Half-saturation Coefficient Research Articles

A New Approach to Quantify Spatial Distribution of Biofilm Kinetic Parameters by In Situ Determination of Oxygen Uptake Rate (OUR)

In order to guide the rational optimization of biofilm reactor design and operation in wastewater treatment, it is essential to comprehend the biokinetic behavior of microorganisms, especially with its depth variation, in biofilms. However, no fast and accurate methods have been established for measuring the stratification of biokinetic parameters in biofilm systems up to now. In this paper, a new approach was presented to quantify the spatial distribution of biokinetic parameters in biofilms with a result demonstration. A multispecies biofilm at endogenous respiration was subjected to a pulse of substrates at various locations. An oxygen microelectrode structurally combined with an additional micropipette for substrate injection was constructed to monitor the in situ OUR (oxygen uptake rate) by measuring the dissolved oxygen concentration with time. Based on the oxygen concentration profiles versus times at a series of substrate concentrations, the spatial distribution of biokinetic parameters, biomassyield coefficient (YH), Monod half-saturation coefficient for substrate (KH,S), and maximum specific growth rate (muH,max) were quantified. The demonstration of its utility showed that YH was within the 0.437-0.449 g (COD in cell)/g COD range, with only a slight difference and no regular change in the spatial distribution. Meanwhile, the results showed that the distribution of muH,max varied from 9.18 day(-1) at the surface layer of the biofilm to 1.69 day(-1) at the substratum layer of the biofilm with a decrease of 80% due to the reduction of biomass activity orthe diverse distribution of microbial species. Additionally, an opposite change tendency of KH,S was found, which increased from 37 mg COD/L at the surface layer of the biofilm to 45 mg COD/L at the substratum layer of the biofilm, indicating larger mass transport limitations with penetration into the biofilm. Compared with high heterogeneity in the biofilm depth, the distribution of biokinetic parameters was less heterogeneous in the horizontal direction at the same depth. In summary,the results provide experimental evidence necessary for biofilm modeling, which could not be accomplished in the past, and enable us to obtain a clearer biokinetic description of the biofilm.

Effect of food quality on energy uptake

The dynamic energy budget (DEB) theory assumes that the feeding of an organism in relation to food density follows the type-II functional response when food consists of purely digestible organic matter. However when faced with a food source high in inorganic content, an organism needs to adapt physiologically to maximise organic extraction. Indeed filter-feeding marine bivalves inhabiting turbid coastal waters cope with large fluctuations in food quality by selectively ingesting and pseudofaeces production. Data from feeding experiments with the New Zealand greenshell mussel Perna canaliculus have demonstrated that inorganic particles contribute some uncertainty to the estimate of the half-saturation coefficient. Incorporating inorganic matter into the functional response would improve the prediction of energy uptake.

Removal of Adsorbable Organic Halides (AOX) from Recycled Pulp and Paper (P&P) Mill Effluent Using Granular Activated Carbon–Sequencing Batch Biofilm Reactor (GAC-SBBR)

Paper mills generate varieties of pollutants depending upon the type of the pulping process. The wastewaters discharged from these mills have high chemical oxygen demand (COD) and colour, in which indicating high concentrations of recalcitrant organics. This study was conducted using a Granular Activated Carbon – Sequencing Batch Biofilm Reactor (GAC-SBBR) of 3.0 L working volume, operated in an aerobic condition and packed with 200 gL-1 of 2-3 mm granular activated carbon (coconut shells) as a medium for the biofilm growth. For the six of months, the hydraulic retention time (HRT) was set at 36 hours and later it was adjusted to 24 hours in order to evaluate the performance of the system. The treated wastewater samples for these studies were taken from a recycled pulp and paper mill factory in Pahang, Malaysia with 4 different batch characteristics. The adsorbable organic halides (AOX) that had been determined and treated were pentachlorophenol (PCP), 2,3,4,5-tetrachlorophenol (2,3,4,5-TeCP), 2,4,6-trichlorophenol (2,4,6-TCP), 2,4-dichlorophenol (2,4-DCP), 2-chlorophenol (CP) and phenol at various concentration ranges. The Monod growth kinetic parameters for the process specific growth rate coefficient (µh), half saturation coefficient (Ks), endogenous decay coefficient (DH) and Yield coefficient (YH) obtained were 0.0037 hr-1, 65.23 mgL-1, 4x10-5 hr-1 and 0.36 mg/mg, respectively. Analysis of the growth kinetic parameters in GAC-SBBR had deduced that the system was suitable to operate on long biomass retention time (BRT) under anoxic condition. The results also indicated that the biofilm attached onto granular activated carbon (GAC) can substantially remove these recalcitrant organics in the wastewater, within the range of 10 – 100% AOX removal depending on the selected HRTs.

