MXPA98008985A - Microplanta of wastewater treatment for small flows - Google Patents

Abstract

The present invention relates to a wastewater treatment plant for small flows characterized by the combination of a primary sedimentation zone followed by anoxic and aerobic packed zones all put in series, with packing, alternating downflows and upflows and aerated according to the oxygen requirement, there being a recirculation of water treated with sedimented mud between the secondary settler and the first anoxic compartment or primary sedimentation zone which produces water treated with sufficient quality for re-use activities prior disinfection (for example, irrigation , washing cars, unloading toilets, washing floors, etc.). The plant requires the use of an air compressor of low energy consumption specially specified to minimize maintenance and noise. The treatment microplant has a compact design, which requires a small area (the size of a water cistern for 1100 L with 1.5 meters of height) and has an internal water recirculation system, preferably of the "airlift" type between compartments which avoids the use of additional rotating equipment to the compressor which recycles the accumulated sludge allowing its degradation and minimizing its discharge and production. For reuse purposes the plant additionally requires a disinfection unit and a water cistern

Description

MICROPLAJSJTA OF WASTEWATER TREATMENT FOR SMALL FLOWS Object of the Invention, At the global level there is a serious problem of the disposal of wastewater generated in urban, industrial and agricultural centers. In the case of domestic wastewater, the problem is aggravated by not counting part of the population with drainage, a situation that occurs when it has a high construction cost due to the nature of the land, when populated areas grow at a higher rate that the urbanization, or in case of a wide dispersion of the houses. To limit the contamination of the environment through the discharge of wastewater, in these cases it is possible to use micro-plants that carry out the treatment of the water at the source of the discharge. The demand for this equipment is potentially large, in addition to the future needs for water reuse. Although one of the most important applications of micro-plants lies in the in-situ treatment of sewage from residential houses (preferential application of the invention), these treatment plants can be applied in the same way in condominiums or private clubs 'sports, hotels and restaurants, offices and centers commercial, hospitals, constructions, or health toll booths of motorways and similar uses. The Microplant treatment can be oriented, and such is the case of the present invention, in the generation of water treated for reuse in activities such as watering areas green, washing floors, ornamental fountains, washing cars, unloading toilets, etc. obtains a considerable saving of potable water for activities of first use.

The aüert-L- of microplantas existing in the market does not fully satisfies the required conditions of simplicity in the operation and particularly the economic ones, of accessible cost, above all if one speaks of an application in a house.

The users of this type of treatment plants require i 20 that the design of these equipment be considered I following items: | • The treatment plant must have dimensions that I allow their installation and operation at single family level and / or in places with limited space and with certain margins of growth in case of increase in water discharges residuals • The treatment plant must be economical in its investment and, above all, in the resources allocated to its operation and maintenance.

• Treatment efficiencies must comply with current regulations.

• The conditions of preventive and corrective maintenance 10 must be minimal and for the most part be able to be carried out by the users themselves.

• The treatment plant should not cause discomfort to the user in relation to bad odors, noise and proliferation of insects and animals in general.

• If necessary, the installation with minimal additions and complexity, must provide the treated water for reuse in the property or inside the house.

In the market there is a variety of treatment plants and package that hardly _J.legan to comply with. all the i | requirements raised above.

The present invention is aimed at the satisfactory fulfillment of these requirements.

BACKGROUND OF THE INVENTION The known antecedents on the state of the art in the matter of treatment of residual waters specially applied for houses, refers to systems that involve in their train of process septic tanks with aerated systems, in the vast majority of type activated sludge and aerated packed areas oriented to the elimination of organic matter basically. The present invention, unlike the treatment plants commonly found on the market, combines a high-rate anaerobic digestion zone by means of two anaerobic filter chambers. followed by a packed aerobic zone formed by more than two compartments in series that allow the extension of the aeration to carry out the nitrification. The compartments of the treatment plant are designed in such a way that they allow an adequate distribution of the water through the treatment train, considerably reducing the dead zones inside the treatment tanks. All compartments are integrated in a compact design that demands little space for their location and facilitates its operation and maintenance. To support the innovative aspects of the present invention, some micro treatment plants that are offered on the market and that may or may not be protected by a patent have been identified. In Fig. 1 the characteristics of these treatment plants are presented and compared with the treatment plant of the present patent application. The information concerning these treatment plants was extracted from their commercial catalogs. The following Table 1 indicates the patents that were found as antecedents and valid within the state of the art, as it was revealed in search of the state of the art of the North American patents.

