Kinetics of soluble microbial product formation in substrate-sufficient batch culture of activated sludge

The kinetics of soluble microbial product (SMP) formation under substrate-sufficient conditions appear to exhibit different patterns from substrate-limited cultures. However, energy spilling-associated SMP formation is not taken into account in the existing kinetic models and classification of SMP. Based on the concepts of growth yield and energy uncoupling, a kinetic model describing energy spilling-associated SMP formation in relation to the ratio of initial substrate concentration to initial biomass concentration (S ₀/X ₀) was developed for substrate-sufficient batch culture of activated sludge, and was verified by experimental data. The specific rate of energy spilling-associated SMP formation showed an increasing trend with the S ₀/X ₀ ratio up to its maximum value. The SMP productivity coefficient (α _p/e) was defined from the model on the basis of energy spilling-associated substrate consumption. Results revealed that less than 5% of energy spilling-associated substrate consumption was converted into SMP. Electronic Publication     

Effects of combining biological treatment and activated carbon on hexavalent chromium reduction

The objectives of the present work were: (a) to analyze the Cr(VI) removal by combining activated sludge (AS) with powdered activated carbon (PAC), (b) to analyze the effect of PAC and Cr(VI) on the growth kinetics of activated sludge, and (c) to determine if the combined method (AS-PAC) for Cr(VI) removal can be considered additive or synergistic with respect to the individual processes. Chromate removal was improved by increasing PAC concentrations in both PAC and AS-PAC systems. Cr(VI) removal using the AS-PAC system was higher than using AS or PAC. The increase of Cr(VI) caused longer lag phase and lower observed specific growth rate (μ_obs), biomass yield (Y_X/S), and specific growth substrate consumption rate (q_S) of activated sludge; additionally, PAC did not enhance the growth kinetic parameters (μ_obs, Y_X/S, q_S). Cr(VI) reduction in AS-PAC system was the result of the additive effect of each individual Cr(VI) removal process.     

Biodegradation and kinetics of aerobic granules under high organic loading rates in sequencing batch reactor

Biodegradation, kinetics, and microbial diversity of aerobic granules were investigated under a high range of organic loading rate 6.0 to 12.0 kg chemical oxygen demand (COD) m⁻³ day⁻¹ in a sequencing batch reactor. The selection and enriching of different bacterial species under different organic loading rates had an important effect on the characteristics and performance of the mature aerobic granules and caused the difference on granular biodegradation and kinetic behaviors. Good granular characteristics and performance were presented at steady state under various organic loading rates. Larger and denser aerobic granules were developed and stabilized at relatively higher organic loading rates with decreased bioactivity in terms of specific oxygen utilization rate and specific growth rate (μ _overall) or solid retention time. The decrease of bioactivity was helpful to maintain granule stability under high organic loading rates and improve reactor operation. The corresponding biokinetic coefficients of endogenous decay rate (k _d), observed yield (Y _obs), and theoretical yield (Y) were measured and calculated in this study. As the increase of organic loading rate, a decreased net sludge production (Y _obs) is associated with an increased solid retention time, while k _d and Y changed insignificantly and can be regarded as constants under different organic loading rates.     

A kinetic model incorporating energy spilling for substrate removal in substrate-sufficient batch culture of activated sludge

Batch assays are currently used to study the kinetic behavior of microbial growth. However, it has been shown that the outcome of batch experiments is greatly influenced by the initial ratio of substrate concentration (S _o) to biomass concentration (X _o). Substrate-sufficient batch culture is known to have mechanisms of spilling energy that lead to significant nongrowth-associated substrate consumption, and the Monod equation is no longer appropriate. By incorporating substrate consumption associated with energy spilling into the balance of the substrate oxidation reaction, a kinetic model for the observed specific substrate consumption rate was developed for substrate-sufficient batch culture of activated sludge, and was further verified by experimental data. It was demonstrated that the specific substrate consumption rate increased with the increase of the S _o/X _o ratio, and the majority of substrate was consumed through energy spilling at high S _o/X _o ratios. It appears that the S _o/X _o ratio is a key parameter in regulating metabolic pathways of microorganisms. Received: 18 January 1999 / Received revision: 7 May 1999 / Accepted: 28 May 1999     

