WO2002002239A1

WO2002002239A1 - Method for the sedimentation and classification of sludges

Info

Publication number: WO2002002239A1
Application number: PCT/MX2001/000042
Authority: WO
Inventors: Simó I. CASTAÑEDA ESCORZA
Original assignee: Castaneda Escorza Simo I
Priority date: 2000-06-23
Filing date: 2001-06-22
Publication date: 2002-01-10
Also published as: AU2001269604A1; MXJL00000004A

Abstract

The sedimentation method with classification of sludges makes it possible to classify in a sedimentation tank such as the one shown in Figure 27 by the following sedimentation speed rates: high, intermediate and low with the purpose of obtaining heavy, intermediate and light sludges having corresponding physical, chemical and biological characteristics. The discretely activated sludges are modified into active, intermediate and stabilized sludges that have been classified and are used for perfecting biological treatment processes of black waters, municipal waters and certain wastewaters. They can be used for biological oxidation of carbonaceous matter, for nitrification and denitrification by appropriately configuring the sedimentation tank and by providing one or several channels that are divided into 2 or 3 sludge collecting chambers in line with the requirements of each process with the purpose of facilitating concentration and removal thereof by means of collecting tubes having calibrated holes to enable uniform and complete removal throughout the extension of said tubes with the aim of preventing anaerobic regions. An assembly of accessories forms a siphon enabling removal by gravity, which is controlled by means of sectioning valves with minimum energy consumption. It can also be controlled using automatic valves.

Description

METHOD OF SEDIMENTATION AND CLASSIFICATION OF MUDS.

Technical Field:

Biological treatment of activated sludge for municipal sewage or industrial wastewater.

Background:

The sedimentation tank designs, regularly used today, can be classified into four large groups, with some particular variants within the same group, not including sedimentation systems induced by chemical precipitation, for leaving the context of biological treatment, in addition to these have a very specific application, within the chemical treatment systems; The aforementioned groups are described below, making the observation that in these a classification is not handled, of the different types of sludge that it is possible to separate, to handle them selectively, so that their management is discretionary.

Horizontal flow sedimentation tank, without mechanical extraction.

Tank in the form of an inverted pyramid, without mechanical sludge extraction, in this type of settler, the collection of sludge is carried out in the lowest part of the tank, the operation of these settlers is normally manual, as regards the eviction sludge, since the concentration is carried out at a single collection point, due to the effects of gravity, the specific weight of the suspended particles and the geometric shape of the tank, its maintenance is minimal; The disadvantage they have is that the capacity, referring to the surface area of sedimentation, is limited by the projected height when increasing its size, since this increases in proportion to the area of the tank, and the way in which greater capacity is obtained loading is, increasing the number of units, to give the capacity required in a given plant, this being an expensive solution when handling large volumes; Because of the way the flow is handled, it is said to be a horizontal flow tank, for the reason that the oxidized waters enter the tank at the top through an inlet pipe, reaching the inlet spout, on one side, the clarified waters are discharged by the outlet spout on the opposite side, which leave through the clarified water pipe, and the sludge is extracted from the lowest point, for its recirculation or removal of the system, through the sludge pipe, by the action of gravity; All particles, which settle from any point on the surface, whether light, heavy, large or small, all converge to the same collection point, so that in the plants where this type of settler is located, the sludge is channeled Without any classification.

Horizontal flow sedimentation tank with mechanized extraction.

Rectangular sedimentation tank with mechanized sludge harrow, in this type of units it is had, that the concrete structure is of rectangular section seen in plan, with the characteristics that cause the accessories of this system; In this unit, the sludge settles on the bottom and on the entire surface of the tank, and by means of a system of harrows, they are dragged to a sludge collection chamber, this being the point where they are concentrated and extracted, through the tube of sludge, the operation of this settler is fully mechanized, having the advantage that the load capacity per unit area is good in proportion to the height, which can affect shorter retention times, the size of the surface area, is limited by the maximum dimensions that can be obtained from a good harrow system; The big disadvantage they have is precisely the expensive maintenance required by the harrows, which are chain-shaped structures, with support rollers at various points, the movement that is required is very slow, in order to be able to drag the sludge without shaking, which move by means of geared motors, all this being a very expensive equipment, besides the inconvenience of having a relative energy consumption; by the flow path, it is said that these settlers are horizontal flow; In this type of units, the oxidized waters enter the tank, through an inlet at one of the ends of the tank, through the oxidized water inlet pipe, coming from the aeration tank, before the sedimentation tank, where you have the highest height, because the bottom floor has a slight slope, to facilitate the sludge drag, in this area is the sludge hopper at the bottom where the sludge is deposited, for its extraction by means of the pipe sludge, the clarified water is collected in the outflow dump, through the clarified water pipe. Mechanized radial flow sedimentation tank.

