Influent Substrate Concentration Research Articles

Advanced Modeling of Mixed Populations of Heterotrophs and Nitrifiers Considering the Formation and Exchange of Soluble Microbial Products

Biological process modeling is advanced by explicitly describing heterotroph and nitrifier biomass, incorporating formation of soluble microbial products (SMP) from both the bacterial groups, and allowing degradation of SMP by the heterotrophs. Biomass decay now has two parts, endogenous respiration and formation of biomass-associated products (BAP). The model is applied to investigate interactions between heterotrophs and nitrifiers. Main attention is directed to evaluating the role that SMP produced by nitrifiers plays as a supply of organic substrate to heterotrophs and to predicting the COD concentration in the effluent. The model quantitatively describes the observed accumulation of SMP in the effluent at long SRT and at high influent substrate concentration. The significance of SMP from nitrifiers to support growth of heterotrophs is clearly elucidated through the model experiments under various operational conditions. The results indicated that a high NH4+-N/COD ratio in the influent would decrease original substrate COD due to increased heterotrophs whose growth is supported by SMP from nitrifiers, but total COD increases. The minimum substrate concentration, Smin, is reduced for heterotrophs by the additional growth from SMP.

メタン生成流動床の処理特性と付着生物膜の成長過程の非定常解析

Accumulation of inert organic solids within biofilm in a methanogenic fluidized bed was investigated by conducting a continuous feed experiment in which the influent substrate concentration was stepwise increased. The previously developed model considering accumulation of inert organic solids and biomass detachment was applied to the simulations of biofilm growth and treatment efficiency in the above-mentioned experiment.The transient response of treatment were well explained with the model by giving the growth kinetic constants and the detachment coefficients of the responsible “active biomass”, whose concentrations were defined with the substrate consumption activities. The biofilm growth was deeply associated with the accumulation of inert organic solids, the rate of which depended on the decay coefficient and the growth yields of “active biomass” as well as the detachment coefficient. The detachment coefficient was estimated to be much smaller for decayed biomass than “active biomass” and bio-polymer. The attached biomass in the methanogenic fluidized bed contained a significant amount of bio-polymers which reached around 8 to 10% of total organic solids of biofilm. The production rate coefficient was estimated at 0.4 to 0.5 [mgCODPoly·mgCODcell-1] with the assumed growth yield of 0.05 [mgCODcell·mgCOD-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.

Kinetics of Anaerobic Treatment

A review of the kinetics of anaerobic treatment and the reported values of such kinetic parameters as the maximum specific substrate utilization rate (k), the half-saturation constant (Ks), the microbial growth yield (Y), and the microorganism decay rate constant (b) are presented. The available kinetic information is presented for each subprocess: (a) hydrolysis of complex, paniculate organic materials; (b) fermentation of amino acids and sugars; (c) anaerobic oxidation of long-chain fatty acids and alcohols; (d) anaerobic oxidation of intermediary products (such as short-chain fatty acids); (e) homoacetogenesis; and (f) methanogenesis. The intrinsic rates of each step as well as mass transfer limitations and their effect on the intrinsic kinetics are discussed and areas requiring further research are also identified. Substantial variation exists in the reported values of the kinetic coefficients. This variation is due in part to the variability in mode of operation, environmental and operational conditions in the various studies as well as to the lack of a widely accepted standard procedure for measuring and expressing the biokinetic coefficients. The hydrolysis step is usually assumed to follow first-order kinetics. Whenever the kinetics of the hydrolysis step were studied, they were generally found to be the limiting-step in the overall conversion of complex substrates to methane. With the exception of the hydrolysis step, all other subprocesses of anaerobic treatment have been successfully modeled by following Monod kinetics. The Contois and Chen & Hashimoto model has also been used quite extensively to account for the effect of influent substrate concentration on effluent quality. Based on a brief overview of the observed phenomena related to the kinetics of mass transfer in methanogenesis, it is concluded that with but few exceptions, the evidence for the significance of mass transfer effects in the different reactor configurations is circumstantial and, in some cases, contradictory. Our understanding of the kinetics of paniculate substrate removal in biofilms is still incomplete for engineering applications, and more research is necessary.