Modelling an aerobic submerged membrane bioreactor with ASM models on a large range of sludge retention time

In this work, modelling of a submerged membrane bioreactor (SMBR) system for municipal wastewater treatment is evaluated using ASM1 and ASM3 models. Dynamic data (and pseudo steady state) collected in an aerobic SMBR working at high sludge retention time (SRT) are considered. Work is focused on suspended solids, excess sludge production, and nitrification kinetics. After a complete wastewater characterisation, satisfying prediction is obtained for volatile suspended solids (MLVSS) with default kinetic parameters. However, assumption of inert organics accumulation ( X I) makes inaccurate the simulation at high SRT (110 days). Results also show that mineral suspended solids are significantly solubilised in such a process, and this should be taken into account for modelling total suspended solids. Default parameters for nitrification (μ a , b a , K N ) were not exact, and thus a new set of parameters was identified. A unique set of values was proposed for μ a and ba, whereas half saturation coefficient ( K N ) was observed to vary with the MBR operating condition.

Biokinetic parameters and behavior of Aeromonas hydrophila during anaerobic growth

The biokinetics of glucose metabolism were evaluated in Aeromonas hydrophila during growth in an anaerobic biosystem. After approx 34 h growth, A. hydrophila metabolized 5,000 mg glucose l(-1) into the end-products ethanol, acetate, succinate and formate. The maximum growth rate, mu(m), half saturation coefficients, K(s), microbial yield coefficient, Y, cell mass decay rate coefficient, k(d), and substrate inhibition coefficient, K(si) were 0.25 +/- 0.03 h(-1), 118 +/- 31 mg glucose l(-1), 0.12 microg DNA mg glucose(-1), 0.01 h(-1), and 3,108 +/- 1,152 mg glucose l(-1), respectively. These data were used to predict the performance of a continuous growth system with an influent glucose concentration of 5,000 mg l(-1). Results of the analysis suggest that A. hydrophila will metabolize glucose at greater than 95% efficiency when hydraulic retention times (HRTs) exceed 7 h, whereas the culture is at risk of washing out at an HRT of 6.7 h.

Steady state characteristics of acclimated hydrogenotrophic methanogens on inorganic substrate in continuous chemostat reactors

A Monod model has been used to describe the steady state characteristics of the acclimated mesophilic hydrogenotrophic methanogens in experimental chemostat reactors. The bacteria were fed with mineral salts and specific trace metals and a H 2/CO 2 supply was used as a single limited substrate. Under steady state conditions, the growth yield ( Y CH 4 ) reached 11.66 g cells per mmol of H 2/CO 2 consumed. The daily cells generation average was 5.67 × 10 11, 5.25 × 10 11, 4.2 × 10 11 and 2.1 × 10 11 cells/ l-culture for the dilutions 0.071/d, 0.083/d, 0.1/d and 0.125/d, respectively. The maximum specific growth rate ( μ max) and the Monod half-saturation coefficient ( K S) were 0.15/d and 0.82 g/L, respectively. Using these results, the reactor performance was simulated. During the steady state, the simulation predicts the dependence of the H 2/CO 2 concentration ( S) and the cell concentration ( X) on the dilution rate. The model fitted the experimental data well and was able to yield a maximum methanogenic activity of 0.24 L CH 4/g VSS.d. The dilution rate was estimated to be 0.1/d. At the dilution rate of 0.14/d, the exponential cells washout was achieved.

