MXPA05004542A - Process for biologically treating wastewaters using anaerobic sludge - Google Patents

Abstract

The present invention refers to a process for biologically and anaerobically treating wastewater based on the UASB concept. The process comprises a wastewater supplying system, a reactor tank, and a system for separating treated wastewater and generated gas. The process of the present invention may be useful for treating any type of wastewater discharge having solved organic pollutants;since the process has a modular concept it may be used in a wide range of organic flow and charge values, each module may act as an anaerobic contact reactor, or as an upflow anaerobic reactor (UASB).

Description

PROCESS FOR THE BIOLOGICAL TREATMENT OF WASTEWATER WITH ANAEROBAL SLUDGE TECHNICAL FIELD The present invention relates to the processes of anaerobic biological wastewater treatment of the type based on the UASB concept (upflow anaerobio sludge 10 blanket), and especially to a process comprising a reactor with a fermentation section, a system to feed the waste water to the fermentation section and a system provided on the fermentation section for the discharge of purified water and the gas collection. fifteen BACKGROUND OF THE INVENTION There are several types of industrial processes for the biological treatment of water, for the transformation of dissolved organic matter into wastewater in order to eliminate it, each with characteristics that make it suitable for certain operating parameters. The most important operating parameters are the flow of water to be treated, the concentration of dissolved organic matter and the organic load. The concentration of dissolved organic matter, mg / l, is usually measured as DB05 (biochemical demand of 5 oxygen in 5 days) or as COD (chemical oxygen demand). The organic load expresses the flow of organic pollutants to the treatment per unit volume of the treatment tank (kg DB05 / m3day).

Aerobic biological purification processes The best known category is that of aerobic biological processes. The consortium of aerobic microorganisms, called "activated sludge", formed in large part by heterotrophic bacteria of spontaneous development in the wastewater, consumes the dissolved oxygen that diffusers of different mechanisms contribute to the water, and it uses it in the oxidation of the organic matter that is released as carbon dioxide. The energy that the cells accumulate is used in the production of more bacteria and then it is necessary to remove and treat the activated sludge generated in excess. This activity, with the waste management that it generates, becomes the main limitation of aerobic treatments. On the other hand, it is recognized that these processes are not practical or economical for the management of high volumes of water to be treated. • 5 U.S. Patent 4,009,098 (Jeris, 1977), for example, describes a water treatment process that is directed primarily to the removal of organic carbon through the use of fluidized activated sludge. Organisms are grown as biologically active suspended solids in aeration tanks, and the oxidation is carried out in said tanks with a concentration of biological solids of 2,000 to 4,000 mg / l. An important parameter to consider is the requirement of at least 0.2 to 0.6 mg of dissolved oxygen per milligram of DB05 removed, considering that a excess or defect makes the process less efficient; It is also notable the need for pumping processes in order to maintain the fluidized bed, which consumes energy.

Anaerobic biological treatment processes 20 The anaerobic treatment of wastewater represents a convenient alternative for the conversion of dissolved organic pollution, especially with a significant amount of suspended biological contamination, in the order of more than 500 ppm of DB05, in a gas containing carbon dioxide (C02) and between 60 and 80% by volume of methane (CH4), commonly called "biogas". A small part of the organic contamination is incorporated into the cellular substance of the microorganisms and must be removed as an excess at some point in the process.

An important aspect in these anaerobic processes is the possibility of capturing the biogas produced in the reactor, in order to subsequently take advantage of its energy. In this sense, a fundamental element of the processes that will be described later are the biogas capture devices.

One of the clearest examples of such a device is provided in the patent 4,116,791 (Marvin, 1979) of the United States, which describes a process of capturing biogas produced in an anaerobic reactor, where said gas stream is passed through a trap and a carbon filter (elimination of entrained liquids / solids) and then taken to a burner.

Mobile bed systems (expanded and fluidized bed). Within the reactors, the bacteria are immobilized on small particles of solid support, varying only the degree of expansion of the bed; in the expanded one between 20 and 40% and in the fluidized one, greater than 40%. In the expanded bed, increasing the superficial velocity of the liquid lengthens the bed, although there is still contact between particles, the porosity increases and the bed is more spongy. They require a high energy consumption, can treat high organic loads and use particles of low diameter and high density.