Role of substrate concentration in particle size distribution of methanogenic granular sludge in UASB reactors

The effect of influent substrate concentration on particle size distribution of methanogenic granular sludge was studied in laboratory-scale UASB reactors fed with propionate as sole carbon and energy source. A mean biomass increase of 60.9 mg VSS/d and 0.95 ml sludge/d was measured in five UASB reactors operated in parallel mode, resulting in a mean SVI of 7.8 ml sludge/g dry wt. Particle size distributions were measured by a gravimetric method and by direct image analysis. Median granule diameter increased with increasing influent substrate concentration and decreased with decreasing concentration. Increasing the influent concentration led to an increase of the methanogenic activity of the granules with propionate or acetate as test substrate.

New Method of Immobilization of Microbial Cells by Capture on the Surface of Insoluble Pyridinium‐type Resin

A new method for the immobilization of microbial cells has been developed. Whole cells of Escherichia coli with aspartase activity were immobilized by capture on the surface of cross-linked poly(N-benzyl-4-vinylpyridinium bromide) containing styrene (BVPS resin), an insoluble pyridinium-type resin. When a suspension of the bacterial cells in buffer solution was passed through a glass column containing beads of BVPS resin, the cells were captured on the resin surface and formed an immobilized cell system. A fixed-bed column reactor containing 300 mg of the bacterial cells immobilized by capture on 10 g of BVPS resin beads was used for the preparation of L-aspartic acid from ammonium fumarate. Continuous operation of tne bioreactor produced L-aspartic acid in a quantitative yield when the influent substrate concentration was 0.1M and the flow rate was 0.41-0.83 bed volumes per hour at pH 7.4-7.7 at 30 degrees C.

Multivariable Long-Range Predictive Control Algorithm Applied to a Continuous Flow Fermentation Process

The dynamics of biotechnological processes are highly complex and usually unknown. These processes are described by a set of non linear and non stationary equations derived from mass balance considerations. The complexity of these systems limits the application of classical control techniques and indicates that adaptive techniques may be of interest. This paper presents a simulation study of the multivariable generalized predictive control applied to a continuous flow fermentation process. The control design is based on predicting the process outputs over several steps and assumptions on future control actions. The control design is based on a linear discrete-time model with unknown and possibly varying parameters. The simulation is performed using a nonlinear and time-varying model of the process . These parameters are estimated by a constant trace adaptation algorithm with necessary features (data filtering and normalisation, UD factorization, dead zone .. ) that enhance the robustness of the resulting self-tuning algorithm. In the parametric model, the dilution rate and the influent substrate concentration are the control variables (Inputs) and the biomass and substrate concentrations stand for the controlled variables (Outputs). Numerical results illustrate the good performance and the excellent properties of the presented control scheme, particularly its ability to cope with varying dynamics and high level disturbances.

Bacterial aggregates of various and varying size and density: a structured model for biomass retention

Models for completely-mixed continuous-flow systems that retain bacterial aggregates have until now only considered reactors containing a single type of aggregate. A novel model is presented, which accounts for the dynamic behaviour of a variety of aggregates in such a reactor during steady state operation. The model predicts reactor performance (in particular biomass concentrations) as resulting from individual aggregate characteristics, which are size dependent. As the main feature a life cycle for an individual aggregate is incorporated, consisting of the growth of small aggregates and the fragmentation of large ones. Wash-out of individual aggregates or, conversely, their retention, is formulated as a function of their settling velocity. The overall biomass hold-up is therefore a complex function, resulting from the interaction of various processes. It is shown to be variable and to decrease with dilution rate (D). The reactor biomass concentration depends in a complicated way on D and on the mechanism of fragmentation. The influent substrate concentration ( s in) positively affects the reactor and the effluent biomass concentrations, but does not influence retention. The distribution of aggregate dimensions is independent of s in, but is strongly determined by D. Increasing D provokes a general increase in aggregate diameter. In nearly all cases, a bimodal distribution of substrate conversion over diameter categories is observed; at elevated D values especially the contribution of intermediate aggregate sizes to total conversion is negligible.

