Karachun V.V., Trivailo M.S., Mel’nick V.N.

National Technical University of Ukraine “KPI”

THE PRINCIPLE OF UNDERLYING CULTIVATION

OF POPULATIONS OF MICROORGANISMS

IN AEROBIC CONDITIONS

Recently in microbiological, food and medical industries it appeared a numerous number of different technical decisions on construction of reactors for aerobic growth of biomass and receiving its metabolits. At last two centuries it was received more than three hundred of patents on these constructions. The situation that formed can be explained not only by necessity of production, but by priority interests of wide general public of researchers, that see of this field.

Plant cells, which have cell wall, and cultures of living cell of animal and man, that do not have, accordingly growing up on the equipping with their specific, corrected instrument features of biotechnological processes. Hence it appears, either high-speed mechanical means of mass-exchange, or contrary – low-speed, without available components of big drawl, frictional and toothed pairs, clutches etc.

The effectiveness of bioreactors is defined by many factors. But the principal of them are used to be the qualitative characteristics of processes of mass-exchange and aeration. The technical decisions of features of constructions of biotechnological equipment are thus subjected to one point – exclusion of risk of appearing of gradient manifestation of these components in polyaggregate structure. The solution of problem serves as subsoil of growth of quality indexes of technological process.

Authors suggest patent-defended technical realizations for apparatus for cultivation of calls with the aim of decision the nagging problems of one of the priority field of development of contemporary state – biotechnology.

Logic of improvement of construction of bioreactors is completely opportune for chemical reactors.

For organization of industrial producing of materials of biological origin, it is utterly necessary the knowledge of chemical technology, biochemistry, microbiology etc. The valuing of the generally recognized contents of production in different fields of industry affirms that big number of processes about their essence is only the new method of approach to use the methods, which are widely used in industry. Thus the achievements of chemical producing may be used in biochemical technology. It is possible to make a couple of interesting comparisons of chemical and biochemical technologies.

1. The main conformities of mass-exchange and energy-exchange, as the concentration of stream of liquid, are general, but with the difference that the productions with treatment of biological processes have deal with narrow temperature diapason and rather often with viscous Newtonian fluid.

2. Many methods, such as filtration, found wide application in biochemical technology.

3. Numerous methods are connected with supporting the demands of sanitary-and-hygienic clauses and realization of sterilizing operations. Zome of them may be qualified as new. These methods ground on using heat, different chemical substances and penetrating radiation of high intensity.

4. The ownership of biology fundamentals is necessary for every aspect of biochemical technology, because often it arise the necessity of struggle against strange micro flora, or with treatment of surprisingly sensitive and unstable materials, in particular, albumens and ferments.

5. Biochemical technology includes number of specific productions, which do not ground on specific qualification. The producing of vaccines, to the point, requires knowledge and skills in medical sphere, in particular, such an aspect, as culture of tissue.

To the sector of biochemical technology refers those fields of industry that are called to produce, manufacture and to keep the materials of biological origin. Here it is necessary to refer processes of treatment the food products – bread-baking, preserving etc., fermentative productions – production of wine, beer, alcohol, acetone, butanol, and other resolvents, producing of yeasts, and also products of microbiological synthesis – antibiotics, vitamins, ferments, organic acids, bacterial defending preparations, steroids, growth accelerators etc.

The important role in biological systems plays heat- and mass-exchange through the surfaces of phase disengagement. Generally, these processes fulfil classic laws; however often do not fulfil usual conceptions.

Sometimes specialists on biochemistry have to slow down or to stop processes, which living organisms take part in, and sometimes – to accelerate them. Thus, in many cases of cultivating of microorganisms it happens the destruct all the collateral microbes to secure optimal conditions of growth of chosen species.

In process of chemical-technology operations substances undergo transformation, which have their own, immanent only them, physic-chemical properties. The nature of chemical interaction is many-sided. Naturally, the number of chemical reactors fulfils this variety. However, in specialized literature it is practically absent any satisfactory classification of chemical reactors, in case of bearing in mind non-constructive features of apparatus, but inner essentiality of processes, their ideology, characterized by concrete defined connection of physical and chemical phenomenon.