Anaerobic Contact Reactor. This process with activated sludge allows to operate with residence times of biosolids (TRS) much higher than the hydraulic residence times (TRH), and consequently to treat fairly dilute wastewater (up to 2 kg COD / m3). It is generally operated with recirculation ratios that range between 80% and close to 100%.

This process can also be used to treat waters with soluble contaminants, to improve the biodegradation of suspended solids, increasing the contact time between the substrate and the microorganism. The digester is usually cylindrical, large and agitated, to maintain the suspension (the agitation is not vigorous).

UASB systems (upflow anaerobio sludge blanket). The UASB process is described in U.S. Patent No. 4,253,956 (Pette, 1981). In a process of the UASB type, the wastewater is introduced through the bottom of the reactor tank through a process of distribution of the feed and passes through the bed of dense anaerobic mud at the bottom of the tank. Soluble COD is rapidly converted to biogas, which is rich in methane, and an upward current of water, gas and mud circulation is established.

In the reactor, the sedimentation section allows an effective separation of the generated biogas to occur. The dense granular particles of the mud, once devoid of the associated gas bubbles, are directed towards the bottom, establishing a downward flow of return. The upward flow of the sludge with gas through the bed is combined with the downflow of sludge already without gas to create a continuous convective flow. This ensures effective contact between the sludge and the wastewater, without the need to consume mechanical energy or hydraulic agitation inside the reactor.

The design of the reactor allows a concentration of highly active biomass in relation to the soluble solids that pass through the mud bed and is responsible for the high rate of organic load (short retention time) that can be processed.

The process is well known and widely used. A full-scale short-time start is possible when sufficient granular material is added before start-up. Granular sludge can be obtained from other UASB processes. This type of sludge consists of granules of active material, which are formed naturally in the UASB reactor; They remain active for years, can be removed from the reactor and can be stored, which makes them very suitable to be used as inoculation material for new plants, or to restart existing plants after a strike. The UASB process is very opriate also for seasonal plants (for example sugar mills) where the process is interrupted for months and a quick restart is essential.

However, the UASB reactors also present some disadvantages, for example, a liquid velocity of 1-2 ßtk-m / h is insufficient to prevent (partial) sedimentation of inert sediments in the reactor. To prevent this, in many cases the wastewater must first be treated in a primary settler to separate this inert sediment. The UASB reactors are also sensitive to the upper air intake, due to its construction, which can result in corrosion. Sometimes they emit bad odors due to the escape of gases from the top. The overpressure in the upper part must be kept low, which makes the transport of biogas (corrosive) practically impossible without the use of a compressor. In addition, the area required for the implementation of such an apparatus, especially if a primary settler is necessary, is large and is not always available in close proximity to the waste water source.

For low concentration wastewater, a modified UASB reactor, called the EGSB (Expanded Granular Sludge Bed) reactor, has been designed (see G. Lettinga and LH Pol, Wat Sci. Tech., Vol.18, No. 12 (1986) pp. 99-108).

When low concentration waste water is fed into a UASB reactor, gas production is very low and mixing due to the gas formed inside the reactor is insufficient, so the reactor does not work properly. To solve the problem, in the EGSB process the ascending liquid is applied at a high speed, which results in the expansion of the sludge bed and consequently in a better water-mud contact and therefore, a better use of the biomass. Commonly, this higher rate of upward flow is achieved by the recirculation of the effluent.

However, the EGSB concept is only suitable for the treatment of relatively cold and very low concentration wastewater. When concentrated water is fed into an EGSB process, large amounts of gas formed in the reactor will disturb the purification process. Part of the mud particles will leave the reactor together with the suspended solids of the input material. In a conventional settler design, these mud particles are difficult to separate from the suspended solids, resulting in a loss of active biomass. Therefore, an EGSB reactor will not work under conditions of a wastewater supply of high concentration of organic matter and therefore normal UASB reactors will be preferred.

Other modifications to the basic concept proposed by Pette, 5 are described in the following patent documents: U.S. Patent No. 4,758,339 (Vellinga, 1988), in which a modification is described consisting of placing 10 gas collection chambers that make at least the area close to the collection medium of the purified water, normally constructed as a carcase of overflow, is free of turbulence and the separation between mud and water is optimal; The use of a double series of bells, one on another, is also appreciated for the capture of biogas.