A zero-dimensional biofilm model for dynamic simulation of moving bed bioreactor systems: Model concepts, Peterson matrix, and application to a pilot-scale plant

A zero-dimensional (0D) biofilm model for dynamic simulation of biological wastewater treatment systems is proposed and applied to a pilot-scale moving bed bioreactor (MBBR). The model, written in Peterson matrix format, does not describe biofilm structure in any form. Biochemical conversions in the model are based on the activated sludge model no. 1 (ASM1). Diffusional mass transport limitations are taken into account implicitly in the model using adapted half-saturation coefficients in the Monod terms of the model. In addition to biochemical conversions, the model contains attachment of particulates from the bulk of the liquid onto the biofilm and detachment of particulates from the biofilm into the bulk of the liquid. Model performance is evaluated using data originating from two intensive measurement campaigns covering 9 days of wastewater treatment with the pilot-scale MBBR. The process dynamics of the MBBR were well reproduced by the model, since a good fit between measured effluent ammonia and nitrate concentrations to the simulation results was obtained. Biofilm related parameters, like biofilm age, attachment rate and detachment rate, were extracted from the model.

Biodegradation of High Phenol Concentration in a Membrane Bioreactor

Phenol biodegradation by mixed culture was studied in a membrane bioreactor (MBR) over a period of 285 days. Activated sludge was used as the MBR biomass, after controlled acclimation to high phenol concentrations. The MBR permeate flux was stabilized quickly (in a few hours) and always maintained above 90 L.h-1.m-2.bar-1. The acclimatized activated sludge allowed significant phenol degradation (95% average COD removal efficiency and greater than 99% phenol removal efficiency) without supplemental reagent addition. After sludge acclimatization, the Haldane kinetics model for a single substrate was used to obtain the maximum specific growth rate (µm = 0.438 h-1), the half saturation coefficient (Ks = 29.54 mg.L-1) and the substrate inhibition constant (Ki = 72.45 mg.L-1). Biodegradation experiments were conducted at different phenol concentrations (4.9 – 8.5 g.L-1 d-1). Although the phenol concentration was high, the Haldane model was still acceptable, and removal capacities were in agreement with literature. Excellent effluent quality was obtained regardless of the extremely short SRT (5 – 17 days). This work shows the potential of MBR for toxic chemical elimination, charged effluents treatment and process stability.

Function of self-forming dynamic membrane and biokinetic parameters’ determination by microelectrode

The self-forming dynamic membrane coupled bioreactor (SFDMBR), which uses coarse pore-sized material to separate solids and liquids in a bioreactor, has some advantages compared with membrane bioreactor (MBR) using micro-/ultra-filtration membranes such as low module cost and high flux. In this study, we investigate the microbial activity change of a self-forming dynamic membrane (DM) during its bio-fouling process by a microelectrode for O2. At a high flux of 40L/m2h, the dissolved oxygen was determined to be depleted at the depth of 1.5–2.0mm in the self-forming DM. Based on the dissolved oxygen concentration profiles in the self-forming DM, a reliable and simple model and computational procedure were developed to estimate the biokinetic parameters in the self-forming DM. Sensitivity analysis of the model revealed that the dissolved oxygen profiles are sufficiently sensitive to the maximum specific rates of oxygen uptake (q⌢max,20), which were computed to be within the range of 3.8–11.1mg O2/gSSh. q⌢max,20 decreased sharply in the first 5 days with the development of the bio-fouling process in the surface cake layer of the self-forming DM and then reached a relatively steady state afterwards. The Monod half-saturation coefficient for oxygen (Ko) was computed to be in the range of 0.16–0.75mgO2/L. In summary, the results gave new experimental evidence on the change of microbial activity in the self-forming DM during its bio-fouling process.

Evaluation of Monod kinetic parameters in the subsurface using moment analysis: Theory and numerical testing

The spatial moments of a contaminant plume undergoing bio-attenuation are coupled to the moments of microbial populations effecting that attenuation. In this paper, a scalable inverse method is developed for estimating field-scale Monod parameters such as the maximum microbial growth rate ( μ max), the contaminant half saturation coefficient ( K s ), and the contaminant yield coefficient ( Y s ). The method uses spatial moments that characterize the distribution of dissolved contaminant and active microbial biomass in the aquifer. A finite element model is used to generate hypothetical field-scale data to test the method under both homogeneous and heterogeneous aquifer conditions. Two general cases are examined. In the first, Monod parameters are estimated where it is assumed a microbial population comprised of a single bacterial species is attenuating one contaminant (e.g., an electron donor and an electron acceptor). In a second case, contaminant attenuation is attributed to a microbial consortium comprised of two microbial species, and Monod parameters for both species are estimated. Results indicate the inverse method is only slightly sensitive to aquifer heterogeneity and that estimation errors decrease as the sampling time interval decreases with respect to the groundwater travel time between sample locations. Optimum conditions for applying the scalable inverse method in both space and time are investigated under both homogeneous and heterogeneous aquifer conditions.