Really, the same reaction may be realized in the cascade of apparatus with mixers and in the columns. The apparatus, in which the reaction realizes, may be bubble, attachment-type, rotor-type or plate-type. As reactor it may be used one of the numerous constructions of contact apparatus. Although the construction of apparatus influences on rate of conversion and selectivity of process, its essentiality is characterized not with the construction of reactor but with definite interconnection of physical and chemical factors, necessary for successful running of reaction. The construction of apparatus is not only the mean of influence on this interconnection buy means of acceleration of individual physical or chemical stages.

It needs to be mentioned that technological parameters of process (temperature, pressure, setted rate of conversion etc.) often play role, analogous to role of the construction of reactor. But not always. Thus, the rise of temperature may put the system out of the zone of stratification into the homogeneous zone that substantially changes the inner matter of process. At once, the rise of pressure may lead to reverse transition.

Thereby, character of reactor work, demands to its work are defined not with construction and technological parameters, but in the first place with those physical processes, which ensures necessary demands of chemical interaction running. Exactly with these positions chemical reactors may be divided into three big groups: homogeneous, heterogeneous and heterogeneous-catalytic.

In homogeneous reactors process occurs in one phase and do not accompanies with phase-transfers. Leak of transference of substance or energy through the boundary of phases is the basic feature of homogeneous processes. At this it is not necessary reactor to contain only one phase. It can be filled with inert solid header for decreasing of the longitudinal mixing, either the inert fluid or gas-substance can be served in it for barbotage mixing or making the airlift. And with it, if in the reactor do not happen the exchange of substance or energy, it might be rating as homogeneous.

Reactionary phase in this case can be heterogeneous at its structure, temperature and concentration gradient may occur in it. Indeed, reactionary phase may exchange energy with the walls of reactor or with built-in heat-exchangers.

Homogeneous reactors can be liquid-phase and gas-phase. Heterogeneous reactors have two features. At first, interphase exchange of substance and energy (or both) happens, and firstly, solid catalyst is absent. The most widespread are heterogeneous reactors for systems liquid-liquid or liquid-gas. Rarely reactors for systems liquid-liquid-gas occur. Uniflow and counterflow, isothermal and non-isothermal reactors have their own features. However these discrepancies are not principle and do not serve as features of particular types of reactors. Some principal features have reactors in which phases exchange only energy. This type of reactors is the intermediate between homogeneous and heterogeneous. To the rank of heterogeneous, reactors of this type are rated in account of their computation needs calculation of interphase surface.

The structure of reactionary phase is one of most important characteristics of heterogeneous reactors. Reaction can occur in continuous or dispersed phase, and also in both phases at same time. In some cases the work of reactor is organizing in such way when the reaction to occur in continuous phase. This makes it possible better to use reactionary volume and increases the opportunity of regulation the process.

The feature of heterogeneous-catalytic reactors is the presence of solid catalyst. It differs the reactors with fixed, movable and with boiling ball of catalytic. Both reactors can be two-phase or three-phase. Two-phase reactors are divided into gas-phased and liquid-phased. Under such conditions, the process occurs in system gas-solid phase or liquid-solid phase. In three-phase reactors process usually occurs in system gas-liquid-solid phase.

There are two types of heterogeneous-catalytic reactors with fixed ball of catalyst: reactors with watering catalyst and reactors with flooded catalyst.

The work of chemical reactors and the description of methods of their calculation is the sense of numerous textbooks and monographs. However, if to take as a point of departure the classification of chemical reactors, previously given, it is ease to convince that in every without exception textbooks and monographs contemplated only a couple types of chemical reactors. Maim attention is spared to homogeneous and two-phased heterogeneous-catalytic reactors. It is also necessary to mention that, although some authors emphasize the difference between gas-phased and liquid reactors, features of homogeneous and heterogeneous-catalytic liquid-phase reactors are not specially conditioned at present time.

Heterogeneous and three-phase heterogeneous-catalytic reactors are being examined rarely than other. Apparatus of this type in general nomenclature of chemical reactors occur enough frequently. For example, appeal to processes of hydroformylation, hydrodesulfurization, liquid-phase oxidation, liquid-phase hydrogenation, synthesis of polyatomic alcohols, synthesis of isoprene etc. This list can be considerably expanded. But in textbooks and monographs it is inadmissible attention to methods of computation of reactors for implementation of reactions in two-phase systems – liquid-liquid or liquid-gas and in three-phase systems gas-liquid-solid phase.

Let’s analyze specific features of reactors of examined types and correlate them with features of other types of reactors. First of all, it becomes obvious the presence of principal disarrangement between heterogeneous and heterogeneous-catalytic reactors. At same time, three-phase heterogeneous-catalytic reactors in certain degree unit features of heterogeneous and heterogeneous-catalytic reactors with certain advantage of features of the last. So what are the features of heterogeneous process.