Table 1 REFERENCES OF UNITED STATES PATENTS PATENT INVENTOR DATE TITLE US4191S47 Mullerheim 4/3/1980 Filtration System for Drainage Williams Casero US4251359 Col ell 17/3/1981 Water Treatment System Freeman Residual "In Situ" US44 S5594 Laak 14/8/1984 Drainage System for the Treatment of Segregated Residual Water.

US5240597 Ueda 8/31/1993 Wastewater Treatment Equipment. US5342523 Kuwashima 8/30/1994 Method and apparatus for purifying tap water. US5534147 Kallenbach 9/7/1996 Method and Apparatus for Modifying Buchanan Waste. Gooddrich Skinner Poncelet Kallenbach Figure 1 shows that the vast majority of treatment plants have a reception area of raw wastewater within what is considered the treatment plant itself, under the framework of a compact design in which in a single tank the different phases of the treatment are involved. In this sense, the plants corresponding to numbers 3, 5 and 10 in Fig. 1 specify a wastewater receiver tank or conventional septic tanks as an extra unit to what is in itself the water treatment package plant, which is also a specification of the plant described here. No plant, with the exception of plant 3 (Fig. 1), have a treatment zone based on a high-rate anaerobic reactor such as the anaerobic filter. Plant No. 3 bases wastewater treatment only on an anaerobic treatment which limits its effectiveness in removing contaminants. Unlike the other treatment plants, the present invention has 2 zones in series based on anaerobic filters that provide greater capacity to absorb organic peaks and limit the production of biological sludge. On the other hand, it is also possible to observe that most of the plants base the water treatment solely on aerobic processes such as activated sludge, trickling filter and submerged filter. Unlike these plants, the plant material of the present invention bases its treatment on the combination of anaerobic and high-rate aerobic processes (2 anaerobic filters _ followed by at least 2 aerated submerged filter-type zones) that provide versatility for adaptation from the microplant to fluctuating conditions in the concentration of organic matter, type of pollutants and residual water flows, conditions frequently found in the treatment of wastewater with small flows. The recirculation of water between the aerobic zone and the anaerobic zone in the microplant makes it possible to carry out the partial elimination of nitrogen from the water by means of nitrification and denitrification. The plant 6 of Fig. 1 carries out the nitrification and denitrification but through a completely mixed system of batch operation. The other treatment plants do not report in their respective documents the capacity to de-nitrify. and only some nitrify, which only implies the oxidation of the ammoniacal nitrogen but not the elimination of the nitrogen of the water. Plants No. 7 and 12 in Fig. 1 carry out the recirculation of water and sediment mud to the raw water reception area by means of pumps in the first case and of an "airlift" system in the second with the intention to store and treat the mud. In these arrangements, the microorganism substrate interaction in a septic tank is poor so that high denitrification yields are not achieved. Unlike these plants, the microplant, subject matter of the present invention, establishes a water recirculation current, preferably by means of the "airlif" system, from the aerobic zone to the anaerobic zone. Under these conditions, the anaerobic reactors of high rate (2 anaerobic filters) have an adequate microorganism substrate interaction, which favors the process of denitrification and elimination of organic matter in suspension and soluble.

