Contact Info

Chemical Engineering

Room No. 14

Telephone: (80) 2293-3108
Fax: (80) 2360-8121     

Mailing Address:

Department of Chemical Engineering

Indian Institute of Science

Bangalore, 560012


Welcome to Jayant M. Modak's Website - Research

Bioleaching of minerals and ores                                         

Dissolution of metals from ores, removal of metal ions from effluents and generation of acidic waters at mine sites are some of the processes which result from mineral-microbe interactions. In the area of mineral biotechnology, we have investigated several processes which result from mineral-microbe interactions, namely, microbial ecology of gold ore and bauxite deposits, dissolution of metals from minerals and ores, removal of metal ions from effluents and generation of acidic waters at mine sites. Our research focuses on understanding the mineral-microbe interactions and developing suitable mathematical models for quantification of these processes. Our work has contributed significantly to elucidating the mechanisms of bacterial leaching. In particular nominee has clearly brought out the importance of direct microbial attachment to sulphide minerals. Increase in leaching rates with particle size is one of the most unexpected and hitherto unreported finding of his work. Our investigations have clearly brought out the dynamic nature of mineral-microbe interactions, that is, both mineral surface and microorganism properties such as hydrophobic, surface charge and composition undergo a change when they come in contact with each other. These changes are shown to result in enhanced attachment of bacteria to the mineral surface, higher metal tolerance and hence higher leaching rates.
One of the impediments in commercial utilization of biomineral technology is the slow kinetics of the processes. We have investigated various strategies for improving the kinetics of the bioleaching process. Serial subculturing is shown to increase the tolerance of the microorganisms to high dissolved metal ion concentrations as well as high solid loading. However, such an acquired tolerance is shown to be stress sensitive. In the absence of stress (high metal concentration), the organisms lose their tolerance. Immobilization of bacteria in polyurethane foam is shown to be a simple technique for enhancing the bioleaching kinetics. Apart from bioleaching, we have also investigated removal of calcium from bauxite ores. Our results have showed that both direct attachment of bacteria as well as leaching by metabolites is responsible for leaching of calcium from bauxite. An equilibrium model is developed for predicting the solubility of calcium in the metabolite solution. The knowledge gained in past several years has resulted in technology development for bioleaching processes. One such process of interest to us is the bioliberation of gold from its sulphidic ores and concentrates. Dissolution of sulphidic matrix by bacteria liberates the gold, which can then be extracted using cyanidation. 

In the last two years, we have initiated studies on extracting cobalt, nickel and copper from manganiferrous ocean nodules using microorganisms and their byproducts. Ocean nodules are a rich source of cobalt and nickel and processing of these nodules has been studied by various routes. But none have been successful. In this study we have isolated a microorganism from the nodules and used the organism and its byproducts for leaching the metals from the nodule. The organism has been characterized to be a halophile , which grows rapidly in artificial seawater nutrient broth at room temperature. In a single stage leaching process using the cell free supernatant, we are able to leach about 40% of cobalt and about 15-20% of copper and nickel within 4 hours. When the residue of the first stage leaching was leached with a fresh metabolite, similar leaching efficiencies were obtained. The cumulative leaching efficiencies are far superior compared to conventional mineral acid leaching. Most importantly, the leaching with the microorganism is carried out in the neutral pH range (pH 7.5), which makes it very attractive when compared to acid leaching. The metabolite produces a reducing environment and also contains siderophore like phenolic compound/compounds with an attached carboxyl group that might form soluble organic complexes with the metals. In the presence of organic reducing agents such as ascorbic acid and salicylic acid along with the metabolite, the leaching of the metal values could be enhanced to more than 60%. These studies have been carried with pulp densities of up to 10%. So far all studies have been done in shake flasks and we intend to extend the studies to a bioreactor.


Biosorption of metals                                         

Biological removal of toxic metal ions is another area in which microbe-mineral interactions are gainfully utilized. We have investigated removal of several metal ions such as nickel, iron, calcium, chromium etc. using waste fungal biomass from fermentation industry. Various important parameters which influence the biosorption have been identified and mechanisms for biosorption proposed. We have shown that biosorption with living cells can completely remove metal ions from solution. However, processes with living cells are time consuming and costly, and therefore, biosorption with nonliving cells have been investigated in detail. For successful scale up of the process, modeling is an essential component. We have developed a framework for mathematical modeling for such processes by combining statistical thermodynamic principles of adsorption with double layer theories of electrostatic interactions. We are able to capture some of the inherent characteristics of biosorption such as effect of pH and metal ion concentration using such a fundamental approach 



