Half-saturation Coefficient Research Articles

Simultaneous nitrification and denitrification in bench-scale sequencing batch reactors

Two bench-scale sequencing batch reactors were fed with domestic wastewater and operated in an anaerobic-aerobic sequence for 139 d. Denitrification during the aerated react period was observed and the factors influencing the extent of simultaneous nitrification and denitrification were examined. It was found that the influence of DO on the nitrification rate during the aerated react period could be described by a Monod kinetic with a high oxygen half-saturation coefficient for autotrophic nitrifiers ( K O.A) of 4.5 mg/l. The dependency of the denitrification rate on DO could be described by a mathematical switching function with a higher switching function constant than expected, meaning that the extent of aerobic denitrification was higher than usual. It was also observed that aerobic denitrification decreased with time over the aerated react period. For most of the time of reactor operation nitrite was the main NO x species in the effluent, instead of the commonly expected nitrate. This led to the conclusion that the activity of Nitrobacter species was probably inhibited in the SBRs studied. It also demonstrated the importance of measuring nitrite in the effluent to ensure that the reactor performance and the extent of aerobic denitrification was not over-estimated.

Kinetic behaviour of waste tyre rubber as microorganism support in an anaerobic digester treating cane molasses distillery slops

The kinetics of anaerobic digestion of cane molasses distillery slops was investigated using a continuous-flow bioreactor which contained waste tyre rubber as support, to which the microorganisms became immobilized. Hydraulic retention times (HRT) ranging from 1 to 10 days were investigated at an average influent chemical oxygen demand (COD) concentration of 47.7 g/l. The maximum substrate utilization rate, k, and half saturation coefficient, KL, were determined to be 1.82 kg CODremoved/kg VSS day and 0.33 kg COD/kg VSS day. The yield coefficient, Y, and sludge decay rate coefficient, Kd, were also determined to be 0.06 kg VSS/kg CODremoved and 0.05 day-1, respectively. Methane production was maximum (6.75 l/l day) at a 2 day HRT corresponding to a biomass loading rate of 2.578 kg COD/kg VSS day. Biogas yield ranged between 0.51 l/g COD (HRT=2 days) and 0.25 l/g COD (HRT=1 day). In addition, the methane percentage in the biogas varied between 70.5% (HRT=10 days) and 47.5% (HRT=1 day). The close relationship between biomass loading rate and specific substrate utilization rate supported the use of Monod equations. Finally, the experimental values of effluent substrate concentration were reproduced with deviations equal to or less than 10% in every case.

Modelling of the anaerobic reactor in a biological phosphate removal process

A kinetic model called SIPHOR has been developed for the biological phosphate removal process. The model is based on IAWQ Activated Sludge Model No 1, and is divided into three sub-models, one anaerobic, one anoxic and one aerobic model. This paper describes the anaerobic model and results from a calibration and verification of the model on batch experiments performed with sludges from a full-scale plant in Helsingborg and a pilot-scale plant in Malmo. Both plants were run as UCT-processes. Anaerobic batch simulations have been used to identify the following constants, P-release rate (kp), fermentation rate (kferm), anaerobic hydrolysis rate (khx), P-release/VFA-storage (fpp) and the half-saturation coefficients, Kva, and Kpop. The stoichiometric constant fpp has been found to be directly related to influent waste water. If acetate is added as carbon source, fpp has a value of 0.43, for primary hydrolysed waste water the value is 0.35 and for normal primary waste water, 0.30 in Helsingborg and 0.35 in Malmö. The rate of anaerobic hydrolysis has been found to be near zero in the anaerobic reactor.

