WO2007060341A1

WO2007060341A1 - Installation and method for single-unit treatment of effluents

Info

Publication number: WO2007060341A1
Application number: PCT/FR2006/002599
Authority: WO
Inventors: Stéphane MULLER
Original assignee: Pöyry Environment S.A.
Priority date: 2005-11-28
Filing date: 2006-11-28
Publication date: 2007-05-31
Also published as: FR2893936A1; FR2893936B1

Abstract

The invention concerns an installation for treating effluents collected by a single-unit wastewater system, characterized in that it comprises from upstream downstream: a device for controlling the flow rate (8) of incident effluents (Q) for separating same into two flows, namely a through flow (Qtn), limited to a specific value (CW), and an excess flow (Qe), a reed-type filter (1) receiving the through flow (Qtn) derived from the flow rate control device (8); a pond (5) receiving the through flow (Qtn) in output of the reed-type filter (1) and the excess flow (Qe) derived from the flow rate control device (8), which consists of at least one tank (5) comprising means for evacuating outwards consisting of a discharge (13) with controlled flow not less than said specific value (Qmax) and a secured overflow (14) arranged at a higher level (h+h').

Description

Installation and method of unitary effluent treatment

The present invention relates to an installation and a method for treating the pollution of effluents collected by unitary sanitation networks of local communities.

Effluent clean-up from local communities is usually done by a collection system, which collects and transports them to a treatment unit, which at best treats the pollution contained in these effluents and then discharges them into the natural environment ( stream, shoreline, etc.) purified effluent. The collecting networks can be unitary or separative. They are said to be unitary when they collect, at the same time, by means of the same pipelines, the effluents and the runoff water coming from the rains, and they are said separative when they consist of two distinct sets of pipes, namely a set collecting the effluent and the other set collecting the runoff.

It is understood that the unit collecting networks are subject to large variations in flow and polluting loads, the extremes of which are respectively reached on the one hand in periods and situations of low discharge (mid-night, in dry weather), and on the other hand in periods and situations of strong rejection (morning, evening in heavy rain). Even for identical moments of the day, the ratio between the dry flow rates and the rainfall flow rates can thus reach values of the order of 10 to 20. These strong variations, and the low pollution contained in runoff water, have led communities to preferentially provide separation networks, avoiding over-sizing of equipment (networks, treatment units) and allowing a more stable operation and therefore more efficient units of these.

However, the creation of separative networks, especially where unitary networks already exist, is usually extremely expensive for various reasons: difficult work in the city center causing considerable disturbance for residents, traders and more generally travel, recovery of the economy. all connections to private properties.

In addition, even when the network is separate, very often there is a high sensitivity of the flows of the wastewater networks to rainy events due to the inevitable leaks of these networks, including the intrusion of parasitic water from the rain infiltrated into the ground, and frequent non-compliant connections (rain or run-off water discharged into wastewater systems), difficult to locate and combat. The search for installation solutions able to absorb very high flow rates and load variations has therefore emerged.

There are currently numerous effluent treatment processes and facilities, including: natural lagooning, aerated lagooning, reed plant filters, bacterial beds, biodisks, activated sludge or free crops, biofilters or crops fixed, membrane filtration. The simplest methods to implement are lagooning and filters planted with reeds. If these processes have lower performance and require large floor areas, they have the advantage of being very inexpensive in both investment and operation. Other techniques, on the other hand, require the construction of civil engineering works and the use of energy, which gives them considerably higher costs both in terms of investment and operation.

Lagooning and reed-type filters are therefore often chosen for small installations receiving, for example, pollution from a few tens of population equivalents to a few thousand (it will be recalled that the "equivalent-inhabitant" unit noted "EH Corresponds to the production of 60 grams of DB05 per day, the DB05 being a measure of carbon pollution which corresponds to the biological oxygen demand over 5 days), installations requiring civil engineering being implemented for networks dealing with several thousand to several million population equivalents.

