properties of the components. A material balance equation containing the Monod model was numerically fitted to uptake data to determine extant kinetic parameters for the individual PAHs. Similarly, equations containing kinetic interaction models derived from enzyme kinetics were fitted to the uptake data obtained from experiments with binary and ternary mixtures. The investigation considered the following interaction types: no-interaction (Monod), pure competitive interaction, noncompetitive or mixed-type interaction, uncompetitive inhibition, and nonspecific interaction based on pure competition (SKIP). Model fit was evaluated based on probabilistic and statistical criteria and inferences were reached about underlying interaction mechanisms based on model fit. Mixture kinetics were most adequately simulated by the pure competitive interaction model with mutual substrate exclusivity. This model is fully predictive, relying only on parameters determined in the sole-PAH experiments. It was shown that for low percent inhibition values and with limited data, pure competitive interaction kinetics may not be evident, resembling no-interaction kinetics. This study is a reasonable starting point for understanding and modeling biodegradation of complex PAH mixtures in engineered and natural systems.

Use of Extant Kinetic Parameters to Predict Effluent Concentrations of Specific Organic Compounds at Full‐Scale Facilities

To use the results of kinetic tests to predict effluent concentrations of specific contaminants in activated sludge systems, the fraction of the biomass that has an ability to degrade the test compound (i.e., competent biomass) must be estimated. A calibration procedure was developed to assess the competent biomass concentration because the chemical oxygen demand (COD) fraction tended to underestimate the degrading fraction for three of the four test compounds. Acetone, for instance, had a measured influent COD fraction of 0.08%, and the actual competent fraction was estimated to be 2.3%, based on the model calibration. Once the competent biomass fraction in the mixed liquor was determined, the extant kinetic parameters were subsequently used to predict activated sludge system performance. Predicted effluent concentrations were within 2, 5, and 16% of the average measured concentrations for acetone, linear alkylbenzene sulfonate, and furfural, respectively. Day-to-day predictions for these compounds were less accurate, possibly because of the non-steady-state nature of the activated sludge systems studied. The difference between the fraction of the influent COD contributed by the target compounds and the competent biomass fraction in the mixed liquor was found to be more significant when the target compound contributed less than 1% of the influent organic matter. The chemical structure of the target compound and chemical composition of the influent likely had an effect on the resulting competent biomass concentration. The total maximum growth rate, microX, was observed to be independent of the influent concentration of acetone and furfural, thus suggesting that the competent biomass concentration for these compounds was not affected by the changes in their influent concentrations. Consequently, a majority of competent biomass growth resulted from the degradation of other substrates, resulting in a competent biomass concentration significantly higher than predicted based on the influent COD fraction contributed by the test compound.

Relative efficacy of intrinsic and extant parameters for modeling biodegradation of synthetic organic compounds in activated sludge: dynamic systems.

The utility of intrinsic and extant kinetic parameters for simulating the dynamic behavior of a biotreatment system coupled with a distributed, unstructured, balanced microbial growth model were evaluated against the observed response of test reactors to transient loads of synthetic organic compounds (SOCs). Biomass from a completely mixed activated-sludge (CMAS) system was tested in fed-batch reactors, while a sequencing batch reactor (SBR) was tested by measuring SOC concentrations during the fill and react period. Both the CMAS system and the SBR were acclimated to a feed containing biogenic substrates and several SOCs, and the transient loading tests were conducted with biogenic substrates along with one or more SOCs. Extant parameters more closely reflect the steady-state degradative capacity of activated-sludge biomass than intrinsic parameters and, hence, were expected to be better predictors of system performance. However, neither extant nor intrinsic parameters accurately predicted system response and neither parameter set was consistently superior to the other. Factors that may have contributed to the inability of the model to predict system response were identified and discussed. These factors included the role of abiotic processes in SOC removal, disparity in the bases used to evaluate parameter estimates (substrate mineralization) and reactor performance (substrate disappearance), inhibitory substrate interactions under the severe loading conditions of the SBR, changes in the physiological state of the biomass during the transient loading tests, and the presumed correlation between the competent biomass concentration and the influent SOC concentration.

Relative efficacy of intrinsic and extant parameters for modeling biodegradation of synthetic organic compounds in activated sludge: steady-state systems.

