WO2002000558A1 - Treatment of contaminated waters by surface aeration and recirculation of classified sludges - Google Patents

Abstract

The invention relates to a surface aeration treatment with recirculation of classified sludges, which is used for treating black waters, municipal waters or, in certain cases, wastewaters, comprising the following steps: screening the influent by means of a solids screen solely for the raw waters; recirculation pumping of waters with the lowest amount of dissolved oxygen from the biological oxidation tank to the surface aerator; injecting air by means of a blade fan with the purpose of maintaining high oxygen concentrations in the air inside the aerator; stirring by means of a mechanical stirrer which optionally provides for stirring, mixing and supplementary aeration; surface aeration by recirculating the mixed liquor and injecting air, which generates the liquid and gaseous interface that provoke oxygen transfer inside the aerator formed by the surface conduits; sedimentation with sludge classification with the purpose of not using sludges whose qualitative characteristics have been activated discretely; in this step, the sludges are classified into heavy, intermediate and light sludges with the purpose of recirculating the light sludges and recirculating or removing the heavy sludges whenever there are excessive sludges. The treatment can use the potential energy that is wasted in rapid black water courses with differences in level between 5 and 30 m, thereby enabling considerable energy savings by reducing the energy required for repumping and stirring.

Description

 TREATMENT OF POLLUTED WATER BASED ON CAPILLARY AERATION AND RECIRCULATION OF CLASSIFIED MUDS.

Technical Field:

Biological treatment of activated sludge for municipal wastewater or industrial wastewater:

Background:

At present, several aeration methods with recirculation of activated sludge are known, discretionally managed in their qualitative characteristics, in the treatment of sewage, municipal or industrial wastewater in some cases, in general, the characteristics of systems that are described are described. have managed, to establish the difference with respect to what has been termed as classified capillary aeration.

Bubble aeration system, these consist of the generation of bubbles at the bottom of aeration tanks, where gas bubbles are diffused in the liquid system, in some cases it is necessary that the flow of rising bubbles causes sufficient agitation, to ensure that the gas that has been transferred, diffuses enough throughout the tank, sometimes stirring equipment is installed, to improve the mixing conditions, one of the most relevant characteristics of this type of systems is that refers to the large amount of interface area that is generated, and that is the surface through which the gas transfer is made, another notable feature is the contact time that is achieved between the volume of gas confined in the bubble and the liquid, which brings as a consequence that in this type of systems high uses of oxygen are obtained, being larger the smaller the diameter of gene bubbles radas; The magnitude of the interface area is a function of the average diameter of the bubbles and the amount of air supplied; the contact time is a function of the bubble ascent rate, which depends on their diameter, and the depth of the tank; considering that two systems participate, one gas and one liquid, both they have a boundary film that divides them, called gaseous interface surface and liquid interface surface respectively, around the liquid system, speaking of a liquid interface film that has to transfer the gas, it is a function of the existing flow conditions in The gaseous system, that is to say, a flow between laminar and transition will have an interphase renewal factor close to the unit, so the transfer in these cases will be a function only of the diffusion coefficient of the gas in the liquid, and of the Thickness of the liquid interface film considered, the renewal factor will increase when the turbulence of the gaseous fluid increases, the transfer of gas to the liquid system, also depends on the concentration conditions of the gaseous system that provides the 0 ₂ .

The transfer can also be analyzed, considering an interphase film in the gas system, in which case it will depend on the flow conditions in the liquid interface and the concentration conditions of the liquid interface; In both cases, both the concentration factor and the renewal factor must accelerate or slow down the speed with which the mass transfer is carried out according to its magnitude.

The tensile materials, high temperatures and high concentrations of pollutants, tend to decrease the rate of oxygen transfer, since the stiffness of the spherical bubble structure, especially in the finest bubbles, demands more energy dissipation so that It is the renewal of the liquid interface surface, specifically this is due to the fact that the surface tension of the liquid is increased and generates a greater resistance, to the deformation of the spherical film of liquid nterfase, when this surface is in equilibrium , as it would be in this case the bubbles.

Some of the disadvantages of this type of aeration system, refer to the impossibility of providing effective agitation in the gaseous system, and although agitation can be applied to the liquid system, the results may not be profitable for its implementation, since due to characteristics of the gas confined in the bubble, the only thing that would be done is to transport it from one place to another, without presenting a high degree of sliding of gaseous particles, precisely in the area of the interface film, and on the other hand the volume confined per unit of generated area is relatively small, causing the effects of a long contact time to be neutralized; Bubble diffuser systems have a relatively high maintenance cost, regardless of the cost of the energy needed to compress the air, and make it reach the diffusers.

Contact aeration systems; These are formed by concrete structural tanks, which are filled with a porous material-based packaging, which can be of mineral origin such as stones, pieces of glass or prefabricated plastic material, these provide an extensive surface where microorganisms adhere forming a biological film, which remains fixed to the surface, until it reaches a thickness in which conditions arise, which allow it to be removed periodically by itself; the organisms in the film breathe the oxygen that exists in the holes formed; the drainage system allows the circulation of air up or down, depending on the temperatures of the influent and the porous medium, in order to improve the oxygen provision, especially for the film that is in the lower parts; the most usual depth is 2 meters; In these systems, the liquid is spread continuously or intermittently, for high load or low load units respectively, at the top by means of a series of nozzles mounted on sprinkler tubes, which can be fixed or have rectilinear movement or circulate, depending on the configuration of the tank; microorganisms receive food from the liquid that drains over the surface; There are currently materials, which can provide 40 to

2. 3

100 m / m of specific surface, to cover a wide range of needs, due to the way of application and arrangement of the area, approximately 40 to 85% of the surface is used, which is wet at intervals of approximately every 5 min. in the case of low load installations or continuously for high load installations; low load units usually handle

3 2 a hydraulic load of 1.5 to 6 m / m x total day, and an organic load of 0.08 to

3

1.5 kg / m useful volume of the tank; high load units can handle

3 2 3 a hydraulic load of 7 to 25 m / mx day and an organic load of 1.6 to 15 kg / m of useful volume of the tank; the contact aeration systems called also drip filters, they can eliminate from 80 to 85% for those of low load and 50 to 79% for those of high load.

In reference, exclusively to the aeration process by contact, it has to be started from the moment, when the nozzles of the sprinklers, generate the set of drops that form a rain, either intermittent or continuous as appropriate, in this stage the contact time and the interface area are very small so their effects are insignificant; When the drops arrive and make contact with the filter medium, the liquid spreads and drains onto the walls of the filter, so that the thickness of the liquid film is becoming smaller until it reaches a time when, Due to the properties of the surface tension and the viscous conditions of the liquid, it moves at a slower speed and due to the effects of gravity, the liquid will be filtered or drained through the small interstices of the film, giving opportunity for the case of the intermittent application, that the film absorbs liquid and this when drained by the effects of gravity, helps the unoccupied spaces to be filled with air, which, upon arrival of a new film of liquid and contaminating organic matter, is it poses in the spaces evicted by the liquid from the previous film, trapping gas microbubbles; It is important to mention that when a continuous feeding is being handled, the process behaves like the activated sludge process, that is, the biological activity in the film, lowers its intensity and a large part of the biological activity is generated, by the bacteria that are suspended in the liquid; Another characteristic of these systems is that they have an immense contact surface, and relatively contact times and a relatively short retention time. The configuration of the system demands a large volume for the generation of the interface surface, that is to say the space that occupies the solid material of the filter and the empty spaces, which constitute one of the characteristics of this type of units.

An advantageous feature of this type of system is its ability to withstand sudden variations in organic load; It is also necessary that, in low load systems, a percentage of nitrification is carried out, which is due to the fact that there are types of nitrifying bacteria that develop adhered to the contact surface, for having enough time and oxygen for its development.

The main disadvantage consists of the large spaces, which are required for the construction of the structures; maintenance to restore operation, when flooding phenomena occur, is one of the most common problems that arise; Another effect that constitutes a disadvantage is the generation of conditions conducive to the development of flies.

There are a number of devices introduced to this type of aeration systems, in order to adapt them to a greater number of treatment needs, such as the recirculation of sludge from the primary settler, the secondary settler, of the same effluent from the aeration tank. , in different percentages; There are also one- and two-stage systems, usually the first stage of high rate and the second stage of low rate.

Mechanical aeration system; mechanical aeration is characterized by the use of electromechanical equipment, which works directly submerged totally or partially in the liquid, such as agitation by means of a propeller or a turbine, a vane agitator or a brush-type agitator from Kessner, which is usually installed over the course of a canal or ditch.