Performance and kinetics of an upflow anaerobic sludge blanket (UASB) reactor treating slaughterhouse wastewater

Abstract A laboratory study was devised to verify the use of Monod kinetics for the modelling of a continuous upflow anaerobic sludge blanket (UASB) reactor treating slaughterhouse wastewater. Eight different hydraulic retention times (4.0–0.3 day) were investigated at an average influent COD concentration of 5.1 g.l‐1. The maximum substrate utilization rate, k, and half saturation coefficient, KL, were determined to be 1.47 kg CODremoved. .kg‐1 VSS‐day‐1 and 1.23 kg COD.kg‐1 VSS‐day1. The yield coefficient, Y, and sludge decay rate coefficient, Kd, were also determined to be 0.17 kg VSS.kg‐1 CODremoved and 0.029 day‐1, respectively. The lose relationship between biomass loading rate and specific substrate utilization rate supported the use of Monod equations and allowed the model to be used predictively for assessing plant performance.

Comparative physiology of phenanthrene degradation by two dissimilar pseudomonads isolated from a creosote-contaminated soil

Two species of bacteria, identified as Pseudomonas stutzeri (P-16) and Pseudomonas saccharophila (P-15) by fatty acid methyl ester analysis, were found in a phenanthrene enrichment culture of a creosote-contaminated soil. The organisms are shown to be physiologically dissimilar, and their genetic relatedness is discussed. Phenanthrene degradation by both organisms followed Michaelis-Menten kinetics, allowing for the determination of half-saturation (Ks) and maximum activity coefficients, using nonlinear regression. Both organisms utilized kinetically similar enzymes for phenanthrene uptake and oxidation, as evidenced by similar Ks coefficients of approximately 0.2 mg/L and temperature optima of 40 degrees C, but levels of expression differed with different media. Each organism degraded phenanthrene via salicylic acid, but patterns of intermediate metabolism were shown to differ. P-15 excreted 1-hydroxy-2-naphthoic acid during growth on phenanthrene and demonstrated Michaelis-Menten kinetics for the oxidation of 1-hydroxy-2-naphthoic acid by resting cells. P-16 excreted only trace amounts of 1-hydroxy-2-naphthoic acid and demonstrated linear kinetics in response to 1-hydroxy-2-naphthoic acid concentration. P-15 was found to form thick biofilms on phenanthrene crystals and was characterized by a hydrophobic cell surface, whereas P-16 grew mostly in suspension and was hydrophilic. Neither organism produced significant amounts of biosurfactants when grown on phenanthrene. The implications of these findings for the design of systems to remediate contaminated soil are discussed.

Scumming due to actinomycetes: Towards a better understanding by modelling

The ACTISCUM model, which represents a condensed summary of hypotheses related to “scumming due to Actinomycetes”, is introduced. In order to simulate the competition between Actinomycetes and heterotrophic floc-forming microorganisms in activated sludge systems hydrophilic and hydrophobic (lipidic) substrates must be differentiated. The most important observations from practice may be simulated with the ACTISCUM model: small concentrations of surfactants and substantial concentrations of hydrophobic substrate may lead to the proliferation of Actinomycetes. Excessive growth of Actinomycetes may be suppressed by aerobic selectors at low solids retention times and by anoxic selectors at all solids retention times. For improved accuracy of model predictions the maximum specific growth rates, the lysis coefficients and the substrate half-saturation coefficients of heterotrophic floc-forming microorganisms and Actinomycetes and the hydrolysis constants should be subjected to further research. It is demonstrated with the ACTISCUM model that especially non-biodegradable, or only slowly biodegradable surfactants, may provoke a dramatic increase of the Actinomycetes population in the activated sludge. It is shown that inoculation of Actinomycetes favours their proliferation, a fact well known in practice. For certain wastewater compositions the anoxic selector has to be significantly enlarged in order to successfully suppress the Actinomycetes. Actinomycetes may be washed out at low solids retention times, but their washout always corresponds with a loss of the nitrifiers.

Kinetics of an upflow anaerobic sludge blanket reactor treating ice‐cream wastewater

Abstract A laboratory study was devised to verify the use of Monod kinetics for the modelling of continuous upflow anaerobic sludge blanket (UASB) reactors treating ice‐cream wastewater. Eight different hydraulic retention times (5.0–0.4 day) were investigated at an average influent COD concentration of 5.2 g.1‐1). The maximum substrate utilization rate, k, and half saturation coefficient, KL, were determined to be 1.39 kg CODremoved.kg‐1 VSS.day‐1 and 0.29 kg COD.kg‐1 VSS.day‐1. The yield coefficient, Y, and sludge decay rate coefficient, Kd, were also determined to be 0.16 kg VSS.kg‐1 CODremoved and 0.028 day‐1, respectively. The close relationship between biomass loading rate and specific substrate utilization rate supported the use of Monod equations and allowed the model to be used predictively for assessing plant performance.