These tanks are formed by a cylindrical concrete structure, where the bottom is conical, with a sludge collector or hopper, in the lower part of the structure, from where they are dislodged through the sludge tube; the operation consists of inducing the sedimented sludge, towards the sludge collection chamber, located in the center of the bottom, by means of a circular drag, which hangs from a bridge-shaped structure, which is supported by a central column, the which in turn rests on the circular wall of the tank; the cost of maintenance and energy consumption is lower than in rectangular tanks, with mechanical sludge extraction; One of the excellent characteristics of this type of settler is its high capacity of the outflow dump; Due to the way in which the flow develops, these sedimentators are said to be of radial flow, the clarified waters are dislodged through the entire peripheral outflow spout, leaving through the clarified water pipe, and the oxidized waters enter through the center through the oxidized water inlet pipe, at a depth close to the surface, through holes on the oxidized water pipe; The way in which the concentration of particles is carried out, at a single point, prevents a profitable classification of the different types of existing sludge.

Vertical flow sedimentation tank without mechanical extraction.

There are also the non-mechanized circular tanks, or non-mechanized vertical settlers, which are formed by a cylindrical concrete structure, where a vertical flow is generated upwards, because the oxidized waters are entered at a certain depth and to the center from the tank through the oxidized water pipe, the speed that is generated upwards, known as the overflow rate (Vo), which is greater than the ascent rate of the mud particles, which are concentrated at a certain height , from where they are extracted through the light sludge tube, where apparently a type of filter is formed that helps retain, part of the small particles or low specific weight; the heavy sludges go to the bottom of a conical hopper, from which they are periodically extracted by means of the heavy sludge tube, the clarified waters are scattered on the perimeter weir, which discharges the waters through the clarified water tube, the main disadvantage, is that the efficiency is greatly influenced by the height, in addition to the removal of light sludge is not very uniform, because what can be generated anaerobic areas, if you do not have the exact speed of ascent, and on the other hand, a higher speed than the design, will cause agitation, inhibiting the separation of light sludge; Due to the shape of the flow, these settlers are also called upstream settlers; although in these two types of sludge are separated, those that are suspended at a certain height or light, and heavy sludges, which manage to settle to the bottom, although there is a classification of two types of sludge, the sedimentation method, not it has spread a lot, since it becomes very difficult to maintain conditions in large units, and its application may require flow regulating units; On the classification of sludge, which is obtained in these settlers, there are no references on a possible selective management.

Description:

The method of sedimentation with sludge classification, consists of grouping the sludge that sediment, in a certain range of sedimentation speed, within a tank, by the appropriate configuration of the sedimentation tank, and by the arrangement of one or more channels, sectioned in the form of sludge compartments or chambers, which can be 2 or 3 sectionings, depending on the needs of each process, where the sludge that accumulates by sedimentation, is extracted by means of a collection tube with calibrated holes, and a set of accessories that form a siphon located at a point and at a convenient height, so that the extraction is done by gravity, and is simply controlled with sectioning valves; resulting in a classification based on the following:

Heavy sludge, the highest sedimentation rate range. Intermediate sludges, of an intermediate speed range. Light sludges, of the lowest speed range.

To this classification, we must add the physical, chemical and biological characteristics of each of them.

The illustration of the concept of sludge classification is given in the following figures:

Figure 21 Shows the graphic distribution of the position of the heavy particles. Figure 22 Shows the graphic distribution of the position of the intermediate particles.

Figure 23 Shows the graphic distribution of the position of the light particles.

Figure 24 Shows the random graphic distribution of the position of the heavy, intermediate and light particles, where the effects of crashes and dragging between particles are illustrated.

Figure 25 Shows a graph of sedimentation rates, against the proportion of particles that have a certain velocity.

Figure 26 Particle path in an ideal sedimentation tank.

Sludge classification; Figure 26 shows a theoretical profile on a coordinate plane, represented by axes (31) and (32), of the trajectories of particles that develop in an ideal settler, where the first correspond to the largest or heaviest particles, that are distributed from the point (20) and as they have trajectories that are moving further away, the particles of the entry point (2), these correspond to particles of smaller weight and size, until they reach the particles defined as light, whose distribution extends to point (30); at the end of the tank is located the outlet spout (3); The tank has sludge chambers (6), to prevent the flow area from being affected by the volume of sludge that is deposited in the bottom; considering this behavior, the design of the sludge tank with sludge classification, is sized with a length (33) and a height (34), which in combination with the flow area, make it possible to have these trajectories, which will allow them to be grouped and conveniently sectioning them with the sectioning of the collectors, which constitutes the mechanism that will result in a classification of the sedimented sludge, as illustrated in figures 21, 22, 23 and 24, and referenced below; the behavior of the particles is, in the sense that at the beginning, the denser or larger sludge particles (No. 21) are sedimented which end in the schematic position shown in Figure 21; subsequently those of an intermediate density and size (No. 22) that also end in the schematic position shown in Figure 22, and finally the particles of low density or smaller sizes, (No 23) of Figure 23, but of course more dense that water, this sorting or classification that can be had of the sludge, within the sedimentation process, when combined, we have the random schematic position that occurs inside the tank, figure 24, with the reservations of each particular case , this leads us to suggest, the most likely characteristics to take into account of these sludges, to channel them in a more objective way, to the destination that they want to be given, more for their qualitative physical, chemical and biological characteristics, than for a simple proportion, of sludge in general, as it is handled in sedimentators that have been traditionally managed, and that can represent an important evolution, in how to commonly treat 5 sewage, municipal and some industrial waste.