In all these systems it is sought that the agitator element, fulfill two basic functions that are: agitation, in order to generate a certain interface surface, and secondly to provide agitation, in order to achieve a mixture that provides adequate contact, between the contaminating organic nutrients, the bacteriological organisms that will be responsible for metabolizing the organic matter and dissolved oxygen, which is transferred through the generated interface surface.

The disadvantages of this type of systems, is that the interface area and the contact time of the same, are small compared to the others systems that handle large interface surfaces, or longer contact times.

Another aspect that compensates for, the deficit effects of a large area of 5 interface and long contact times, in these cases, is the application of longer retention times, a concept that involves managing large structures, making this a disadvantage of economic type .

The main advantages refer to the excellent conditions of 0 concentration, both in the liquid and gaseous interfaces, which are very favorable, and the renewal factors are excellent in both the liquid and gaseous systems, to the extent that they compensate for the deficits of a large interface area, or a long contact time.

5 There are some patented aeration processes, which are based on any of the three previous systems, but introduce some modifications to the processes as follows, they can be summarized in the following terms:

o Conventional aeration; this consists of subjecting the sludge to the aeration process, which can be mechanical or of bubbles, during a certain period of time from 6 to 8 hrs; recirculating, from 20 to 30% of sludge, which is mixed with the influent; The conventional process may be provided with a primary sedimentation stage, and a secondary sedimentation stage. 5

Staggered aeration; In this system, the influent is distributed in several points of the tank, and the recirculated sludge is introduced at the initial point, where the influent's waters are entered, this implies that the concentration of solids is greater at the beginning and decreases, at as the waters go or moving towards the other stages; With this modification it is possible to reduce the retention time by up to 50%, as long as the residence time of sludge is handled between 3 to 4 days, in this process the basic aeration system is by means of bubbles, although it can also be Mechanic in some cases. Graduated aeration; This process has the peculiarity of assuming that the largest BOD is at the beginning of the. tank, and it decreases as it progresses, so that a greater injection of air is made at the beginning, and it decreases as it approaches the effluent outlet, in this process the basic aeration system is by means of bubbles.

Extended aeration; Also known as prolonged aeration, this process is characterized by the application of longer retention times, to achieve high levels of BOD depletion, therefore the process can be applied with bubble aeration systems and mechanics.

Aeration activated; here the excess sewage sludge is channeled, mixed with raw sewage, subjected to aeration to condition them and thus maintain a source of active sludge, which allows intensifying or restoring the continuity of biological activity, when it is affected by the introduction of toxic substances, or sudden overloads that inhibit biological activity; The basic aeration process can be mechanical or bubble.

Description

Classified aeration method, consists in subjecting the sludge within a treatment system, to any compatible aeration process, but with recirculation of previously classified sludge, that is, it will no longer be recirculated discreetly, based on the following:

Through a sludge classifier settler, three possible types of sludge are available, which are:

Heavy sludge; This is in terms of one of its physical characteristics such as its high sedimentation rate, these correspond to sludges that have a high degree of treatment, which have been chemically reduced by oxidation to simpler substances and which can be considered biologically stable; Depending on the objectives pursued with the treatments, most of the processes are designed for reasons of profitability, to achieve the stabilization of a part of the BOD and mineralize another part, depending on the efficiency of the plant, a small percentage it goes into the effluent, so in these cases, the stabilized BOD is constituted by residual or excess sludge, this matter unnecessarily increases the viscosity of the sludge, since its permanence inside the tank, instead of encouraging the process biological, inhibits it by occupying a space, which would be more convenient for active bacteria or organic matter to occupy; Due to its characteristics, it will facilitate its subsequent treatment, which may be its thickening, final stabilization or drying.

Intermediate sludge; formed by developing flocs, which, due to their physical, chemical and biological characteristics, have an intermediate sedimentation rate; the content of stabilized matter is regular, as well as the content of particles and bacteria of small sizes is regular; All this gives certain characteristics to the sludge, which makes them very versatile to make adjustments, in the concentration of sludge inside the plant, without falling into extreme concentrations, these sludges allow any handling, which obviously does not represent any risk, but neither they provide effects of considerable importance, such as when they return, the inoculation effect may be sufficient to maintain biological activity or, for example, their withdrawal if necessary, unpleasant odors should be less intense, as would be caused by unsorted sludge and much less than light sludges, which contain a higher concentration, of fresh organic matter and active organisms.

Light sludge; these are constituted by fine particles that have the lowest sedimentation rates, which can be of organic matter, partially stabilized matter, or that has been assimilated in the generation of new bacteria, also small flocs formed by bacteria that initiate their development, which due to their size, they settle along with light sludge; All this makes light sludge the most biologically active, a quality that must be considered, to handle them more conveniently within the plant. As in many processes already known, different proportions of sludge are handled, although this is very relative, since the main objective pursued with recirculation is to maintain an adequate concentration of bacteriological sludge, depending on the organic load that the plant is being fed, so maintaining this concentration will depend on the skill of the operator and the way in which it is carried out, recirculation or removal of excess sludge, based on this relativity, and with the purpose of giving more certainty to sludge management operations, the proportions that serve as a design basis for the classified aeration treatment processes, suppose that of the total of the sludges that settle, the heavy ones correspond to the that are collected over 33.33% of the length of the settler; For most applications, 2 sections of 33.33% each will be considered light; when there is a specific application then, the intermediate section will be considered for the intermediate sludge.

With a well-designed sludge operation regime, it will be possible to generate any concentration that is effective for the system.

The objective of classified aeration is to contribute to improve the operation of treatment plants in the following aspects:

It can help maintain active sludge with better levels of effectiveness, being able to always remove more stabilized sludge, and recirculating the most biologically active sludge.

It allows to have a more adequate control in the age of the active sludges, due to the fact that the inert bacteria, which are the ones that mainly make up the largest and heaviest flocs, that is, the most stabilized ones, being these the ones that can be removed without running the risk of eliminating new sludge, and by recirculation, of the light sludge, it is guaranteed that the sludge in the process of development or new sludge, continue its development inside the tank, until they acquire the characteristics that can make them reach the section of heavy sludge.

Sludges that are channeled to be removed as excess sludge, can be handled with less intense unpleasant odors, since they have been classified and They correspond to the most stabilized, so in case they are applied a final stabilization treatment, this will be with shorter retention times, and by the same degree of stabilization, the concentration or thickened operation is facilitated more, for its post treatment that can be drying in sand beds.

Regardless of the known aeration systems, to which the sludge classification method can be implemented, the development of the capillary aeration system is presented below as described below.

Capillary aeration system as such; It consists of a set of ducts that form plates or sheets of ducts, which can be manufactured with environmentally resistant covers, such as high density polyethylene and PVC, this system provides most of the oxygen that the process demands, since a Small part of oxygen is transferred on the surface of the oxidation tank, by the action of a small-scale mechanical aeration system, which is applied for mixing purposes to facilitate the contact of 0 ₂ , bacteria and contaminating organic matter, in addition to achieve a complementary aeration within the same tank; The set of ducts, was conceived in such a way that practically 100% of the available surface can be used, which is achieved by generating a liquid sheet over the entire perimeter of the duct internally, this is achieved through the design of flow deflectors, which are illustrated in the following:

Figure 1, plan view of a flow deflector, within the capillary duct. Figure 2, view of a section of a side section of a flow deflector. Figure 3, side view of a flow deflector. Figure 4, view of a front section of a flow deflector.

The ducts formed by PVC sheets (No 1), inside which are inserted a series of baffles (No 2), which can be of the same material as the duct, or a soft rubber to allow the introduction of a tool , to uncover if any type of plugging; These baffles are attached to the duct sheet, by means of the baffle support (No 3), these baffles provide several features that are described below:

This system, is one of the most manipulable treatment systems, and also predictable, allow to vary flow conditions in the liquid system, flow conditions in the gas system and biological conditions of the sludge that is recirculated, all these variations can be managed independently to be studied, they can be observed and measured, so that they make the system among other applications suitable for the implementation of prototypes for scientific and university research; during the operation of the system, at the time of exposure, and due to diffusional characteristics, an amount of oxygen is absorbed by the liquid system, to be transported to the oxidation tank in the form of microbubbles or dissolved oxygen OD, an action that is facilitated because at the interface surface, intermolecular forces are in imbalance, so this surface will be more receptive to the OD; Due to their handling characteristics, it is clear that the effects of limitation, as they are confined volumes, as in the case of bubble systems, can be compensated here with the injection of more air, without considerable increases in energy or, of higher dosage of liquid.

