WO2021160644A1

WO2021160644A1 - Phyto-purification method and apparatus for treating wastewater

Info

Publication number: WO2021160644A1
Application number: PCT/EP2021/053149
Authority: WO
Inventors: Philippe Sauvignet; Béatrice HOUSSAIS
Original assignee: Veolia Water Solutions & Technologies Support
Priority date: 2020-02-10
Filing date: 2021-02-10
Publication date: 2021-08-19
Also published as: EP4103521A1; FR3107054B1; FR3107054A1

Abstract

Method and apparatus for biologically treating wastewater using a bioreactor (4) comprising a bed (12) of chemically inert aggregate in which emerged macrophytes (13) are rooted, characterised in that it comprises: - a preliminary dilution step consisting in diluting the water to be treated according to a dilution ratio between 8 and 50 and preferably between 10 and 20, - organising the supply to the bio-reactor (4) with, and the emptying of the bio-reactor of, water thus diluted according to tidal cycles lasting less than two hours, preferably less than one hour, during each of which at least one portion of the bed (12) of chemically inert aggregate is dewatered and then submerged by the water so as to provide, in the bed (12) of chemically inert aggregate, successive periods of aeration and non-aeration, - a step of evacuating the treated water, the preliminary dilution step consisting in diluting the water to be treated with water originating at least partially from the method.

Description

DESCRIPTION

TITLE: Phyto-purification process and installation for the treatment of wastewater Technical field

The invention relates to the field of methods and installations for the treatment of wastewater.

More particularly, the invention relates to the treatment of urban wastewater. The invention thus finds its application in particular in the field of water reuse.

It can thus be implemented to create decentralized semi-collective or non-collective sanitation stations, optionally with the possibility of reusing the water produced. Thus, the present invention is part of a sustainable development approach.

Prior art

It has already been proposed in the state of the art of methods for treating wastewater with a view to its reuse as drinking water. Although such reuse, at least as drinking water, still faces regulatory and administrative constraints in many states, there is no doubt that it is one of the solutions that will allow the future of responding to the growing challenge of managing water resources in order to meet the ever-growing needs of the world's population.

Thus, for example, FR2984874B1 proposes a process and an installation for the reuse of wastewater implementing a biological treatment of water in a bioreactor by activated sludge then microfiltration of the water originating from this biological treatment then treatment of part of the filtrate obtained. by reverse osmosis. The other part of the filtrate can be reused in industry or for domestic purposes after having undergone a disinfection step for services that are not very demanding in terms of water quality. The permeate leaving the reverse osmosis unit is subjected to a conditioning treatment by mineralization followed by disinfection and can be used for more demanding services in terms of water quality. This type of technique, which combines conventional biological treatment and membrane filtration by reverse osmosis, however has the drawback of being costly to realize and operate. Indeed, it involves in particular the use of aeration devices and reagents of the coagulant and flocculant type, depending on the separation technology used, to carry out the biological treatment, as well as the production of sludge by the latter. which also need to be dealt with at a later date. The mineralization step also consumes chemicals. The associated costs in terms of corresponding equipment and reagents are therefore high.

It has been proposed in the state of the art concerning the treatment of water in general to replace the conventional stages of biological treatment by activated sludge by phyto-purification in basins designed for this purpose. Phyto-purification consists in creating an artificial wetland made up of basins filled with a mineral substrate and planted with plants, in particular macrophytes. These plants are selected for their root system and / or their highly developed rhizomes on which the biomass is fixed. These are mainly emerged macrophytes, such as for example Phragmites australis, Typha latifolia, Scripus Lacustris. Wastewater passes through such ponds, and macrophytes transfer oxygen through their root systems and rhizomes to the bottom of them, providing an environment below the water level that is conducive to leaching. 'establishment of aerobic micro-organisms which ensure the degradation of carbon pollution, nitrogen pollution and part of the phosphorus. A small amount of the nutrients, especially nitrogen in the form of nitrates and phosphate, are also taken up by plants. A water treatment technique implementing such a phyto-purification is for example described in EP1414756B1.

A disadvantage of the use of phyto-purification to purify urban water lies in the surface necessary to implement it.