Overflow rate (Vo), in figure 25, this concept is illustrated, which refers to the upward velocity of the fluid, considering the surface area of the tank as a flow area, for which the number of particles that settle or at that speed, it is maximum; the understanding of this parameter helps to understand the operation of a sedimentation tank, because it allows establishing a relationship between the proportion of particles, represented on the axis of the ordinates (No 27), whose sedimentation rate Vsi is represented on the axis of abscissa (No 26), in the figure it is observed that for Vsi <Vo, most 5 of these particles will settle, because the retention time is sufficient for this condition to exist, there is the possibility that a proportion of particles, are dragged out of the tank, depending on the design of the sedimentation tanks, the proportion of these particles is represented by the graph (No 28) of the same figure; Vo is that speed (No 25) for which, or the concentration Ci or proportion P¡ of particles (No 24) that settle just at this speed is maximum; It can also be observed that all particles settle when Vsi> Vo.

It is important to keep in mind that as a result of an analysis of the sedimentability of a particular mud, it is possible that the graph of proportions or distribution of particles, has its maximum value loaded on the left, indicating that the sludge is constituted by a high proportion of thin or light sludge, or that you have a graph with the maximum loaded on the right, which will indicate that the sludge will be heavy, this can help us or to determine with more objectivity, if the times Retention in sedimentation tanks are short or long, that is, a fine mud will require a longer retention time, and a heavy mud will require a short retention time.

The type of particle distribution graph will allow us to have an idea about the frequency, with which any of the different extracts will have to be evicted, that is:

A symmetric distribution curve has two coverages, the first for the case in which the collecting section is divided in two, the eviction frequency for sludge, from light to intermediate, may be more frequent, because we are possibly talking about a larger volume with a lower density, but with a non-significant difference; in the case of three collecting sections, the intermediate sludge will have a frequency of 3 to 5 times greater than the frequency of evacuation of light and heavy sludge; It is important to note that these assessments are very relative due to the heterogeneous nature of sewage, municipal and industrial wastewater.

An asymmetric distribution curve loaded to the area of light sludge, has the following coverage, the first in the case where there are two collecting sections, the frequency of sludge removal, from light to intermediate, may be more frequent, Because we speak considerably of a larger volume with a lower density, and with a significant difference with respect to heavy sludge, in the case of three collecting sections, light sludge will have a frequency of 1.5 to 2 times higher, than the frequency of evacuation of the intermediate sludge, and 3 or 4 times greater than the frequency of extraction of heavy sludge.

An asymmetric distribution curve loaded to the area of heavy sludge, has the following coverage, the first one in the case where there are two collecting sections, the frequency of sludge removal, from heavy to intermediate, may be more frequent, because we speak considerably of a greater volume with a higher density, and with a significant difference, with respect to sludge, from light to intermediate; In the case of three collecting sections, light sludge will have a lower frequency with respect to the frequency of evacuation of intermediate sludge, which in turn is less 3 or 4 times than the frequency of extraction of heavy sludge.

Applied Kinetic Theory:

In sedimentators with sludge classification, the formulas derived from the sedimentation theory are the following:

A) Flow area; For the different versions of sedimentators, with sludge classification, in general it is trapezoidal, so the calculation of this area is given by:

Af = hx (B + b) / 2 Ec. 1 Where:

h = useful height of the sedimentation tank, where the flow develops, or the distance between B and b of the trapezoid that limits this area in m.

B = Major base of the trapezoid that forms the flow area in m.

b = Minor base of the trapezoid that forms the flow area in m.

B) Useful volume of the sedimentation tank; This volume is used to determine the retention time, which is given to the water in the process of clarification, and its determination is made as follows:

Vu = Af x L Ec. 2

Where:

L = useful length of the sedimentation tank in m.

C) Surface capacity: The surface capacity of a unit with sludge classification refers to the capacity of the unit to process a certain volume, per unit area and per day, based on the experience obtained in the different types of settlers, you have to have a value of

3 2 recommended reference is 25 m / m x day, and is expressed as follows:

chap. His p. = You / As Ec. 3

Where:

Vd = daily volume of fluid that passes through the settler in m / day.

As = B x L = surface area of the tank in m. Ec. 4

D) Discharge capacity; This capacity, refers to the capacity of the sedimentation tank to handle a daily volume per unit of length of the output pourer, this capacity, serves to limit the formation of currents generated by overflows, which can drag particles of sedimentable sludge out of the sedimentation tank, a reference number, recommended based on the experience, which has been had in different types of sedimentators is 200 m / mx day; The way it is calculated is as follows:

For unidirectional flow units.

chap. v = Vd / B Ec. 5

For divergent flow settlers.

chap. v = Vd / (2 x B) Ec. 6

E) Retention time; It is the time that the waters remain in the process of sedimentation, within the sedimentation tanks, the way to calculate this retention time is as follows:

Tr = Vu / Qd Ec. 7

Where:

3 Qd = design flow in m / s.

F) Horizontal particle velocity; is the speed at which the particles suspended in the liquid are dragged, to the horizontal distance (No 33) of Figure 26, which the particles travel and which is between the points (No 20) and (No 30), the The way to relate this distance to the design of the tanks is to multiply the retention time by the horizontal velocity of the flow; and that according to the practical purposes that are handled in the sedimentation processes, this is considered equal to the horizontal velocity of the liquid flow inside the sedimentation tank, that is:

Vh = Qd / Af Ec. 8

G) Sedimentation rate; the sedimentation rate is determined, by the application of Newton's second law, and with Stokes' drag coefficient, on the sedimentation of discrete particles, which is a function of the Reynolds number; From this speed and retention time, a calculation of the depth (No. 34) of Figure 26 that the particles reach, between the points (No. 32) and (No. 30) can be obtained. Starting from Newton's second law: df = dm xg Ec 9

That is:

Gravitational Forces = (De - Dr) x V x g

According to Stokes, gravitational forces are equal to the frictional force exerted on a particle that travels through a fluid, that is:

Gravitational forces = Drag forces due to friction.