As a larger surface area is being managed, in turbulent conditions such as mechanical aeration systems, and as physical, chemical and biological conditions are improved, it is logical that there will be greater oxidation or mineralization of contaminating organic matter, which added to the atmosphere in the form of carbon dioxide, or transformed into water, which is added to the liquid system, the latter occurs mainly in the nitrification of nitrogen material; the assimilation of a part of pollutants that result in the generation of new cells, will always be in a position to develop in better conditions, since the stable matter is constantly removed and the sludge is returned, which forms the inoculation system in better conditions and on the other hand, it can be expected that the absorption of organic matter that generates stabilized sludge, decrease to some degree, which should imply a greater reduction by oxidation or mineralization, this being a desirable condition in most plants; It is important to keep in mind that the changes may be barely noticeable to the naked eye or that these are minimal, compared to a properly designed and operated process, this is due to the fact that any process that operates correctly, in case of overcoming it it will be in a few hundredths of efficiency, other indications will be lower energy consumption and the use of smaller facilities, being able to handle shorter retention times.

The capillary aeration system has a novel feature, which refers to the possibility of designing and building an aeration system, which allows taking advantage of both the upper and lower surface of a duct, according to the profile shown in fig. 2, with this, the contact surface of the interface is increased by the use of the entire possible surface, that is, the liquid flows throughout the inner periphery of the pipeline, this can be generated thanks to the surface tension property of the water , which allows it to slide over the upper surface, under certain conditions of slope and roughness, allowing a second internal gaseous flow to pass, such that the oxygen concentration in the gas interface is improved, at levels that favor oxygen transfer, with Low power consumption

The way in which a duct plate is placed with respect to others, is illustrated in the following figures:

Figure 5, plan view of a sheet of capillary ducts. Figure 6, side view of a block of capillary duct sheets. Figure 7, front view of a block of capillary duct sheets.

The shape that refers to the arrangement of the duct assembly, which is in the form of plates as illustrated in Figures 5, 6 and 7, so that in a very simple way, we can generate the amount of interface surface, by the fact that we can stack "N" number of duct plates; the space required to generate any surface requirement, within ranges reasonable, it is extremely small but above all efficient; Another important detail consists in the fact that the plates of the aerator are mounted on a concrete structure, which allows the agitation tank necessary to mix and optionally achieve a complementary transfer of oxygen. , to meet high oxygen demands, if required.

Applied Kinetic Theory:

The theory that has been taken as a base assumes a theoretical model, which has two reference surfaces for the study of oxygen transfer, very similar to the proposed concept of two interface films, one gas and one liquid, proposed by WK Lewis and WC Whitman in (Principie of Absortion, Ind. Eng. Chem.), according to Gordon Maskew Fair, John Charles Geyer and Daniel Alexander Okun, in his book Water Purification, Treatment and Wastewater Removal; in the capillary aeration system some concepts are handled, such as a factor of concentration conditions at the interface FCIL and FCIG, which can have a liquid or gaseous system respectively, to increase or decrease the transfer rate of a certain amount of mass , depending on the degree of saturation or deficiency achieved by the system; To illustrate this concept, we have that, in a mechanical aeration system, we have the best conditions both to receive in the case of the liquid system, or to yield in the case of the gaseous system, for the reason that, the liquid system during the operation, it is subject to intense agitation, which allows liquid films with low oxygen concentrations to be exposed one after another, a number of times that is determined by the liquid interface renewal factor, and by the conditions of the liquid system, the films that are exposed, can be considered to start with a Ctil concentration, which is the starting concentration of the interface film; However, this interface will increase its concentration, as much as the conditions of the degree of saturation in the gaseous system permit, which is equal to the concentration of 0 ₂ of the atmospheric air, as well as the number of films of the gas interface, participating in said transfer; similarly it happens in the gas system.

Fig. 18 shows the behavior of the concentration, in the liquid system within the capillary aerator, first of all, the graphs (No 3), represent the variation of the concentration in the liquid interface films, which have a period of time, which It is a function of the contact time and the surface renewal factor, each cycle of these graphs starts with a corresponding Ctil concentration, to which the liquid sheet has inside the duct at that precise moment, reaching the concentration that allows the exposure of a new movie; the graph (No 4) represents the behavior of the oxygen concentration, in the liquid sheet inside the duct, the initial concentration of this graph is the Cio concentration of oxygen, which is normally maintained as an average in the biological oxidation tank; The Clt (No 15) output concentration is that which is reached in the time of (No 8), in the liquid film inside the duct it can reach the saturation concentration Cls (No 1) in a time tls ( No 9) if you have enough length in the ducts, or the conditions of availability of oxygen and the thickness of the liquid film allow it, but usually, the length of the ducts, should be the one that allows to reach the concentration Clt (No 15) in time Te (No 8), this is usually handled for reasons of profitability in the level of use of atmospheric oxygen; The graph (No. 5) shows the time (No. 10), which would take the system to reach saturation concentration within the volume of the tank, under conditions of biological equilibrium; the graph (No 6) shows the time (No 11) that is necessary, to satisfy the biochemical oxygen demand, of a volume equal to that of the oxidation tank, the time to achieve the BOD satisfaction of the tank volume, is what is commonly known as retention time TR, if this time is divided by the time required for saturation of the volume of the tank, this will indicate the number of times to be saturated, completely the volume of the tank , to meet the BOD demand of the tank volume; The graph (No 7) serves as a reference point, since we will always try to provide sufficient oxygen to achieve the metabolism of BOD, contained in the daily volume, in the unit of time (No 12), which is usually one day, this serves to modulate our system at the time of design; the axis of the ordinates (No 10) represents the concentration of dissolved oxygen in mg / l, and the axis of the coordinates represents the time in seconds, on a logarithmic scale.

Fig. 19 represents the behavior of the gaseous system, within a treatment system, where the transfer takes place through a contact surface, so that the mathematical model of the interface films is applicable, which can be deduced from the figure in question; The graph (No 4) represents the behavior of the oxygen concentration, in the atmospheric air inside the capillary duct, where in an analogous way, if it is of sufficient length and the conditions of the liquid system allow it, the oxygen concentration can decrease up to a concentration Cgs (No 2) in the time tgs (No 6), it is also necessary that in the gas flow, within the conduit the concentration Ctg (No 9) can be reached in the contact time TC (No 5), which may be the same as that used in the liquid system; the graph (No 3) represents the behavior of the concentration in the gas interface, which begins in each cycle with the concentration Ctigo, which has the gas flow, within the duct at that precise moment; The gas flow will always start with the concentration of atmospheric air.

The factors that determine the flow turbulence, and with it the surface renewal factors are: the thickness of the flow sheet, the slope of the sheets, the number of baffles as well as the interior dimensions of the duct, all this allows manipulate or vary the Reynolds number, which is an indicator of the turbulence conditions being handled; the way in which the energy dissipates, is producing turbulent conditions precisely in the entire liquid film, to achieve high transfer rates, with lower energy consumption, than in the mechanical aeration systems, and with retention times Lower; the energy that is supplied to the fluid begins to be released in the descent of the liquid, developing a flow rate, which is a direct function of the slope and the roughness conditions, equivalent of the diffusers that have three specific functions, induce the formation of the upper fluid sheet, increasing the interface surface, It limits the speed of the flow, improving the contact time and helping to increase the turbulence, favoring the renewal of the interface limit film.

There are other factors that influence the generation and renewal of the surface, such as the lateral runoff that is inside the conduit, the effect of this runoff, contributes to the improvement of the renewal factor within the conduit, its effect must be important, and its precise determination, it is feasible that it can be determined in a prototype, considering that its effects are positive, and for not having major references, its effect we consider negligible; On the other hand, it is necessary to calculate the interface surface, based on the inner perimeter of the duct, formed by the inner peripheral sheet of the fluid, the size of the inner duct, must consider sufficient space to allow gas flow, even with the presence of the bacteriological film, although it is important to mention that the system plans to prevent the formation of the biological film, by preventing the incidence of light on the surface of the ducts, and intermittent conditions are not handled, in the application of the liquid on the surface, so that the conditions conducive to the development of a possible biological film are minimal.