At first, in heterogeneous liquid-phase reactor process occurs in liquid-phase, that frequently serves to the necessity of accounting the features of kinetics of reactions of this class.

At second, in heterogeneous reactor one of transport phases is simultaneous the reactionary phase, that limits residence time of this phase in apparatus.

At third, in reactors for implementation of heterogeneous and heterogeneous-catalytic processes it occurs the distinctive aspect of interphase boundary, type of mass-exchange, and thus, its mechanism, although in all cases the heat transfere through the interphase boundary precedes the chemical reaction.

The work of heterogeneous chemical reactor may be characterized in such way. Two phases come into the apparatus: continuous and dispersed, each of them contains one or several reagents. To come into chemical interaction, reagents, which come into apparatus by means of transference phase, are due to move in reactionary phase at first. Products that form in the course of reaction are distributing among phases.

If to analyze different factors that influence on the work of heterogeneous reactor, they can be united in five groups:

- thermodynamic factors. These are constants of chemical and physical balance. Thermodynamic factors describe the direction of reaction, technological parameters of its carrying out, influence on the velocity and selectivity of process;

- kinetic factors. This group includes constants of velocity and energy of activation all general and collateral reactions, that occur in system, and also real and imaginary order of reaction;

- mass-exchange factors. These are mass-transference coefficient of initial and intermediate substances, and final product of the reaction.

-heat-exchange factors. Current group consists of heat-transference coefficient, between phases and heat-transference coefficient between environment and heat-exchange devices. Furthermore, surface area of external heat-exchange can be rated as thus group;

-hydrodynamic factors. Formally characteristics of interfacial area and mixing in solid and dispersed phases are a part of this group. However role of hydrodynamic factors is considerably wider, because hydrodynamic situation in reactor determines finally not only integral velocity of heat- and mass-exchange, but also the integral velocity of chemical reaction.

It can be separated constructional factors into special group, but, as it was marked, they do not play independent role. Constructional features of apparatus are only the influence implement on physical processes in reactor. In the first place, on hydrodynamic factors.

The main stage in producing any product of microbiological synthesis, on which the effectiveness of technology depends a lot, is the stage of cultivation of microorganisms in aerobic or anaerobic conditions. In industry underlying methods of cultivation are used and surface methods are used not so often. Accordingly to conditions and methods of cultivation, all industrial reactors and plants may be divided into three groups: reactors for underlying aerobic cultivation, reactors for underlying anaerobic cultivation, and plants for surface cultivation.

Principle of underlying cultivation of populations of microorganisms in aerobic conditions consists in permanent arrival of air into reactor environment receptacle – air at simultaneous intensive mixing of nutrient environment. Meanwhile processes on micro- and macro-level are being elapsed in reactor. To micro-level are conditionally attributed biochemical and physics-chemical phenomenon, which occur on the level of cells and do depend on morphological and physiological features of microorganisms. To macro-level belong hydrodynamical, heat and other phenomenon, which much determines constructive features of reactors. But such a dividing is relative, because processes that occur in reactor have germaneness. Phenomenons, which have a position on micro- and macro-levels, have a great role at modeling, scaling and creating high-intensive reactors.

Ferment environment is complex many-phase system, which condition depend on nature of microorganisms, their morphological and physiological features, substratum, rate and intensity of aeration, mixing etc. The complicacy of mathematical formulation of occurring in fermenter processes prevents from creating a strict mathematical model. The identification of similar to real models, will make it possible to calculate with using ECM optimal industrial specimens with the smallest expenditure.

At once, scale conversion from laboratorial to industrial fermanter without using intermediate stages became possible only for its certain assemblies today. It is created a great number of simplified and complex structural mathematical models of fermenters.

It exists a great number of monographs and tutorials, devoted to physic-chemical bases of computation of chemical reactors and their mathematical modeling. However the problems of computation of reactors for liquid-phase processes are elucidated in them either fragmentary or totally untouched.

Firstly it concerns heterogeneous reactors for implementation of reactions in two-phase systems liquid-liquid or liquid-gas, and also in three-phase systems gas-liquid-solid catalyst. Thereby, the computation of similar reactors is quite specific and in majority of its cases it essentially differs from computation of apparatus for homogeneous processes.