Modeling of fermentation processes                                           

Bioprocess involving microbial cells and enzymes are multiphase processes with biotic phase (microorganisms) and abiotic phase consisting of gas, liquid and solid. Our research in the area of modeling of bioprocesses has focused on understanding the interactions between multiphase transport phenomena and biochemical reaction kinetics. Several processes investigated include multiphase multienzyme oxidation of glucose, growth and metabolite production in hollow fiber bioreactors and bioremediation using immobilized cell systems. We have developed a generalized model for flow fields in hollow fiber bioreactor in the presence of growth of the microorganisms. Our analysis of the model shows that the secondary flows arising in these reactors can change the nutrient and/or product distributions significantly , and thereby, alter the bioreactor performance. We have been able to bring out the complex interactions between multiphase transport phenomena and biochemical reaction kinetics . Several interesting criteria for assessing the limitations posed by the mass transfer processes on the performance of the bioreactor for processes have been proposed. Growth and metabolite production by cells involves complex network of reactions at two levels: metabolite and gene. We have developed a model for pyruvate decarboxylation for multienzyme pyruvate dehydrogenase complex. The model predicts interesting dynamic behavior including multiplicity of steady states and oscillations. This work provides insights into pyruvate metabolism in the cells and predicts experimentally observed multiplicity of steady states. We have applied powerful Metabolic Control Analysis (MCA) tools to analyse complex metabolic pathways in the living cells. The application of MCA to pyruvate metabolism demonstrates for the first time the difference in control of metabolism under different steady states. This work also explains the differences observed between in vitro and in vivo responses of the metabolic reactions. It has been possible to identify the rate-controlling com ponent of the complex. It is expected that such an understanding would lead to better genetic engineering of the cells.  




Optimization and control of fermentation processes                                           

Optimization of bioprocesses is a challenging problem due to complexity and time variant nature of the bioprocesses. Determination of feed rates for fed-batch processes is one such problem. We have carried out pioneering work in the area of optimization fed-batch bio-reactor system. This work utilizes rigorous application of control theory in unraveling the general characteristics of optimal operating strategies of fed-batch processes. The kinetics of the processes influences the operating reactor strategies and therefore, selection of optimal mode of operation, batch, continuous or fed-batch. Various modern optimal control strategies involving neural networks have been applied to the optimization problem. The optimal control problem is first discretized and then the optimal feed rate is determined. It is possible to use this technique even when detailed model is not available. Neural network is able to recognize the optimal feeding pattern directly from the experimental data. Genetic algorithm is another optimization tool based on the principle of survival of the fittest. An optimisation procedure based on genetic algorithm approach is developed for the determination of substrate feed pro-files 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. Hybrid techniques combining rigorous control theories and search algorithms such as GA are being developed. We are also investigating multiobjective optimization problems for fermentation problem using genetic algorithm MCA is a powerful theoretical metabolic engineering technique by which effect of changes in enzyme activities and other regulators on fluxes and concentrations characterizing the metabolic pathway are identified. By using MCA, the distribution of control of various fluxes and species concentrations is determined. These coefficients help in identifying the targets for the modification of metabolic pathways (fluxes), which is a central goal of metabolic engineering. MCA is generally applied to metabolic pathways under steady state (or pseudo-steady state) conditions. After realizing strong potential MCA for analyzing system at steady state, we have extended the approach to analysis of bioreactor system. The key requirement of such an approach is the representation of the biochemical reactor as a network of various processes. Such a formulation of a chemical/biochemical process enables application of MCA to different systems leading to better understanding of mechanistic aspects; which are difficult to find through conventional analysis. The control coefficients obtained using MCA approach has been used for steady state analysis of continuous bioreactors as well as optimization.  


Biomethanation of biomass                                           

Various types of biomass residues such as leafy waste, domestic solid waste, are potential source of energy if they can be efficiently converted to biogas. Unfavourable physical properties - biomass particles generally have a lower density than the digester liquid or acquire it as soon as biogas bubbles adhere to them, render conventional biogas reactors such as slurry reactors unsuitable for the treatment of biomass. Pre-treatment alternatives are costly. We, therefore, are focusing of using solid state fermentation processes and bioreactors for the treatment of biomass residues. The process of transformation of polysaccharide from biomass to biogas consists of two steps: acidogenesis, polysaccharide to acids and methanogenesis, acids to methane. Each step requires different type of bacteria. Using the concepts of plug flow reactors, we have developed reactors in which profiling of the bacteria develop as a natural anaerobic digestion process. Models are being developed to understand the complex phenomena and these models have been used to identify the key operating parameters. During anaerobic digestion of the biomass feedstock, very large numbers of methanogens colonise the insides of typical plant cells at a stage when all other exposed simple feedstock constituents have been digested, converted to gas and only a partially exposed lignocellulose complex is available for decomposition. This stage is reached between 10-30 days in a SSB fermentor depending upon the feedstock characteristics. This ligno-cellulosic skeleton with methanogenic bacteria attached to it was used as a whole cell immobilised system to determine its capability to digest liquid waste with moderate suspended solids content (simulating sewage and agro-industrial wastes). Laboratory results with agro-industry wastes showed17 that compared to a 0.5 kg VS converted/L/d to gas in a typical dung reactor, it was possible to convert around 10kg VS/L/d @24h retention time.  