Measuring maximum specific growth rate and half saturation coefficient for activated sludge systems using a freeze concentration technique

To measure the maximum specific growth rate (μ max) and the half saturation coefficient ( K s ), a simple respirometric technique was used, where differing volumes of concentrated wastewater were contacted with biomass in a respirometer and the response measured as a change in oxygen uptake rate (ΔOUR). The ΔOUR was then related to the growth rate, and a series of substrate concentration/growth rate relationships determined from which μ max and K s were calculated. A freeze concentration technique was developed to concentrate the wastewater. The concentration technique did not alter the response of the microorganisms to the wastewater. Maximum specific growth rates (μ max) and half saturation coefficients ( K s ) were found to vary between 1.3 and 1.9 d −1 and 1.5 and 3.2 mg l −1, respectively.

Observations on the Kinetics of Nitrification under Inhibiting Conditions Caused by Industrial Wastewater Compounds

Within the next few years nitrogen removal will be obligatory for both municipal and industrial wastewater treatment plants in Austria. During the operation of pilot plants, severe inhibition of the nitrification process has been observed in several cases. Further investigations have been carried out at two biochemical factories at temperatures in the range of 22 to 32 ±C, in one case at two pilot plants, in the other case at a full-scale plant in order to estimate kinetic parameters of nitrifying biomass under the particular inhibiting conditions of these wastewaters. In both cases competitive inhibition occurred during the start-up period for about two months. The ammonia nitrogen half-saturation coefficient for autotrophic biomass was in the range of 10 mg/l. In one case also maximum autotrophic specific growth rate varied in a wide range. It could be proved that the compounds of this wastewater have an inhibiting but no toxic effect on Nitrosomonas. The effluent ammonia concentration can be kept within the limits in case of competitive as well as non-competitive inhibition up to about 60% by increased minimum SRT. In case of severe non-competitive inhibition it is not possible to achieve feasible biological nitrification. In any case the inhibiting compounds should be located and removed from the wastewater.

Biodegradation kinetics of Methylosinus trichosporium OB3b at low concentrations of chloroform in the presence and absence of enzyme competition by methane

The kinetics of chloroform and trichloroethylene (TCE) degradation by the methanotroph, Methylosinus trichosporium OB3b, were measured in batch kinetic experiments. The experiments focused on initial concentrations of around 100 μg/l for chloroform and around 1 mg/l for TCE. The pseudo first-order rate constants ranged from 0.2 to 0.41/mg TSS-day for chloroform and from 0.5 to 3.31/mg TSS-day for TCE in the absence of methane. Comparison of the TCE rate constants to other work indicates that the organisms were producing the soluble form of their methane monooxygenase. The presence of methane caused significant enzyme competition at methane concentrations as low as 0.35 mg/l, resulting in smaller chloroform rate constants. The decreases in the rate constant were consistent with the predictions of an enzyme competitive inhibition model, which indicated a half saturation coefficient for methane in the order of 0.3 mg/l. The predominant degradation products from chloroform was carbon dioxide.

Factors affecting microbial sulfate reduction by Desulfovibrio desulfuricans in continuous culture: Limiting nutrients and sulfide concentration

