Jayant M. Modak

Optimisation of fed-batch bioreactors using genetic algorithms

An optimisation procedure based on genetic algorithm approach is developed for the determination of substrate feed profiles for the optimal operation of fed-batch bioreactors. The problem specific knowledge generated through the rigorous application of the optimal control theory is used to formulate the set of decision variables representing the qualitative and quantitative aspects of the feed rate profile. A customized genetic algorithm with suitable genetic operators is used for generating the optimal feed profiles. Even though the optimal control theory is not explicitly used, the feed rate policies thus evolved are shown to retain the characteristics of the profiles generated through the application of optimal control theory. The efficiency of the proposed algorithm is demonstrated with two fermentation processes: secreted protein and yeast cell mass production.

A comparative study of the mass transfer kinetics of metal biosorption by microbial biomass

A comparative study of the kinetics of lead and zinc biosorption was carried out using the biomass of Streptoverticillium cinnamoneum, Penicillium chrysogenum and Citrobacter sp. The uptake of metals in all cases was found to be rapid in the first 10 min, reaching an equilibrium within 30 min of contact. The rate of metal uptake was independent of initial metal concentration. The metal concentration profiles could be well predicted using a batch kinetic model.

Biobeneficiation of bauxite using Bacillus polymyxa: calcium and iron removal

Calcium and iron removal from a bauxite ore by Bacillus polymyxa has been demonstrated. Within a period of 7 days, the above organism could remove all the calcium and about 45% of iron from the ore in the presence of 2% sucrose in a Bromfield medium. The highest removal of calcium and iron corresponded with the maximum in extracellular polysaccharide production by the organism. Scanning electron microscopy of the biobeneficiated bauxite surfaces indicated tenacious attachment of the bacteria onto the ore particle. Some calcium and iron removal was observed even in the presence of bacterial metabolites such as polysaccharides, organic acids and slime. However, the calcium removal in the absence of microorganism (by metabolites alone) was found to be 50% of that obtained in its presence. These observations clearly indicate that both a direct mechanism through bacterial attachment to the ore and an indirect mechanism through leaching with metabolites are involved in the biobeneficiation process.

Mathematical model for evaluation of mass transfer limitations in phenol biodegradation by immobilized Pseudomonas putida

A mathematical model is proposed to analyze the mass transfer limitations in phenol biodegradation using Pseudomonas putida immobilized in calcium alginate. The model takes into account internal and external mass transfer limitations, substrate inhibition kinetics and the dependence of the effective diffusivity of phenol in alginate gel on cell concentration. The model is validated with the experimental data from batch fermentation. The effect of various operating conditions such as initial phenol concentration, initial cell loading, alginate gel loading on the biodegradation of phenol is experimentally demonstrated. Phenol degradation time is found to decrease initially and reach stationary value with increase in cell loading as well as gel loading. The model predicts these trends reasonably well and shows the presence of external mass transfer limitations. A new concept of effectiveness factor is introduced to analyze the overall performance of batch fermentation.

LbL Fabricated Poly(Styrene Sulfonate)/TiO2 Multilayer Thin Films for Environmental Applications

Fabrication of multilayer ultrathin composite films composed of nanosized titanium dioxide particles (P25, Degussa) and polyelectrolytes (PELs), such as poly(allyl amine hydrochloride) (PAH) and poly(styrene sulfonate sodium salt) (PSS), on glass substrates using the layer-by-layer (LbL) assembly technique and its potential application for the photodegradation of rhodamine B under ultraviolet (UV) irradiation has been reported. The polyelectrolytes and TiO(2) were deposited on glass substrates at pH 2.5 and the growth of the multilayers was studied using UV/vis spectrophotometer. Thickness measurements of the films showed a linear increase in film thickness with increase in number of bilayers. The surface microstructure of the thin films was characterized by field emission scanning electron microscope. The ability of the catalysts immobilized by this technique was compared with TiO(2) films prepared by drop casting and spin coating methods. Comparison has been made in terms of film stability and photodegradation of rhodamine B. Process variables such as the effect of surface area of the multilayers, number of bilayers, and initial dye concentration on photodegradation of rhodamine B were studied. Degradation efficiency increased with increase in number of catalysts (total surface area) and bilayers. Kinetics analysis indicated that the photodegradation rates follow first order kinetics. Under maximum loading of TiO(2), with five catalyst slides having 20 bilayers of polyelectrolyte/TiO(2) on each, 100 mL of 10 mg/L dye solution could be degraded completely in 4 h. The same slides could be reused with the same efficiency for several cycles. This study demonstrates that nanoparticles can be used in wastewater treatment using a simple immobilization technique. This makes the process an attractive option for scale up.

Studies on multi-metal ion tolerance of Thiobacillus ferrooxidans

The influence of different concentrations of base metal ions, such as CU2+, Zn2+ and Fe3+, when present either alone or in different possible binary and ternary combinations in a 9K medium, on the fel rous ion oxidation ability of Thiobacillus ferrooxidans was studied. Levels and degree of toxicity of these ions have been quantified in terms of toxicity index (TI). Copper and zinc tolerant strains of the bacteria were developed through serial subculturing and their activity tested in the presence of the above metal ions in comparison with the behavior of wild unadapted cells under similar conditions. Copper tolerant strains (25 g/L Cu2+) were found to be more efficient in the bioleaching of both copper and zinc concentrates than wild unadapted strains, while zinc tolerant strains (40 g/L Zn2+) exhibited better leaching efficiency only in the bioleaching of sphalerite concentrates. The significance and relevance of multi-metal ion tolerance in Thiobacillus ferrooxidans has been highlighted with respect to bioleaching of sulphide mineral concentrates

Fermentation properties of agro-residues, leaf biomass and urban market garbage in a solid phase biogas fermenter

he decomposition and gas production pattern of eight unprocessed biomass feedstocks representing annual weeds, leaf litter, agro residues and market wastes were monitored in this laboratory study. Solid phase fermentation was effected with a weekly fed biomass bed sprinkled twice daily with recycled fermentor liquid to initiate and sustain biogas production from the decomposing biomass bed. Fermentors were fed from the top with gradually increasing feed rates to determine maximum feed rates sustainable. Feed rates of 1 g total solids

Modeling of heat and mass transfer for solid state fermentation process in tray bioreactor

(TS) 1^{-1}d^{-1}

Optimization of fed-batch bioreactors using genetic algorithm: multiple control variables

was possible which lead to pseudo steady state gas production rates between

Dissolution of particles of pyrite mineral by direct attachment of Thiobacillus ferrooxidans

0.26-0.98 11^{-1}d^{-1}