Another drawback lies in the production of odors resulting from the biological degradation of the organic matter contained in the wastewater. Indeed, anaerobic conditions are created in the bottom of the basins, conditions which lead to the production of malodorous gases (ammonia, hydrogen sulphide, mercaptans in particular) which pass into the atmosphere.

Objectives of the invention An objective of the present invention is to provide a technique for treating wastewater making it possible to obtain treated water meeting high quality criteria, and thus allowing its reuse to be considered and thus reducing the consumption of water resources.

Another object of the present invention is to disclose such a technique which, at least in some embodiments, allows complete reuse of wastewater without any release of waste to the environment.

Another objective of the present invention is to provide such a technique which is less costly in energy than the techniques for reusing wastewater known from the prior art.

An objective of the present invention is to disclose such a technique which does not produce sludge or odors.

Another objective of the invention is to provide an installation for implementing such a method.

Another objective is to offer decentralized wastewater treatment which allows water to be recycled for use in sustainable buildings, such as office buildings, hotels, housing estates, "eco-districts" or hamlets with of few natural water resources.

Description of the invention

These objectives, as well as others which will appear subsequently, are achieved thanks to the invention which relates to a process for the biological treatment of wastewater using a bioreactor comprising a bed of chemically inert aggregate in which macrophytes emerged are rooted, characterized in that it comprises: a preliminary dilution step consisting in diluting the water to be treated according to a dilution ratio between 8 and 50 and preferably between 10 and 20, the organization of food and emptying said bioreactor with water thus diluted, according to tidal cycles lasting less than 2 hours, and preferably less than 1 hour, during each of which at least part of said bed of chemically inert aggregate is depleted and then submerged by said water so as to provide in said bed of chemically inert aggregate successive periods of aeration and non-aeration, a step of evacuating the filtered water, said preliminary dilution step consisting in diluting said water to be treated with water originating at least in part from said process.

The term “tidal cycle” therefore means a cycle during which the bioreactor is at least partly filled with diluted water and then emptied thereof. According to the invention, the proposed technique makes it possible to do away with the use of activated sludge and the associated drawbacks, by implementing a phyto-purification step under specific conditions that do not produce an odor and do not require large implantation surfaces. The reduction in the organic matter content of water is essentially effected by the biofilm developing on the surface of the chemically inert aggregate. The roots of macrophytes rooted in the aggregate allow them to filter the water and thus retain some of the suspended matter they contain. Macrophytes also contribute to the reduction of nitrogenous and phosphorous organic matter present in these waters.

An important feature of the process lies in the dilution of the water to be treated with water constituted at least in part by treated water. According to the invention, this dilution must be carried out according to a ratio of the volume of dilution water to the volume of waste water of between 8 and 50 and preferably between 10 and 20.

Such a dilution according to such a ratio makes it possible to bring to the bio-reactor dilute water little loaded with suspended matter and organic matter, and thus to avoid the clogging of the bed of aggregate and consequently to ensure good aeration of the roots. macrophytes. This dilution step can be carried out with only treated water, or again partly with treated water and partly with make-up water such as rain water.

Another important feature of the process according to the invention lies in the mode of feeding and emptying of the bio-reactor according to tidal cycles. Such tidal cycles allow a forced aeration of the aggregate bed with the oxygen of the air present around the aggregates when the water withdraws from it, aeration which promotes the action of microorganisms and therefore the purification of the water. . Such cycles thus make it possible to arrange aerobic and anoxic phases within the aggregate bed favorable to the degradation of nitrogen pollution in water. According to the invention, each of these cycles (feed + drain) must last less than 2 hours, preferably less than 1 hour. In this way, the bed of aggregate and the roots of the macrophytes are often sufficiently ventilated to effectively oxygenate the biomass which they receive and thus optimize the degradation of the organic matter contained in the water. Such cycles (feed + emptying) and their duration of less than 2 hours, preferably less than 1 hour, also make it possible to avoid the appearance of anaerobic zones in the bed of aggregate conducive to the release of bad odors.

Preferably, during each cycle the bed will be ventilated for 30% to 50% of the duration thereof.