New method of immobilization of microbial cells by capture on the surface of insoluble pyridinium‐type resin

A new method for the immobilization of microbial cells has been developed. Whole cells of Escherichia coli with aspartase activity were immobilized by capture on the surface of cross-linked poly(N-benzyl-4-vinylpyridinium bromide) containing styrene (BVPS resin), an insoluble pyridinium-type resin. When a suspension of the bacterial cells in buffer solution was passed through a glass column containing beads of BVPS resin, the cells were captured on the resin surface and formed an immobilized cell system. A fixed-bed column reactor containing 300 mg of the bacterial cells immobilized by capture on 10 g of BVPS resin beads was used for the preparation of L-aspartic acid from ammonium fumarate. Continuous operation of tne bioreactor produced L-aspartic acid in a quantitative yield when the influent substrate concentration was 0.1M and the flow rate was 0.41-0.83 bed volumes per hour at pH 7.4-7.7 at 30 degrees C.

嫌気性流動床におけるメタン生成に及ぼす流入基質濃度および流入負荷の影響

嫌気性消化法の効率化のため, 二相消化法のメタン生成相に嫌気性流動床法を導入した。そして, 流入基質濃度や流入負荷が, 流動床の基質除去特性および菌体保持特性に対し, どのような影響を及ぼすかを検討した。使用した基質は, 酢酸単一基質ならびに, グルコースを少量添加した酢酸, プロピオン酸およびn-酪酸からなる混合酸基質である。流入基質濃度の実験の結果, 酢酸単一基質では, 流入基質濃度が増大するにつれ, 流出基質濃度も増大すること, 床内菌体量は, 流入基質濃度が増大するにつれ, グルコース添加の混合酸の系では増大するが酢酸単一基質の系では減少することがわかった。さらに, 流入負荷の実験の結果, 流入負荷が30kgCOD・m-3・d-1までは, 酢酸単一基質, グルコース添加の混合酸基質のいずれの系とも, 良好な処理が行われたが, 酢酸単一基質の系では, 処理水質が変動しやすいことがわかった。

Dynamic modeling of an immobilized cell reactor

A mathematical model has been developed to describe the dynamic aerobic reaction occurring in a semibatch type of mixed flow reactor, containing cells immobilized in gel beads. This modeling is an extension of that developed in our previous study, for an immobilized cell reactor involving ethanol fermentation. In contrast to anaerobic reactions such as ethanol fermentation, (wherein the influent substrate concentration can be set at any desired level), aeration becomes necessary to provide additional substrate (oxygen) for most aerobic reactions occurring in immobilized cell reactors. Tobacco cell cultivation was chosen as a representative aerobic reaction, and the effect of aeration was assessed in terms of the volumetric coefficient of oxygen from gas to liquid phases.

Optimization of a two‐phase anaerobic digestion system treating a complex wastewater

Abstract The performance of a two‐phase anaerobic digestion system consisting of a CSTR acidogenic reactor and a methanogenic fluidised bed reactor was assessed for different ratios of the hydraulic retention times of the two reactors. Furthermore, different influent substrate concentrations and different organic loading rates were applied. The results have shown that the two‐phase system is capable of COD removals superior or similar to the single‐stage system, when the volume of the methanogenic reactor is reduced by up to 25% and an equal volume of acidogenic reactor is introduced. The effect of phase separation on the effluent characteristics, biogas production and biomass hold‐up are also discussed.

Methane generation from chemically pretreated cellulose by anaerobic fluidized-bed reactors

Alkali cooking of cellulose at 10% (w/v) consistency, performed at 250°C, gives a liquor containing organic acids as main components (lactic, acetic and succinic acids). A synthetic substrate, representative of this liquor, was used as feed for two anaerobic fluidized-bed reactors operating at 35°C. The effects of hydraulic retention time and influent substrate concentration on substrate consumption and methane generation were studied. Organic removals of up to 95% and methane generation rates of 1·09 litres CH 4 litre R −1 day −1 were achieved at a retention time ( θ R ) of 8·3h and at an influent substrate concentration of 1400 mg COD litre −1. At θ R = 3·5 h, conversion decreased to 60%. When feeding the cooked liquor, conversions were slightly lower, around 50% at θ R = 4 h and 1300 mg COD litre −1 of influent substrate concentration. However, the methane volumetric production rate was as high as 2·5 litres CH 4 litre R −1 day −1 under the same conditions. The results suggest that alkaline cooking with subsequent methane fermentation offers a viable process for the treament of cellulosic materials, such as municipal solid waste.

