Modeling and optimization of granulation process of activated sludge in sequencing batch reactors

Aerobic granulation is a promising process for wastewater treatment, but this granulation process is very complicated and is affected by many factors. Thus, a mathematical model to quantitatively describe such a granulation process is highly desired. In this work, by taking into account all of key steps including biomass growth, increase in particle size and density, detachment, breakage and sedimentation, an one‐dimensional mathematic model was developed to simulate the granulation process of activated sludge in a sequencing batch reactor (SBR). Discretization methodology was applied by dividing operational time, sedimentation process, size fractions and slices into discretized calculation elements. Model verification and prediction for aerobic granulation process were conducted under four different conditions. Four parameters indicative of granulation progression, including mean radius, biomass discharge ratio, total number, and bioparticle size distribution, were predicted well with the model. An optimum controlling strategy, automatically adjusted of settling time, was also proposed based on this model. Moreover, aerobic granules with a density higher than 120 g VSS/L and radius in a range of 0.4–1.0 mm were predicted to have both high settling velocity and substrate utilization rate, and the corresponding optimum operating conditions were be determined. Experimental results demonstrate that the developed model is appropriate for simulating the formation of aerobic granules in SBRs. These results are useful for designing and optimizing the cultivation and operation of aerobic granule process. Biotechnol. Bioeng. 2013; 110: 1312–1322. © 2012 Wiley Periodicals, Inc.     

Modeling continuous bioleach reactors

The results of recent research have shown that the bioleaching of sulfide minerals occurs via a two‐step mechanism. In this mechanism, the sulfide mineral is chemically oxidized by the ferric‐iron in the bioleaching liquor. The ferrous‐iron produced is subsequently oxidized to ferric‐iron by the microorganism. Further research has shown that the rates of both the ferric leaching and ferrous‐iron oxidation are governed by the ferric/ferrous‐iron ratio (i.e., the redox potential). During the steady‐state operation of a bioleach reactor, the rate of iron turnover between the chemical ferric leaching of the mineral and the bacterial oxidation of the ferrous‐iron will define the rate and the redox potential at which the system will operate. The balance between the two rates will in turn depend on the species used, the microbial concentration, the residence time employed, the nature of the sulfide mineral being leached, and its active surface area. The model described proposes that the residence time and microbial species present determine the microbial growth rate, which in turn determines the redox potential in the bioleach liquor. The redox potential of the solution, in turn, determines the degree of leaching of the mineral; that is, conversion in the bioleach reactor. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 64: 671–677, 1999.     

Modeling,simulation, and embryology

Summary A delightful book to get the whole picture of simulation applications in developmental biology and easily readable for those who would like to overlook the field in one quick sweep. If you would like to get a more detailed perspective, a great number of literature references provides this opportunity.     

Thermophilic bacterial leaching of manganese dioxide

Summary Thermophilic bacterial leaching of low-grade manganese oxide ore was, demonstrated at 50°C and 70°C. A static culture system was used with cane molasses as the nutrient source. By employing batch cultures, with an acid wash to redissolve adsorbed Mn²⁺ at completion of each batch, the bacterial reduction could be driven to completion.     

Modeling of biofilm reactors with consecutive reactions

Modeling of biofilm reactors has been carried out by several authors. Most of the models use first-order or zero-order kinetics, because of the simplicity of the solution of the mathematical problem. However, the reaction kinetics for many practical situations is a non-linear Monod kinetics, which requires numerical solutions. This paper deals with the modeling of biofilm reactors and effectiveness factor calculations for a biofilm particle with Monod kinetics and two consecutive reactions. The model is applied to biological denitrification in a fluidized bed bioreactor, in which the liquid phase is assumed to be in plug flow. Effectiveness factors of biofilm are numerically calculated by solving the system of ODES by orthogonal collocation. Axial concentration profiles of nitrate and nitrite species are calculated and compared with experimental results.     

Direct and indirect mechanisms in the bacterial leaching of covellite

Summary Bacterial leachings of sample of covellite using a strain of Thiobacillus ferrooxidans in 9 K medium with and without iron were made at several pulp densities. Rates of solubilization with and without iron correspond to total and to direct mechanism respectively. Orders of reaction (at each pulp density) for each mechanism at two temperatures were calculated.     