Bioisomerization kinetics of γ-HCH and biokinetics of Pseudomonas aeruginosa degrading technical HCH

Bioconversion kinetics of γ-HCH and biological growth kinetics of Pseudomonas aeruginosa degrading technical HCH was investigated in flask experiments under aerobic condition. Degradation studies for various isomers of technical HCH were also performed. The biodegradation of the most persistent β-HCH and δ-HCH isomers was also observed. At lower technical HCH concentrations (1–10 mg/l), above 99% of the degradation was observed whereas at higher concentration (20–50 mg/l), the degradation efficiency was dropped. This may be due to inhibitory effect of technical HCH at higher concentrations. The technical HCH inhibitory behavior and bacterial growth kinetics could be correlated well by simple Haldane's growth kinetic model. The value of decay and yield coefficient was also determined. Further experimental results also revealed that degradation of the γ-HCH isomer is faster (after incubation of 5 days) in the presence of other isomers of technical HCH, whereas γ-HCH alone does not degrade even after a long period of incubation (14 days), but isomerizes to α-HCH isomer by the P. aeruginosa. The rate constant for the bioisomerization was found to be 0.0474 day −1. The above estimated parameters (maximum specific growth rate, half saturation coefficient, inhibition constant, decay coefficient, yield coefficient and bioisomerization rate) are invariably required for the design and simulation of batch and continuous bioreactors treating HCH containing wastewaters.

Isolation and characterization of hydrogen‐oxidizing bacteria induced following exposure of soil to hydrogen gas and their impact on plant growth

In many legumes, the nitrogen fixing root nodules produce H2 gas that diffuses into soil. It has been demonstrated that such exposure of soil to H2 can promote plant growth. To assess whether this may be due to H2-oxidizing microorganisms, bacteria were isolated from soil treated with H2 under laboratory conditions and from soils collected adjacent to H2 producing soybean nodules. Nineteen isolates of H2-oxidizing bacteria were obtained and all exhibited a half-saturation coefficient (Ks) for H2 of about 1 ml l(-1). The isolates were identified as Variovorax paradoxus, Flavobacterium johnsoniae and Burkholderia spp. using conventional microbiological tests and 16S rRNA gene sequence analysis. Seventeen of the isolates enhanced (57-254%) root elongation of spring wheat seedlings. Using an Arabidopsis thaliana bioassay, plant biomass was increased by 11-27% when inoculated by one of four isolates of V. paradoxus or one isolate of Burkholderia that were selected for evaluation. The isolates of V. paradoxus found in both H2-treated soil and in soil adjacent to soybean nodules had the greatest impact on plant growth. The results are consistent with the hypothesis that H2-oxidizing bacteria in soils have plant growth promoting properties.

Modelling of biological processes during aerobic treatment of piggery wastewater aiming at process optimisation

A dynamic mathematical model was developed for the simulation of the aerobic treatment of piggery wastewater. This model includes the carbon oxidation, the nitrification and the denitrification. According to the experimental results obtained during this study, a modified version of the activated sludge model No. 1 has been developed. The model includes (1) nitrite as intermediate of nitrification and denitrification, (2) the distinction between the anoxic heterotrophic yield and the aerobic heterotrophic yield, respectively equal to 0.53 and 0.6 and (3) the first-order hydrolysis of the slowly biodegradable fraction. The calibration and the validation of the model was performed using experimental data from three experiments with two piggery wastewaters. A set of kinetic and stoichiometric parameters emerged from these tests. Except the kinetic of hydrolysis of the slowly biodegradable organic matter varying from 6 to 25 g COD (g COD day) −1, all other parameters were similar for all experiments. The dissolved oxygen concentration was identified as the main variable influencing the nitrite accumulation during nitrification. In the calibrated model, the oxygen half-saturation coefficient of the ammonium oxidisers (0.3 g O 2 m −3) was lower than for the nitrite oxidisers (1.1 g O 2 m −3), leading to nitrite accumulation when the dissolved oxygen concentration was low. Simulations with the proposed model could be very useful for improved design and management of biological treatment of piggery wastewaters, particularly in case of partial nitrification to nitrite directly followed by denitrification.