Kinetics of Microbial By‐Product Formation in Chemostat Pure Cultures

Microbial by‐products are present in large quantities in both activated sludge (AS) systems and chemostat pure cultures. In wastewater AS systems, these by‐products impose additional organic loads on downstream processes. These by‐products are primary contributors to the dependence between effluent and influent substrate concentrations. Also, their presence in AS systems is partially responsible for producing the same effluent quality by either completely mixed AS or plug flow system. The specific rate of product formation (v) was investigated using chemostat pure cultures of Sphaerotilus species, S. natans, and Pseudomonas species. The results clearly indicate that v is an exponential function of the dilution rate (D). When D approaches zero, large quantities of microbial products are possibly caused by cell maintenance and/or endogenous respiration. As D increases, the concentration of products decreases to a minimum level. Further increases in D result in significant increases in the concentration of microbial by‐products. Also, both the by‐product concentrations and the v are reduced under nitrogen limiting or low dissolved oxygen conditions for the two obligate aerobic Sphaerotilus species. At low dissolved oxygen concentrations, the microbial by‐products for facultative anaerobic Pseudomonas species increase significantly.

Anaerobic acidogenesis of a complex wastewater: I. The influence of operational parameters on reactor performance

The influence of operational, parameters, such as hydraulic retention time, organic loading rate, influent substrate concentration, pH, and temperature, on the performance of the first phase of anaerobic digestion has been investigated. A complex substrate based on beef extract was used, and six series of experimental runs were conducted, each one showing the effect of one operational variable. The predominant fermentation products were always acetic and propionic acid, independent of the values of the operational parameters. For initial COD concentrations and hydraulic retention times above the critical values identified as 3 g/L and 6 h, respectively, the degree of acidification achieved was between 30 and 60%. The degree of acidification was found to increase with the hydraulic retention time and decrease with the influent substrate concentration and organic loading rate, while the opposite held true for the rate of product formation. Furthermore, it has been demonstrated that acidification is primarily determined by the hydraulic retention time and the rate of product formation by the influent substrate concentration. The concentration of the acetic acid produced was found to depend on the operational parameters. However, the concentration of propionic acid produced depended only on the substrate availability with a consistent proportion of 8% initial COD converted to it. The optimum pH and temperature were 7 and 40 degrees C, respectively. The percentage of acetic acid as a proportion of the total volatile fatty acids produced was found to increase with increasing pH and temperature, while the percentage of propionic acid seemed to decrease accordingly. Finally the effect of the temperature on the rate of acidification followed an Arrhenius type equation with an activation energy equal to 4739 cal/mol.

Effects of SMP on Biofilm‐Reactor Performance

The extended steady state biofilm model is utilized to predict the performance of a completely mixed biofilm reactor in terms of substrate removal, biofilm accumulation, soluble microbial products (SMP) formation, and total soluble organic carbon (SOC) removal. Three important aspects of how SMP formation affects the effluent quality from biofilm reactors for the concentration range of practical interest are relevant to advanced wastewater treatment, groundwater recharge, and drinking water treatment. First, for intermediate surface loadings, the concentrations of the effluent SMP and SOC are directly proportional to the influent substrate concentration, and SMP comprises the majority of effluent SOC. However, for high and very low loading, residual substrate is most of the effluent SOC. Second, SMP formation and SOC removal by the steady state biofilms are affected by both substrate utilization kinetics and reactor conditions. Changing reactor conditions, such as hydraulic detention time, affect the actual surface loading, while kinetic parameters, such as biofilm loss rate and cell yield, control the minimum achievable substrate concentration (S\dm\di\dn) and the minimum flux to give a deep biofilm (J\dd\de\de\dp). Third, in order to achieve the best treatment efficiency in terms of organic carbon (C), the biofilm reactor must maintain an optimum biofilm thickness that gives the lowest SOC concentration. At least in concept, biofilm thickness can be controlled by manipulating the shear loss component of the biofilm loss rate.