U.S. Patent No. 5,338,445 (Zumbragel et al, 1994) describes a separation system of the three phases (gas, water and biosolids) in the form of semi-spherical domes 20 completely flooded and distributed in a plurality of superposed rows of modular construction rectangular to increase separation efficiency.

U.S. Patent No. 5,500,118 (Coenen et al, 1996), describes a modality of the biogas collection process, characterized by its arrangement in a stacked arrangement, and because the level of the liquid and the cross-sectional area are maintained. constants inside the collection hood of biogas.

The most active companies in the sector internationally have some recent examples representative of their activity. USF Deutschland GmbH Gutling has the patents of the United States 6,478,963 and 6,602,416 (Rossmanith, 2002, 2003). In the first, the purification method is carried out using the gas formed to separate the sludge that agglomerates in the bottom of the tank, and in addition the sedimented sludge is used, which is sucked by a method of elevation using the same gas produced. In the second, the detail of the invention used to suck the sludge and return it loose to the upper part of the digestion tank is described. Paques BV, with US patents US 5,972,219 (Habets et al, 1999) which employs a reactor based on the UASB concept in an aerobic process; US 6,063,273 (Habets et al, 2000) which couples a UASB reactor under an aerobic reactor in a column, separated by a partition that nevertheless allows the flow of the effluent of the UASB rector in the aerobic reactor. The international application WO 01/23062 (Lanting, 2001) is another example of a separation system of the three phases that are produced in an anaerobic reactor, based on a principle of modular spacers arranged in arrangement of multiple units. BIOTHANE Systems International B.V., with the European applications EP0776862 Al (Versprille, 1996) and EP0849229 Al (Versprille, 1996) both referring to the processes of purification by activated sludge in aerobic reactors.

Regarding Mexican patents, it is important to point out the proposals of Noyola, especially the patent 172,965 (Noyola, 1994) that focuses on the homogeneous distribution system of the water fed in the cross section of the upward flow of water inside the tank. The three-phase separation system of this invention has bases similar to those described in 5,338,445 (Zumbragel et al., 1994). The application 9404619 (Coenen et al, 1995) describing a UASB reactor for sewage treatment with bells placed in a staggered manner. The application 9803705 (Kuppusamy, 1999) for an anaerobic process of expandable bed for water treatment with low content of suspended solids but with textile dyes. Finally, the patent 163,838 (Poggi, 1992) which describes a fluidized granular bed process type UASB, focusing on the obtaining of renewable energy from biogas. More recently, application PA / a / 2000/007546 (Von Nordenskjold, 2002) was published, which in turn describes a process for the treatment of water with a high organic load.

All these processes offer options to improve the efficiency of the anaerobic processes of wastewater treatment of the UASB type, which still presents aspects that can be improved.

BRIEF DESCRIPTION OF THE INVENTION The present invention relates to a process for the anaerobic treatment of wastewater, considered as a secondary treatment since it is capable of reducing dissolved pollution and a certain amount suspended in the wastewater fed up to acceptable concentration levels, measured as DB05 and solids. total suspended (SST), as compliance discharge parameters, for example, with the Mexican standard NOM-SEMARNAT-001, part of which is reproduced in Table 1.

Basically, the process of biological water treatment ^ V 5 residuals with anaerobic sludge of the invention is based on an UASB process with an improved biogas capture system and which has been conceived as modular in order to adapt to a wide variety of values of the operating parameters, especially at flow rates , wastewater compositions and organic load. The process is also conceived as antecedent to an aerobic treatment of the resulting waters, and recirculation flows can even be established with the purpose of reducing dissolved nitrates.

The wastewater treatment process of the invention can be used in any type of wastewater discharge with dissolved organic pollution.

TABLE 1 MAXIMUM PERMISSIBLE LIMITS FOR BASIC POLLUTANTS P.D. = Average Daily; P.M. = Monthly Average; N.A. = Not applicable, (A), (B) and (C): Receptor Body Type. SOURCE: Norma Oficial Mexicana NOM- 001 -SEMARNAT- 1996 OBJECTS OF THE INVENTION Considering the problems encountered in this technical field, it is necessary to achieve a development with the following objectives: It is an object of the present invention to provide a process for the treatment of wastewater, highly versatile to adapt to operating conditions (such as flow rates, composition and concentration of waste water) varying over a wide range of values.