Energetics of the growth of Methanococcus thermolithotrophicus

Methanococcus thermolithotrophicus was grown in a mineral salts medium at 65° C in a fermenter gassed with H₂ and CO₂, which were the sole carbon and energy sources. Evolution of growth parameters during batch culture experiments showed the existence of an uncoupling phenomenon. The growth was then studied using a continuous technique and steady states for various gas flow rates were obtained. Y _{CH 4}and the maintenance coefficient varied with the gas input. The maximum Y _{CH 4} determined for Methanococcus thermolithotrophicus was 3.33 g·mol^-1 CH₄. An excess of energy and carbon sources induced uncoupling of growth.     

The accumulation of fixed biomass increases the observed growth yield of a nitrifying biofilm

The observed growth yield (Y _obs) of a nitrifying biofilm metabolizing ammonia in a continuous flow reactor was constant below a fixed biomass concentration of 40–50 g COD-biomass cm^–2. Beyond this range, an increased Y _obs with the additional accumulation of fixed biomass could be due to a considerable accumulation of inactive materials within the nitrifying biofilm.     

Substrate consumption and excess sludge reduction of activated sludge in the presence of uncouplers: a modeling approach

A mathematical model with a consideration of energy spilling is developed to describe the activated sludge in the presence of different levels of metabolic uncouplers. The consumption of substrate and oxygen via energy spilling process is modeled with a Monod term, which is dependent on substrate and inhibitor. The sensitivity of the developed model is analyzed. Three parameters, maximum specific growth rate (μ _max), energy spilling coefficient (q _max), and sludge yield coefficient (Y _H) are estimated with experimental data of different studies. The values of μ _max, q _max, and Y _H are found to be 6.72 day^-1, 5.52 day^-1, and 0.60 mg COD mg^-1 COD for 2, 4-dinitrophenol and 7.20 day^-1, 1.58 day^-1, and 0.62 mg COD mg^-1 COD for 2, 4-dichlorophenol. Substrate degradation and sludge yield could be predicted with this model. The activated sludge process in the presence of uncouplers that is described more reasonably by the new model with a consideration of energy spilling. The effects of uncouplers on substrate consumption inhibition and excess sludge reduction in activated sludge are quantified with this model.     

Practical design equations for trickling-filter process

The concept of solid retention time (SRT) was applied in the trickling-filter process. A rational model of the trickling-filter process employing activated-sludge-process operational parameters was presented. The design equation was developed as follows; 1/SRT = [(S₀ ? S_n)/X ]·(F/V)·Y ? k_d, where SRT is the sludge retention time, S₀ is the influent substrate concentration; S_n is the effluent substrate concentration; X is the total cell mass retained per unit filter volume; V is the total volume of the filter; F is the influent flow rate; Y is the cell yield, and k_d is the cell decay rate. A laboratory-scale trickling-filter pilot plant treating synthetic sucrose waste-water was studied to verify the present design equation. The solid retention time was evaluated from the total slime mass (active and inactive) retained and the sludge wasted daily. It was found that the present design equation could be applied for designing the trickling-filter process by the application of SRT employed in the activated sludge process. Also, the SRT could be related to the hydraulic loading and influent substrate concentration for a given filter medium. The variation of SRT by the hydraulic loading at constant organic loading was observed and could be expressed by the mechanistic model. When SRT was maintained more than 12 days, it provided the highest five-day biological oxygen demand (BOD₅) removal, minimum sludge production, and lowest sludge volume index (SVI) value. The present model does include both microbial growth kinetic concepts, which can be more practical and meaningful for the design of a trickling filter.     

Influence of the ratio of the initial substrate concentration to biomass concentration on the performance of a sequencing batch reactor