It will also be noted that the method according to the invention has the advantage of not using aerators. The method is therefore less expensive than the methods of the prior art using such equipment.

According to a preferred variant of the invention, said process can be supplemented by at least one adsorption step consisting in passing the water drained from said bioreactor over a bed of adsorbent material, and / or by at least one membrane filtration step. consisting of passing the water drained from said bio-reactor or the water coming from said adsorption step over filtration membranes, such as low pressure microfiltration and / or ultrafiltration membranes and / or nanofiltration membranes and / or reverse osmosis membranes.

According to a preferred variant of the invention, the method comprises a stage of dilaceration of the compacted organic matter contained in the water, said dilaceration stage being carried out before, during or after said preliminary dilution stage. The purpose of such a shredding step is to break down the compacted organic matter (such as faeces) present, if applicable, in the urban wastewater to be treated and therefore to bring more homogeneous water into the bio-reactor that is less likely to clog. the bed of chemically inert aggregate.

According to another variant of the invention, the method comprises a final step of disinfecting the water coming from said at least one filtration step. The objective of such disinfection is to obtain, at the end of the process, water of sufficient quality to allow its reuse. In order to obtain the tidal cycles in the bio-reactor, different ways of organizing the supply and the emptying of the latter can be envisaged.

Thus according to a variant, the supply of said bio-reactor is clocked and the emptying of the latter is continuous. The term “timed feed” is understood to mean the fact that the feed to the reactor with dilute water is not carried out with a constant flow rate during the tidal cycle. Thus, for example, the feed can be carried out first at a given rate and then stopped.

According to another variant, the supply of said bioreactor is continuous and the emptying of said bioreactor is timed. The term “timed emptying” is understood to mean the fact that the emptying of the reactor is not carried out at a constant rate during the tidal cycle. Thus, for example, the emptying can be carried out first at a given flow rate and then stopped.

Whatever way is chosen to organize the tidal cycles, the process according to the invention will preferably be carried out by keeping an upper zone of the bed of chemically inert aggregate dry, the supply of the bioreactor with dilute water being carried out under said zone. superior. Such a dry zone makes it possible to further reduce the risk of the appearance of bad odors and of larval organisms such as mosquitoes.

According to a preferred variant of the invention, the dilution step is carried out using water originating from said bioreactor and / or from said adsorption step and / or from said membrane filtration step. The invention also relates to an installation for the biological treatment of wastewater with the method described above, characterized in that it comprises a dilution tank, a bio-reactor comprising a basin accommodating a bed of chemically inert aggregate and macrophytes emerged rooted in said aggregate, means for feeding said bio-reactor from the dilution tank and means for emptying said bio-reactor according to tidal cycles, and means for conveying part of the treated water to said dilution tank. For the purposes of the present invention, the term “dilution tank” is understood to mean a simple tank making it possible to carry out a dilution.

According to a preferred variant, said chemically inert aggregate forming the bed of the bioreactor consists of beads having an average diameter of between 5 mm and 50 mm and preferably between 5 and 10 mm. Such a size of beads optimizes the volume of air that can be lodged in the interstices separating them and facilitates the emptying of the bio- reactor. Also preferably, said balls are balls of expanded clay. This material has the advantage of being light, of retaining its properties over time, and of having a very high specific surface on which such a large surface of biofilm can form, allowing the purification of water. According to a variant of the invention, the installation preferably further comprises an adsorption unit on an adsorbent material such as activated carbon supplied with water coming from said bioreactor and / or at least one membrane filtration unit for water coming from said bioreactor. of said bioreactor or of said adsorption unit.

Such equipment makes it possible to further reduce the content of organic matter and suspended matter in the treated water.

According to a preferred variant of the invention, the installation further comprises means for shredding compact organic matter such as faeces which may be contained in said waste water. Advantageously, such means could be constituted by a macerator pump. The destructuring of the compact organic materials made possible by such means leads to obtaining wastewater that is more homogeneous and therefore less likely to block the interstices existing between the granulate balls. According to one variant, the installation further comprises at least one unit for disinfecting the filtered water coming from said at least one filtration unit. Such a unit makes it possible to obtain water of sufficient bacteriological quality to allow its reuse as water for human consumption, in particular as drinking water. It is also possible to envisage the reuse of such water for watering gardens or else for supplying devices leading to gray water such as washing machines or dishwashers.

