FR2828189A1 - Treatment of effluents from noncollective sanitation units comprises stripping off volatile and odorous compounds and treating them in a trickle biofilter, and treating the remaining effluent in a reed bed - Google Patents

Abstract

Treatment of effluents from noncollective sanitation units comprises passing the effluent through a grating, stripping off volatile and odorous compounds and treating them in a trickle biofilter, and treating the remaining effluent by infiltration and percolation in a reed bed. An Independent claim is also included for apparatus for treating effluents from noncollective sanitation units, comprising a grating (1), optionally a storage or decanting pit, a stripper vessel (2), a trickle biofilter (3) and a reed bed (4).

Description

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 The present invention relates to a method for treating effluents from non-collective sanitation. The invention also relates to a device for treating effluents from non-collective sanitation for the implementation of this method.

3 septiques est ainsi de l'ordre de 4 millions de m3 par an. In rural areas, where there are no sewerage and sanitation systems, sewage effluents are discharged, usually by truck, into septic tanks or pits. decanting. In France, for example, the population under autonomous sanitation is estimated at about 11 million inhabitants. With regard to the production of sludge per user, the volume of effluents resulting from the autonomous sewerage dumped in the pits

3 septic is thus of the order of 4 million m3 per year.

 Thus, these pits regularly have to be cleared of the effluents from the autonomous sewerage, commonly called domestic waste materials.

Subsequently, these effluents must be treated before they can be released into the natural environment.

 The effluent resulting from non-collective sanitation is characterized by very high concentrations of suspended solids (which may exceed 100 g / l), organic matter (COD greater than 100 g / l) and nitrogen compounds (ammoniacal nitrogen). at more than 1 g / l). In addition, this effluent is highly septic, poorly odorous and difficult to treat due to its large quantitative variability (irregular inputs) and qualitative (variable composition).

 At present, the treatment of effluents resulting from non-collective sanitation follows two main sectors: - the use of effluents in agricultural spreading or in composting after pretreatment.

the biological elimination of the effluents on a purification plant by injection of this type of effluent into a ventilation tank after pre-treatment.

 Nevertheless, these two techniques are limited by strict legislative constraints and by various constraints of the type availability of the fields and agreement of

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 the farmer for the spreading, or by technical constraints imposed for treatment on treatment plants.

 The lagooning technique has also been considered for treating domestic waste materials (FR 2 721 310), but this technique has various drawbacks such as installation problems of the installation. Indeed, before installing a lagoon on a site, an impact study of the geological and hydrogeological characteristics of the proposed site must be carried out in order to avoid any risk of pollution of the subsoil. In addition, any establishment of lagoon near sources or water catchments is prohibited by regulation; olfactory nuisances are not treated by this type of process. And finally, the treatment of effluents by lagooning generates relatively high investment costs, in particular by the number of structures required and the large area required for this type of installation.

 There was thus a need to develop a method and a device for treating effluents resulting from the autonomous sewerage, said method and device not having the disadvantages of the techniques of the prior art and respecting the legislative standards imposed. on the quality of the effluents before being able to join the sanitation networks, the treatment plants or the natural environment.

 The present invention fills this need. The Applicant has surprisingly discovered that the treatment of effluents resulting from autonomous sanitation could be carried out efficiently and simply by a process comprising a stripping step, followed by percolation using a macrophyte-based system. , having not only the advantage of greatly reducing the pollution contained in this effluent but also eliminating the olfactory nuisances associated with this effluent, via treatment on a biofilter.

 The method which is the subject of the present invention is also harmless (without odor, without noise, and with good integration of the device in the landscape), of small surface area and of low investment and operating costs. In addition, the treatment device according to the present invention, for the implementation of such a method, can be easily installed near a sewerage network or in rural areas that do not have sewage treatment plants. great

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 capacity and such a device can be easily implemented, requires little maintenance and can control the high variability of the flow of effluents to be treated, which varies according to the time of year, according to the regions and which is a function of the frequency of unloading and emptying of septic tanks carried out irregularly.

 The treatment method that is the subject of the present invention, based on plants of the macrophyte or reed type, also has the advantage of being ecological. Herbal treatment methods have already been used to treat domestic or industrial wastewater (water from collective sanitation) or sludge from aerobic and / or anaerobic wastewater treatment plants, as is the case in patent FR 2 782 508 which describes a method of treating effluents from wastewater treatment plants of small communities comprising a filtration stepcomposting on filters planted with reeds. However, the direct application of emptying materials (effluents resulting from autonomous or non-collective sanitation) from septic tanks on beds planted with reeds had never been realized until now because of the composition of the waste materials. which differs significantly from that of domestic wastewater or sewage sludge, particularly in terms of nitrogen pollution, DB05, septicity and odor. Indeed, the very high concentration of ammoniacal nitrogen and sulfur compounds in the discharge materials makes these effluents harmful to the growth of reeds and inevitably leads to necrosis of the plant. In addition, the direct spreading of waste materials on beds planted with reeds is currently almost impossible because of the strong odor nuisance it entails.