Regarding the renewal that is given by the condition of the turbulence, that is to say a laminar flow, it will have a unit interface renewal factor and as the speed increases, the turbulence generated will cause the interface film renewal, renew with greater intensity; In the case of capillary aerators, these effects are associated with the slope of the aerator, that is, when the slope is close to zero, the flow velocity is very low and consequently, the flow tends to be laminar and the renewal factor FRS surface tends to unity; As we increase the slope, the speed increases, greater turbulence is generated, which helps the interface film to be renewed with a greater intensity, being able to handle for outstanding profitability issues between 0.1 and 0.2, the large slopes significantly reduce, the contact time of the liquid interface, and demand more energy. There is another stage of the type of flow that develops in a moving fluid, called transition flow, in this type of flow, the liquid film of the interface zone, begins to renew slowly, so that it is very feasible that there is a Reynolds number, which limits the laminar flow in order to establish the transfer that occurs in laminar flow conditions, so that later, a reference can be made with other speed conditions, for which the Reynolds number and the transfer, can give an idea of the theoretical number of films involved in a given system.

Around the Reynolds number, and taking as reference the behavior of the different stages through which a flow goes through, we have to, as long as a laminar flow prevails, under certain conditions of the thickness and the linear dimension involved, the boundary layer in Contact with the gas remains in the area of the interface, and so a certain time may pass as long as the flow conditions do not change, this implies that if a certain oxygen transfer is carried out, this would occur very similarly as the phenomenon occurs in a static volume, with the difference that, here the volume is shifting, and although there is a displacement, between particles of the film adhered to the surface, on which the liquid film slides, for mass transfer analyzes that they are raised in the theory of the two interface films in capillary flows, they define a fairly well defined stage, which, must be characterized, by Because the transfer of gas per unit of exposed liquid surface depends directly on the diffusion coefficient of the gas in the liquid Kd; if the Reynolds Number is determined, for different speed conditions whose gas transfer does not change, a value of the Reynolds number can be determined, for which the transfer begins to increase with the speed increases, which you must indicate the conditions that limit a constant transfer rate, with respect to this number, and that determine the beginning of a transfer that changes with respect to a surface renewal factor, which is very likely, to keep a logarithmic relationship with the Reynolds number. The criterion for determining the Reynolds number based on analogous parameters may not be determined precisely given the complexity of the different treatment systems, but can give a clear idea of its effects on the surface renewal factor, considering it as The following is stated:

No. R = Ei x Vi / (v) Ec 1

Where:

Ei = Thickness of the interface film in m.

Vi = Speed with which the interface moves in m / s.

For the capillary aeration system, it is necessary to have a reference speed with which the flow sheet is moved, for a particular case it is:

Vil = 0.83 m / s

It should be taken into account that this speed depends on the slope of the ducts, the density of baffles per unit length, the thickness of the flow sheet and the kinematic viscosity of the fluid, the indicated speed corresponds to a specific design , driving water at 20 ° C with a slope

-4 3 of 0.125, with a flow through duct of 1.25 x 10 m / s with 3 deflectors per m. duct length, which can be from 1.25 to 2 meters; the interface area

2 for a particular case is 0.1818 m ./(mg / 1) of BOD, entered per second with which the length of the ducts for various conditions can be determined, as discussed below; This factor results from considering that it is feasible to achieve the same transfer as in a mechanical aeration system, applying a factor, for example, 2.5 on an average of applied surface, said factor is relative, so for a more defined application, It could be tuned based on observations to a prototype. The velocity of the gas flow within the duct can be determined for a particular state of conditions in the following way:

Vig = Qge x Vd / 86400 x NC x 0.048x 0.08 Ec 2

Where:

3 3

Qge = Air flow in m / m of sewage.

3 Vd = Daily volume in m / day of sewage.

NC = Number of ducts.

0.048 and 0.08 are the interior dimensions, intended for the passage of gas flow in a given duct.

two

= Kinematic viscosity of the fluid that forms the interface in m / s.

two

The kinematic viscosity considered for the liquid is: 0.00000101 m / s

two

The kinematic viscosity considered for air is: 0.0000135 m / s

Ecl = Qs / ai Ec 3

Where:

3

Qs = Flow or recirculation flow of sewage in m / s, necessary, for

3 transfer the required oxygen in Kg / m, considering that the receiving capacity depends on the initial concentrations and the concentration reached within the Cío and Ctlc conduit, respectively:

2 ai = Interface area that intervenes in m / s. ai = No. of sheets x ARL x L = Ec 4

The thickness of the gas interface film is determined based on the flow provided by the required transfer, based on the utilization coefficient of each type of system.

Ecg = Qg / ai Ec 5

By managing the concentrations in terms of the dissolved oxygen deficiency, as well as the covered deficiency, the behavior can be analyzed by a first-order equation as follows:

dD / dt = - K D Ec 6

Sorting terms:

dD / D = - K dt Ec 7

Integrating has:

/ dD / D = / -K dt Ec 8

Ln Dt - Ln Do + C1 = -K (t - to) + C2 Ec 9

By the logarithm rules you can write as:

Ln (Dt / Do) = - Kt + C3 Ec 10

The following can be inferred from the graphic behavior:

Dt = Cs - Ct Ec 11

Do = Cs - Co Ec 12 Eliminated the natural logarithm of equation 10, and considering that the constant part, we can represent it as a sum of constants, without altering equality, and substituting equations 11 and 12 in 9, we have:

-Kt

Cs-Ct = (Cs-Co) e + Cs + Co Ec 13

Clearing Ct you have:

-Kt

Ct = (Cs-Co) - (Cs-Co) e + Co Ec 14

-Kt

Ct = Co + (Cs-Co) (1 -e) Ec15

As the velocity constant K, it must consider factors that accelerate or decelerate the transfer within the conduit, said constant is a function of the diffusion coefficient of oxygen in the liquid, the thickness of the film considered, the varying concentration conditions, and of the surface renewal factor of the FRS system, and of a Kp factor, which represents the number of times, the oxygen diffusion coefficient, referenced at 20 ° C and at sea level, is multiplied by the level of saturation in the interface zone; Considering all these aspects, it is necessary that the rate constant in the oxygen concentration change, in the flow sheet inside the duct is:

Kdlc = - Kdl x FRIG x Kpl Ec 16

Where:

Kdlc = Speed coefficient with which the oxygen concentration change is made, in the liquid system within the ducts.

Kdl = Kd / Ecl Ec17 -09 2

Kd ₂₀ »c = Oxygen diffusion coefficient = 2.4167 x 10 cm / s.

(For a specific application, the value of the oxygen coefficient must be referred to the average operating conditions of the process where it is applied, considering the temperature and concentration of suspended solids.)

Ecl = Thickness of the liquid layer inside the capillary duct.

FRIG = Renewal factor of the interface surface in the gas system, has dimensions s ^"1 and the initial value that this factor can have, is 1 due to the behavior of the films or sheets in a laminar flow in the gas system, and it can increase up to a value determined by the turbulence conditions induced by some means.

FRIG = Kdgi / Kdgc Ec 18

Kpl = Adjustment factor that allows to adjust the mathematical model, developed for the liquid system, represents the number of times that Kd is multiplied due to the concentration conditions.

FRIL = Renewal factor of the interface film in the liquid system, which has dimensions s ^"1 and depends on the flow conditions, that is, its minimum value must be 1 and corresponds to the static conditions or laminar flow At the transition flow, its optimum value will be when the turbulence conditions are provided that provide the highest transfer rate in profitable conditions.

FRIL = Kdli / Kdlc Ec 19

In an analogous way you have:

Kdgc = - Kdg x FRIL x Kpg Ec 20

Where: Kdg = Kd / Ecg Ec 21

Kpg = Adjustment factor that allows to handle the mathematical model developed for the gas system, represents the number of times that Kd is multiplied, due to the oxygen concentration conditions in the gas system.

For the corresponding calculations, it is necessary to handle the oxygen available in the gaseous system, as a proportion of the volume of the gas, which the biological treatment system is able to extract, varying the concentration in the gaseous system, for which, it is necessary to consider a concentration analogous to the Cls concentration in the liquid, which we represent as:

Cgs = 0.84 Catm. = 229.32 mg / l Ec 22

The coefficient 0.84 is based on the consideration, that the conditions that occur in bubble aeration systems are similar in terms of the way in which the transfer is carried out, but with their respective characteristics each, so It is considered that, on equal terms, there must be the same use, which is considered 16% of atmospheric oxygen, that is, in terms of this percentage, it is said that if a system uses 100% of usable oxygen, in. real terms, the system only takes advantage of 16% of the atmospheric oxygen that passes through the system; However, it is possible that this coefficient differs when there are changes in the equilibrium conditions, from the stresses on the interface surface, which determine the intensity of the surface tension, due to the forces of Van der Walls, which is very feasible , and in the event that this hypothesis is confirmed, it would be positive as shown by mechanical aeration treatment systems, in these the interface surface is very small, but its reception capacity is very large, which may be due, in addition to the favorable concentration factors, to the condition of imbalance of the intermolecular forces, characteristics on a flat surface of a liquid such as water and that determine the surface tension, because as some studies of physics, the spherical surface of a drop or a bubble, they represent a surface whose efforts due to Van der Walls forces are balanced, which implies very rigid surface structures that can constitute a resistance, to a certain transfer being made through it, and of course, it is also very This structure is likely to represent a resistance to the surface renewal process, causing the transfer to be hampered by the limitations that represent saturation concentrations.