Analysis, evaluation, and optimization of kinetic parameters for performance appraisal and design of UASB reactors

Studies have been undertaken to explore the applicability of different kinetic models for the performance appraisal of upflow anaerobic sludge blanket (UASB) reactors treating wastewater in the range of 300-4000 mg COD/l. Three kinetic models namely, Monod, Grau second-order, and Haldane model are considered for the analysis. Both linear and nonlinear regressions have been performed to examine the best-fit among the kinetic models. In this process, five error analysis methods have been used to analyze the data. Apart from optimization of kinetic coefficients with minimization of associated errors, prediction of effluent COD has also been undertaken to verify the applicability of kinetic models. In both the cases, Grau second-order model is found to be the best class of fit for wide range of data sets in UASB reactor.     

Modeling, docking, and simulation of the major facilitator superfamily

X-ray structures are known for three members of the Major Facilitator Superfamily (MFS) of membrane transporter proteins, thus enabling the use of homology modeling to extrapolate to other MFS members. However, before employing such models for, e.g., mutational or docking studies, it is essential to develop a measure of their quality. To aid development of such metrics, two disparate MFS members (NupG and GLUT1) have been modeled. In addition, control models were created with shuffled sequences, to mimic poor quality homology models. These models and the template crystal structures have been examined in terms of both static and dynamic indicators of structural quality. Comparison of the behavior of modeled structures with the crystal structures in molecular dynamics simulations provided a metric for model quality. Docking of the inhibitor forskolin to GLUT1 and to a control model revealed significant differences, indicating that we may identify accurate models despite low sequence identity between target sequences and templates.     

Modeling evolution of spatially distributed bacterial communities: a simulation with the haploid evolutionary constructor

Background

Multiscale approaches for integrating submodels of various levels of biological organization into a single model became the major tool of systems biology. In this paper, we have constructed and simulated a set of multiscale models of spatially distributed microbial communities and study an influence of unevenly distributed environmental factors on the genetic diversity and evolution of the community members.

Results

Haploid Evolutionary Constructor software http://evol-constructor.bionet.nsc.ru/ was expanded by adding the tool for the spatial modeling of a microbial community (1D, 2D and 3D versions). A set of the models of spatially distributed communities was built to demonstrate that the spatial distribution of cells affects both intensity of selection and evolution rate.

Conclusion

In spatially heterogeneous communities, the change in the direction of the environmental flow might be reflected in local irregular population dynamics, while the genetic structure of populations (frequencies of the alleles) remains stable. Furthermore, in spatially heterogeneous communities, the chemotaxis might dramatically affect the evolution of community members.

     

Modeling bacterial growth responses

Summary The main steps of modeling bacterial growth responses are summarized and a new model for growth curves is shown. Its advantages are analyzed from some theoretical and practical points of view. The new model fits better and has more advantageous statistical properties than the Gompertz curve.     

An arsenic(III)-oxidizing bacterial population: selection,characterization, and performance in reactors

AIMS: To select an autotrophic arsenic(III)-oxidizing population, named CASO1, and to evaluate the performance of the selected bacteria in reactors. METHODS AND RESULTS: An As(III)-containing medium without organic substrate was used to select CASO1 from a mining environment. As(III) oxidation was studied under batch and continuous conditions. The main organisms present in CASO1 were identified with molecular biology tools. CASO1 exhibited significant As(III)-oxidizing activity between pH 3 and 8. The optimum temperature was 25 degrees C. As(III) oxidation was still observed in the presence of 1000 mg l(-1) As(III). In continuous culture mode, the As(III) oxidation rate reached 160 mg l(-1) h(-1). The CASO1 consortium contains at least two organisms - strain b3, which is phylogenetically close to Ralstonia picketii, and strain b6, which is related to the genus Thiomonas. The divergence in 16S rDNA sequences between b6 and the closest related organism was 5.9%, suggesting that b6 may be a new species. CONCLUSIONS: High As(III)-oxidizing activity can be obtained without organic nutrient supply, using a bacterial population from a mining environment. SIGNIFICANCE AND IMPACT OF THE STUDY: The biological oxidation of arsenite by the CASO1 population is of particular interest for decontamination of arsenic-contaminated waste or groundwater.     