Hydrogen-dependent control of the continuous anaerobic digestion process

Membrane inlet mass spectrometry was used to directly measure the concentrations of CH4 and H2 in a mesophilic (37°C) completely mixed, laboratory scale, anaerobic digester, continuously fed at a retention time of 7 days with a glucose (50 mM) mineral salts medium. When the digester was overloaded by an increase in the influent substrate concentration, equivalent to 15.5 kg (COD) m-3 (digester) day-1 the concentrations of H2 and short chain fatty acids increased with a concomitant decline in the pH: following an initial stimulation methanogenesis was inhibited. Regulation of the H2 signal from the mass spectrometer in a closed feedback loop by controlled addition of carbon source under a potential overload condition, enabled the H2 concentration to the controlled around 1μM and a high steady state rate of methanogenesis of 42 μM min-1 to be maintained; this is equivalent to 1.4 volumes of CH4 per culture volume per day. The hydrogen-dependent control system was also used to prevent inhibition of methanogenesis when the digester was subject to volumetric overloading potentially equivalent to a retention time of 1 day.

Toward optimum control of the activated sludge process with reliability analysis

Abstract A scheme to maximize reliability and to identify upsets caused by influent and process disturbances of the activated sludge treatment system with recycle is presented. Reliability is the probability that the effluent wastewater quality meets the maximum contamination standard for BOD5. The plant is assumed to operate under steady-state conditions. Since influent flow and substrate concentration have significant variation, they are introduced into the model as random variables. thus concerns about plant stability are addressed. Reliability is expressed as a function of return sludge concentration and recycle flow. Control charts are used to identify upsets caused by influent disturbance, combinations of flow and BOD5. and process disturbance, combinations of F/M (food to microorganism ratio) and MLSS (mixed liquor suspended solids). Recommendations to maximize reliability in the overall context of plant performance are presented and discussed.

Soluble microbial products (SMP) formation kinetics by biofilms

Soluble microbial products (SMP) formation kinetics were investigated by employing a laboratory-scale biofilm reactor and naturally-grown oligotrophs. The experimental results indicated that the majority of effluent soluble organic carbon(SOC) was SMP, while only a small fraction of the effluent SOC was the residual original substrate. Utilization-associated products (UAP), which were produced directly from substrate metabolism, were more important than biomass-associated products (BAP), which were produced by basic metabolism. The SMP contained mainly high-molecular-weight organic compounds, although the organic carbon source to a biofilm reactor was a low-molecular-weight compound. The steady-state concentrations of the effluent SMP and SOC were directly proportional to the influent substrate concentrations in this study. An extended steady-state biofilm model was developed by incorporating into the steady-state biofilm model an SMP formation model based on two types of SMP (i.e. UAP and BAP). The model described successfully the experimental substrate utilization, SMP formation, and the removal of total soluble organic matter (SOC).

Growth Kinetics of Attached Iron-Oxidizing Bacteria

A model of growth and substrate utilization for ferrous-iron-oxidizing bacteria attached to the disks of a rotating biological contactor was developed and tested. The model describes attached bacterial growth as a saturation function in which the rate of substrate utilization is determined by a maximum substrate oxidation rate constant (P), a half-saturation constant (K(s)), and the concentration of substrate within the rotating biological contactor (S(1)). The maximum oxidation rate constant was proportional to flow rate, and the substrate concentration in the reactor varied with influent substrate concentration (S(0)). The model allowed the prediction of metabolic constants and included terms for both constant and growth-rate-dependent maintenance energies. Estimates for metabolic constants of the attached population of acidophilic, chemolithotrophic, iron-oxidizing bacteria limited by ferrous iron were: maximum specific growth rate (mu(max)), 1.14 h; half-saturation constant (K(s)) for ferrous iron, 54.9 mg/liter; constant maintenance energy coefficient (m(1)), 0.154 h; growth-rate-dependent maintenance energy coefficient (m'), 0.07 h; maximum yield (Y(g)), 0.063 mg of organic nitrogen per mg of Fe(II) oxidized.