However, from the mass of gas available, the aeration system is capable of transferring a percentage of this gas, as mentioned by Motarjemi and Jameson according to Michael A. Wintler in his book Biological treatment of wastewater, on the use of oxygen in a bubble system, in such a way that under certain considerations, some proposed values have been estimated in the capillary systems, so a practical application should be supported with laboratory tests.

The calculation of the nterfase area, which in the case of capillary systems, is the internal area of the conduit in operation, which limits the liquid system of the gas system, is determined as follows:

aic = NC x (ANC + HNC - ENLF) x 2 x LRL Ec 23

Where:

ANC = Nominal duct width.

HNC = Nominal duct height.

ENLF = Nominal thickness of the flow sheet, without baffles.

LRL = Actual length of duct sheet.

It is important to define the direction in which the interface surface may have changes, such as the height of a bubble aeration tank, or the radius equivalent of the surface area of a mechanical aeration tank, or the length of the capillary ducts, through which changes in the interface surface are presented, to consider the relevant variations for each case, that is, the change is analyzed which manifests the surface within 1 s of this path; so we would have a series of bubbles of 1 mm in diameter, will travel a length of 0.13 meters. that is, at a speed of 0.13 m / s, which would correspond to a specific time of 1 s. in such a way that if the tank is 3 meters. deep, the contact time would be 23 s; in the case of ducts with a density of 3 deflectors per m. in length, driving a

3 flow of 0.000125 m / s per duct, where the speed developed by the flow is 0.83 m / s, with a slope of 0.125 and for a particular design, we would have:

TC = contact time in s.

Tci = 1 / FRS Ec 24

The definition of the times TC and Tci, allow to make a theoretical analysis of the changes that each element of interface area undergoes that can be in the fluid sheet inside the duct, or a nterfase film respectively.

Another concept involved is that which refers to a correction factor for the interface area, which, in the case of bubbles, depends on the difference in pressure, to which the air is injected and the pressure at which it is released, which corresponds to atmospheric pressure; The analogous factor for capillary aeration systems is to establish a correction to the original area, produced by the structure of the duct walls, depending on the thickness of the liquid fluid sheet, and the variations that will occur, when develop a growth of biological film, on the inner walls of the duct; although it is sought not to promote this film when working the system continuously, and not to allow light infiltration, so that the surface of the ducts will generally be submerged, preventing the bacteria that develop attached to the walls, do not find the conditions conducive to your development; assuming that some biological development could occur, this can be limited by maintenance actions, when a film of 0.004 meters is presented, although it is feasible that these conditions do not occur, it is assumed that in case of certain bacteriological development, this behaves in the same way, as it behaves in percolating filters or fixed culture systems, that is, the film as part of its development cycle, starts, grows and reaches a thickness that promotes the cells that are attached to the wall, die leading to the detachment of the film, and in the latter case, the design of the aerator can allow, with the use of a suitable tool to uncover the ducts in a simple way, therefore for design purposes, with the dimensions of the duct and thickness of biological lamina indicated, it can be established that:

FCS = ai / ac = 0.62 Ec 25

The retention time is the time that the waters in process are subjected, to reach a certain degree of treatment, depending on the process that is applied, as well as the BOD levels of the influent and the BOD admitted in the effluent, making a study comparison between bubble aeration systems, a mechanical aeration system and classified capillary aeration systems, and given that the magnitude of the interface area is considered to be reasonably exceeded to the mechanical aeration system in the extended aeration mode, and assuming that the conditions of concentration, and interface surface renewal, are the most suitable for having a high oxygen transfer rate, and with an adequate culture of microorganisms, the estimated retention times will be between 6 and 12 hrs, depending on the objectives and conditions of each case.

TR = Retention time in s.

Having defined most of the parameters, which in some way intervene in the determination of oxygen transfer, we can define in the terms of the interface film theory, the rate with which said transfer is given as follows: BOD = Qge x Catm x% O dx% O, a / (1000 x 10000) Ec 26

Where:

3 3

Qge = flow of gas supplied in m / m of sewage.

Catm = O ₂ concentration in atmospheric air in mg / l.

% 0 ₂ d = Percentage of atmospheric oxygen, which biological treatment systems can provide.

% 0 „a = Percentage of oxygen available, which is used by the treatment system with the conditions of each system.

The instantaneous air flow is determined by:

Qgi = Qge x Vd / 86400 Ec 27

It may be practical to establish an instantaneous biochemical demand, or BODI oxygen transfer rate, that is, the demand that the waters in process, or, that the system must handle in Kg 0 ₂ / s, and which is determined by:

BODi = BOD x Qli Ec 28

3 Where BOD is the biochemical demand for oxygen in Kg 0 ₂ / m of sewage;

The instant transfer rate can also be obtained from the following equations:

DBOil = TTL x ac x FCS x VI x TC x Ecl / 1000 Ec 29

BOD = TTG x ac x FCS x Vg x TC x Ecg / 1000 Ec 30 The units used are:

TTL and TTG in mg / (l x s), Ac in m / m, VI and Vg, in m / s, TR in s and Ecl and Ecg in m.

The amount of oxygen in Kg 0 ₂ that is required to lower the BOD, of the volume of sewage entered in the TR period, for practical purposes can usually be determined experimentally in a laboratory, not to rely on bibliographic references, for the reason of that the physical chemical and biological characteristics of water change from one place to another, theoretically, the Kg O can be calculated by.

TTLO = TTL x (ai x VI x TC x TR x Ecl) / 1000 Ec 31

TTGO = TTG x (ai x Vg x TC x TR x Ecg) / 1000 Ec 32

2 ai = Interface area in m / m duct length.

VI = Speed of liquid flow inside the duct, in m / s.

Vg = Speed of the gas flow inside the duct, in m / s.

TC = Contact time

Ecl = Thickness of the fluid sheet inside the duct in m.

Ecg = Thickness of the gaseous sheet inside the duct in m.

The rate of change of oxygen concentration in the liquid gas system would be determined by:

TTL = 1000 x BODI / (at x VI x TC x TR x Ecl) Ec 33

TTG = 1000 x DBOg / (ax Vg x TC x TR x Ecg) Ec 34 Starting from the fact that the transfer is a mass flow, which occurs through a succession of interface films, an equation can be raised that allows us to determine the variation of the oxygen concentration, which the system experiences in the unit of time and per unit area, and considering only for this approach, that the changes in the interface films were uniform, handling the concentrations in mg / l, one could write:

TTL = (Ctil - Cltio) x FRIL / x 1000 Ec 35

O well:

TTL = (Ctlc - Cloc) / (TC x 1000) Ec 36

Where:

Ctil = Oxygen concentration in the liquid interface film, achieved in a period of time t = 1 / FRIL.

Cltio = Initial concentration for the liquid interface film, as it is being considered that the magnitude of the change in concentration is uniform, the schematic representation of this approach is only possible, making the assumption that Cltio = Cio, at t = 0.

Ctlc = Concentration of the liquid sheet leaving the duct for t = TC.

Cío = Initial concentration for the liquid sheet inside the duct at t = 0.

Similarly you have:

TTG = (Ctig - Cgtio) x FRIG / 1000 Ec 37

O well:

TTG = (Ctgc - Catm) / (TC x1000) Ec 38 Where:

Ctig = Oxygen concentration in the gaseous interface film, which has a period of time t = 1 / FRIG.

Cgtio = Initial concentration for the gaseous interphase film, in the same way, as the magnitude of the change in concentration is being considered, is uniform, this approach is only possible, making the assumption that Cgtio = Catm, at t = 0.

Cgtc = Concentration of gas sheet leaving the duct at time t = TC.

Catm = Initial concentration for the gaseous lamina inside the duct, at time t = 0.