The effects of sulfate and nitrogen concentrations of the rate and stoichiometry of microbial sulfate reduction were investigated for Desulfovibrio desulfuricans grown on lactate and sulfate in a chemostat at pH 7.0. Maximum specific growth rates (micro(max)), half-saturation coefficients (K(sul)), and cell yield (Y(c/Lac)) of 0.344 +/- 0.007 and 0.352 +/- 0.003 h (-1), 1.8 +/- 0.3 and 1.0 +/- 0.2 mg/L, and 0.020 +/- 0.003 and 0.017 +/- 0.003 g cell/g lactate, respectively, were obtained under sulfate-limiting conditions at 35 degrees C and 43 degrees C. Maintenance energy requirements for D. desulfuricans were significant under sulfate-limiting conditions. The extent of extracellular polymeric substance (EPS) produced was related to the carbon: nitrogen ratio in the medium. EPS production rate increased with decreased nitrogen loading rate. Nitrogen starvation also resulted in decreased cell size of D. desulfuricans. The limiting C : N ratio (w/w) for D. desulfuricans was in the range of 45 : 1 to 120 : 1. Effects of sulfide on microbial sulfate reduction, cell size, and biomass production were also investigated at pH 7.0. Fifty percent inhibition of lactate utilization occurred at a total sulfide concentration of approximately 500 mg/L. The cell size of D. desulfuricans decreased with increasing total sulfide concentration. Sulfide inhibition of D. desulfuricans was observed to be a reversible process.

Effects of temperature and phosphorous concentration on microbial sulfate reduction by Desulfovibrio desulfuricans

The effects of temperature and phosphorous concentration on the rate and the extent of microbial sulfate reduction with lactate as carbon and energy source were investigated for Desulfovibrio desulfuricans. The continuous culture experiments (chemostat) were conducted at pH 7.0 from 12 to 48 degrees C. The maximum specific growth rate (micro(max)) was relatively constant in the range 25 degrees C-43 degrees C and dramatically decreased outside this temperature range. The half-saturation coefficient was minimum at 25 degrees C. Cell yield was highest in the optimum temperature range (35 degrees C-43 degrees C) for growth. Maintenance energy requirements for D. desulfuricans were not significant. Two moles of lactate is consumed for every mole of sulfate reduced, and this stoichiometric ratio is not temperature dependent. Steady state rate and stoichiometric coefficients accurately predicted transient behavior during temperature shifts. The extent of extracellular polymeric substance (EPS) is related to the concentration of phosphorous in the medium. EPS production rate increased with decreased phosphorous loading rate. Failure to discriminate between cell and EPS formation by D. desulfuricans leads to significant overestimates of the cell yield. The limiting C:P ratio for D. desulfuricans was in the range of 400:1 to 800:1.

Biokinetics of an upflow anaerobic sludge blanket reactor treating whey permeate

A laboratory study was performed to determine the kinetic model and to evaluate kinetic coefficients of continuous upflow anaerobic sludge blanket (UASB) reactors treating whey permeate. Eight hydraulic retention times (5·-0·4 day) were investigated at fixed influent substrate concentration (10·4 ± 0·2 g COD/litre). The maximum substrate utilization rate, k, and half saturation coefficient, K L, were determined to be 0·941 kg COD rmvd/kg VSS/day and 0·773 kg COD/kg VSS/day. The yield coefficient, Y, and sludge decay rate coefficient, K d, were also determined to be 0·153 kg VSS/kg COD and 0·022/day, respectively.

Biodegradation of phenolic wastes

Phenolic biodegradation kinetics were determined in bioreactors with large solids retention times (SRT). Long term kinetic experiments were conducted in pulse-fed batch reactors for single substrate (phenol) and multiple substrates (combinations of glucose, phenol and pentachlorophenol). Short term initial rate experiments were also conducted on the single and multiple substrate reactors. Results indicate that phenol is metabolized at a maximum rate of 0.55 h −1 with a half saturation coefficient of 10 mg/1. Phenol concentrations in excess of 50 mg/1 inhibit the biodegradation rate. Our results also indicate that pentachlorophenol is cometabolized in the presence of phenol. It can be concluded that biodegradation of phenolic waste is a viable treatment option because the organisms, through their metabolic processes, reduced the waste concentrations below our detection limits.