On the other hand, reference is made below to some US patents related to the treatment of wastewater for homes that cover the years from 1980 to 1996. The patent US4191647 (1980) refers to a wastewater treatment system for treatment in si tu en casas habitación that includes a filtration unit based on paper and vacuum suction that separates the solid material from the liquid from the waste water, where the liquid is treated with chemical oxidants for subsequent disposal and treatment on the ground, while the solids separated from the water and the filter paper are subjected to a composting process. This treatment system requires area, chemical reagents, vacuum system and that the soil is able to eliminate the discharged contaminants. This treatment scheme is considerably different from what was stated in the treatment microplant material of the present invention, since the microplant has a compact design, is based on biological treatment and promotes the elimination of nitrogen. In addition, in the treatment microplant is carried out, for the most part, the digestion of the generated sludge. Patent US4251359 (1981) describes a wastewater treatment system based on a conventional septic tank and on a sand filter. The treatment system removes material suspended basically in the septic tank and dissolved and colloidal organic matter in the sand filter. Both units are in separate tanks. On the other hand, regarding the removal of nitrogen, mention is made of a possible nitrification process inside the filter, which only involves the oxidation of the ammoniacal nitrogen but not its elimination as molecular nitrogen. The differences between this patent and the treatment microplant material of the present invention basically focus on the treatment process, compact design and nitrogen elimination capacity that the microplant possesses and not the process indicated in the patent. In patent document US 4465594 (1984) a treatment system for wastewater is protected for dwellings, which comprises the separation of black and gray wastewater. The black wastewater passes through a holding tank that serves as a septic tank followed by a filter based on sand and stone placed in alternating layers within the filter whose purpose is to eliminate organic matter and nitrify. The filter is aerated. The treated effluent water from the filter is mixed with the gray water that previously passed through a holding tank. The mixture is deposited in a tank for the denitrification process to take place. The organic matter necessary for this process is provided by gray water. Unlike this patent, the microplant of matter treatment of the present invention treats in a single tank with compact design the gray and black discharges of the house. The patent US5240597 (1993) describes a semicompact wastewater treatment system for houses that involves a phase of anaerobic decomposition of the organic matter in a septic tank compartment as well as three aerated compartments that work according to the principles of the activated sludge system . In the septic tank is a submerged pump whose function is to agitate the medium and add certain amounts of fluorine to qoue, as stated in the patent, increase the rate of degradation of solids in the septic tank. In the aerobic zone, the distribution of air is carried out by means of a blower and diffusers with different geometry that in turn have the capacity to retain biomass on its surface. A secondary settler and a disinfection unit are specified within the water treatment train but in separate tanks.

In contrast to the treatment microplant material of the present invention, this system does not have the conjunction of the elements of the process train in a single tank, which is a semicompact system, and does not have the capacity to eliminate nitrogen. The aerobic treatment system is based on the activated sludge system and not on the series of aerobic submerged filters, alternating ascending and descending flows that the microplant possesses. The patent US5342523 (1994) describes a wastewater treatment system for houses that consists of 4 tanks where the first two (separating tanks) are in parallel and the next two in series. Separating tanks in parallel can be operated alternately (every 6 months) in such a way that at the same time only one tank works and until it has been saturated with sedimented and floating mud. When this happens, the waste water begins to enter the other separator tank (in parallel) through valves for the diversion of waste water. The separating tank that was saturated with mud is injected with air until the complete digestion of the mud is achieved. The separating tanks in parallel work as conventional septic tanks during the entry of water and as aerobic sludge digesters when the water does not enter the tank separators. Both separating tanks in parallel are connected to a digestion tank, where the water, coming from one of the two tanks in parallel (the one that is in operation), is treated by aerobic route. Subsequently, the water enters the last tank for disinfection. This patent proposes a semilote treatment of the waste water where the wastewater is treated continuously and the mud in batch through the parallel tanks whose feeding is controlled by valves. Unlike this patent, the treatment microplant material of the present invention has a system of continuous treatment of both the waste water and the sludge produced under a compact design with the elimination of nitrogen included. Patent US5534147 (1996) describes a wastewater treatment system with separate tanks for houses consisting of a conventional septic tank, an anaerobic tank for recirculation and an aerated unit for nitrification packed with granulometric stone less than% " A recirculation current is established between the nitrification tank and the conventional septic tank.The effluent from the treatment plant is obtained from the anaerobic tank for the recirculation of water that is discarded to an absorption well. The wastewater treatment plant microplant, which is the subject of the present invention, produces an anaerobic effluent with a higher content of COD and SST, also has a non-compact design, denitrification is carried out in an anaerobic unit tending to complete mixing (tank of recirculation) and in the septic tank whose microorganism substrate interaction is poor.