(De - Dr) x V xg = Cd x Ae x De x Vs ^2/2 Equation 10

Where:

De = Relative density of the particle,

g = acceleration of gravity.

V = Volume of the particle.

Cd = Stokes drag coefficient.

Ae = Area exposed by the particle.

Vs = Sedimentation rate.

Dr = Relative fluid density.

Clearing Vs from equation 10 you have:

1/2

Vs = (2xgxV (De-Dr) / (CdxAexDr)) Ec11

Assuming that the particles are spherical in shape with diameter "d" you have:

V = PixDezines ^2/4 EC12

Substituting 12 in 11 you have: 1/2

Vs = ((4 x d x g x (De - Dr) / (3 x Cd x Dr)) Ec 13

The drag coefficient is a function of the Reynols number according to the equation developed by Stokes for different types of flows:

Cd = 24 / Nr + 3 / (Nr) ¹ ' ² + 0.34 Ec 14

Where:

Nr = Reynolds number.

For laminar flow conditions, which occur in sedimentation systems, it should be taken into account that the Reynolds number must be less than or equal to 1, in order to assume that inertial forces are considered negligible, a condition necessary to satisfy , the solution of the Stokes equation on the dragging of particles, based on this, and assuming that after the first term of equation 14, the terms are negligible, it can be assumed:

Cd = 24 / Nr Ec 15

Applying equation 15 in equation 13 you have:

Vs = gxd ² χ (Pe - 1) / (18 xv) Ec 16

What is the sedimentation rate, for discrete particles in a sedimentation tank, where laminar flow conditions around the particle develop.

Where:

v = kinematic fluid viscosity (0.00000101 m / s)

Pe = Specific weight of the fluid.

Horizontal flow sedimentation tanks, with sludge classification.

The design of the sludge tank with sludge classification consists of a tank designed for the sedimentation of particles within the process of sewage treatment, municipal or residual for certain cases, objective that is pursued in all the different types of sedimentators commented in general terms but, with the difference that have been incorporated, some devices that allow classifying sludge, through the appropriate design of the sedimentation tank, with the objective of selectively channeling them according to their physical, chemical and biological characteristics, to make the biological treatment of activated sludge more efficient; To be able to handle a wide range of capacities, there was a need to condition the tank configuration, so that it can have a greater surface load capacity, or a greater capacity of the output dumps, as described below .

Sedimentation tank with unidirectional horizontal flow classification, for flow rates up to 15 Ips.

This tank is illustrated by the following figures:

Figure 1 Drawing of the sectional view of a sedimentation tank, with sludge classification, unidirectional horizontal flow, two collecting sections and a single channel for sludge chambers.

Figure 2 Side view of Figure 1.

Figure 3 Side view of the sludge extraction system.

Figure 4 Front view of Figure 3. Figure 5 Drawing in plan, showing the details of the way, in which the calibrated holes of the sludge collecting tube are distributed.

Figure 6 Front view of figure 5.

Figure 10 Plan drawing of a sediment tank with sludge classification, unidirectional horizontal flow, single channel for collectors, of three collecting sections.

Figure 11 Left side view, of Figure 10 showing only the input and output spout, as well as the channel for collecting chambers.

Figure 12 Right side view, of Figure 10 showing the input and output spouts as well as the channel for collecting chambers. Figure 13 Front view of Figure 10.

Figure 27 Perspective view of a sedimentation tank, with sludge classification, unidirectional horizontal flow, single channel for collecting pipes and with 3 collecting sections. The sedimentation tanks, with unidirectional horizontal flow, are illustrated: in Figures 1 and 2, which refers to a single channel settler for collecting pipes, of two sludge collecting sections; the extraction system is illustrated in figures 3, 4, 5 and 6; as mentioned, the settlers can also be of 3 collector sections, as illustrated in figures 10, 11, 12, 13 and 27 show a unidirectional settler of three collector sections, in general; These types of tanks have the shape of an inverted triangular prism, in this type of units, the oxidized waters enter at one end through the oxidized water pipe (No 4), reaching the inlet dump (No 2), the sludge concentration is carried out in the lower part of the prismatic structure, identified as a sludge chamber (No 6) where the sludge classification is carried out, and are separated by separating structures (No 8), which can be build of masonry or concrete, they also have the function of concentrating the sludge, in a shorter length of the lower edge of the sludge chambers, to shorten the length of the collecting chambers (No 6); The design of the extraction system begins precisely with the collecting tube (No. 10), which is sufficiently separated, from the walls of the tank structure, by means of spacer rings (No. 35), to allow sludge to pass , towards the calibrated holes (No 12), all along the collection tube and which are located, in the lower part of the collecting tubes, to cause the sludge to flow, in such a way as to prevent the formation of anaerobic areas; The lifting tube is connected through a PVC tee (No 11), to the hose (No 13), which is attached at the ends, by means of flanged ends, and a spike (No 14) and (No 15 ) appropriate to the hose, then pass through a sludge conduction line (No 18), which has an air purge valve installed (No 16), in the pipe section, at a level barely covered by water in the process of clarification, but outside the tank, to restore the function of the siphon, when it is lost; In the final section of this sludge line, a sectioning valve (No. 17) is installed, which will be operated, depending on the intensity so that the sludge is generated.