According to a variant, said means for supplying said bioreactor comprise a supply line provided with a valve and said means for emptying said bioreactor comprise an evacuation line provided in the lower part of the bioreactor.

According to another variant, said means for supplying said bioreactor comprise a supply line and said means for emptying said bioreactor comprise an evacuation line provided with a pump provided in the lower part of said bioreactor. Also according to a variant, the bio-reactor of the installation according to the invention is provided on the roof of a building, the macrophytes emerging from the latter then forming a green cover of said building.

The green roof technique can make it possible on a large scale to reduce the negative impacts linked to climate change. On a city scale, it improves air quality, regulates temperature, and also optimizes rainwater management. It also eliminates the need for irrigation and the supply of nutrients to the vegetation, saves energy costs and provides acoustic insulation for buildings. Figures

The invention, as well as the various advantages that it presents, will be better understood thanks to the following description of a non-limiting embodiment thereof given with reference to the figures in which:

[Fig. 1] Figure 1 is a sectional view of an embodiment of a bioreactor that can be used in the context of an installation according to the invention.

[Fig. 2] FIG. 2 is a diagram of an installation according to the invention incorporating such a bioreactor.

Description of an embodiment

Installation With reference to FIG. 1, a bioreactor 4 comprises a basin 10 having a depth which may be between 20 cm and 1 m and preferably between 30 cm and 50 cm. A layer of draining gravel 11 can be placed in the bottom of this basin 10 over a height of between 0 and 10 cm. The bio-reactor 4 comprises a bed 12 of chemically inert mineral aggregate, here expanded clay balls having a diameter of 5 mm to 10 mm, provided above the layer of gravel over a height of between 20 and 90 cm . Emerged macrophytes 13 are rooted in said bed 12 of aggregate.

Means 14 for supplying the bio-reactor 4 with water comprise a simple pipe 14a opening into the bed 12 of aggregate at a distance of approximately 3 cm to 5 cm below the surface 12a thereof so as to provide a zone hair 12b across the top of it. Means 15 for emptying the bioreactor 4 for their part comprise a pipe 15a allowing the evacuation of the treated water by gravity.

Referring to Figure 2, the installation according to the invention comprises a dilution tank 1 capable of receiving on the one hand waste water by means of supply means 2 comprising a pipe provided with a macerator pump 2a and d '' on the other hand the dilution water via a recycling pipe B.

The installation furthermore comprises the bio-reactor 4 described above with reference to FIG. 1, and a pipe allowing it to bring the water coming from the dilution tank 1 into the latter. The installation also comprises an adsorption unit 5 comprising a bed of granular activated carbon, and a pipe 4a making it possible to bring the water coming from the bioreactor 4 into the latter.

The installation also includes a chlorination or ozonation unit 6 provided downstream of the adsorption unit 5 and a pipe 5a provided with a pump (not shown) for conveying the filtered water from unit 5 to that -this.

The installation also comprises a first membrane filtration unit 7 comprising low pressure microfiltration and / or ultrafiltration membranes and a pipe 6a provided with a pump (not shown) for conveying the chlorinated or ozonated water in the unit 6. to this one. The installation also includes a second membrane filtration unit 8 comprising high pressure nanofiltration and / or reverse osmosis membranes and a pipe 7a provided with a pump (not shown) for conveying the water coming from the first filtration unit. membranes 7 in the second membrane filtration unit 8 towards it. The installation also includes a disinfection unit 9 provided downstream of the reverse osmosis stage 8 and a pipe 8a provided with a pump (not shown) for conveying the water filtered through a membrane into the low membrane filtration unit. press 7 towards it.

Finally, the installation comprises a pipe 9a for discharging treated water. According to the embodiments, the pipe S for supplying the tank 1 with dilution water may be connected either to the pipe 4a, or to the pipe 5a, or to the pipe 6a, or to the pipe 7a.