The performance of intrinsic and extant kinetic parameters as predictors of synthetic organic compound (SOC) concentration in biotreatment systems operated at steady state was evaluated. Two laboratory-scale, completely mixed activated-sludge systems were sampled on a routine basis, and SOC concentrations were quantified using gas chromatography with flame-ionization detection coupled with solid-phase microextraction for analyte concentration. At the same time, intrinsic and extant respirometric tests were performed periodically, and the kinetic parameter estimates obtained were used to predict effluent SOC concentrations for comparison with the measured values. Out of 28 comparisons that could be made between intrinsic and extant predictions, extant parameters were superior in 27 cases and intrinsic parameters were comparable, at best, to extant parameters in the remaining case. Given their superior performance and relative ease of measurement, extant parameters are preferable for use in design and operational decision-making.

Estimation of biodegradation parameters of phenolic compounds on activated sludge by respirometry

The bio-oxidation of phenol, catechol, resorcinol, m-cresol and 5-methylresorcinol on activated sludge was investigated by oxygen uptake measurements. In addition, the degradation of acetate with the same microbial population was studied. The substrate-dependent oxygen uptake data were analysed on the basis of the Michaelis–Menten kinetics. The extant kinetic parameters, the maximum rates of oxygen consumption and half-saturation constants for the processes with different substrates were determined. The simple respirometric approach also made it possible to determine the short-term oxygen demands of the substrates which formed 23–38% of the theoretical oxygen demand of the studied compounds.

Evaluation of biodegradation kinetics of specific organic constituents at full-scale facilities

The present work was aimed at determining the feasibility of applying the extant kinetic technique to evaluate the ability of the biomass to degrade specific organic pollutants at full scale facilities and to determine the ability of these kinetic parameters to predict effluent concentrations of the target compounds. Biodegradation of acetate, ethylene glycol, acetone, and furfural was studied at two full scale facilities, the Cedar Rapids Water Pollution Control facility and the Boone Water Pollution Control Plant. Acetone and ethylene glycol biodegradation at Cedar Rapids exhibited fairly stable kinetic parameters over the entire period of observation. The mean values of the kinetic parameters were calculated at three month intervals, and those mean values varied within a 20% range. Three month mean values for furfural at Cedar rapids and ethylene glycol at Boone varied within a range of 300 % and 100 %, respectively. Standard deviations of the mean values within each of the 3 months period were used to evaluate short term variability. Standard deviations within 3 month periods were less than 60 % for K S and less than 50 % for the rest of parameters. Observed standard deviations were similar to those reported for laboratory scale reactors operated at steady-state in previous studies. Based on the results of extant kinetic tests and measured effluent concentrations during a calibration period, the competent biomass fractions for furfural and acetone were estimated in the mixed liquor from the Cedar Rapids WPCF as 2.3 % and 1.8 %, respectively. These values were more than an order of magnitude higher than the fraction of influent COD contributed by respective compounds. Consequently, it was evident that the competent biomass derived a significant portion of their carbon and energy requirements from other substrates. As a result, the concentration of the biomass with the enzymatic ability to degrade certain compounds was greater than would be predicted based on the influent concentrations of those compounds. After the calibration period, the extant kinetic parameters and estimated competent fractions were used to predict the effluent concentrations of furfural and acetone. The results indicated that the extant kinetic parameters provided a fairly good prediction of the effluent furfural concentration (e.g., within 13% on average). The prediction of the effluent acetone concentration was not as consistent, possibly due to the fact that the treatment facility was not at steady state and the influent concentrations of acetone varied more widely than furfural.

Extant Biodegradation Testing With Linear Alkylbenzene Sulfonate in Laboratory and Field Activated Sludge Systems