It is another object of the present invention to provide a process for the treatment of wastewater, with modularity characteristics that allow it to be adapted to the treatment of fractions of the design values.

It is still another object of the present invention to provide a process for the treatment of wastewater with an improved biosolids retention system, separation and recovery of treated water and collection of generated biogas.

It is another object of the present invention to change the operation of the reactor between the definition of anaerobic contact and that of UASB to accommodate variations in the organic load and the feed flow.

These and other objects will be evident to a person with average knowledge in the matter from the description that follows and the figures that accompany it.

BRIEF DESCRIPTION OF THE FIGURES To better understand the description of the present invention, it should be read in conjunction with the appended figures, which illustrate a preferred embodiment of the invention, and in which similar elements maintain the same numerical reference in all of them.

Figure 1 is a schematic top view of the process of the invention, showing the wastewater feed system from the bottom of the tanks.

Figure 2 is a side schematic view of the process of the invention showing the wastewater feed system.

Figure 3 is a schematic, disaggregated view of the waste water supply system of any one of the modules, showing their constituent elements.

Figure 4 is a simple perspective schematic view of one of the tubes for the supply of waste water, showing the outlets of the water.

Figure 5 is a schematic top view of the process of the invention, showing the system of recovery of treated water, retention of biosolids and uptake generated gas, exclusively.

Figure 6 is a schematic, disaggregated view of the system for recovering treated water, retaining biosolids and capturing gas generated from one of the modules, showing their constituent elements. The water treated and separated from the biogas and biosolids is collected in overflow stations that pass next to the minor base of the pyramid that forms each bell.

Figure 7 is a simple perspective view of one of the ^ 5 improved gas collection hoods, which forms part of the treated water recovery system, biosolids retention and gas uptake generated of the present invention.

Figure 8 is an enlarged view of a detail of the zone of ^ 5 decanted from the hood of Figure 6, and the optional detail of the screens is shown with projections that improve the separation of very small bubbles adhered to the biological flocs to return them to the reactor. Figure 9 is a simple perspective view of the gas scrubber tank to remove the foam that it could drag, with a cut to show its interior.

Figure 10 is a schematic side view of the system for recovering treated water and gas fully assembled for a module.

Figure 11 is a schematic side view of the system for recovering treated water and gas generated, for a module, mounted in the reactor.

Figure 12 is a schematic side view of a module, showing the systems for feeding wastewater and recovery of treated water and gas mounted in the reactor.

DETAILED DESCRIPTION OF THE INVENTION The water treatment process of the present invention will now be described with constant reference to the accompanying Figures, which relate to one embodiment of the invention presented for illustrative purposes. The terms "biogas", "generated biogas" and "generated gas" will be used interchangeably when referring to the gaseous mixture obtained from the fermentation in the reactor.

Modular arrangement of the digestion tanks Starting from Figure 1, which shows a schematic view of a preferred embodiment of the invention, it can be seen that as part of the proposed process, there is a reactor (100) found constituted by a series 5 of modules (110), (120), (130), (140), formed as concrete tanks, but which could be constructed of fiberglass, metal with anticorrosive coating or other material resistant to corrosion by the hydrogen sulfide that potentially forms in the adhered part of biofilms on the walls. The tanks are illustrated in the form of a rectangular prism with a square base, but may have other geometric configurations. The geometry of the cross-sectional area of the tank, in the direction of the upward flow of water, should correspond to that of the feeder of the water to maintain its homogeneous distribution in that section. The tanks (110), (120), (130) and (140) can be connected in series or operate in parallel, depending on the wastewater flows to be treated, their concentrations of dissolved material, and the quality of the desired effluent.; for change from the parallel mode illustrated to the serial mode, it is only necessary to add absorption pipe from the discharge of one of the modules and discharge to the next, with pumping means if necessary. It is also possible to generate an anaerobic-anoxic-aerobic sequence to correct high concentrations of nitrogen and phosphorus compounds.