A level probe lb slaved to a set of automatic valves (not shown) is provided in the dilution tank 1 to control the dilution of the wastewater by the dilution water conveyed through the pipe B. Thanks to this level probe lb , the. water drained from the bioreactor 4, from the adsorption unit 5, or from the oxidation unit 6, or from the low pressure filtration unit 7 are directed into the dilution tank 1 when the water level in the dilution tank 1 detected by this probe is below a predetermined level. The treated water is directed to the units considered when the water level in the dilution tank 1 is greater than or equal to this predetermined level. Process

During a first process step, the wastewater conveyed by the macerator pump 2a, and whose compacted organic matter (faeces) have been destructured by the action thereof, are diluted in the dilution tank with l dilution water according to a ratio of the volume of dilution water to the volume of wastewater between 8 and 50 and preferably between between 10 and 20.

The diluted water is conveyed from the dilution tank 1 and admitted by the means 14 into the basin 10 of the bioreactor 4 below the dry zone 12b of the bed 12 of granulate beads. At the same time, the pump 15b of the emptying means is not actuated. The water gradually rises in the bed 12. The pump 15b of the emptying means is, after a predetermined time, actuated to empty the basin 10 faster than it fills. The bed 12 is thus irrigated and then exposed to the air according to a tidal cycle the total duration of which is less than 2 hours, preferably less than one hour. Such a cycle makes it possible to ensure forced aeration of the bed of clay balls and the bringing into contact of the microorganisms contained in this bed with the oxygen contained in the air. After one cycle, the pump 15b can again be stopped and another tidal cycle started.

The basin is therefore fed and emptied according to a repeating tidal cycle. In practice, this cycle lasts less than two hours, preferably less than an hour. During each cycle, the bed is depleted for a period representing 30% to 50% of the total duration of the cycle.

The repetition of tidal cycles creates an alternation of aerobic and anoxic conditions allowing the biomass to degrade not only the carbonaceous pollution of the waters but also their nitrogen pollution.

In addition, each cycle having a duration of less than two hours, preferably one hour, the bed is never in an anaerobic condition. The development of anaerobic biomass which generates bad odors is thus prevented.

The water passing through the reactor is thus filtered by the roots and rhizomes of the macrophytes and biologically purified mainly by the microorganisms developing in bed 12.

It will be noted that the absence of a water level above the bed 12 prevents the development of algae on the surface, the presence of mosquitoes and the release of odors.

The water coming from the bioreactor 4 is then conveyed by line 4a to the upper part of the filtration unit 5 containing a bed of powdered activated carbon and passes through the latter before being recovered in its lower part. This passage adsorbs dissolved organic matter and micropollutants that may be present in the water coming from the bioreactor 4.

The water coming from the activated carbon filtration unit 5 is then conveyed to the unit 6 via the pipe 5a where it undergoes oxidation. The object of this oxidation is to prevent the clogging of the membranes used in the low pressure membrane filtration unit 7 to which the water is conveyed from the oxidation unit 6 via the pipe 6a.

The filtered water coming from the low pressure membrane filtration unit 7 is then routed through line 7a into the high pressure membrane filtration unit (nanofiltration and / or reverse osmosis) 8.

The filtered water coming from the high pressure membrane filtration unit 8 is then conveyed through the pipe 8a to the final disinfection unit.

The disinfected water is evacuated through line 9a.

This water is of sufficient quality to allow its use, for example for the operation of flushing water or supply water for washing machines or washing machines. dishes, or even for use as drinking water when regulatory provisions allow.

The process was tested with wastewater having the following composition: a suspended solids content (SS) of between S00 and 1000 mg / L, a COD (chemical oxygen demand) of between 200 and 500 mg O2 / L, an organic nitrogen content (NTK) of between 8 and 35 mg / L, and a total phosphorus content of 1 to 5 mg / L.

The water from the low pressure filtration unit 7 was analyzed. The results of this analysis are shown in Table 1 below.

[Table 1]

These results show that the water treated by the process is of a quality that allows it to be reused.

Another embodiment In another embodiment, the bioreactor used may correspond to that shown in FIG. 1 but with the modifications consisting in removing the pump 15b from the emptying means and in providing a supply valve on the pipe. 14a means for supplying diluted water.