Technology Development                                           

Demonstration Bioreactor Plant for Hutti Gold Mines Limited, Hutti, Karnataka

Gold, a precious noble metal, occurs in nature in its native form and usually associated with quartz. Such ores, referred to as free milling ores, are treated in a conventional process with cyanide to solubilize gold-cyanide complex. The gold is then recovered from the solution by using either zinc (old technology) or more recent, carbon-in-pulp technology. With extensive mining activities over centuries, the reserves of such free milling ores are fast depleting worldwide. Increasingly, the gold ores are found to be refractory in nature, that is, gold is associated with sulphides such as pyrite and arsenopyrite. In early nineties, The Hutti Gold Mines Company Limited (HGML) faced with dwindling grade free milling ores and ex-cavations of sulphidic zones, recognized the need for exploring new technology for gold processing. Initial collaborative research project sponsored by HGML between 1990-95 dealt with exploring the feasibility of biotechnological route for gold processing. These projects were essentially a laboratory scale study of investigating microbial ecology of Hutti Gold Mines and establishing a process for biotreatment of sulphidic ores. Having successfully demonstrated the technology at laboratory level, a need was felt to scale up this process and demonstrate it on a larger scale. In collaboration with Department of Metallurgy-IISc, We have successfully setup a demonstration plant to process about 100 kg/day of sulphide gold bearing concentrate using Thiobacillus ferrooxidans. Without biooxidation the gold recovery was about 40%. But after biooxidation, the gold recovery increased to 90% while silver recovery increased to 95%. This technology has potential for increasing the production of gold by using some of the newly explored reserves in Karnataka.

High thoughput waste water treament plants

Coffee is a major commercial crop of the country. The processing of coffee fruits to remove bean results in an effluent, which is high in organic load. If untreated and discharged into streams, this causes many a health and environmental hazard. A technology is being de-veloped to treat these effluents as a part of collaborative research with ASTRA, IISc. The cof-fee pulping is done only in winter months from November to February. Constructing an efflu-ent plant that only serves during pulping season is not likely to be acceptable, and therefore, a multipurpose biogas plant is being designed. During the pulping season, system functions with coffee plantation effluent at high throughput while low-level operation using biomass feedstocks such as coffee skin, weeds, and fallen leafy litter is carried out in the remainder of the year. In order to address this challenging problem of environmentally acceptable discharge from coffee plantations, high throughput bioreactors were developed with funding under Indo-Norwegian Environmental Program. Bioreactors were developed and deployed by the ASTRA Center with INEP funding to treat coffee effluents into biogas and compost. The project attempted to show that the high degree of pollution caused to Karnataka's rivers by coffee processing wastewater could in-stead become a resource (energy /fuel) that may be recovered for local and environmental benefits. This process of resource recovery also brought down the pollution levels. Bioreac-tors were also low cost options. Bioreactors substituted the large and unwieldy anaerobic la-goons that spread over acres of prime estate land. These bioreactors cost about 10% of con-ventional anaerobic-aerobic lagoon costs on typical coffee plantations. It provided up to 80 m3 biogas (about 3 LPG cylinders) for every ton clean coffee produced. It removed >85% pollution (COD/BOD) in a single step and this facility could be used throughout the year (with other solid biomass feedstocks when coffee processing season concluded). Under ideal conditions, it showed a potential to recover the cost within 2 years. This successful demon-stration resulted in many plantations coming forward to use the bioreactors without subsidy or incentives. Currently, there are more than 20 such bioreactors in operation at different coffee plantations in Chickmangalore district of Karnataka. It was envisaged that these multi-feed bioreactors could also be utilized for processing segregated urban solid wastes (USW) with minor design modifications to reap similar benefits. Several organizations including Munici-pal Corporations and Industrial Units have shown interest in utilizing these reactors.