 The subject of the present invention is thus a process for the treatment of effluents resulting from non-collective sanitation, characterized in that it comprises the following stages: - screening of the effluent, then - treatment of the effluent by stripping so as to to separate the most volatile and odorous compounds from the rest of the effluent, then - treatment of the most volatile and odorous compounds using a trickle biofilter,

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 treatment of the remainder of the effluent by infiltration and percolation using at least one bed planted with reeds.

 The effluent from non-collective or autonomous sanitation is first screened to remove larger waste such as solid bodies (rags, wood and plastic). At the screening outlet, the effluent can be sent to a metering / storage pit to control the quality of the discharged effluent and smooth the flow before sending it to the rest of the die. In order to control the quality of the effluent, an automatic sampling can be carried out in order to measure the content of what has been removed, a control by badge of the emptier to attest the origin. The effluent can be stored for several days or even weeks in this pit.

 The effluent then undergoes stripping treatment. For the purposes of the present invention, the term "stripping" means the extraction of the most volatile and odoriferous compounds, such as ammonia, from the rest of the effluent by bubbling air. These compounds, passed in gaseous form by air / water exchange, are then treated on a trickle biofilter in which a nitrifying biomass (Nitrosomonas and Nitrobacter) degrades the ammoniacal nitrogen to nitrate, while the raw effluent, freed of the elements the more fragrant and harmful elements for the plant such as sulphides and ammonia, is treated on at least one bed planted with reeds. The suspended solids and the pollution contained in the particles of the raw effluent are retained by filtration of the effluent through this (s) bed (s). Sludge mineralization that takes place over time within the bed (s) planted with reeds allows nitrification of the effluent that percolates in these beds by the bacterial flora that develops there (mainly Nitrosomonas and Nitrobacter). A denitrification reaction can also take place during the stay of the percolate in this (s) bed (s).

 Advantageously, according to the method which is the subject of the present invention, the step of treating the effluent by stripping is carried out by air injection, even more advantageously at the bottom of the stripping vessel. The air flow required for stripping is determined according to the volume of effluent to be stripped, based on 1 Nm / h of air per 200 liters of stripper draining material (usually per week). The most volatile compounds as well as the strongly odorous compounds of the effluent

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 The process, including ammonia, is then passed into the gas phase and is then conducted via a conduit to the inlet of a trickle biofilter for further processing.

 Advantageously, according to the method that is the subject of the present invention, the height of the effluent in the stripping vessel is between 1 and 2 m.

 In a particular embodiment of the present invention, the supply of the stripping tanks is done by batch from the storage pit or unloading.

The emptying materials are advantageously stripped in the tanks at the frequency of once a week.

 Advantageously, according to the method which is the subject of the present invention, the step of treating the effluent by stripping is carried out at a pH of between 7 and 11, even more advantageously at a pH of 9. The pH of the effluent can thus be modified by adding sodium-type reagents according to the objectives of the stripping step. The greater the amount of ammonia to be removed, the higher the pH must be.

 In a particular embodiment of the present invention, the ammonia removal efficiency at the end of this stripping step is greater than 50%. In addition, the aeration of the discharge materials makes it possible to oxidize the sulphides of the effluent, which are highly responsible for the olfactory nuisances, and thus to eliminate more than 70% of the sulphides, in the form of Soc42- sulphates, during stripping. Consequently, the stripping step makes it possible both to reduce the ammoniacal nitrogen load of the effluent arriving on the beds planted with reeds and to limit the odors and the injection on these beds of compounds that are harmful to the growth or growth. the survival of reeds (such as sulphides).

 Following the stripping step, the most volatile and odoriferous compounds in gaseous form are treated continuously on a trickle biofilter in which a nitrifying biomass degrades the ammoniacal nitrogen to nitrate. Pollutants, passing through the filter medium, are absorbed in the liquid film that covers it (formed by watering water), before being degraded by biomass. The biofilter is advantageously seeded into sludge at the start of treatment. Sludge develops in biofilter thanks to incoming pollution

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 (such as ammonia present in the gas) and the nutrients present in the water of irrigation which are necessary for their growth. The bacterial population is regulated by the flow of irrigation water and the entrainment of excess sludge in the percolate.