Biomass behaviour and COD removal in a benchscale activated sludge reactor have been studied alternating anaerobic and aerobic conditions. Particular attention has been paid to the influence of the ratio of the initial substrate concentration (S ₀) to the initial biomass concentration (X ₀) on the reactor performance. Tests at very low ratios (S ₀/X ₀<2) demonstrate the existence of a threshold below which the reactor performance is seriously affected (S ₀/X ₀=0.5). Under conditions of total suppression of cell duplication, substrate maintenance requirements have also been calculated for the microbial consortium present in the activated sludges. The results obtained show that stressed biomass can survive conditions of substrate lack better than unstressed biomass.List of Symbols b h^–1 specific death rate - COD g/l chemical oxygen demand - DO g/l dissolved oxygen concentration - K _s g/l Monod saturation constant - MLSS g/l mixed liquor suspended solid concentration - P g/l phosphorus concentration - S g/l substrate concentration - S ₀ g/l initial substrate concentration - SS g/l suspended solid concentration - t h time - X g/l biomass concentration - X ₀ g/l initial biomass concentration - Y _SX g/g yield of growth on substrate - _max h^–1 maximum specific growth rate     

Modeling of growth and lactate fermentation by Lactococcus lactis subsp. lactis biovar. diacetylactis in batch culture

The kinetic behaviour of Lactococcus lactis subsp. lactis biovar. diacetylactis was studied in batch culture under non-limiting conditions that allow high growth and product formation. A model based on laboratory results is proposed for growth and l-lactate fermentation. It shows the necessity for differentiating biomass into three physiological states, two active, X_g (growth + acidification) and X_ng (acidification), and one inactive, X_i. The kinetic theory of the model demonstrates the non-competitive nature of fermentation end-product inhibition on growth and acidification, and describes the passage from one physiological state to another. Satisfying simulations were obtained for batch fermentations, and the use of this type of model for determining and optimizing fermentation parameters is discussed. Correspondence to: C. Diviès     

The oxygen requirements of yeasts for the fermentation of d-xylose and d-glucose to ethanol

Summary The effect of oxygen availability on d-xylose and D-glucose metabolism by Pichia stipitis, Candida shehatae and Pachysolen tannophilus was investigated. Oxygen was not required for fermentation of d-xylose or d-glucose, but stimulated the ethanol production rate from both sugars. Under oxygen-limited conditions, the highest ethanol yield coefficient (Y_e/s) of 0.47 was obtained on d-xylose with. P. stipitis, while under similar conditions C. shehatae fermented d-xylose most rapidly with a specific productivity (q_pmax) of 0.32 h^-1. Both of these yeasts fermented d-xylose better and produced less xylitol than. P. tannophilus. Synthesis of polyols such as xylitol, arabitol, glycerol and ribitol reduced the ethanol yield in some instances and was related to the yeast strain, carbon source and oxygen availability. In general, these yeasts fermented d-glucose more rapidly than d-xylose. By contrast Saccharomyces cerevisiae fermented d-glucose at least three-fold faster under similar conditions.Nomenclature q_pmax maximum specific rate of ethanol production (g ethanol per g dry biomass per hour) - Y_e/s ethanol yield (g ethanol per g substrate utilized) - Y_p/s polyol yield (g polyol per g substrate utilized) - Y_x/s biomass yield (g dry biomass per g substrate utilized) - _max maximum specific growth rate (per hour)     

A new kinetic approach to microbial storage process

In this work, a new kinetic approach was proposed to describe the microbial growth, substrate consumption, and formation and utilization of the intracellular storage products (X _STO) in activated sludge. It was found that the formation of X _STO was coupled with energy generation and respiration and that the X _STO formation rate was proportional to the substrate utilization rate. A high amount of external substrate resulted in a relatively rapid storage process with a large fraction of substrate electrons for X _STO formation. The maximum growth rate of active biomass on X _STO and the yield coefficient for growth on the storage polymers were estimated as 0.12 h⁻¹ and 0.60 g chemical oxygen demand (COD) _X g⁻¹ COD_STO, respectively. This established model was verified with the experimental results from two different case studies with pure and mixed cultures. Results showed that this kinetic model was able to accurately and mechanistically describe the microbial storage processes.     