From equations 35 and 37, and with the same consideration of uniform concentration changes, the concentrations that would reach the interface films, liquid and gas, with this perspective would be:

Ctil = (TTL x 1000 / FRIL) + Cltio Ec 39

In an analogous way you have:

Ctig = (TTG x 1000 / FRIG) + Catm Ec 40

Actually, the changes in oxygen concentration, both in the liquid system and in the gas system, are not uniform, as can be seen in figs. 18 and 19, so you can apply equations 16,17,18,19 20 and 21 in equation 15, which leads to the following equations 41, 42, 43 and 44:

The initial concentration in the liquid interface, for the last film exposed considering that, in the time Tci = 1 sec, FRIL films are exposed, for t = TC-1 / FRIL is: _Λ -Kdlcx FRIGx (TC-Tci / FRIL) XKp¡l

Ctloι, = _TC -ι / FRiL = Cltoc + (Cls-Cltoc) xFCIGx (1-e) Ec 41

In an analogous way, the initial concentration at the gas interface must be considered, for t = TC-1 / FRIG is:

_Λ -Kdgcx FRILx (TC-Tc¡ / FRIG) XKpig

Ctgoι, = τc-ι _{/ FR} ig = Cgtoc + (Cgs-Cgtoc) xFCILx (1-e) Ec 42

Applying equations 16 to 21 respectively, in equation 15, and developing it, you get to equations 41, 42, 43 and 44, which describe the concentration in the fluid sheets, and also for the interface films, to the concentration in t = TC, considering the gain that is had in the last interface film respectively as follows:

-Kdl¡xFRIGx (Tci / FRIL) xKp¡l Ctlc _t = τc = Ctloi _{t = τc-1 / FR} i _L + (Cls-Ctloi _t = τc-ι _{/ FR} i) xFCIGx (1-e) Ec 43

-Kdl¡xFRILx (Tci / FRIG) xKpig

CtgC _t = τc = Ctgoi _t = τc-ι / _FR ig ⁺ (Cgs-Ctgoi, _{= T} c-ι / _FR ig) xFCILx (1-e) Ec 44

FCIL = Concentration factor in the liquid interface, which normally has an initial value of 1 and will vary depending on the conditions of each system.

(Cls - CI c)

EASY = Ec 45 (Cls - Cío)

FCIG = Initial concentration factor in the gaseous interfaces, this factor is dimensionless and will have an initial value of 1, for most cases, this factor, in capillary aeration systems, usually decreases to longer duct lengths, depending on the conditions of each system.

(Cg -Cgs)

FCIG = Ec 46

(Catm -Cgs) Equations 41 and 43 represent the mathematical model of the behavior of the liquid system as can be seen in fig. 18, where; the axis of the ordinates (No 14) represents the concentration of oxygen in mg / l of the liquid system, the axis (No 13) represents the time in seconds on a logarithmic scale; mass transfer is the sum of millions of transfer events in each cycle formed by the division of each second, in a number of cycles determined by the surface renewal conditions, these events are represented by the graphs (No 3) which are derived from the graph (No 4), and represents the transfer of oxygen that is transferred in each interface film segment, which as you can see, each cycle is different in the first place because the initial concentration Ctil is increasing as the liquid sheet moves; the speed with which the transfer is carried out is not constant and finally the reference frame that corresponds to the concentrations of both one system and the other changes with respect to time, so that the constants used in the equation must consider all these adjustments; Cls saturation concentration (No 1) is a transfer limiting factor; The initial Cio concentration within the ducts (No 2) as the flow of the liquid sheet shifts varies until it reaches the Ctlc concentration (No 15) at the contact time (No 8) 0 determined by the length of the ducts and by the velocity of the flow, therefore, if it were of sufficient length it would reach saturation in a time Tls (No 9); the graph (No 5) shows the time (No 10) that the system would take to saturate the volume of the tank under biologically stable conditions; the graph (No 6), shows the time TR (No 11) that the system would take to satisfy the BOD of the 5 volume of the tank and finally the graph (No 7) shows the reference time and that corresponds to a day, this mark the time (No 12) in which the system must satisfy the BOD of the daily volume.

For the application of equations 41 and 43 in the liquid interface, represented or by the graph (No 3) of fig. 18 it is important to note that the proportionality coefficient is the renewal factor of the interface surface considered for the liquid system, that is: Equations 42 and 44 represent the mathematical model of the behavior of the gas system as can be seen in fig. 19, is a graph analogous to that of Figure 21, but in this case instead of the mass entering, it leaves the system; In the first place it is necessary that the gas flow enters the ducts with the concentration of atmospheric oxygen Catm (No 1), on the other hand there is a critical concentration Cgs (No 2) of oxygen, reached by the graph (No 4) which is the concentration, to the extent that most aerobic biological systems are capable of functioning, as long as the other necessary conditions of their ecosystem exist in the manner required, in this case, if the ducts are of sufficient length, the Cgs concentration (No 2) will be reached in time tgs (No 6), the graph (No 4) also shows the time TC (No 5) that the system takes in stable biological conditions, to descend to the Ctg concentration (No 9), the graph (No 3) represents the transfer in an interface film; the axis of the ordinates (No 8), represents the concentration of oxygen in mg / l, and the axis of the coordinates (No 7), represents the time in seconds, on a logarithmic scale.

As can be seen in the capillary system, the transfer capacity depends on the flows of liquid and gas, which are channeled to the set of ducts, to form the surface of the liquid and gas sheet, with the appropriate thickness, in the In a more economical and practical way, it can be immediately observed that the management of the gaseous flow does not have any handling problem, due to the low amount of energy that its management requires, referring to the liquid flow, this requires greater care in the analysis, due since it is the means of transport of dissolved oxygen, which is transferred to the oxidation tank, so that the flow of liquid must be sufficient so that the flow of oxygen is as required, and does not have obstacles due to the concentration of sewage, to operating conditions such as temperature among others; The efficiency of the system will obviously depend, on handling the lowest concentration at the entrance of the ducts, to achieve the greatest difference with the liquid outlet concentration, it will depend on achieving the longest possible contact time, and on the greatest possible turbulence but with the slope that implies the lowest height, so that the energy consumption is the lowest possible. Next, the generalities of the components, which make up the system shown in fig. 8 independently.

Solids Screen; The purpose of the sieve design is to strain the influent's sewage so that it passes directly from the sieve to the oxidation tank, without the need for a discharge pipe at the outlet of the flow already cast, this element significantly decreases the BOD, by separating a certain amount of organic matter in the form of small suspended solids, which if introduced into the aerators could possibly cause blockages in the capillary systems; on the other hand, if the aeration system has the capacity to provide sufficient oxygen, to process these solids biologically, they can go through a crushing process and return them to the treatment, so as not to cause a large amount of untreated organic solids, which can cause contamination problems, proper management of these could be drying in the sun for subsequent incineration, or bury them in previously sealed pits, then close them and by an anaerobic process cause degradation; in this way, the oxidizing capacity of the treatment plants that could be applied to these solids is used to achieve better effluent quality; the design of the screen, considers that the structure is balanced in order to facilitate its assembly, its construction can be made of carbon steel, with a suitable coating; The screening specifications that normally meet the requirements are:

Maximum diameter of solids passage 0.00095 mts. Flow capacity, as required. Nominal sieve slope: 1,428

The screening being also an important element in the process, the following figures are illustrated in the following figures:

Figure 9, plan view of the screen. Figure 10, side view of the screen. Figure 11, front view of the screen. Its operation consists of entering the waters, through the inlet pipe (No 3) to a landfill box (No 1), which distributes all the inlet flow, along a landfill plate; The sieve is designed in such a way that the waters fall directly to the aeration tank, the waters that leave the spout, fall to the sieve (No 2), all separated solids skid over the sieve and fall into a wheelbarrow, where periodically they are removed for later handling; the screen box has a purge (No 4), which has the function of maintaining cleaning and unwrapping if required; The construction materials normally used are:

The entire structure can be made of carbon steel, and optionally stainless steel, the element that forms the sieve, as it is constituted by very thin elements, it is necessary that it invariably be stainless steel.

Mechanical stirrer; It is an optional element, which in certain circumstances, can provide agitation, to prevent the formation of sediments in the oxidation tank, can reinforce the mixing action, or it can add by agitation, a complementary transfer of oxygen, this element, is illustrated in the following:

Figure 12; plan view of the mechanical agitator. Figure 13; front view of the mechanical stirrer. Figure 14; side view of the mechanical stirrer.