In such another embodiment, the repetition of the tidal cycles will be created by intermittently closing this supply valve. Thus, when the valve is closed, the basin of the bio-reactor will be able to empty and the bed of aggregate will thus be aerated. When the feed valve is reopened, the aggregate bed will again be submerged. Thus, by intermittently closing such a supply valve, the tidal cycles can follow one another.

Claims

1. Method for the biological treatment of wastewater using a bioreactor comprising a bed of chemically inert aggregate in which emerged macrophytes are rooted, characterized in that it comprises: a preliminary dilution step consisting in diluting the water to be treated according to a dilution ratio of between 8 and 50 and preferably between 10 and 20, the organization of the supply and emptying of said bio-reactor with water thus diluted according to tidal cycles of a duration of less than two hours, preferably one hour, during each of which at least part of said bed of chemically inert aggregate is depleted and then submerged by said water so as to provide in said bed of chemically inert aggregate successive periods of aeration and non-aeration, a step of evacuating the treated water, said preliminary dilution step consisting in diluting said water to be treated with water originating at least in part from said pro ceded.

2. Method according to claim 1 characterized in that it comprises at least one adsorption step consisting in passing the water drained from said bioreactor over a bed of adsorbent material and / or at least one membrane filtration step consisting in carrying out passing the water drained from said bio-reactor or the water coming from said adsorption step through filtration membranes.

B. Method according to claim 1 or 2, characterized in that it comprises a stage of dilaceration of the water, said stage of dilaceration being carried out before, during or after said preliminary stage of dilution.

4. Method according to one of claims 1 to 3 characterized in that it comprises a final disinfection step.

5. Method according to one of claims 1 to 4 characterized in that said supply of said bioreactor is clocked and in that said emptying of said bioreactor is continuous.

6. Method according to one of claims 1 to 4 characterized in that said supply of said bioreactor is continuous and in that said emptying of said bioreactor is clocked.

7. Method according to one of claims 1 to 6 characterized in that it is carried out by keeping an upper zone of said bed of chemically inert aggregate dry, the supply of the bio-reactor with dilute water being carried out under said upper zone.

8. Method according to one of claims 1 to 7 characterized in that the dilution step is carried out using water from said bioreactor and / or from said adsorption step and / or from said at least a filtration step.

9. Installation for the biological treatment of wastewater with the method according to one of claims 1 to 8 characterized in that it comprises a dilution tank (1), a bio-reactor (4) comprising a basin (10). ) receiving a bed (12) of chemically inert aggregate and emerged macrophytes (13) rooted in said aggregate, feed means (14) of said bio-reactor (4) from the dilution tank (1), means of emptying of said bio-reactor (4) according to tidal cycles and means for conveying part of the treated water to said dilution tank.

10. Installation according to claim 9 characterized in that said chemically inert aggregate consists of expanded clay balls having an average diameter of between 5 mm and 50 mm, preferably between 5 mm and 10 mm.

11. Installation according to one of claims 9 to 10 characterized in that it comprises an adsorption unit (5) on an adsorbent material such as activated carbon supplied with water from said bioreactor (4) and / or at least one membrane filtration unit (7) for the water coming from said bioreactor (4) or from said adsorption unit (5).

12. Installation according to one of claims 9 to 11 characterized in that it comprises means for splitting (2a) of said water.

13. Installation according to one of claims 9 to 12 characterized in that it comprises at least one disinfection unit (9) of the filtered water coming from said at least one filtration unit (7,8).

14. Installation according to one of claims 9 to 13 characterized in that said means for supplying said bioreactor (4) comprise a supply pipe provided with a valve and in that said means for emptying said bioreactor (4) include an evacuation pipe provided in the lower part of the bio-reactor (4).

15. Installation according to one of claims 9 to 13 characterized in that said means for supplying said bioreactor (4) comprise a supply line and in that said means for emptying said bioreactor (4) comprise an evacuation pipe (15) provided with a pump (15a) provided in the lower part of said bioreactor (4).

16. Installation according to one of claims 9 to 15 characterized in that said bioreactor (4) is provided on the roof of a building, said emerged macrophytes (13) from said bioreactor (4) forming a vegetated cover of said building.