Pantothenate limitation does not induce uncoupled growth of Zymomonas in chemostat culture

Summary Growth coefficients ofZymomonas mobilis were compared in glucose-limited chemostat culture using a complex medium and a defined minimal growth medium at non inhibitory concentrations of ethanol. Under carbon and energy limited conditions in the complex medium containing yeast extract, the max. molar growth yield (Y_G ^max) and maintenance energy coefficient (m_e) were 10.8 g cell/mol glucose and 8.3 mmol glu/g cell/hr, respectively. Glucose-limited growth in the minimal medium with NH₄Cl as nitrogen source promoted slight energetic uncoupling, as reflected in the decrease in the maximum growth yield. The growth yield with respect to calcium pantothenate was calculated to be 1.4×10⁴ g cell/g Ca-pantothenate. However, pantothenate-limited growth did not result in a decrease in growth yield nor an increase in the specific rate of glucose catabolism. Steady-state growth measurements failed to confirm the previously held view of Belaïchet al. (1972) that pantothenate deficiency induces energetic uncoupling inZymomonas.     

Conversion of paper sludge to ethanol. I: Impact of feeding frequency and mixing energy characterization

In this paper, conversion of paper sludge to ethanol was investigated with the objective of optimization of the overall operation costs. Experimental work was undertaken to optimize cellulase loading, and to determine mixing energy requirements. It was found that decreasing feeding frequency (feed additions per residence time) allows the cellulase loading to be decreased at least two fold with no decrease in cellulose conversion but also entails mixing a slurry of higher solids content and lower conversion at the beginning of the operating cycle. The viscosity of paper sludge slurries was found to increase exponentially with decreasing conversion and increasing solid content. In particular, the viscosity (V) was described well by equation V = e^(kX−X ₀^)(S−S ₀^)+C (V viscosity (cp), X conversion, S solid content (g/L), k, X ₀, S ₀, C are empirical parameters). Added costs associated with operating at low feeding frequencies (including higher mixing energy and higher capital costs for the motor and for sludge hold tasks) were found to be small compared to the economic benefits resulting from reduced cellulase loading.     

Existe-T-IL des chromosomes sexuels multiples chez le campagnol,Microtus arvalis pallas?

The conclusions ofRaicu, Kirillova & Hamar (1969), according to whichMicrotus arvalis has multiple sex chromosomes (X ₁ X ₂ Y ₁ Y ₂, X ₁ X ₁ X ₂ X ₂), are in contradiction to the earlier work ofRenaud (1938) andMatthey (1953) who have reported heterogamety of the XY, XX type for this species as is the situation in the majority of mammals. The mechanism proposed byRaicu and his coauthors in unknown in mammals where only cases of multiple sex-chromosome mechanisms XY ₁ Y ₂, XX and X ₁ X ₂ Y, X ₁ X ₁ X ₂ X ₂ have been described. It was necessary therefore to reexamine the situation in this vole. The author is of the opinion that the conclusions ofRaicu and his coauthors cannot be substantiated and that in this case we have indeed the common type of sex determination.     

Production of medium-chain-length polyhydroxyalkanoates by activated sludge enriched under periodic feeding with nonanoic acid

The potential use of activated sludge for the production of medium-chain-length polyhydroxyalkanoates (MCL-PHAs) was investigated. The enrichment of bacterial populations capable of producing MCL-PHAs was achieved by periodic feeding with nonanoic acid in a sequencing batch reactor (SBR). Denaturing gradient gel electrophoresis analysis revealed Pseudomonas aeruginosa strains to be predominant in the bacterial community during the SBR process. The composition of PHA synthesized by the enriched biomass from nonanoic acid consisted of a large concentration (>89 mol%) of MCL monomer units and a small amount of short-chain-length monomer units. Under fed-batch fermentation with continuous feeding of nonanoic acid at a flow rate of 0.225 g/L/h and a C/N ratio of 40, a maximum PHA content of 48.6% dry cell weight and a conversion yield (Y_p/s) of 0.94 g/g were achieved. These results indicate that MCL-PHA production by activated sludge is a promising alternative to typical pure culture approaches.     

Modeling predation processes in activated sludge

Predation by protozoa plays an important role in activated sludge. In this work, the kinetics for protozoan predation of active bacteria (X_H), extracellular polymeric substances (EPS), and intracellular storage products (X_STO) are added into a previously expanded unified model that describes the dynamics of EPS, X_STO, and soluble microbial products (SMP). The new biomass growth–decay–predation model describes the biomass fractions, soluble organic components, and oxygen‐uptake rates considering EPS, X_STO, and predators during dynamic operating conditions in activated sludge. Model calibration using batch experimental data provides the new parameter values for predation processes and insights into mechanisms involving predators. The calibrated value of the maximum specific growth rate for the predators is much slower than for the bacteria, confirming that predators are relatively slow growers. However, the predators and bacteria have similar decay rates and dissolved oxygen affinities. Model testing with results independent of the calibration data shows two things. First, the model and calibrated parameters accurately simulate the independent results when predators are present. Second, eliminating predation by high salinity significantly lowers the OUR, and this is captured by the model. Biotechnol. Bioeng. 2010;105: 1021–1030. © 2009 Wiley Periodicals, Inc.     