The agitator has been designed to suction a flow vertically and project it horizontally, to induce mixing or agitation within the capillary aeration tanks, optionally it can provide a complementary aeration within the classified capillary aeration process, for the treatment of sewage , where it is required to direct the flow conveniently, the agitator consists of a deflector elbow (No 1) that is submerged in the waters under treatment, in the lower part of the elbow the propeller (No 2) is housed, formed by blades, which they are solidly screwed to a blade holder, which has a cradle that solidly fixes the arrow, which is moved by the gearmotor (No 3), which can be replaced by a speed variator, to be able to supply a larger energy at certain times; the elbow is supported by a structural steel pedestal (No. 4), which hangs from a structural base (No. 5); The design of the propeller is based on the following formulation:

The width of the propeller blade is:

a = Qag / (L x Vtan x Cos ang x Tan ang x 4) Ec 47

Where:

The design attack angle is in the following range:

ang = (30 ° to 36 °)

Qag = Flow generated to create the required mixing conditions, approximately 60 Ips for each Ips to be treated in case it is required to achieve an additional oxygen transfer, the corresponding analysis should be done.

Vtan = mean tangential velocity, which for practical purposes is considered the tangential velocity of a point, located 2/3 of the center of the propeller towards the end of it.

Vtan = RPM / 60 Dme x p¡ Ec 48

Number of blades = 4.

The manometric height developed by the propeller is given by:

HMT = Vtan x Tan ang / (2 x 9.81) Ec 49

Where:

two

The acceleration of gravity is: 9.81 m / s. The length of the blade is a function of:

L = 0.5 x0.9xDHE Ec50

Where 0.9 is a factor that depends on the size of the blade holder's mamelon.

DHE = outer diameter of the propeller.

The power transmission capacity of the arrow is given by:

2 21/2

P = NDf x ((S (2 x F / pi x Df)) Ec51

Where:

F = axial thrust = P / m x PHE + propeller weight + Ke x HMT. Ec 52

P / m = Weight of the arrow in Kg per m. of length.

PHE = depth at which the propeller is in m.

Axial thrust constant of the propeller.

Ke = 234.25 x DHE ² Ec53

Mean diameter of the propeller in m.

Dme = 2 x DHE / 3 Ec54

The power demand of the propeller is given by:

BHP = QagxHMTxPe / 76xEf Ec55

Pe = Specific weight of the waters in process

Ef = Volumetric efficiency of the propeller, considering approximately 0.8. Functioning:

Assorted capillary aeration tank consists of an aration system, which is illustrated by fig. 8, this works as follows:

The influent's waters, together with the classified sludge that is recirculated and that can come from any stage that is, of primary or secondary treatment, depending on the objective, enter through an inlet pipe (No 5) and normally in the First stage, they pass to a sieve (No. 11), which separates all the solids from the fresh waters that could obstruct, the aerator duct system; sewage already screened or strained, enters the oxidation tank (No. 10) from which the mixed liquor is recirculated by means of a pumping equipment (No. 8) to the distributor tank No. (No. 4), to be distributed as watering can by means of the perforated plate (No 2); to all duct sheets, which form blocks of plates or duct sheets (No 1), which are placed on a concrete ramp, which is constructed with the required slope, and is supported by supporting columns (No 9 ); when the system is in operation, blade fans (No 3) induce an air flow, which is induced to circulate through all the ducts, to always maintain high concentrations of oxygen in the gas interface; Moderate agitation and aeration can be optionally applied, by means of a stirrer, formed by a geared motor (No 7) and a deflector elbow (No 6) which houses the propeller inside, this elbow serves to conveniently direct the flow currents inside the tank, depending on the objective pursued; the treated waters, leave the settler through the outlet pipe located at the lowest point of the tank floor, in order to be removing all the flocs that are formed, with good sedimentability characteristics, the bottom has a slope greater than 15% in order that with little agitation, heavy sludge can be induced to the outlet pipe, which must have a record of heavy sediment purge, such as fine sand that could be induced and accumulated as sediment, this is in order to avoid azolve inside the tank and outlet pipe; the capillary aeration system, formed only by the aerados (No 1) and the fan of blades (No 3), can be conditioned, to be installed in tank structures, built on the course of streams or rivers of sewage, suppressing the use of recirculation pumps and agitators, generating intensive treatment systems with lower energy consumption.

Typical applications of a treatment based on capillary aeration, with recirculation of classified sludge; Below are three types of treatment processes, which it is feasible to develop, but here the only thing that should be clear is the "way of handling" the different sludge extracts, in the different stages they go through, which it will be necessary to analyze for each particular case, taking into account the type of organic load, which can be low, medium and high; the constitution of the nature of the organic load, such as carbonaceous organic matter and nitrogen organic matter, as well as the possibilities of each type of process, to provide oxygen and the concentration of required organisms.

In fig. 15 shows a flow chart, where a treatment system is schematically represented, based on capillary aeration with recirculation of 2 strata of classified sludge, of a single stage, to remove the carbonaceous matter, which is described below:

The influent enters through a sieve of solids (No. 7), reaching the oxidation tank (No. 1), in this tank, where the waters are aerated and agitation is provided to have adequate mixing, in addition to that optionally, a greater amount of energy can also be dosed to generate a complementary aeration; after having received sufficient aeration, the treated liquor passes to the sedimentation tank (No 2), provided with a sludge sorting system, where the aerated liquor is clarified; the clarified water leaves the settler through the outlet pourer (No 5), towards the next stage that will usually be a tank where chlorine is applied, in order to eliminate pathogenic bacteria; In this case, the classification of sedimented sludge is in two strata, which are: heavy sludge (No 6), which will be removed from the system, when there is an excess of sludge in the aeration tank, so that these do not acquire anaerobic conditions, they can be recirculated by a branch in section (No 3) of the sludge pipe heavy the intermediate and light sludge will form the second layer (No. 4), which will be recirculated on a daily basis; With this operation, whenever excess sludge occurs, the most stabilized sludge will always be removed and more intense inoculation will be exercised, by recirculating the most active sludge, 5 which will improve the biological activity of the plant.

In fig. 16 shows a flow chart, where a treatment system is schematically represented, based on capillary aeration with recirculation of 2 sludge strata classified, in two stages, to metabolize or the BODC in a first stage, and a nitrification that starts In the first stage and complemented in a second stage, this process is described below:

The influent enters through a sieve of solids (No 11), when it comes to the first stage, or by going to the oxidation tank (No 1)

5 directly when it comes to subsequent stages, where the same conditions occur as in an aeration tank of a single stage system; After having received sufficient aeration, to achieve the removal of a good part of the BODC, a small part of nitrogenous organic matter is achieved, said in other words, a small or part of the biochemical demand of the matter is reduced Organic nitrogen (BOD), the treated liquor passes to the sedimentation tank (No 2), provided with a sludge sorting system, where the aerated liquor is clarified in the first stage, the clarified water leaves the settler towards the second stage of aeration, heavy sludge (No. 5), sedimented in the first stage of sedimentation, is

5 will recirculate or remove as required by the system, the intermediate and light sludge, sedimented in the first stage, will be recirculated daily to maintain in the aeration tank of the first stage, very active biological conditions, the clarified water in the first stage of sedimentation , it passes to the biological oxidation tank of the second stage (No 3), normally provided with the same aeration systems, in this tank, depending on the objectives and the specifications of the treatment, it is feasible that the BODc is finished down and partially a good proportion of the BOD, the aerated liquor in this tank passes to the final settler (No 4), where the heavy sludge settled in this stage, can be recirculated daily to the first stage, for the reason that they will carry a good proportion of nitrifying bacteria, which are of a slow development and therefore, it is not convenient to eliminate them at this stage, since by recirculating them, it is possible to return all viable nitrifying bacteria, causing the nitrification to start from the First stage, the intermediate and light sludge, are recirculated in this process to the tank (No 3) so as not to lose the nitrifying sludge, which develops mainly in this tank; the clarified waters in the second stage, largely nitrified, leave the settler of the second stage, to pass to a chlorination tank where it is disinfected by the application of chlorine, in order to eliminate pathogenic bacteria; With the classification of sludge, the biological control of the treatment plant is facilitated by having the possibility of making more objective adjustments, since the most stabilized sludge can always be removed and the most active sludge will be recirculated according to the stage of concerned, which will improve the biological activity of the plant.