Effect of mineral media on trichloroethylene oxidation by aquifer methanotrophs

The effect of growth in different mineral media on subsequent oxidation of trichloroethylene (TCE) by type I and type II aquifer methanotrophs was evaluated. Mixed culture MM1, containing a type II methanotroph, and a type I pure culture tentatively identified as aMethylomonas sp., were enriched and isolated from an uncontaminated groundwater aquifer. The second-order rate coefficients (k/Ks) for TCE oxidation by these cultures varied by more than an order of magnitude when the cultures were grown in different mineral media. The presence of a chelator (NaEDTA) in one of these media, termed Whittenbury, significantly enhanced rates of TCE oxidation by all the cultures tested. When pregrown in this mineral medium, the resting cells of the pure cultureMethylomonas sp. MM2 exhibited second-order TCE oxidation rates as great as 0.78 liter/mg·day, whereas when pregrown in Whittenbury lacking the chelator, the rates did not exceed 0.018 liter/mg·day. The rate of TCE oxidation byMethylomonas sp. MM2 pregrown in another mineral medium formulation, devoid of chelators (termed Fogel), was intermediate in value (0.26 liter/mg·day), and adding EDTA to this medium did not affect the rate. Adding 1.6 μM copper to both Whittenbury and Fogel mineral media reduced the TCE oxidation rates about an order of magnitude; subsequent addition of 84 μM EDTA partially alleviated this effect. The maximal rate coefficients (k) for TCE oxidation byMethylomonas sp. MM2 were significantly higher, and the half saturation coefficients (Ks) for TCE significantly lower, following growth in the presence of EDTA. Stationary phase TCE oxidation rates as great as 2.3 liter/mg·day were achieved whenMethylomonas sp. MM2, grown in Whittenbury medium was provided formate as a source of reducing power. Omitting EDTA from Whittenbury medium also significantly reduced the methane oxidation rate and the growth yield. Copper addition did not significantly affect the methane oxidation rate or growth yield. The internal membrane structures ofMethylomonas sp. MM2 evaluated by transmission electron microscopy showed the presence of internal membranes, the ultrastructure of which was the same regardless of growth medium or TCE oxidation rate. The methane monooxygenase responsible for TCE oxidation inMethylomonas sp. MM2 under the conditions of this study appears to be associated with the particulate fraction.

Sensitivity Analyses of Biodegration/Adsorption Models

The research was directed toward additional development and refinement of mathematical models of simultaneous adsorption and biodegradation in granular activated carbon (GAC) columns used in the treatment of low concentrations of synthetic organic chemicals. The sensitivity of models to individual parameters was investigated, as well as alternative formulations for mass transport resistances within the biofilm and at the biofilm/GAC interface. The sensitivity analyses identified three important parameters: the Monod half-saturation coefficient, the GAC surface diffusion coefficient, and the amount of biomass initially attached to the GAC. Small values of the half-saturation coefficient, which are characteristic of oligotrophic microorganisms, were required to simulate the entire range of experimental data. Models with and without a diffusive transport resistance through a biofilm matched the experimental data well. The substrate concentration, however, was quite low, and biofilm diffusion probably would be important at somewhat higher concentrations. A model having a transport resistance at the biofilm/GAC interface did not perform well, implying that sorbed substrate is readily available to microorganisms even under conditions that select for scattered growth of microorganisms on the GAC surface.

Comparison of population dynamics between slow- and fast-growing strains of the rotifer Brachionus calyciflorus pallas in continuous culture.

The population dynamics of a slow- and a fast-growing strain of the rotifer Brachionus calyciflorus are compared. Rotifers were grown in steady-states, at various specific growth rates (μ), in both two-stage chemostat and turbidostat cultures on the green alga Chlorella pyrenoidosa. Population variables, including specific ingestion (I), loss (L) and filtration (F) rates, yield (Y), production (P) and half-saturation coefficient of growth (K g), were calculated using a growth model based on saturation kinetics. I, L, F and K g were shown to be higher and Y and P lower for the fast-growing strain. Differences between the two strains with regard to these variables may represent tradeoffs associated with the faster potential growth rate. Steady-state relationships between these values and μ for the fast-growing strain, however, deviated from model predictions which suggest a possible shift from carbon to non-carbon growth limitation.