In the preferred embodiment illustrated, in parallel, the tanks have been designed with a height of 7 meters, which decreases the probability of escape of the biosolids and increases the efficiency of anaerobic digestion in the area where the particles are smaller (diffuse bed zone (B), Figure 12), above the bed of heavier sludge (bed zone with upward flow (A), Figure 12) that remains close to the bottom of the treatment tanks (110), (120), (130) and (140). The biogas is adhered to the biosolid by the presence of extracellular polysaccharides in the flocs, which makes them float and reach the point of separation of the phases (separation zone (C), Figure 12) whose efficiency has been proven.

The modular configuration in separate tanks, but with communication possibilities, means that the total volume required for the purification of the wastewater is distributed among them, in order to manipulate the hydraulic residence time (THR) as a function of the composition of the water residual, which may vary for various reasons. In the illustrated mode, four chambers (110), (120), (130) and (140) were designed either to distribute the wastewater flow with independent supply to each of the chambers (maximum residence time for a flow). given) or to manage the flow in series in the chambers, reducing the residence time of the water in each one of the chambers but providing a sequential treatment that allows achieving discharge conditions with lower concentrations. The sequential arrangement, or the distribution of flows in the chambers, allows to manipulate the speed of ascent of the residual water to maintain the efficiency of the depuración before variations of the organic load and the available flow Wastewater system (200) Feeding of sewage to tanks (110), (120), (130) and (140) is done through a common head (205), which is subsequently divided into subheads (210), (220), (230) and (240) corresponding to each modular tank (110), (120), (130) and (140), respectively. Each subhead (210), (220), (230) and (240) runs along the upper edge of each modular tank (110), (120), (130) and (140) and then descends towards the bottom, as shown in FIG. illustrated in Figure 2. This pipe arrangement allows the water supply to be connected in a variety of arrangements.

Near the bottom of the tanks (110), (120), (130) and (140), each subheader branches into a plurality of tubes running parallel to the bottom of the tank and to each other (251) - (258) (see Figure 3), in the preferred embodiment, the tubes are made of polypropylene (PP) or another polymer such as high density polyethylene (HDPE) or polyvinyl chloride (PVC) of adequate diameter to the flow that is handled; The tubes have three series of perforations aligned equidistantly along the axis of the tube, spaced 45 ° apart (270), (271) and (272) (see Figure 4) that allow the fluid to escape and its homogeneous dispersion in the sludge bed through the cross-sectional area of the upward flow of water; Said series of perforations, in order to ensure a homogeneous distribution of the fluid, one of them is located, on the highest part of the tube (at 90 ° of the horizontal for the configuration of perforations upwards) (series 271) and two more on both sides of this line at an angle (a) of the order preferably of 45 ° (series (270) and (272)), preferably with a diagonal pattern between the holes of adjacent series.

When the process is in operation, the incoming "raw" water flow is regulated by the valves (260) (Figure 3) of each subheading, to avoid sedimentation of the strict anaerobic activated sludge flocs, which have a slightly higher density than that of water, by frictional dragging the updraft of water with the flocs. This allows avoiding the formation of large biogas bubbles, which would reduce the efficiency of anaerobic digestion.

System for recovery of treated water and capture of biogas (300).

The system developed for the recovery of treated water and collection of biogas produced, has been tested in tanks with a capacity of 20 and 2,000 liters and tests with tanks of 375 m3 were also satisfactory.

The system (300), illustrated in Figure 5, includes a plurality of bells (310) of truncated pyramid shape with a square base, which in the illustrated embodiment have dimensions of the order of 3.6 m on each side and 2.0 m in height; each hood (310) has a zone of blinds (320) (see Figure 6) that occupies the area near the base of the hood (310), extending upwards to approximately one third of the total height of the hood (310). 310), through which the water passes without dragging biosolids and the release of the biogas is allowed to catch it and accumulate it in the upper next zone of the bell (310).

The overflow stations (500) for the collection of the treated water define the level of the liquid in the tank. The level of liquid inside the bells (310) is lower than that which is kept out of them. The difference is due to the manometric pressure that is allowed in the gas.