Description of the figures In Fig. 1 a table is shown where the comparison of different micro plants that are commercialized in the market is made, with the microplant material of the present invention. Fig. 2 shows the location of the treatment microplant material of the present invention (2) within the wastewater treatment train recommended for its application. The treatment train consists of a conventional septic tank (1), of the treatment microplant in question. (2), of a water disinfection unit (3) that can be based on chlorine or light U.V. and finally of a treated water cistern (4) with a pump (5). Waste water flows through the components of the process train by gravity. In Fig. 3 only the water treatment sequence that is carried out inside the treatment plant is shown in order to facilitate its description and visualization of the arrangement. The numbering shown in this figure is the same as that shown in Fig. 4. Fig. 4 is a plan view of the treatment plant in its preferred geometry. The numbering shown in Fig.3 is the same as that shown in this figure. In Fig. 5 a three-dimensional drawing of the microplant material of the present invention is presented in its preferred geometry. In Fig. 6 a photograph of the prototype used to evaluate the operation of the treatment plant is shown. In Fig 7 a photograph is shown that shows part of the interior of the prototype of the microplant used to evaluate its operation. Fig. 8 shows the dissolved oxygen concentration profile at different points of the prototype at a steady state operating with a flow of 1 m3 / d and an internal recirculation of 2 m3 / d at a temperature of 18 ° C. In the graph, the plant view of the treatment plant is inserted, where the sampling points corresponding to the abscissa are indicated. Fig. 9 shows the flows used throughout the experimentation where the operation of the prototype of the treatment microplant was tested. Figure 10 shows the profile of flows used to simulate a profile of wastewater discharge in a room house which was applied in a stage of experimentation to evaluate the operation of the prototype of the treatment microplant material of the present invention. Fig. 11 shows the variation of COD in the influent to the treatment plant (1), in the effluent of the anaerobic filters (2) and in the outlet of treated water (3) as a function of the variation of flow rates. Fig. 12 shows the efficiency of removal of the CODt as a function of the variation of flow rates. Fig. 13 presents the variation of CODs in the influent to the treatment plant (1), in the effluent of the anaerobic filters (2) and in the outlet of treated water (3) as a function of the variation of flow rates.

Fig. 14 shows the efficiency of COD removal as a function of the variation of flow rates. Fig. 15 shows the variation of SST in the influent to the treatment plant (1), in the effluent of the anaerobic filters (2) and in the outlet of treated water (3) as a function of the variation of flow rates. Fig. 16 shows the removal efficiency of the SST as a function of the variation of flow rates. Fig. 17 shows the variation of ammoniacal nitrogen in the influent to the treatment plant (1), in the effluent of the anaerobic filters (2) and in the outlet of treated water (3) as a function of the variation of flow rates. Fig. 18 shows the variation of oxidized nitrogen in the influent to the treatment plant (1), in the effluent of the anaerobic filters (2) and in the outlet of treated water (3) as a function of the variation of flow rates. Fig. 19 shows the variation of 02 in the influent to the treatment plant (1), in the effluent of the anaerobic filters (2) and in the outlet of treated water (3) as a function of the variation of flow rates. In Fig. 20 the average operating results of the treatment microplant without the action of the air compressor are shown. Anaerobic operation Description of the invention • Hydraulic retention times and flows - The wastewater treatment plant microplant of the present invention can be applied in any residual water flow interval. The size of the treatment plant can be adjusted depending on the flow you want to treat or failing that it is possible to use several units of a smaller and same size placed in parallel. You can locate as many treatment micro plants as are necessary to treat the wastewater flow in question. The total hydraulic retention time of the wastewater treatment plant microplant of the present invention ranges between 16 and 30 hours, preferably 24 hours.

• Adaptive geometries The treatment process that makes up the microplant can be adapted in tanks with different geometries, for example in tanks with square, rectangular, triangular, polygonal bases with "n" sides, etc. The preferred arrangement being that which conforms to a circular base which forms a cylindrical geometry.

• Description of the wastewater treatment micro plant with the preferred geometry (circular base, cylindrical geometry) The present invention relates to a microplant for treating wastewater that produces water treated with sufficient quality for reuse activities (for example, irrigation, car washing, sanitary discharge, floor washing, etc.). The microplant package consists basically of 4 zones (Figures 3, 4 and 5), that is to say, water reception area (3,1), anaerobic-denitrifying zone ((3,7) and (3,10)), an area nitrifying compartmentalized aeiobia, in this case in 7 units (compartments of (3,11), (3,14), (3.15), (3.16), (3.17), (3.18) and (3.19) and a secondary sedimentation zone (3.24).