By way of reference, the concept of unidirectional can also be applied to multi-channel tanks for collecting pipes, whose cross-section is in the form of a saw as illustrated in Figures 14, 15, 16, 17, 18 , 19, 20 and 29 that refer to unidirectional settlers, but with multiple channels for collecting chambers, so they can handle larger flows as discussed below. Settling tank with sludge classification of divergent horizontal flow, for flow rates of 10 to 30 Ips.

This type of tanks is illustrated by the following figures:

Figure 7 Plan view of a sedimentation tank with sludge classification, divergent horizontal flow, of a single collector channel, and of three collector sections for each outflow spout, with central inlet spout. Figure 8 Side view of Figure 7. Figure 9 Front view of Figure 7.

Figure 28 Perspective view of a sedimentation tank, with sludge classification, horizontal flow, divergent, single channel for collecting pipes and with 2 collecting sections.

The second group of settlers are defined as: Settling tank with sludge classification, with divergent horizontal flow, Figures 7, 8 and 9 show a unit of a single collecting channel, of three collecting sections for each dump; Figure 28 shows a unit with two collecting sections for each dump, this type of settler can also be two or more channels for collecting pipes; In this type of models, the capacity of the discharge is increased in the same concrete structure, with a single input spout located in the central part (No 7), due to the fact that this model has two output spouts (No 3) one at each end of the tank, which allows to handle higher flow capacities in a given sedimentation unit, with lower risks of causing flow currents, which cause sedimentary particles to escape.

Sedimentation tank with sludge classification, multi-channel horizontal flow, for flows greater than 30 Ips.

This type of settler is illustrated by the following figures:

Figure 14 Plan drawing of a sedimentation tank, with sludge classification, unidirectional horizontal flow, three collector channels, and three collecting sections.

Figure 15 Side view of Figure 14, showing the input and output spouts.

Figure 16 Front view of Figure 14. Figure 17 Drawing of the front view of a sedimentation tank, with sludge classification, unidirectional horizontal flow, two collecting sections and two channels for sludge chambers. Figure 18 Side view of Figure 17. Figure 19 Side view of the sludge extraction system, for two channels for collecting pipes.

Figure 20 Front view of Figure 19.

Figure 29 Perspective view of a sedimentation tank, with sludge classification, horizontal, unidirectional flow, two channels for collecting pipes and with 2 collecting sections.

The third characteristic group of settling tanks, with sludge classification, is represented by the multi-channel sludge settling sedimentation tank; what forced the search of this new group of units, was the limitation that had in the other models for the superficial capacity of load, that is to say, this model of sedimentadores can handle bigger flows, in a single unit; the height resulting from the structure of the previous models, for the same capacity is too large, so that, with the use of more channels for collecting tubes within the same unit, the problem of height could be conveniently handled, which it would be presented in the units of a single triangular section, in case they handled, the flows that can be managed with the multi-channel units.

Figures 14, 15 and 16 show a unidirectional horizontal flow sedimentation tank, multi-channel for collecting tubes, in this case, these are three channels for collecting tubes, and with three collecting sections; Figures 17, 18, 19 and 20 show the extraction system for this type of settler; Figure 29 shows a two-channel tank for collecting tubes and two collecting sections; it is necessary that the aerated or oxidized waters, arrive through the pipe of oxidized waters (No 4) until the entrance pourer (No 2), the sludges enter the collecting tubes (No 10) through the calibrated orifices ( No. 12), then passing through the coupling manifold (No. 20) and passing through the accessories, from (No. 13), to (No. 19), it is important to mention, that due to the density and viscosity of the sludge , the maximum number of channels, which is recommended to install is 8, in two batteries of 4, one on each side of the tank, this application depends on the design and hydraulic calculation of the components of the extraction system, which form the siphon through the which are extracted by the effects of gravity; in this kind of settlers, when handling more than two channels for collecting pipes, it is necessary to implement a mobile bridge, in order to facilitate maintenance maneuvers; It is important to mention, that due to the density and viscosity of the sludge, the maximum number of channels, which is possible to install is 8, in two batteries of 4, one on each side of the tank, this application depends on the design and calculation hydraulic, of the components of the extraction system.

General information about sedimentators with sludge classification:

As can be seen in all types of settlers, with sludge classification, the structures are of a relatively simple configuration, easy to build, do not carry pipes that cross the walls in the lower parts, their operation requires very little maintenance and when this It is required, it is very simple, as it will normally consist of uncovering the sludge collector tubes, which are very light and easily accessible, it has an operation that depends 100% on gravity, its operation does not require any motorized and complicated mechanism , so the energy consumption is zero compared to mechanized settlers.