In fig. 17 a flow chart is shown, where a treatment system is schematically represented, based on capillary aeration with recirculation of 3 strata of classified sludge, of three stages, this process partially eliminates a quantity of the BODC, and a small part of the BOD in the first stage, in the second stage the remaining BODc is eliminated and gradually a greater BODn, in the third stage the elimination of the BODn is complemented; The process is described below:

The influent enters through a sieve of solids (No. 17), arriving at the oxidation tank (No. 1), where the same conditions occur as in an aeration tank of a single stage system; After having received sufficient aeration to achieve the removal of a good part of the BOD, reaching a small part of the biochemical demand of the nitrogen organic matter (BOD), the treated liquor passes to the sedimentation tank ( No 4), provided with a classifying system of three types of sludge, where the aerated liquor is clarified in the first stage, the clarified water leaves the settler towards the second aeration stage (No 2), the heavy sludge (No 7) , sedimented in the first stage of sedimentation, together with the heavy sludge of the second stage (No 10), are recirculated or are removed as excess sludges moving towards a final stabilization stage or thickening for subsequent drying; the intermediate sludge (No. 8) of the first and second stage (No. 11), is recirculated to the aeration tank (No. 2) of the second stage, in order to maintain a balanced biological activity in the second stage of aeration, in this stage can remove an important proportion of the BODc, and gradually a greater removal of the BOD, in situations where the organic load is mixed and relatively high; The light sludge (No 9), the light sludge of the second stage (No 12) and the heavy sludge of the third stage, are recirculated to the first aeration stage, with the aim of generating a high degree of inoculation of both bacteria heterotrophic as nitrifiers of the first and second stage of nitrification, that is to say nitrosomonas and nitrobacter in this way, there is a gradual nitrification from the first stage; the liquor treated in the tank of the second stage passes to the sedimentator of the second stage (No 5), where, as already indicated, three types of sludge are obtained; the clarified water in this settler, passes to the biological oxidation tank (No. 3), of the third stage, where the nitrification process is predominantly carried out, so that the treated liquor passes to the settling tank (No. 6), where By means of sedimentation, the nitrifying bacteria are retained, which, as already indicated, the heavy sludges that settle in this stage, are recirculated to the first stage, to promote nitrification from the first stage, and thus maintain a long time of residence, of the nitrifying bacteria that are of very very slow development, especially the nitrosomones that metabolize the ammoniacal nitrogen to nitrites; the light sludges are recirculated to the tank of the third stage, to always maintain the most intense nitrification in stage three; finally the clarified waters of this stage can pass to a chlorination tank, where chlorine disinfection is carried out, with disinfectant purposes to eliminate pathogenic bacteria; it is possible to make different combinations in the channeling of sludge, depending on the degree of contamination of the influent, the proportion of carbonaceous and nitrogen contaminants, the capacity of the process and the desired quality in the effluent, for example; The organic carbon that contains the heavy sludge, and intermediate, can be recirculated, to provide a part of the organic carbon necessary for the denitrification of the waters coming from a nitrification stage.

Claims

 Reindications

Having sufficiently described my invention, I consider as a novelty and therefore, claim as my exclusive property, what is contained in the following clauses:

1- The treatment of contaminated water based on capillary aeration and recirculation of classified sludge, consisting of the following stages:

a) Solids screening; It consists of casting the raw water in the first stage, through a screening structure, designed to be able to pour the screened water directly to the biological oxidation tank, without the need for a flanged tip in the discharge, the screen has the function of separating all the solids that can clog the capillary aerator.

b) Recirculation pumping; by means of axial flow pumps, which pump large volumes at a low height of mixed liquor inside the biological oxidation tank, and from a point where the oxygen concentration has dropped to the lowest levels, to send to the aeration stage, the more receptive oxygen waters, to a distributor tank, which distributes through a lattice-shaped plate the flow in the form of a shower, to all capillary ducts, so that a surface of liquid interface is generated, within the blocks of duct sheets; When the process is installed on the rapid course of a stream or river, recirculation pumping may not be required.

c) Air injection; by means of a fan of blades, which handles large volumes at low pressure, whose cover is conditioned to generate the gaseous flow, through the capillary ducts, where the liquid in the form of a sliding film on the inner wall, becomes the contour of a second conduit, where the gas interface surface is generated; The air flow does not overcome any static charge of liquid, overcoming only the friction losses that are generated, and which are minimal. d) Agitation; Stirring is provided by means of an optional mechanical stirrer to have a suitable mixing, in addition to that, a greater amount of energy can also be dosed to generate a complementary aeration, this agitator by means of a deflector elbow, takes a liquid flow in a vertical position and projects horizontally, to direct the flow to the point of entry of the influent and promote its diffusion, it can also develop mixing functions and prevent sedimentation inside the tank; When the process installs over a rapid course of a river or sewage stream, the agitator may not be necessary, with an appropriate tank design.

e) Capillary aeration, with recirculation of classified sludge, a function that is performed when the recirculation of the mixed liquor and the injection of air is working, within the capillary aerator, where the conditions are generated for it to be carried out, the transfer of oxygen, for maintain adequate levels of dissolved oxygen in the biological oxidation tank.

f) Sedimentation and classification of sludges, which leave the biological oxidation tank through the outlet pipe, which is preferably located in the lower part of the biological oxidation tank bottom, so that sediments do not accumulate in the In the background, this outlet leads the treated waters to the sedimentation stage, where, instead of handling sludge activated in a discretionary way in terms of its qualitative characteristics, they are classified in this stage, in active, intermediate and stabilized, recirculating to the aeration tank the most biologically active sludge and removing the most stabilized when excesses are generated, achieving better biological conditions in the biological oxidation tank, which result in a good quality effluent, with low energy consumption.

Treatment characteristics:

a) Simpler, easier and more reliable control over the residence time of active sludge, particularly useful in nitrification processes. b) Ease of maintaining a higher proportion of active bacteria within the process and, consequently, reducing the proportion of stabilized matter within this tank, which allows handling lower concentrations of suspended solids, which implies increasing the oxygen saturation concentration , in the waters that are sent to the aerator, increasing the possibilities of oxygen transfer.

c) More effective inoculation, having the possibility of recirculating the most biologically active sludge.

d) Better quality in the degree of stabilization of heavy sludge, which is recirculated or removed when they constitute an excess of sludge in the oxidation tank, thus facilitating the stages of its subsequent treatment.

e) Greater possibility of manipulating the interface conditions, both in the liquid and gaseous systems, to achieve good levels of overall efficiency.

2. -The capillary aeration tank, as a whole, illustrated in (fig. 8) which is formed by the following components:

a) The structure of the tank in whose interior there is a structure supported by columns, which is used to mount on ramps, the blocks of duct sheets, the same structure is used to mount on it, the recirculation pumps, the mechanical agitators and the fans; on a part of the tank wall, a sieve is mounted, when it is the first aeration stage; The bottom of the tank has a slope greater than 15%, to facilitate with gentle agitation, that the sediments are induced towards the outlet pipe, which can take at the most strategic point, a record for purging heavy sediments.

b) The optional mechanical agitator has the function of promoting adequate mixing and preventing sediment formation, conveniently directing the flow of the liquid, being able to supply enough energy through it to generate a complementary transfer of oxygen, thus stopping , have greater oxygen transfer, which can be optionally handled in the critical hours of higher organic load, generating energy savings and generating the capacity, in the system to provide an additional transfer, when this is required at certain times, this is feasible by actuating by means of a speed variator instead of the gearmotor; This agitator, in terms of the specification of the materials, is feasible for its construction of the following materials: support pedestal in carbon steel, stainless steel arrow, propeller and bronze bearings, or total manufacturing in stainless steel, to meet different needs regarding the chemical quality of the water.

c) The blade fan, which provides the necessary air flow to generate the gas flow inside the capillary ducts; and whose roof configuration is adequate to the structural needs of the capillary aeration system; the cover of said stainless steel fan being, for the reason that it is exposed to splashing of the waters in process, which generally can have corrosive characteristics, the thickness of the sheet, is not required to be thick, since the structure, although it will handle large volumes of air, will work at very low pressures; The propeller can be made of aluminum and the recommended motor can be TCCVE frame.

d) Screening of solids, which is designed to be able to pour raw water, free of solids that can obstruct the capillary aerator, directly to the biological oxidation tank, without the need for an additional discharge tube, that is, the structure in the bottom, it is open with the purpose of allowing the drainage of the 100% cast water so that its operation is simpler, on the other hand the structure is balanced, so that its placement can be done in the most Easy on any point of the tank wall.

e) The capillary aerator, which serves to achieve the formation of liquid and gaseous films, in a controlled manner, in order to manipulate the different factors involved in the transfer of oxygen, of the aeration processes, in the aerobic treatment of Contaminated water, through the set of constructed ducts, in the form of plates, and whose installation can be done inside a tank, outside the liquid as illustrated in (fig. 8).