It is known that the decomposition of pollution in lagooning processes is mainly carried out on the one hand by decantation, and on the other hand by the action of naturally occurring aerobic bacteria, the oxygen being supplied by the air which is found above the surface of the water, by insufflation of it in the case of aerated lagoons, or by emission by algae by photosynthesis.

The lagoon is in fact, in the sense of chemical engineering, a "mixed reactor", in which the input flows are identical to the output flow, since permanently evacuated by overflow. This mode of operation gives the lagooning a good stability of performance against significant variations in flow rate or charge, as long as the charge remains sufficiently diluted. Thus, when the lagoon is for example at the outlet of a unitary effluent collection system and receives effluents in rainy weather, the volume stored in the lagoon plays a buffer role by mixing the water already present and the flow rates of the water. rain, and the momentary decrease in the residence time, while there is already a developed bacterial flora, does not affect the purification capacity too much, like the so-called activated sludge purification systems.

Reed-planted filters have emerged more recently, and usually include two tiered ponds planted with reeds (often phragmites), namely a gravel first stage and a second sand stage. The first stage retains on its surface all the particles contained in the effluents, so that a layer of sludge is formed on this surface, but thanks to the presence of the reeds whose stems pass through this layer, it does not occur. clogging and the effluents continue their percolation through the different layers of the filters. The pollution is partially degraded inside the filter by the bacteria present on the surface of the chippings and the roots of the reeds. Reeds absorb some of the pollution thus decomposed. The second filter serves to refine the purification.

The necessary surface of the filters themselves is of the order of 2 to 2.5 m ² / EH, an overall surface of the order of 8 to 10 m ² / EH being however necessary because of the design of the basins and the traffic and development in successive stages. Reed-type filters have been found to be more effective in treating pollution than lagoons, because filtration through gravel and sand substrates allows retention of suspended solids. and micropollutants much higher than the lagoon settling and, secondly, due to the natural aeration of the substrates related to the vertical feeding mode, their grain size and the movements of the stems of the reeds. This aeration allows the development of aerobic bacteria that break down carbon pollution and nitrifying bacteria capable of reducing ammonia to nitrates.

Because of these purification performances superior to those of the lagoons, it has been proposed to install reed-type filters downstream of existing or new lagoons, these filters thus allowing a "refining" of the pollution after the lagoon, in addition of it.

However, if these filters allow a fairly efficient purification, they do not support, however, prolonged or significant increases in flow, which can either drown the substrate or the "wash". The effluents collected during heavy rains can not therefore be fully accepted on the filters, and are therefore discharged directly to the natural environment, without being cleaned up.

In conclusion, among the simple techniques of purification, namely lagoons and reed type filters, none appear totally satisfactory: - lagooning, if it is very robust in the face of variations in flow, is of implemented inexpensively, and remains of poor performance, especially for the treatment of nitrogen pollution. The establishment of a downstream treatment (bacterial bed or filters planted with reeds) is possible to refine the treatment, but represents an important additional cost, - the reed type filters allow a more advanced treatment of the pollution, with particular a partial nitrification, but poorly support prolonged increases in flow and therefore can not admit all the effluents of rainy weather, leaving part of them direct to the natural environment without prior clearance. The aim of the invention is to propose a simple implementation of wastewater treatment that has all the desired advantages, namely a thorough treatment of pollution, including nitrogen pollution, and an ability to admit and treat wastewater. effluents collected during rainy weather, therefore for flows considerably larger than those collected during dry weather.

It thus makes it possible to propose a satisfactory solution to a community having unitary networks for the purification of its effluents.

The subject of the present invention is thus a plant for treating effluents collected by a sewerage network of unitary nature, characterized in that it comprises from upstream to downstream:

a device for controlling the flow of the incident effluents making it possible to separate them into two flow rates, namely a through-flow, limited to a determined value, and an excess flow rate; a reed-type filter receiving the flow rate coming from the flow control device,

a lagoon receiving, on the one hand, the through-flow at the outlet of the reed-type filter and, on the other hand, on the other hand, the excess flow from the flow control device, which consists of at least one basin with outward discharge means consisting, on the one hand, of a controlled flow evacuation at most equal to the said determined value and, on the other hand, a safety overflow arranged at a higher level (h + h) '.