 Advantageously according to the present invention, the irrigation water is industrial water, or drinking water and the watering frequency is between 1 and 2 minutes every half hour, for a watering rate instantaneous 0.4 m3 / m2 of biofilter area / h.

 Advantageously, according to the process that is the subject of the present invention, the step of treating the most volatile and odoriferous compounds is carried out by adding phosphorus, even more advantageously in the form of orthophosphoric acid, into the trickle biofilter. The addition of phosphorus may be necessary to avoid bacterial deficiency.

 The ammonia present in the gases from the stripping is thus nitrified in the trickle biofilter. The nitrification yield varies between 40% and 90%. At the outlet of the biofilter, the treated gas is no longer a source of olfactory nuisance and is released into the atmosphere.

 The liquid from the biofilter, freed of the most volatile and odoriferous compounds that have been treated, can then be sent either to a purification plant or to the sewerage network.

 The remainder of the effluent from the stripping, which has not passed in gaseous form and which has not been treated on the biofilter, is spread and treated on at least one bed planted with reeds. The purification of the effluent is carried out by infiltration and percolation.

 Advantageously according to the present invention, the reeds are of the type Phragmites communis.

 Advantageously according to the present invention, the bed planted with reeds is used in vertical filtration. For the purposes of the present invention, the term "vertical filtration" is intended to mean a flow of the raw effluent vertically on the bed planted with reeds, in order to retain the particulate pollution.

 Reeds that develop in the bed play an important role in draining the effluent. The ammonia and sulphide concentrations of the effluent feeding the reeds are such, after the stripping step, that they do not penalize the shoot.

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 reeds or are harmful to plants. The sludge retained in the beds of reeds is mineralized, allowing a significant reduction in the volume of sludge.

 Advantageously according to the present invention, the bed planted with reeds is ventilated by venting, advantageously at the floor of the bed, to allow the oxygenation of nitrifying bacteria and the good development of the shoot reeds. Aeration of the floor of the beds is provided for example by ventilation columns.

 Advantageously according to the present invention, the step of treating the remainder of the effluent by infiltration and percolation on reed beds is carried out at a pH of 7, in order not to damage the reeds and to hinder their growth. At the end of the stripping, the pH of the effluent can thus be adjusted to neutrality, in particular by adding acid before injection on the beds.

 The quality of the materials of the filter bed (granulometry in particular) governs the hydraulic performance of the installation. The treated water is recovered at the floor of the beds, and introduced at the head of the treatment plant or directly into the sewerage network.

 It is advantageous to maintain a rest period between two sludge inputs in order to allow a good drainage of this sludge in beds planted with reeds. In a particular embodiment of the present invention, the frequency of treatment of the effluent by stripping is once a week and the frequency of treatment of the effluent by infiltration and percolation on beds planted with reeds is of a once a week or once every two weeks, depending on the water requirements of the reeds.

In summer or in warmer areas, it is best to feed beds planted with reeds once a week. In the case of a diet of once every 15 days, the beds are supplied shifted, in turn, so that the treatment frequency of the effluent by stripping remains once a week.

 In a particular embodiment of the present invention, the yields on the main physicochemical parameters at the outlet of the treatment die are the following: removal of more than 90% of the COD and the MES, elimination of more than 80% total nitrogen, removal of more than 70% of ammonia (expressed as N-NH4) and removal of more than 70% of the sulphides. The outlet effluent is very close to the concentration of an effluent entering the wastewater treatment plant.

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 except for the presence of nitrates. The nitrate concentration is less than 100 mg / l (expressed as N-N03) for the outlet effluent. The pollution flows out of the processing chain are minimal because of very low outflow rates.

 Therefore, after having been treated by the process according to the present invention, the effluents can be very easily discharged into the wastewater network, and treated on a treatment plant, even of very low capacity (<100 equivalent inhabitants). .

 The present invention also relates to a device for treating effluents from non-collective sanitation, characterized in that it comprises: a grate (1), - optionally a storage or de-aerating pit, at least one tank stripping device (2), a trickling biofilter (3), at least one bed planted with reeds (4).

 Advantageously according to the present invention, the grid has a spacing of bars between 15 and 25 mm so as not to interfere with the de-stuffing operations by a too small spacing, nor allow the refusals to pass because of a gap too important.

 In the context of the device that is the subject of the present invention, a storage or disposal pit is not necessarily present. Such a pit is, however, advantageously used because of the variability of the amount of dumped waste material.