The volume of gas within the bell (310) is kept constant by adjusting the pressure of the gas line. The gas height will be adjusted as gas pressure measured in water column. That is, the height of the water inside the tanks is defined by the position of the overflow stations (500), which collect it and send it to the next stage of biological aerobic treatment (refining). The height of the water within the separation hoods (310) is defined by the pressure maintained in the gas. For the 5 annotated dimensions of the bells, a 15-inch water pressure gauge is used as biogas overpressure.

The blinds (320) are made of screens (345), indicated in detail in Figure 8 corresponding to the circle "D" in Figure 7, made of stainless steel sheet, preferably of the type 316L (or polymeric materials such as polypropylene PP, high density polyethylene HDPE, polyvinyl chloride PVC or fiberglass according to the convenience of manufacture) in order to avoid corrosion by contact with the hydrogen sulfide that can be generated by sludge eventually adhering to the profile suggested in Figure 8 and an angle of inclination (ß) of the order of 45 °, corresponding approximately to the angle of inclination of the sides of the pyramid, although this angle may vary with respect to the horizontal; the screens (345) forming the blinds (320) are separated from each other by approximately 10 cm, taking the measurement from center to center of the support rods (360) of two adjacent screens (345).

Figure 8 further shows the optional detail of the screens with a plurality of projections (365) directed vertically downwards, which improve the separation of very small bubbles adhered to the biological flocs to return them to the reactor.

Each bell (310) has a pipe (340) preferably connected in stainless steel of a suitable diameter, for example 4 inches (10 cm) in the illustrated embodiment, to allow unrestricted flow. of the biogas generated through it, in order to get it to a header and from there connect to a washing tank (350).

In the washing tank (350) the entrained foams are eliminated by means of a water wash that is introduced through the pipe (380) towards a sprinkler (370) that distributes the water in a counterflow by gravity with respect to the biogas , which is fed from the heads (355) in the area near the bottoms of the washing tank (350); the water, in this way, drags the biosolids and other soluble matters towards the bottom of the tank (350), leaving through the nozzle (390) and finally the gas leaves through the conduit (400) and is sent either to burners in which the gas is combusted to take advantage of the energy or to another appropriate destination.

The treated water passes through the blinds (320) of the hoods (310) and is collected by overflow boxes (500) on its outside to remove it from tanks (110), (120), (130) and (140) the illustrated modality.

Figure 10 shows a schematic side view of a part of the system (300) fully assembled, and in Figure 11 this same system (300) is seen placed in its place in the reactor tanks (110), (120), (130 ) and (140), confining to the upper zone thereof, denoted as the separation zone (C in Figure 12).

The inner walls of the tanks (110), (120), (130) and (140) are preferably coated with a commercially available epoxy compound, to prevent adhesion of biofilms and to avoid the risk of generation of hydrogen sulfide in the anoxic zone of the biofilm which is the point of adhesion to the wall.

Finally, Figure 12 schematically illustrates the biological wastewater treatment process with anaerobic sludge of the invention, showing two modules (110), (120) of the reactor (100), the corresponding visible section of the water distribution system residuals (200) as well as the system for recovering treated water and capturing generated biogas (300). In the Figure are also indicated, as a reference, the fluidized bed zones, (B), the expanded bed zone, (A) and the separation zone (C), characteristics of a UASB process.

In an alternative embodiment of the present invention, the inclusion of a water recirculation line from the output of an aerobic treatment that could follow the anaerobic treatment of the process of the invention is contemplated, specifically from the final clarifier to one of the modules anaerobes (110), (120), (130) and (140) of the present invention, to allow the reduction of nitrates to molecular nitrogen, by effect of a negative oxide-reduction potential and in the order of less than -100 V .

Claims (15)

CLAIMS Once the invention is described, what is considered novel and therefore its property is claimed is contained in the following clauses:

1. A process for the anaerobic treatment of wastewater, comprising: a wastewater supply system, a fermentation reactor, a system for recovering treated water and capturing generated biogas where the water to be treated is introduced into the fermentation reactor by means of the feeding system constituted by a plurality of tubes arranged parallel to the reactor floor and to each other, with a plurality of holes for the homogeneous distribution of the liquid in an upward direction through a bed of activated sludge that is expanded by the action of rising currents of fresh liquid; and where the biogas resulting from the anaerobic fermentation process is directed upwards in the direction of the system of recovery of treated water and capture of biogas, for its separation and use; said waste water treatment process characterized in that: a) the reactor is constituted by a plurality of tanks that can operate in a parallel or series system, b) the activated sludges are in granular form, c) the system of recovery of treated water and capture of gas is formed by a plurality of collection bells that are joined together in the upper area of the reactor, known as a separation zone, and have blinds in their lower third to let the treated water pass and avoid the passage of biosolids to the treated water area, and d) the gas collection system brings said biogas generated to a water washing tank for the removal of foams and other entrained materials and finally leads it to its final disposal in burners to obtain energy from it.