Said determined value will preferably be equal to the maximum flow rate in dry weather existing at its inlet. In addition, the volume of the lagoon will allow the storage of the excess flow admitted, up to a flow corresponding to a given reference rain.

In one embodiment of the invention, the flow control device may consist of a vortex type regulator.

The subject of the present invention is also a method for treating the effluents collected by a sewerage network of unitary nature, characterized in that it comprises the steps of: controlling the incident flow rate admitted at the inlet of an installation in order, when it exceeds a given value, to separate it into two flow rates, namely a through-flow and an excess flow beyond said given value, - to treat the through-flow by means of a reed-type filter, to treat, in a lagoon, the through-flow from the reed-type filter, and the excess flow rate when the incident flow rate exceeds said given value, - rejecting the two combined flows with a flow rate at most equal to said given value. An embodiment of the present invention will be described hereinafter by way of nonlimiting example, with reference to the appended drawing in which:

- Figure 1 is a schematic top view of an installation according to the present invention.

- Figure 2 is a schematic vertical sectional view of an embodiment of a lagoon forming part of the installation according to the invention.

The installation shown in Figure 1 consists essentially of a reed type filter 1 which is connected by a pipe 3 to a lagoon 5 disposed downstream thereof. The arrival of the effluents in the installation is done, with an incident flow Q, through a pipe 7 which leads to a flow control device 8. The latter sends, through a pipe 9, a through flow Q _tr to the filter reed type 1 by limiting it to a specific value Q _maxr sending to the lagoon 5, through a pipe 10, any excess flow Q _e . The flow control device 8 is designed so that the specific value determined Q _max is equal to an average of the maximum flow rates in dry weather measured for example during measurement campaigns at the inlet A of the treatment plant. The reed type filter 1 may be composed of one or more basins la arranged in parallel operating alternately (three basins la in the embodiment shown in Figure 1). It is dimensioned on the basis of the flow rate Q _max and the associated polluting load, according to the prior state of the art. Thus, this one-stage filter may be sized to about 1.5 m ² / EH, or a little less, its power can be carried out continuously or by sheeting. It will be noted that the design of the installation according to the invention in which the flow rate admitted on the reed type filter 1 is limited to the maximum flow rate Q _max of dry time, without taking into account an additional flow rate representing a fraction of rainwater, can significantly limit the surface of the filters.

The lagoon 5 is shown in vertical schematic section in Figure 2. It is preferably constituted by a basin 6 at the upper part of which open the pipes 3 and 10 which bring flow through Q _tn and over Q _e respectively from the Reed type filter 1 and the flow control device 8. The evacuation of the liquids at the outlet of this basin 6 is done by two means, namely a discharge pipe 13, flow rate limited at most to said Q _max value. and an overflow discharge overflow 14. The discharge line 13 is disposed at a level h of the bottom of the basin. The overflow overflow 14 is disposed at a level h 'of the discharge pipe 13. The level h of the controlled flow discharge 13 and the upper level h + h' of the overflow 14 thus define a retention volume V _r able to receive and store the effluents from the flow Q _e for a certain time depending on this flow. Under these conditions, it is understood that the entire evacuation is done by the pipe 13, except in the case of unusually heavy rains where the volume V _r of the basin 6 would be completely filled and where the surplus would then be evacuated by the overflow 14.

The basin 6 comprises at the entrance a pit 15 adapted to capture the solid elements contained in the stream collected, in particular the excess flow Q _e .

The lagoon will preferably be sized according to the prescriptions of the CEMAGREF publication "le natural lagooning in France: state of the art and recent trends ", the sizing calculation logically ignoring the first settling lagoon. It will be important here to take into account its operating conditions, namely that the effluents arriving at the lagoon are: o partially, diluted (rainy weather effluents) o partly, already treated by the reed type filter in dry weather. The pollutant load contained in the effluents arriving at the lagoon 5 is therefore very significantly lower than that of the standard situation of a lagoon directly receiving effluents.