In most practical cases, only 2 classifications will be required, and only in very special situations will it be necessary to handle 3 classifications, such as in a prototype research plant; for design reasons, it may be that, a settler has 3 sectionings, considering the first heavy sludge, the second intermediate sludge, and the third corresponding to light sludge, the latter two come together to generate a single mud, Considered as light, the reason for installing in some cases, 3 sections, when only 2 are required, is because the sludge collecting tubes cannot be too long, so, when the length of the tank is relatively large, sectioned into 3 parts, to give greater fluidity to sludge, whose kinematic viscosity is relatively high.

As expected, the variation of the influent flow implies that an analysis of the operation and application of this type of settler is made, considering the following:

For systems whose influent can be considered as constant, the classification regime is achieved with characteristics that can be considered homogeneously well defined at any time, so the withdrawal of excess sludge is effected, without any risk of mishandling; intermediate and light sludges, as they are normally recirculated, are handled with fewer risks; The operation of the settlers at constant flow, is very attached to the concepts that are defined for an ideal settler, it is convenient to note that, although these cases are not presented as such in reality, there are some applications, which can be considered as such, a very similar case, would be in a treatment application, near the mouth of a river, to a large lagoon, where you can have a practically constant water supply, or some system that has facilities to dose a constant flow, which obviously would not be profitable in small installations, the management of a constant flow, would allow to adjust the valves manually and permanently, with good results, as long as the amount of flow, is the minimum necessary, to make circulate the sludge fluidly, otherwise, the operation of the valves should be done intermittently, as required.

In cases where there is, that the flow of the influent is variable, some considerations must necessarily be made, as follows:

a) The sedimentation tanks are normally designed, considering criteria of maximum, medium and minimum flow that are feasible that may occur in the operation of the sedimentators, taking into account these flows, the dimensions must be such that they allow to obtain the grade Design clarification, which is a function of the hydraulic load capacity and the pouring capacity of the sedimentation tank, under maximum flow conditions.

b) The management of heavy sludge consists of its classified separation, its recirculation or removal when there is an excess of sludge; However, when the minimum flow is being handled inside the tank, in the collecting section corresponding to the heavy sludge, both heavy sludge, intermediate sludge and possibly light sludge can arrive, therefore, the removal of excess sludge should not be carried out during the hours of minimum flow; when medium flow conditions are being managed, with a certain tolerance, it is possible that in this area, heavy sludges and possibly some intermediate ones will settle, which does not represent any risk from the operational point of view, since in addition, the removal of Excess sludge is usually done on the day, which is when you have medium or maximum flow conditions; when the maximum flow is handled, and given that the design dimensions are based on this flow, the expected classification must be presented, therefore it can be concluded that the Excess sludge removal can be removed without causing any opposite effect, when medium to maximum flow conditions are present, a function that can be carried out manually or automatically, taking care that recirculation is not carried out, when the sedimentation tank has fallen to its minimum level of operation.

c) Intermediate sludges constitute an unusual but feasible classification, which is proposed as a classification, which could help to make adjustments with less risk of inducing concentrations, which have a high concentration of stabilized sludge or active sludge; although its application must be supported by, the result of a laboratory analysis; Some possible applications that could be considered for this type of sludge, apart from prototype facilities for scientific research, consist of the following:

The intermediate sludges of the first stage are mixed with fresh water and channeled to a denitrifying tank, to compensate for deficiencies of organic carbon and with the purpose of reaching a greater degree of stabilization, and to reduce the application of methanol.

The intermediate sludges that can be developed in a nitrification tank, can be conditioned in a tank with controlled pH and temperature, to have a culture of nitrosomonas, which are those with the longest development time and sensitive to low temperatures, alkaline pH and toxic substances In this way, the system can be protected from a total loss of the most difficult bacteriological sludge to regenerate in the nitrification tank.

As you can see the variation of the flow, it does not represent risks for the application of intermediate sludge, although it can mean a reduction of active sludge in the minimum flow schedules, this decrease would occur, only in the case that the removal of sludge heavy, is carried out in the hours of minimum flow, although, due to the way in which the removal of excess sludge can be programmed, the effects of the minimum flow can be eliminated, for this reason, the line of operation of these sludges, It can be operated without many problems, in addition, the implementation of an intermediate classification is optional, for cases where they are required for a specific application, in which case, to achieve sludges with intermediate characteristics, it would be advisable to operate the valve when flows occur medium to maximum, which can be carried out manually or automatically. d) Light sludge; The effect of the variation in the handling of light sludge is as follows: When minimum flow conditions are handled, the corresponding sludge chamber does not capture light sludges, but since it is the minimum flow conditions, it does not have a important or worthy effect to be taken into account; when the medium or maximum flow is handled, the collection of light sludge is significant, and sufficient to generate the required inoculation, therefore, the variation of the flow does not cause radical effects, worthy of consideration, this allows to establish, that The valves of this type of sludge may be open when raw water is supplied to the system and must remain closed when the sedimentation tank has the minimum level of operation.

e) With the previous approaches, and considering that the sludge within a treatment, is managed based on concentrations, which have a reasonable margin of tolerance, the flux variation in the influent does not constitute an obstacle, for the application of the classification of sludge in treatments.