In this preferred arrangement, the wastewater or effluent from the septic tank (Fig. 2) enters the microplant through the compartment (3,1) that is located in the center of the package floor and which is designed to carry the sedimentation and retention of suspended solids contained in the residual water (3,2). Fats and oils and floating solids will be trapped in the upper part of it (3,3). The compartment (3,1) is divided by a screen (3,4) that allows the retention of floats in the compartment (3,1) and a downward and upward flow in the same compartment. The compartment (3.1) has the functions of a primary settler. The water subsequently flows to four registers (1,6) that have the function of homogeneously distributing the water in the bottom of the next compartment (3,7). In the compartments (3,6) the flow of water is descending and in (3,7) it is ascending. The compartment (3,7) is packed with material (3,8) that can be synthetic (plastic, ceramic, etc.) or natural (stone, wood, etc.) in which the biofilm of anaerobic microorganisms is developed and / or anoxic responsible for the degradation of organic matter and the denitrification process. At the bottom of the compartment (3,7) an anaerobic mud bed accumulates, which will also have the function of degrading the organic matter and denitrifying it. Because of this, the compartment (3,7) is a combination of a sludge-bed anaerobic system with a biofilm system, which increases its water treatment efficiency. The elements (3,9) and (3,10) have the same function as the registers (3,6) and the compartment (3,7) respectively. By placing the anaerobic compartments (3,7) and (3,10) in series, the system tends to work with piston flow, which for biological reactions described with first order kinetics is highly convenient. In addition, the piston flow decreases dead zones within the system. After the anaerobic-denitrifying zone, the water flows into the compartment (3,11), which is packed and aerated. The aeration is supplied by means of an air compressor (3, 12) and a diffusing unit (3,13) placed in the bottom of the compartment (3,11), as well as in all other aerated compartments in this area. On the surface of the packaging, heterotrophic and nitrifying autologous aerobic bacteria are developed, which will be responsible, on the one hand, for degrading the remaining organic matter of the anaerobic compartments (3,7) and (3,10) and on the other hand for oxidizing the ammonia nitrogen present in the water. The compartments (3,14), (3,15), (3,16), (3,17), (3,18) and (3.19) in this example have the same characteristics as (3.11). The compartments (3,14), (3,16) and (3,18) have an upward flow and the compartments (3,11), (3,15), (3.17) and (3.19) one descending. The water flows below the dividing walls (3.20), (3.21), (3.22) and (3.23) in order to connect the compartments (3.11) and (3.14) , (3,15) and (3,16), (3,17) and (3,18), and. (3,19) and (3,24) respectively. On the other hand, the water flows over the dividing walls (3.25), (3.26) and (3.27) in order to connect the compartments (3.14) and (3.15), ( 3.16) and (3.17), and (3.18) and (3.19), respectively. The set of aeration chambers from the compartment (3,11) to the (3,19) have a design that favors a flow pattern that tends to flow piston with which increases the efficiency of operation of the plant of treatment and decreased dead zones in it The compartment (3,24) is a sedimentation chamber where the suspended solids generated in the aerobic compartments will be captured. This compartment has a tube (3.28) which serves to recycle in a variable manner water that is preferentially treated to the compartment (3.5) (it can be to (3,1). The recirrilation is carried out by means of a controlled injection of air into the tube. , with the principle of pumping by "air-lift" effect.

The recirculation of water from the compartment (3.24) to (3.5) (or to (3.1)) has a triple function; the first consists in recycling sedimented mud to the anaerobic compartment so that, on the one hand, the accumulation of this in the anaerobic section during the start-up phase is facilitated, and on the other hand, its cellular residence time in the plant is increased, thus favoring its partial stabilization or digestion. The second function of the recirculation stream is to supply oxidized nitrogen to the denitrifying bacteria present in the anaerobic compartments (3,7) and (3,10) in order to reduce oxidized nitrogen to harmless molecular nitrogen gas to the environment and thus remove it from water. The third function consists of incorporating water treated with low content of organic matter into the water coming from the compartment (3,1), which allows a better control of the organic load applied to the plant and a dilution of toxic compounds that could enter the plant . The only electromechanical equipment that the treatment plant needs is the compressor (3.12) and an adequate distribution of the air in the pack plant is achieved through the adjustment of the valves (3.29) installed in the air pipes. This arrangement allows the control of the oxygenation of the aerobic compartments according to the oxygen requirements in long periods without substrate feeding, as well as the flow in the "airlift" system. The effluent from the package plant is obtained in the tube (3.30) whose arrangement allows the retention of floating solids. Figures 6 and 7 show photographs of the prototype of the wastewater treatment micro plant.

• Aeration In the preferred arrangement, the compressor (4.12) feeds 5 aeration zones in the cylindrical conformation evenly distributed in the 'aerated zone of the treatment plant. For this purpose, a minimum of 5 air diffusers placed at the bottom of the compartments can be used. Anyone that provides a fine bubble can be used as air diffusers. A sixth zone of injection of air is located in the water recirculation tube type "Airlift" (4, 28). The supply of air that varies between 40 to 100 1 / min (1 atm and 20 ° C), preferably 80 1 / min, maintains a concentration of dissolved oxygen in the aeration chambers in a concentration range between 2 and 6 mg02 / L. This allows maintaining sufficient oxygen concentrations for the degradation of organic matter and nitrification, but at the same time, does not affect the denitrification in the anaerobic compartments (4,7) and (4,10) through the recirculation of water between the aerobic zone, and anaerobic (4.28). Oxygenation of the aerobic zones ((4,11), (4,14), (4,15), (4,16), (4,17), (4,18) and (4,19) can be controlled to adjust the supply of oxygen depending on their demand. This will reduce operating costs and have better control over the impact that could be in the anoxic areas (4.7) and (4.10). Fig. 8 shows the dissolved oxygen concentration profile obtained in the operation of the wastewater treatment micro plant.