2. A process for the anaerobic treatment of wastewater, according to claim 1, characterized in that the individual tanks forming said reactor can have any geometrical configuration, preferably, but not limited to that of a rectangular prism.

3. A reactor for a process for the anaerobic treatment of wastewater, according to claim 2, characterized in that said tanks preferably, but not necessarily, are constructed of a corrosion resistant material, taken from the group including, for example, concrete, fiberglass and metals.

. A reactor for a process for the anaerobic treatment of wastewater, according to claim 2, characterized in that the inner faces of the vertical walls of said tanks are covered with an anticorrosive material if they are constructed of a material susceptible to corrosion, just like a metal.

A process for the anaerobic treatment of wastewater, according to claim 1, characterized in that the interior height of said fermentation reactor is sufficient to decrease the probability of escape of the biosolids and increase the efficiency of the anaerobic digestion in the area in that the particles are smaller, of the order of 7 m.

6. A process for the anaerobic treatment of wastewater, according to claim 1, characterized in that said tanks that constitute the fermentation reactor, can operate separately as individual reactors or in a parallel distribution, when the waste water flow is high or the organic load is high

7. A process for the anaerobic treatment of wastewater, according to claim 1, characterized in that said tanks that constitute the fermentation reactor, can operate in an on-line distribution, where each successive tap receives the treated water from the preceding one, maintaining different levels of concentration in descending order; The connection in series is achieved by the installation of tapped water from one module and its injection as power to the next in the series.

8. A process for the anaerobic treatment of wastewater, according to claim 7, characterized in that said serial distribution of said tanks is used when the organic load is very high and it is desired to reduce it to very low values.

9. A process for the anaerobic treatment of wastewater, according to claim 1, wherein said system for recovering treated water and capturing gas formed by a plurality of bells is characterized in that said bells have the shape of a truncated pyramid, the bells being immersed in the liquid inside the reactor, with the larger area facing the interior of the reactor in the direction of the digestion zone and the smaller area is directed upwards, to capture inside the gas that is released from the sludge particles of water, and where the water level inside the hoods is kept constant and below the level of the overflow stations of the water, by adjusting the gas pressure to a water column equal to the difference of the levels within and outside the bells.

10. A system for recovering treated water and capturing gas formed by a plurality of hoods, according to claim 9, characterized in that said hoods are in close proximity to the height of their larger bases, said joints being preferably sealed.

11. A system for recovering treated water and capturing gas formed by a plurality of hoods, according to claim 9, characterized in that said bells show in their lower third, a shutter composed of screens that overlap each other, but that maintain a space open to each other to allow the passage of liquid from inside the hood to its outside.

12. A system for recovering treated water and capturing gas formed by a plurality of hoods, according to claim 11, characterized in that said screens forming the blinds are preferably made of a corrosion resistant material, taken from the group that includes the stainless steel, polypropylene, high density polyethylene, polyvinyl chloride or fiberglass.

13. A system for recovering treated water and capturing gas formed by a plurality of hoods, according to claim 11, characterized in that said screens forming the blinds can be movable in relation to their longitudinal central axis to allow increasing or decreasing the opening between them and thus control the passage of treated water.

14. A system for recovering treated water and capturing gas formed by a plurality of hoods, according to claim 11, characterized in that said screens forming the blinds optionally have a plurality of projections that are directed downwards, which improve the separation of Very small bubbles adhered to the biological flocs to return them to the reactor.

15. A process for the anaerobic treatment of wastewater, according to claim 1, further characterized in that in an alternative embodiment, said system can be used to denitrify the water, if a pipe circuit is added that takes the discharge of the final clarifier after an aerobic treatment subsequent to the anaerobic process, to return the exit current to the anaerobic chambers of the process.