Two 1-L porous pot (65 µ stainless steel mesh) reactors were fed synthetic wastewater with a COD of 200 mg/L including 2 mg/L linear alkyl benzene sulfonate (LAS) to evaluate the influence of specific operating conditions (i.e, hydraulic retention time, HRT, and solids retention time, SRT) on the measured rate of LAS biodegradation. The reactors were operated in parallel under a constant SRT of 10 d, and HRTs of 2, 4, 6, and 12 h. Subsequently, the reactors were operated under a constant HRT of 6 h, and SRTs of 3, 6, 10, and 15 d. The biodegradation responses of LAS were measured using a respirometric method, and the extant kinetic parameters were evaluated using the Monod model. The extant kinetic parameters obtained from these experiments suggest that the HRT had little impact on the measured kinetic parameters (µ ˆ = 0.14 ± 0.06 h -1 , K S = 0.4 ± 0.3 mg COD/L, and Y = 0.67 ± 0.02 mg biomass COD formed/mg LAS COD utilized) at a constant SRT of 10 d. The SRT had a more noticeable effect on the measured biodegradation kinetics (e.g., Y increased from 0.50 ± 0.08 to 0.66 ± 0.05 mg/mg when the SRT increased from 3 to 10 d at a constant HRT of 6 h). Extant kinetics for LAS biodegradation were measured in the field at two activated sludge wastewater treatment plants operated at different conditions. The field results were similar to the results from laboratory systems operated to simulate the field conditions (µ ˆ values ranged from 0.02 - 0.05 h -1 , K S values ranged from 0.11 0.39 mg COD/L, and yield values ranged from 0.46 - 0.50 mg biomass COD formed/mg LAS COD utilized). The week to week variability in measured LAS kinetic parameters was greater with the field samples than with the laboratory samples, possibly due to the non-steady state nature of the treatment plants. The long term variability in the field kinetic parameters was comparable to the laboratory variability. These results confirm the efficacy of the extant respirometric technique to measure biodegradation rates of surfactants in laboratory and field systems operated at a range of HRT and SRT conditions.

Development of a respirometric assay to measure the transient load response of activated sludge to individual organic chemicals

This study described a new respirometric technique to monitor the transient response of activated sludge systems to individual synthetic organic compounds (SCOs). The assay used a fed-batch reactor system which contained mixed liquor from the parent reactor and received a biogenic feed and the target SOC at the same F/M ratio as was applied to the parent reactor. The fed-batch reactor was oxygenated using a hollow-fiber reaeration module to meet the steady-state oxygen demand. The reaeration module was characterized by means of KL a studies. The assay monitored the dissolved oxygen concentration profile after application of a shock load achieved by switching to a fed-batch feed with the target SOC at an elevated concentration. Mathematical descriptions of the transient profiles were derived and the experimentally observed dissolved oxygen profiles were subsequently compared to profiles predicted using extant kinetic parameters for SOC removal measured using an earlier developed assay. The use of the assay were complicated by the difficulty in maintaining a reaeration capacity at constant and low capacity. As a result, the adequacy of the measured extant kinetic parameters as predictors of the transient response could not be confirmed.

Development of a respirometric assay to measure the transient load response of activated sludge to individual organic chemicals

This study described a new respirometric technique to monitor the transient response of activated sludge systems to individual synthetic organic compounds (SOCs). The assay used a fed-batch reactor system which contained mixed liquor from the parent reactor and received a biogenic feed and the target SOC at the same F/M ratio as was applied to the parent reactor. The fed-batch reactor was oxygenated using a hollow-fiber reaeration module to meet the steady-state oxygen demand. The reaeration module was characterized by means of KLa studies. The assay monitored the dissolved oxygen concentration profile after application of a shock load achieved by switching to a fed-batch feed with the target SOC at an elevated concentration. Mathematical descriptions of the transient profiles were derived and the experimentally observed dissolved oxygen profiles were subsequently compared to profiles predicted using extant kinetic parameters for SOC removal measured using an earlier developed assay. The use of the assay were complicated by the difficulty in maintaining a reaeration capacity at constant and low capacity. As a result, the adequacy of the measured extant kinetic parameters as predictors of the transient response could not be confirmed.

Very low-pressure pyrolysis (VLPP) of 3-chloropropionitrile

The thermal decomposition of 3-chloropropionitrile has been investigated over the temperature range 942–1152 K using the technique of very low-pressure pyrolysis (VLPP). The experimental results are consistent with the reaction proceeding via the unimolecular elimination of HCl CH2ClCH2CN → C2H3CN + HCl. The high-pressure Arrhenius parameters obtained via the application of RRKM theory are given by log (k∞/s–1)=(13.2 ± 0.3)–(241.0 ± 4 kJ mol–1)/2.3 RT.In contrast to its decomposition in a conventional static system, no radical reactions occur under VLPP conditions. No evidence could be found for the unimolecular elimination of HCN. When compared with the extant kinetic parameters for the unimolecular elimination of HCl from ethyl chloride, the results show that β-cyano substitution has a retarding effect on the rate of HCl elimination. This is consistent with a polar transition state.