• Internal recirculation of water through an "Airlift" type system One of the main elements of control in the operation of the treatment plant is the rate of recirculation of water between the aerated and anaerobic zones. The nitrogen removal capacity will depend on this rate. The preferred design of the package plant sets a recirculation rate of 2: 1, although this may vary in a range between 0.5: 1 to 4: 1. With this recirculation ratio it is possible to supply the oxidized nitrogen to the denitrifying anaerobic zones (4,7) and (4,10) without causing greater inhibition problems by the action of the oxygen contained in the recirculation current (4,28). One of the economic options to operate the internal recirculation of water is the use of air ("Airlift"), since it already has a compressor and avoids the use of a pump or additional rotating equipment that would complicate the operation of the plant, although they are also feasible to use in this invention. The operation of the "Airlift" system, this being the preferred system, depends on the diameter of the pipe used to transport the recycling water, the water flow and the water line that is being handled. The water recirculation tube can have a diameter between 2 inches being the preferred 1 inch.

Removal of suspended and dissolved organic matter In order to show the operation of the treatment microplant material of the present invention, a prototype was constructed and operated (Fig. 6) thereof, which was subjected to different residual water flows. The wastewater used in said experimentation was domestic.

The flows are specified in Fig. 9. Within the experimentation, the prototype was subjected to a variation of typical flow to that produced in a house between 5 and 10 people which was designated as "simulation" in Fig. 9. In Fig. 10 the profile corresponding to said simulation is presented. Figures 11, 12, 13, 14, 15 and 16 show the graphs corresponding to the variation and efficiencies of removal of CODd, CODs and SST according to the flow rates used. As it is possible to observe in Fig. 12 the removal efficiency of CODt, for the flow of 1 m3 / d, they are above 90%. We experimented with twice the design flow, maintaining a constant recirculation rate of 1: 2, where an average removal efficiency of 80% was observed.

In the following experiment, the plant was subjected to a high hydraulic load corresponding to 8 times the design hydraulic load, thereby obtaining an average elimination of COD of 65% and with decreases in the removal efficiency of CODt up to 40%. The elimination percentage of S? T, independently of the flow condition used, except for the 8 m3 / d, was higher than 90%. In Figure 15, it is possible to observe an exponential increase in the concentration of solids in the effluent (2) corresponding to the outlet of the denitrifying zone. This is explained by the accumulation of solids in the compartment after 6 months of operation. The plant was purged at that time reflected this in the sudden decrease in the concentration of SST at the outlet of the denitrifying zone. The behavior of the treatment microplant with the water simulation flow corresponding to a dwelling house was similar to the behavior presented with the flow of 1 m3 / d which implies that the treatment microplant has the capacity to absorb the sudden variations in the flow and organic load., indispensable requirement for the application of the plant in a house, for example.

In the final phase of the experimentation, the response of the plant to the removal of CODd in the presence of detergents was evaluated. For this purpose, an amount of detergent equivalent to double what was used by a domestic washing machine was used. Under these conditions, the removal of COD was not significantly affected.

• Nitrogen removal The elimination of nitrogen is carried out through the interaction between the aerobic and anaerobic zones of the treatment microplant effected by the recirculation of water. - '- For the flow of 1 m3 / d there are removals of N-NH4 * close to 100%, even for a flow of 2 m3 / d. However, as is to be expected, nitrification capacity declines when handling flows as high as 8 m3 / d (Figures 17 and 18). For a flow of 1 m3 / d, in the treated water, concentrations of N-NH4 + lower than 5 mg / L and an oxidized nitrogen concentration (N-NO. "+ N-N02") lower than 20 mg / L are obtained. . The concentration of dissolved oxygen in the aerobic chambers ranged between 2 and 4 mg / L. The total removal of total nitrogen in the plant was between 60 and 70% for the same flow. A higher flow of recirculation would increase these values in principle, but would also incorporate more dissolved oxygen into the anoxic zones, which would affect denitrification. The concentration of oxygen in the aerobic chambers evidently favors the process of organic matter removal and nitrification, however, due to the connection with the denitrifying zone, the aerobic chamber must not be supersaturated with oxygen because it affects, through the recirculation of water, the process of denitrification, indispensable for the global removal of nitrogen. In general terms, the plant is capable of removing nitrogen even when subjected to strong variations in flow and organic load.