Simulating a cyclic activated sludge system by employing a modified ASM3 model for wastewater treatment

To interpret the biological nutrient removal in a cyclic activated sludge system (CAS), a modified model was developed by combining the process of simultaneous storage and growth, and the kinetics of soluble microbial product (S _SMP) and extracellular polymeric substance (X _EPS) with activated sludge model no. 3 (ASM3). These most sensitive parameters were initially selected whilst parameters with low sensitivity were given values from literature. The selected parameters were then calibrated on an oxygen uptake rate test and a batch CAS reactor on an operational cycle. The calibrated model was validated using a combination of the measurements from a batch CAS reactor operated for 1 month and the average deviation method. The simulations demonstrated that the modified model was capable of predicting higher effluent concentrations compared to outputs of the ASM3 model. Additionally, it was also shown that the average deviation of effluent S _COD, S _NH, S _SMP and X _EPS simulated with the modified model was all less than 1 mg L⁻¹. In summary, the model could effectively describe biological processes in a CAS reactor and provide a wonderful tool for operation.

     

Quantitation of the Population Size and Metabolic Activity of a Resin Acid Degrading Bacterium in Activated Sludge Using Slot-Blot Hybridization to Measure the rRNA:rDNA Ratio

Abstract The 16S rRNA:rDNA ratio is a useful parameter for measuring metabolic activity of a selected member of a complex microbial community, as in pulp effluent activated sludge systems. The RNA:DNA ratio of Sphingomonas sp. DhA-33, previously isolated from a sequencing batch reactor treating pulp mill effluent, is positively correlated with its growth rate (μ) under steady-state conditions. DhA-33 was grown in a chemostat with growth rates ranging from 0.04 to 0.15 cell divisions per hour. DhA-33 was also able to degrade dehydroabietic acid in bleached kraft mill effluent (BKME) plus mineral medium in batch culture. Slot-blot hybridization with radioactively labeled species-specific oligonucleotide probes for 16S rRNA and 16S rDNA was used to measure rRNA, rDNA, and the RNA:DNA ratio of this strain when in a mixed sludge community. An increase in DhA-33 rDNA indicated growth of DhA-33 within the community. The RNA:DNA ratio of DhA-33 increased sharply during exponential growth and declined as cells entered stationary phase. The RNA:DNA ratio decreased earlier and faster in DhA- 33/sludge co-cultures than in DhA-33 pure cultures, presumably due to an earlier depletion of nutrients. The species-specific quantification of the RNA:DNA ratio makes it possible to estimate the metabolic activity of selected members of a microbial community in situ. Received: 15 March 1999; Accepted: 8 July 1999; Online Publication: 15 February 2000     

Determination of the maximum product yield from glucoamylase-producing Aspergillus niger grown in the recycling fermentor

Aspergillus niger has been grown in glucose- and maltose-limited recycling cultures to determine the maximum growth yield, the maximum product yield for glucoamylase production, and the maintenance requirements at very slow specific growth rates. Using the linear equation for substrate utilization, and using the experimental data from both recycling experiments, both the maximum growth yield, Y_xsm, and the maximum product yield, Y_psm, could be determined. The values estimated were 157 g biomass per mol maltose for Y_xsm and 100 g protein per mol maltose for Y_psm. Expressed on a C₁-basis these values are 0.52 and 0.36 C-mole per C-mol for respectively Y_xsm and Y_psm. The found value for Y_psm is half the value found for alkaline serine protease production in Bacillus lichoniformis, and it can be concluded that formation of extracellular protein is more energy consuming in filamentous fungi than in prokaryotic organisms. Maintenance requirements are no significant factor during growth of Aspergillus niger, and reported maintenance requirements are most probably due to differentiation.