Application of sedimentators with sludge classification, to clarify waters of a biological oxidation tank.

For the different sedimentation units, applied in processes where carbonaceous matter is being removed, we can have the following characterization of sludge:

Heavy or high density sludges, are sludges that are collected in the first collecting section, which have reached a high degree of sedimentability, formed by flocs or particles, which agglomerate bacteria active in the peripheral area mainly, in the center is accumulated a significant amount of dead bacteria or inorganic matter, product of the metabolization of organic matter, it is very likely that small microbubbles of CO ₂ are found in the peripheral area product of the metabolization of active bacteria, and also in the peripheral area , O ₂ can be found that has been retained by the flocculation and that has not been used by active bacteria, for breathing, and in general, other chemical elements can be found, depending on the chemical composition, wastewater and type of bacteria developed; These sludges for their final stabilization, require that a moderate concentration of dissolved oxygen (OD) be maintained, since their composition will have a high proportion of inorganic matter, which has already been metabolized in a large proportion, so It is the most viable to withdraw, such as excess sludge in a treatment plant, and that will be produced in a greater amount when the plant's metabolism efficiency is lower and will be minimal when the plant's metabolism efficiency is high, The general characteristics of these sludges is what makes them more suitable for removal, this implies the advantage that the thickening or stabilization process will be carried out more easily, which is one of the objectives that are sought, that is to achieve better natural results, instead of implementing complicated and expensive mechanisms.

Intermediate sludge in relation to its density and size, are those that are collected in the second sludge collection section, are the flocs or particles formed by growing bacteria, the contaminating organic matter, the active bacteria, CO ₂ , O ₂ and a medium amount of metabolized matter, are dispersed throughout the floc, such characteristics demand for their final development, an intermediate amount of nutrients and OD, so this makes them relatively more versatile, for recirculation within of the same process, or withdrawal according to the demand for activated sludge, there is also the possibility of recirculating them according to their physical, chemical and biological characteristics, such as their sedimentability characteristics, high content of raw sludge, which can make them suitable for recirculation, after mixing with fresh water, to a tank where a stage of denitrification is implemented In addition to the fact that its constitution covers a very wide range of types, sizes and ages of bacteria, it is feasible to analyze in the laboratory, the proportion of predominant bacteria and especially the facultative ones, which can be conveniently channeled, in the transition of a aerobic to anaerobic process, where the metabolic function of facultative bacteria, would not end with the absence of free oxygen, but will adapt to anoxic conditions and vice versa, which could possibly reinforce biological activity.

Unless there is a specific need for intermediate sludge, in most applications, it will be sufficient to have 2 sludge classifications, in this case, we will talk about heavy and light sludge, and proportionally the light sludge, will be the ones that are collected about 2/3 of the length of the settler.

You can make a third classification of sludge, light or low density that are collected in the third collector section of the settler, these sludges are formed by freshly formed flocs or particles, that is to say that they just begin their development, active bacteria, nutrients , O ₂ and CO ₂ together with a small amount of metabolized matter, are distributed throughout the floc; This conformation gives the sludge a characteristic, defined in the following terms: The sedimented bacteria in this area, form the smallest flocks and consequently those of recent creation, whose number of flocs or bacteria per unit volume must be the largest , which gives light sludges, high diffusivity characteristics, so that if these sludges are properly mixed, sufficient nutrients are provided and good levels of OD are maintained, it is very likely that high bacteriological growth rates will be obtained. , which favors the degradation of contaminating organic matter; taking into account the previous reasoning, these sludges require a high demand for nutrients for their total stabilization, and they will also have a relatively higher demand for OD, this characteristic makes these sludge the most viable to be recycled when an influent is being handled, with high loads of organic matter and consequently makes them the least viable to be removed; the slow sedimentability of these sludges, is another indication that they must return to the process, so that the flocs continue their development, reaching greater weight and size, and logically improve their sedimentability; It can also be considered that due to the number of bacteria per unit volume, and due to their diffusion characteristics they can be considered as a seed for sowing sludge in other plants, and as their sedimentability is the lowest, it is logical, It would be counterproductive to send them to a sludge thickener system.

Application of sedimentators with sludge classification, to clarify sewage from a nitrification tank.

When treatment systems are implemented, where nitrification of the nitrogenous pollutants is carried out, it is important to keep in mind that this process, requires more time and more oxygen, the nitrosomonas and nitrobacter bacteria, which can be collected with the sludge heavy in the first sludge collection section, and which are mainly responsible for metabolizing this type of pollutants in its two stages, that is, the ammonia and ammonium hydroxide in nitrites are first metabolized, and then nitrates in nitrates, These bacteria are of a slow development, sensitive to temperature and conditions, of high or low Ph for nitrifying water, so that the sedimentation system with sludge classification is particularly important due to the fact that it allows recirculation ios excess sludge from the process, to the biological oxidation tank of matter carbonaceous, so as not to lose the possible nitrifying bacteria, which could be transported in this type of sludge, and have a more significant partial nitrification in the tank of biological oxidation of the carbonaceous matter; the light sludge, collected in the second section of the nitrifying sludge settler, which can be considered the most biologically active, when recirculating them, it will always be certain that the most convenient sludge is being returned to the nitrification process; Due to the characteristics that have been formed, around the flocs that are formed from the nitrosomonas and nitrobacter bacteria, which are said to be slow growing, it implies that in this process, the size and weight distribution curve of the particles that settle, be an asymmetric curve, charged to the left, that is, most of the particles that participate in the process, will be included among those that have been defined as light and intermediate, on the other hand it has, that the The amount of nitrifying sludge is relatively low, for this condition, it is reasonable to consider that the length of the sludge collector is 2/3 the length of the tank, this is consistent with the fact that the residence times, for sludge Nitrifiers is relatively large.