Modelling and dynamic simulation of a moving bed bioreactor for the treatment of municipal wastewater

A model for the dynamic simulation of a pilot scale moving bed bioreactor (MBBR) used for the treatment of municipal wastewater is proposed. The proposed MBBR model includes attachment of particulates to the biofilm and detachment of biofilm into the bulk liquid. The biofilm growth kinetics are modelled with the activated sludge model no. 1 (ASM1). Diffusional mass transport limitations are implemented implicitly by ASM1 and manifest by adapted half-saturation coefficients in the Monod expressions of the activated sludge model. The model layout incorporates completely mixed aeration tanks and flow splitters and can be implemented using the respective standard blocks available in wastewater treatment plant simulators. A calibration guideline is proposed. Attachment and detachment rates are adjusted during calibration in order to match the measured biofilm solids in the MBBR and effluent ammonium and nitrate data. The process dynamics of the MBBR were well reproduced using ASM1 with default parameter values. The biofilm age was calculated analogous to the sludge age in an activated sludge plant and it was found to be 2.6 d in the first and 2.1 d in the second compartment of the MBBR, which is small compared to typical sludge ages in nitrifying activated sludge plants.

Kinetics of the Microbial Reductive Dechlorination of Pentachloroaniline

The microbial reductive dechlorination kinetics of pentachloroaniline (PCA) and less chlorinated anilines (CAs) were investigated with a mixed, fermentative/ methanogenic culture. Batch dechlorination assays were performed with all available CAs at an initial concentration of 3 microM, and an incubation temperature of 22 degrees C. Dechlorination of PCA, two tetrachloroanilines (2,3,4,5- and 2,3,5,6-TeCA), five trichloroanilines (2,3,4-, 2,3,5-, 2,4,5-, 2,4,6-, and 3,4,5-TrCA), and one dichloroaniline (3,5-DCA; low extent) was observed but none of the five remaining dichloroanilines and three monochloroanilines were dechlorinated by the enrichment culture during batch assays. The dechlorination rates (k') and half-saturation coefficients (Kc) were measured using nonlinear regression based on the integrated Michaelis-Menten equation under conditions of electron donor saturation and assuming constant biomass concentration over the relatively short batch incubation period. At an initial concentration of CAs of about 3 microM, the values of k' and Kc ranged from 0.25 to 1.19 microM/day and from 0.11 to 1.72 microM, respectively, corresponding to half-lives in the range of 1.5-8.5 days. Model simulations of the sequential dechlorination reactions based on a branched-chain Michaelis-Menten model and using independently measured k' and Kc values matched the experimental data very well.

Growth Kinetics and Competition Between Methanosarcina and Methanosaeta in Mesophilic Anaerobic Digestion

Methanosarcina species with a high maximum specific growth rate (mumax) and high half-saturation coefficient (KS) and Methanosaeta species with a low mumax and low KS are the only known aceticlastic methanogens. Because of Methanosaeta's low KS, the low acetate concentrations in conventional, mesophilic anaerobic digestion yield Methanosaeta dominance. However, Methanosarcina absorbs increases in acetate more efficiently and thus promotes more stable digestion. This paper tests the hypothesis that decreasing digester feeding frequencies can increase Methanosarcina predominance. Two acetate-fed reactors were established at a 17-day solids retention time. One reactor was fed hourly, and one was fed once daily. Microscopic and molecular methods were used to verify that the hourly fed reactor enriched for Methanosaeta, while the daily fed reactor enriched for Methanosarcina. Growth and substrate-use kinetics were measured for each reactor. A digester overload condition was simulated, and the Methanosarcina-enriched reactor was found to perform better than the Methanosaeta-enriched reactor. These findings indicate that Methanosarcina dominance can be achieved with infrequent feedings, leading to more stable digestion.