Dissolved 02 variation In Figure 19 the variation of dissolved 02 is shown. The oxygen dissolved in the aerobic zone was supplied and controlled by the diaphragm compressor, which proved to be the best option available due to its low maintenance, absence of noise and efficiency, although it has a high cost.

On the other hand, the handling of detergents did not affect the operation of the treatment plant. Discharges of 105 and 210 g of detergent were added to the influent. The doses may represent the load of detergents applied to conventional household washing machines. The detergent was added at 10 a.m. on Tuesdays and Thursdays of each week. We worked with a flow of 1 m3 / d and 2 m3 / d of recirculation.

• Sludge production The treatment plant accumulates sedimented and suspended sludge at a rate of 0.5 to 1.5 kg dry mud base / month in all treatment chambers considering a house with 5 to 10 inhabitants. The sludge should be purged approximately every 6 to 12 months if a continuous operation of the treatment plant with domestic wastewater is considered. The purge of the sludge accumulated in the treatment plant is carried out by emptying the total water content of the plant through the. tubes (3.31) installed in the compartments (3,7), (3,10), (3,14), (3,16) and (3,18). These tubes allow the introduction of the suction pipe of a pump to the bottom of the plant without having to remove the packing material from the compartments. This allows emptying the water content in all the compartments, except the compartment (3.1) that does not require a pipe to be emptied.

• Operation without aeration By suspending the air provided by the compressor, oxygenation of the aerobic zone is avoided, transforming it into an anoxic zone and then anaerobic; it also ceases to operate the water recirculation 73,28). For three months the treatment plant was operated without the action of the compressor where the treatment process was transformed into a water reception area, into an anaerobic filter with 7 zones placed in series (2 that already contained, plus the 5 aerobic ones that become anaerobic) and in a secondary sedimentation system. The average pollutant removal efficiencies are shown in Fig. 20. The plant was operating with a flow of 1 m3 / d without the recirculation of water. When comparing the results of a purely anaerobic operation with the operation of the preferred design treatment plant, the advantage of maintaining aeration in the system is appreciable. However, if for some reason the compressor fails and its composure or replacement takes some time, it is possible to expect a behavior similar to that shown in Fig. 20. The plant, under this circumstance, would not stop operating at any time I would do it with less efficiency. It is also feasible to use the treatment microplant considering only the purely anaerobic operation, conserving the preferred geometry and compartmentalization.

• Practical example of application with preferred configuration Type of wastewater to be treated: Domestic wastewater Household room with 5 to 10 inhabitants Estimated wastewater flow: 1 to 1.5 ± 1 m3 / d Concentration of organic matter measured as total COD: 500 to 1500 mg02 / L Concentration of suspended solids Total: 200-600 mg / L Concentration of ammonia nitrogen (N-NH): 80-100 mg / L Oxidized nitrogen concentration (N-NO + N-N02"): 0 mg / L Concentration of dissolved 02: 0 mg / L Waste water is a mixture of water from toilets, toilets, bathrooms, kitchen and washing machine effluents.

Arrangement of the treatment process: The process consists of a conventional septic tank (1 m3), of the package plant in question, of a disinfection unit and a treated water cistern (1 m3) (Fig. 2). The dimensions of the microplant are as shown in Table 2: Table 2.

Quality of treated water: The treatment microplant produces water treated with the following characterization: Concentration of organic matter measured as total COD: less than 60 mg02 / L Total suspended solids concentration: less than 20 mg / L Ammoniacal nitrogen concentration (N-NHt *): less than 10 mg / L Oxidized nitrogen concentration (N -N03"+ N-N02 ~): between 25 and 35 mg / L Concentration of dissolved 02: greater than 2 mg / L

Claims (1)

Claims Having described the invention, the following is claimed as our property:

1) A microplant for the treatment in pack for small aqueous flows characterized by the combination of the following parts (a) A primary sedimentation compartment where the sedimentation and retention of suspended solids contained in the wastewater is carried out, and where fats and oils and floating solids are trapped in the upper part thereof and which is divided by a screen that allows floating retention in said compartment and allows a downward and upward flow of water in the same primary settling compartment and by (b) At least two records that homogeneously distribute the water from the primary settler compartment to the bottom of the anaerobic compartments, of which at least one feeds the first anaerobic compartment and at least one other between the first and second anaerobic compartment with the object to feed the latter and where (c) said anaerobic compartments are characterized because they are packaged in series on which the biofilm of anaerobic and / or anoxic microorganisms responsible for the degradation of organic matter and the denitrification process develops, and (d) at least 2 aerobic compartments, aerated by a compressor and packaged and placed in series where heterotrophic aerobic and nitrifying autotrophic bacteria develop on the surface of the packaging that degrade the organic matter remaining from the anaerobic compartments and oxidize the ammonia nitrogen present in the water where alternating downward and upward flow of water and by (e) A compartment called a chamber or sedimentation compartment located after the aerobic zones, where the suspended solids generated in the aerobic compartments are captured and by (f) Vertical tubes installed in the anaerobic and aerobic compartments that allow the introduction of the suction pipe of a pump to the bottom of the plant without having to remove the packing material from the compartments, in order to allow the purge of the the sludge accumulated in the treatment plant when emptying the total content. of water from the plant and where the micro plant is also characterized by (g) A recirculation stream serving to recycle in a variable manner treated water from the settling compartment to, preferably, the first packaged anaerobic compartment which is preferably carried out by means of a controlled injection of air into a tube that operates with the principle of pumping by "air-lift" effect although any rotary equipment can be used as an alternative and that has as an objective to recycle sludge sedimented to the anaerobic compartment so that on the one hand it is. facilitate the accumulation of this in the anaerobic section during the start-up phase and, on the other hand, increase its cellular residence time in the plant and thus favoring its partial digestion, as well as supplying oxidized nitrogen to the denitrifying bacteria present in the anaerobic compartments in order to reduce oxidized nitrogen to molecular nitrogen gas Inocuous to the environment and thus remove it from water in addition to incorporating treated water with low content of organic matter to the water coming from the influent waste water receiver compartment which allows a better control of the organic load applied to the plant and a dilution of toxic compounds that could enter the plant and (h) An air compressor and valves installed in the air pipes for the control of the oxygenation of the aerobic compartments according to the oxygen requirements in long periods without substrate supply, as well as to provide the necessary air for the operation- of the "Airlift" system and (i) The ability of the treatment microplant to transform into a high-rate anaerobic plant by suspending the air supply. A microplant for the package treatment for small aqueous flows according to claim 1, characterized by a recirculation of treated water to the first compartment or primary sedimentation zone based on air that simultaneously allows the pumping of sedimented mud, the supply of oxidized nitrogen and the dilution of influent organic loads to the treatment plant. ) A microplant for the package treatment for small aqueous flows according to claim 1, characterized by the purging of accumulated sludge in the treatment plant through the insertion of tubes in the packed bed. ) A microplant for the package treatment for small aqueous flows according to claim 1 characterized by the control of the oxygenation of the aerobic compartments according to the oxygen requirements in long periods without substrate feeding. ) A microplant for the package treatment for small aqueous flows according to claim 1 characterized by a suitable anaerobic operation, produced without the use of an air compressor and keeping all the internal elements of the treatment micro plant. ) A microplant for the package treatment for small aqueous flows according to claim 1, characterized in that the plant has the capacity to transform into a high-rate anaerobic microplant. Summary A wastewater treatment plant for small flows is presented characterized by the combination of a zone of "primary sedimentation followed by anoxic and aerobic packed zones all in series, with packing, alternating descending and ascending and aerated flows according to the requirement of oxygen, there being a recirculation of water treated with sedimented mud between the secondary sedimentator and the first anoxic compartment or primary sedimentation zone which produces water treated with sufficient quality for reuse activities prior disinfection (for example, irrigation, car washing, discharge of toilets, washing of floors etc.) .The plant requires the use of an air compressor of low energy consumption specially specified to minimize maintenance and noise.The micro treatment plant has a compact design which requires little area (of the size of a water cistern for 1100 L with 1.5 meters of height) and has - a system of recirculation of internal water, preferably of type "airlift" between compartments that avoids the use of additional rotating equipment to the compressor which recycles the accumulated sludge allowing its degradation and minimizing its discharge and production. For reuse purposes, the plant additionally requires a disinfection unit and a treated water cistern.