Application of sedimentators with sludge classification, to clarify sewage from a denitrification tank.

The heavy sludge that can be separated, in the first section of a sediment tank with sludge classification, with two collecting sections, is recycled as excess sludge from the denitrification tank, to the biological oxidation tank of carbonaceous matter, for the purpose of preserve and develop possible facultative bacteria, which could be developed in the process, and to achieve greater stabilization of these sludges; how in the denitrification stage OH ions are generated, it is convenient that said channeling is done, taking care not to cause PH imbalances in the target tank

The second section will receive the lightest sludge, which will be constituted by an important concentration of heterotrophic denitrifying bacteria, among which the following can be named: Alcaligenes, Achromobacter, Pseudomonas and Micrococcus; which are the most common and are mainly responsible for metabolizing nitrates and in some cases also nitrites, which are broken down to release nitrogen that escapes into the atmosphere, Together with C0 ₂ that also occurs in this process, these sludges will be recirculated on a daily basis, within the same stage of denitrification.

Claims

Reinvindications: 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 method of sedimentation with sludge classification, which consists of classifying sludge, within certain ranges of sedimentation speed within a tank as illustrated in (fig. 26), by the appropriate configuration of the tank of sedimentation, and through the provision of one or several channels, sectioned in the form of sludge compartments or chambers, which can be 2 or 3 sectionings, depending on the needs of each process, where the sludge that accumulates by sedimentation, are extracted by means of a collecting tube and a set of accessories, which form a siphon located at a convenient point for each collecting section, to carry out the extraction that is by gravity, and that is simply controlled with sectioning valves, manually operated or automatic; obtaining as a result 3 or 2 types of sludge with different physical, chemical and biological characteristics, which are a different concept than activated sludge, generally managed at discretion, and which allow to improve the biological treatment processes.

2.- The sedimentation tank with sludge classification, with a unidirectional horizontal flow, as illustrated in (fig. 27) built with reinforced concrete, provided with a single inlet and a single outlet; the tank can have 2 or 3 sludge collecting sections; in the case of 2 sections, there are 2 classifications of sludge, heavy and light, and in the case of 3 sections, there is an additional classification of intermediate sludge; The tank has a sludge collection tube of plastic material, with calibrated holes that together with some hydraulic accessories, form a siphon for each collecting section, through which the sludge is removed by gravity.

The purpose of this tank is to sediment the sludge and classify them based on the different sedimentation rates, its configuration allows to manage flow rates of up to 15 Ips. The tank receives the fluid with suspended sludge, which sediment due to gravity, and due to the inclination of the walls, these are concentrated in the collection chambers, where by means of a siphon system, which begins with a sludge collection tube that has a series of calibrated holes, which in combination with some hydraulic fittings, induces sludge displacement evenly along the collecting tube; On the sludge discharge pipeline, at least two valves are installed, one for sectioning, which allows the sludge to be handled with the frequency required for each case, and another valve for air purging that allows the siphon action to be formed.

3.- The sedimentation tank with sludge classification, with divergent horizontal flow, as illustrated in (fig. 28), provided with a single input spout and two output spouts; the tank can have 2 or 3 sludge collecting sections; in the case of 2 sections, there are 2 classifications of heavy and light sludge, and in the case of 3 sections, there is an additional classification of intermediate sludge; The tank has a sludge collection tube of plastic material, with calibrated holes that together with some hydraulic accessories, form a siphon for each collecting section, through which the sludge is removed by gravity.

The purpose of this tank is the same as that described for reinvindication 2, with the only difference that by having 2 output dumps for each tank, flows between approximately 10 and 30 Ips can be managed.

4.- The sedimentation tank with sludge classification, by means of the design of multiple collecting channels, such as the one illustrated in (fig. 29), of unidirectional or divergent horizontal flow, also having 2 or 3 collecting sections sludge, for each outflow pourer; The quality of this type of settler is that it has more than one sludge collecting channel, being able to be 2, 3, 4, 5, 6, 7 and 8, this allows to have a greater surface capacity of hydraulic load, with what the concrete structure of the settlers, project relatively small heights; The sludge extraction system is similar to that of the first reinvindication, with the only difference, which can have more than one sludge collecting channel, in addition, the interconnection of the collecting pipes, for the same collecting section, is made by means of a manifold for 2, 3 or 4 collecting tubes, which are part of the siphon system similar to that described in reinvindication 1.

The purpose of this tank is the same as that described for reinvindication 2, with the difference that it can be unidirectional or divergent, with their respective options, but in this case the number of collector channels is 2 or more; This allows handling capacities greater than 30 Ips.