 Advantageously according to the present invention, the stripping tank (2) is constituted by a closed tank equipped with an aeration system (10), even more advantageously situated at the bottom of the tank.

 According to a particular feature of the present invention, the stripping vessel (2) is black HDPE, but can be constructed of any other acid and base resistant material. The aeration system advantageously consists of membrane diffusers fixed at the bottom of the tank. Their number is determined according to the air flow required for the treatment.

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 Advantageously according to the present invention, the trickling biofilter (3) consists of a biofilter covered by a liquid film, the liquid film being advantageously formed by watering industrial water or drinking water (11). Even more advantageously according to the present invention, the biofilter contains a packing material which constitutes the support of the biomass consisting mainly of nitrifying bacteria present in the biofilter. In a particular embodiment of the present invention, the lining material is a mineral material of the marble or pozzolan type.

 The sizing of the trickling biofilter (3) is carried out from the ascending rate of passage of the gas in the biofilter, which is generally 500 m / h.

 Advantageously according to the present invention, the bed planted with reeds (4) contains a filter bed consisting of several layers of gravel and / or sand, reeds planted on the filter bed, a ventilation system preferably located at the bottom of bed and an air circulation system preferably located at the bottom of the bed.

 In a particular embodiment of the present invention, the filter bed consists of two successive layers of gravel of two different particle sizes, such as 4/8 mm and 2/5 mm. The height of the filter bed is advantageously of the order of 40 cm.

 Advantageously according to the present invention, the air circulation system is constituted by slabs and / or drains, which also allow the collection of percolate, preferably at the bottom of the bed. In a particular embodiment of the present invention, a geotextile separates the gravel from the air circulation system.

 Advantageously according to the present invention, the reeds are of the type Phragmites communis.

 Advantageously according to the present invention, the surface area of the beds planted with reeds necessary for the treatment of the effluents according to the present invention is determined according to the number of septic tanks to be treated, on the basis of 1 m2 of beds planted with reeds for the treatment of 3 septic tanks. 1 m2 of beds planted with reeds can thus treat the effluents of about 10 people not connected to the sewerage and sanitation networks (on the basis of 3.5 people per septic tank).

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 The mass load of effluents spread on the bed planted with reeds is advantageously between 10 and 40 kg DM / m 2 of beds / year and varies according to the solids concentrations of the sludge.

 The operation of the treatment according to the invention will be better understood on reading the description given hereinafter with reference to the appended FIG. 1, which schematically illustrates a particular embodiment of the present invention.

 The effluent treatment device resulting from the non-collective sanitation according to the present invention comprises at least one grid (1), a stripping tank (2), a trickle biofilter (3), a bed planted with reeds (4). ). The effluent to be treated (5) passes first through the grid (1) to remove the largest waste and then enters the stripping tank (2). Air (10) is sent to the bottoms of the stripping tank (2) and the most volatile and odoriferous compounds, such as ammonia and sulphides, are entrained as a gas (6) out of the stripping tank (2) to the inlet of the trickle biofilter (3) where the gas is treated. The biofilter (3) is covered by a liquid film formed by watering (11). The treated gas (7), which is no longer a source of olfactory pollution, is released into the atmosphere. The raw effluent (9), in liquid / solid form, which leaves the stripping vessel (2) and which has not been entrained in gaseous form as it passes through the stripping vessel, is spread on the bed planted with reeds (4). The treated water (8), which exits the trickle biofilter (3) and the bed of reeds (4), is directed towards the entry of purification plants or to the wastewater network (12).

 The following example is given as a non-limiting example and illustrates the present invention.

Embodiment of the invention: The process for treating effluents resulting from the non-collective sanitation that is the subject of the present invention was implemented on a device comprising 4 stripping columns (tanks) of 300 liters each, a biofilter with runoff 15 cm in diameter

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 1.5 m high and 4 beds planted with reeds of 1 m2 each and 1.5 m high. A screening system and a de-stocking / storage pit was available on site.

500 liters of effluents per week were introduced into the device.

The elimination efficiencies of the different types of pollution present in the effluent are presented in Table 1 at the end of the stripping step and in Table 2 at the outlet of the treatment die.