Use of dynamic energy budget and individual based models to simulate the dynamics of cultivated oyster populations

We successfully tested a Dynamic Energy Budget (DEB) model of the oyster Crassostrea gigas using published environmental data and growth data collected in Thau lagoon (France). Estimates of most DEB parameters were based on independent datasets and only two parameters were calibrated using our datasets: the shape parameter, which was used to convert body volume into shell length, and the half-saturation coefficient, which controlled the functional response of assimilation to food concentration, represented by chlorophyll-a concentration. The DEB model proved to be robust and generic: it was able to reproduce oyster growth in Thau lagoon and other ecosystems. We also assessed population dynamics by coupling DEB equations and an Individual Based Model (IBM) of cultivated oyster populations. The results were compared with previously published simulations of harvested production and standing stock based on an empirical growth equation and a partial differential equation of population dynamics. Differences between the two studies were explained by the difference between the predictions of oyster growth with the empirical and the DEB models. We also accounted for growth variability between individuals and showed that IBM offers a powerful alternative to continuous equations when several physiological variables are involved.

Application of a dynamic energy budget model to the Pacific oyster, Crassostrea gigas, reared under various environmental conditions

The Dynamic Energy Budget (DEB) model (Kooijman, S.A.L.M., 1986. Energy budgets can explain body size relations. J. Theor. Biol. 121, 269–282; Kooijman, S.A.L.M., 2000. Dynamic Energy and Mass Budgets in Biological Systems. Cambridge University Press, Cambridge, 424 pp.) has been adapted to describe the dynamics of growth and reproduction of the Pacific oyster ( Crassostrea gigas) reared in different areas under conditions ranging from controlled to natural. The values of the model parameters were estimated from available physiological data and from published information. The sets of data used to validate the model came from three long-term growth experiments (> 5 months) performed on Pacific oysters reared under different conditions of food and environment. The forcing variables were temperature and phytoplankton densities, the latter being assessed from in vivo fluorescence and chlorophyll-a concentration measurement. The successful validation of the model on the three data sets demonstrated its ability to capture the dynamics of the energy budget in the Pacific oyster in various environments with the same set of parameters. The only parameter that varied between simulations was the half-saturation coefficient (X K), because of a different diet composition between the three environments under test. The model successfully reproduced quantitatively the growth and reproduction and the timing of spawning. These first simulation data led us to propose several promising perspectives of application for this model in shellfish ecosystems.

Pseudo-faeces production in bivalves

Many filter feeders produce pseudo-faeces from selected particles that are filtered; pseudo-faeces does not pass the gut. Food intake can be limited by the filtering (acquisition) as well as the digestion (processing) rate. Its dynamics can be analysed in a straightforward way in the context of the Dynamic Energy Budget (DEB) theory using the closed hand-shaking protocol of Synthesizing Units. The model reveals how food intake depends on the relative size of the filtering and digestion machinery, which can be used to model differentated growth of these structures if allocation is linked to their relative workload. It turns out that non-digestible particles modify the apparent half-saturation coefficient, which makes that estimates for this coefficient can be used to quantify the mean silt load in a given habitat.

Effects of Oxygen on Aerobic Solid-State Biodegradation Kinetics

Oxygen is a critical control variable for composting and other solid-state biodegradation processes. In this study we examined the effect of varying oxygen concentrations (1%, 4%, and 21% O2 (v/v)) on biodegradation kinetics under different substrate (sewage sludge and synthetic food waste), temperature (35, 45, 55, and 65 degrees C), and moisture (36-60% H2O) conditions. Three forms of a saturation or Monod-type model and one form of an exponential model were evaluated against data from extensive experiments under carefully controlled environmental conditions. The exponential model performed well at temperatures from 35 to 55 degrees C but had problems at higher temperatures. The Monod-type models yielded the best fit based on R2 values. Multiple linear regression was used to express the oxygen half-saturation coefficient as a function of temperature and moisture. For a modified one-parameter saturation model the half-saturation coefficient varied from -0.67% to 1.74% v/v O2 under the range of conditions typical of composting systems. While the positive correlation of biodegradation rate with oxygen concentration reported by previous researchers held true for temperatures below 55 degrees C, an inverse relationship was found at 65 degrees C. Although this study did not directly examine anaerobic conditions, the results under microaerophilic conditions suggest oxygen may not offer kinetic advantages for extreme thermophilic biodegradation processes.