A modeling study of the effect of pH on carbon limited algal biofilms

A model was developed that describes concentration profiles and flux of carbon into inorganic carbon-limited algal biofilms. The model considers carbon dioxide utilization and production from photosynthesis and respiration, diffusion of the inorganic carbon species, and pH changes due to CO 2 utilization. The overall material balance gave a nonlinear ordinary differential equation coupled with an integral differential equation. This system was solved using a Runge-Kutta-Verner fifth and sixth order method. The bulk (interfacial) total carbon and pH were assumed fixed. The boundary value problem was solved with a shooting technique, where the interfacial slope was initially guessed and subsequently adjusted using the secant method. The results showed that bulk carbon concentration and bulk pH were both important aspects of inorganic carbon limitation. Parameter sensitivity was also addressed; model parameters that were found to be important to the results include diffusion coefficients, maximum utilization rate, half-saturation coefficient, and biofilm density. Results were found to be insensitive to the respiration coefficient.

Calcium alginate-Immobilized hepatic microsomes: Effect of NADPH cofactor on oxidation rates

An important function of the liver is detoxification of drugs, toxins and foreign compounds. Within the liver cell, the endoplasmic reticulum, isolated as the microsomal fraction, is especially active. Microsomal oxidation is the major oxidation pathway for many compounds, and the requirement for NADPH, an expensive cofactor, is an important consideration in bioreactor design. This paper presents design information for NADPH- and substrate-dependent oxidation rates for free and immobilized microsomes. The primary goal of this paper is determining NADPH requirements for oxidation. The effect of various initial levels of nicotinamide adenine dinucleotide phosphate (NADPH) on chlorpromazine oxidation rate has been studied for a crude hepatic microsomal fraction immobilized in calcium alginate gel. At an initial NADPH concentration of 600 nmoles/ml, immobilized microsomes accelerate to a maximal velocity of ≈ 240 nmoles min −1 ml −1 of oxygen consumption. In comparison, free microsomes reach a maximal velocity of approximately 150 nmoles min −1 ml −1 at an initial NADPH concentration of 220 nmoles/ml. By fitting the “initial” rate as a function of NADPH concentration to Michaelis-Menten kinetics, the apparent half-saturation coefficients ( K m) app are 3.5 nmole/ml for free microsomes and 134.4 nmole/ml for immobilized microsomes, however the maximum reaction velocity, V max, for immobilized microsomes is calculated to be 322 nmoles min −1 ml −1 compared with 145 nmols min −1 ml −1 for free microsomes. Preliminary studies indicate that is is possible to obtain significant reaction rates using calcium alginate immobilized microsomes and that this system may offer advantages due to its simplicity and lower cost.

The development from kinetic coefficients of a predictive model for the growth of Eichhomia crassipes in the field. I. Generating kinetic coefficients for the model in greenhouse culture

The kinetics of N- and P- limited growth of Eichhornia crassipes (Mart .) Solms were investigated in greenhouse culture with the object of developing a model for predicting population sizes, yields, growth rates and frequencies and amounts of harvest, under varying conditions of nutrient loading and climate, to control both nutrient inputs and excessive growth in eutrophied aquatic systems. The kinetic coefficients, maximum specific growth rate (Umax), half saturation coefficient (Ks) and yield coefficient (Yc) were measured under N and P limitation in replicated batch culture experiments. Umax values and Ks concentrations derived under N limitation ranged from 5,37 to 8,86% d + and from 400 to 1 506 µg N ℓ1respectively. Those derived under P limitation ranged from 4,51 to 10,89% d 1 and from 41 to 162 fig P ℓ1 respectively. Yc values (fresh mass basis) determined ranged from 1 660 to 1 981 (87 to 98 dry mass basis) for N and from 16 431 to 18 671 (867 to 980 dry mass basis) for P. The reciprocals of Yc values (dry mass basis), expressed as percentages, adequately estimated the minimum limiting concentrations of N and P {% dry mass) in the plant tissues. Kinetic coefficients determined are compared with those reported for algae. The experimental method used and results obtained are critically assessed.