Table 1:

<Tb>
<tb> Effluent <SEP> input <SEP> Effluent <SEP> stripped <SEP> Yield <SEP> of
<tb> stripping
<tb> N-NH4 <SEP> 213 <SEP> mg / l <SEP> 90 <SEP> mg / l <SEP> 57%
<tb> Sulfides <SEP> 83 <SEP> mg / l <SEP> 18 <SEP> mg / l <SEP> 78%
<Tb>
Table 2:

<Tb>
<tb> Effluent <SEP> Input <SEP> Effluent <SEP> of <SEP> Output <SEP> Yield
<tb> elimination
<tb> MES <SEP> 35 <SEP> g / l <SEP> 250 <SEP> mg / l <SEP> 99%
<tb> COD <SEP> 44 <SEP> g / l <SEP> 680 <SE> mg / 198%
<tb> N-NH4213 <SEP> mg / 142 <SEP> mg / 180%
<tb> N-N03-8 <SEP> mg / 1
<tb> Ntotal1095 <SEP> mg / l <SEP> 75 <SEP> mg / l <SEP> 93%
<Tb>

Table 1 shows that the stripping step makes it possible to eliminate more than 70% of the sulphides and more than 50% of the ammoniacal nitrogen. Table 2 shows that the elimination efficiencies of the different types of pollution are very high at the end of the treatment process, thus proving the effectiveness of the treatment method that is the subject of the present invention.

Claims (19)

1. A method for treating effluents from non-collective sanitation, characterized in that it comprises the following steps: - screening of the effluent, then

 - treatment of the effluent by stripping in order to separate the most volatile and odoriferous compounds from the rest of the effluent, then - treatment of the most volatile and odorous compounds using a trickle biofilter, - Treatment of the rest of the effluent by infiltration and percolation using at least one bed planted with reeds.  2. Treatment process according to claim 1, characterized in that the step of treating the effluent by stripping is performed by air injection, preferably at the bottom of the stripping vessel.  3. Treatment process according to claim 1 or 2, characterized in that the height of the effluent in the stripping vessel is between 1 and 2 m.  4. Treatment process according to any one of claims 1 to 3, characterized in that the step of treating the effluent by stripping is carried out at a pH between 7 and 11, preferably at a pH of 9.  5. Treatment process according to any one of the preceding claims, characterized in that the treatment step of the most volatile and odoriferous compounds is carried out by adding phosphorus, advantageously in the form of orthophosphoric acid, in the runoff biofilter.  6. Treatment method according to any one of the preceding claims, characterized in that the reeds are of the type common Phragmites.  7. Treatment process according to any one of the preceding claims, characterized in that the bed planted with reeds is used in vertical filtration.  8. Treatment process according to any one of the preceding claims, characterized in that the plant bed of reeds is vented by venting, preferably at the floor of the bed. <Desc / Clms Page number 13>  9. Treatment process according to any one of the preceding claims, characterized in that the treatment step of the remainder of the effluent by infiltration and percolation is carried out at a pH of 7.  10. Treatment process according to any one of the preceding claims, characterized in that the treatment frequency of the effluent by stripping is once a week and the frequency of treatment of the effluent by infiltration and percolation beds planted with reeds is once a week or once every two weeks.

 11. Device for treating effluents from non-collective sanitation, characterized in that it comprises: a grate (1), - optionally a storage or desludging pit, at least one stripping tank (2), a trickling biofilter (3), at least one bed planted with reeds (4). 12. Device according to claim 11, characterized in that the stripping tank (2) is constituted by a closed vessel equipped with a ventilation system (10), preferably located at the bottom of the tank.  13. Device according to claim 11 or 12, characterized in that the trickle biofilter (3) is constituted by a biofilter covered by a liquid film, the liquid film being advantageously formed by watering industrial water or drinking water ( 11).  14. Device according to claim 13, characterized in that the biofilter contains a packing material which is the support of the biomass mainly consisting of nitrifying bacteria.  15. Device according to any one of claims 11 to 14, characterized in that the plant bed of reeds (4) contains a filter bed consisting of several layers of gravel and / or sand, reeds planted on the filter bed, a ventilation system advantageously located at the bottom of the bed and an air circulation system advantageously located at the bottom of the bed. <Desc / Clms Page number 14>  16. Device according to claim 15, characterized in that the filter bed consists of two layers of successive gravel of two different particle sizes.  17. Device according to any one of claims 15 or 16, characterized in that the air circulation system is constituted by slabs and / or drains.  18. Device according to any one of claims 11 to 17, characterized in that the reeds are of the type Phragmites communis.  19. Device according to any one of claims 11 to 18, characterized in that the area of beds planted with reeds necessary for the treatment of effluents is determined according to the number of septic tanks to be treated, on the basis of 1 m2 of beds planted with reeds for the treatment of 3 septic tanks.