Isolation,screening, and optimization of bacterial strains for novel transglutaminase production

Transglutaminases are a class of transferases known to form isopeptide bond between glutamine and lysine residues in a protein molecule. Increasing demand for transglutaminase in food and other industries and its low productivity have compelled researchers to isolate and screen micro-organisms with potential to produce it. In the present investigation around 200 isolates were screened for extracellular secretion of microbial transglutaminase (MTGase). Isolate B4 showed enzyme activity of 1.71?±?0.2?U/mL followed by isolate C2 which showed 1.61?±?0.17?U/mL activity, comparable with the activity of industrially used microbial strains. Biochemical analysis along with 16S r-RNA sequencing revealed these isolates (B4 and C2) to be Bacillus nakamurai and a variant of Bacillus subtilis, respectively. Amongst the various production media screened, a medium containing starch and peptone was found best for MTGase production. Correlation between growth, enzyme production, and sugar utilization was also studied and maximum enzyme production was obtained after 48 to 60?hr. Highest MTGase titer (3.95?±?0.03?U/mL for B4 and 2.65?±?0.17?U/mL for C2) was obtained by optimization of parameters. The enzyme was characterized for temperature and pH optima, pH and thermal stability, and effect of metal ions, suggesting its potential use in future applications.     

Modeling and estimating bacterial lag phase

A branching process model of a bacterial population with initial lag phase is developed. Approximations are established in order to facilitate parameter estimation. The validity of approximations and estimation procedures is tested with simulated data.     

Modeling,analysis and simulation of ant-based network routing protocols

Using the metaphor of swarm intelligence, ant-based routing protocols deploy control packets that behave like ants to discover and optimize routes between pairs of nodes. These ant-based routing protocols provide an elegant, scalable solution to the routing problem for both wired and mobile ad hoc networks. The routing problem is highly nonlinear because the control packets alter the local routing tables as they are routed through the network. We mathematically map the local rules by which the routing tables are altered to the dynamics of the entire networks. Using dynamical systems theory, we map local protocol rules to full network performance, which helps us understand the impact of protocol parameters on network performance. In this paper, we systematically derive and analyze global models for simple ant-based routing protocols using both pheromone deposition and evaporation. In particular, we develop a stochastic model by modeling the probability density of ants over the network. The model is validated by comparing equilibrium pheromone levels produced by the global analysis to results obtained from simulation studies. We use both a Matlab simulation with ideal communications and a QualNet simulation with realistic communication models. Using these analytic and computational methods, we map out a complete phase diagram of network behavior over a small multipath network. We show the existence of both stable and unstable (inaccessible) routing solutions having varying properties of efficiency and redundancy depending upon the routing parameters. Finally, we apply these techniques to a larger 50-node network and show that the design principles acquired from studying the small model network extend to larger networks.     

Modeling long-term compost application effects on nitrate leaching

Application of compost to agricultural soils may be beneficial for crop production by increasing soil fertility and supplying plant nutrients, however, any raise of the soil organic matter content may increase the potential for unintended groundwater contamination by nitrate leaching. In this paper, the effect of long-term compost applications on nitrate leaching, soil organic matter content, and crop production is analyzed using results of simulation scenarios for agricultural sites with loamy and sandy soils. Simulations were carried out using the Danish Nitrogen Simulation System (DAISY) which describes the nitrogen balance in a one-dimensional soil-plant-atmosphere system and considers compost type and application rate as well as management and cropping practice. Estimations of hydraulic and solute transport parameters are based on pedotransfer functions. Data from a 4.5-year period of field experiments with compost applications in northern Germany as well as from laboratory experiments with compost amended soil are used for model calibration. Simulation results suggest that: (i) with respect to nitrogen turnover the differences between compost types (i.e., non-matured and matured) are small compared to site-specific properties (i.e., soil temperature and water balance) and management practices (i.e., crop rotation) when considering a compost application period of 50 years; (ii) with respect to nitrate leaching the effect of different compost application scenarios is highly sensitive at the sand and relatively small at the loam site; and (iii) relatively high crop yields and acceptably low nitrate concentrations in the drainage water are obtained at the sand site when applying a combination of 10 t compost/ha/yr and soil- N_min adjusted mineral nitrogen additions of about 20 kg/ha/yr to a winter-grain dominated crop rotation. Further optimization may be possible by applying reduced rates of the (economically interesting) non-matured compost. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date.