As a result, a single-storey lagoon, typically a single basin, with a floor area reduced to about 5 m ² / EH, is normally sufficient, instead of 6 m ² / EH for a first settling basin. 2.5 + 2.5 = 5 m ² / EH for second and third finishing tanks (ie a total of 5 m ² / EH instead of 11 m ² / EH). The present invention is particularly interesting in that it combines the advantages of the reed-type filters and the lagoon, without however having the disadvantages, namely: high purification performance, - admission and treatment of rainfall flow rates, Slow accumulation of sludge in the lagoon (the sludge being mostly accumulated on the surface of the reed-type filter).

Moreover, its implementation is as economical as those using only reed-type filters or lagoons, despite the presence of both, because their combination allows to retain existing networks and to reduce the ground surfaces: a total of 1.5 + 5 = 6.5 m ² / EH suffices, whereas: a reed-type filter typically requires a surface of the order of 2.5 m ² / EH , this for a flow rate Q _max I ^e dimensionneitient being increased proportionally for flow rates greater than Q _max a lagoon typically requires a surface of the order of 11 m2 / EH, while the device can treat pollution: - more thrust than the lagoon more fully than the reed-type filter (admission of rainfall flow rates)

The cumulated surface of the reed-type filter and the lagoon can thus be less than 6.5 m ² for 60 grams of pollution received per day, on average in dry weather, this pollution being expressed in biological oxygen demand over 5 days (BOD5).

The present invention makes it possible above all to preserve the sanitation networks as they are, without the users being forced to engage in extremely expensive separative networking works and, as mentioned in the introduction, to the often mediocre efficiency, to ensure the limitation of rain flow rates.

In a particularly advantageous embodiment of the invention, the flow control device 8 may advantageously consist of a vortex type regulator. It is known that these devices are regulators which, without a moving part, operate exclusively by vortex effect under the effects of a liquid flow. It has been found that these devices are particularly suitable for the management of effluents from unitary networks, insofar as they allow to evacuate the chippings, even the stones carried by these flows.

The reed-type filter may, for its part, advantageously be composed of alternating operating basins, each of which may be constituted as follows:

a layer of gravel with a particle size of 2 to 6 mm and a thickness of 60 cm for filtration and treatment,

- a gravel layer with a grain size of 15 to 25 mm and a thickness of 20 cm for drainage,

- a geomembrane waterproofing,

- a reed plantation with a density of 4 reeds per m ² ,

- an adjustable overflow by stainless steel cofferdams allowing the possible dewatering towards the lagoon.

Feed basins can be made by sheeting calibrated to bring a blade of water of about 2 cm on the basin in use.

The discharge pipe 13 at the outlet of the lagoon 5 may be provided with means capable of measuring the flow rates at the outlet.

The evacuation 13 controlled flow can advantageously be connected to a flow control device, or regulator, vortex type. The use of the vortex type device makes it possible to facilitate the adjustment of the flow rate at the outlet of lagoon 5. The dimensions of the regulator will in particular be chosen so that the flow rate at the outlet of lagoon 5 is between the mean flow rate in dry weather. and the determined value flow Q _max . The installation according to the invention therefore has much higher performance than current installations at a very advantageous cost, both in investment and operation. It allows the treatment of all effluents from a unitary system, except in case of unusually heavy rains, without resorting to a very costly segregation of the sanitation network.

Claims

1.- Installation for the treatment of effluents collected by a sewerage network of a unitary nature, characterized in that it comprises from upstream to downstream: a device for controlling the flow (8) of the incident effluents (Q) allowing separation these in two flow rates, namely a flow rate (Q _tn ) _r limited to a determined value (Q _max w and excess flow (Qe), a reed-type filter (1) receiving the flow rate (Q _tn) ) from the flow control device (8), a lagoon (5) receiving, on the one hand, the flow rate (Q _tn ) at the outlet of the reed-type filter

(1) and, on the other hand, the excess flow (Q _e > resulting from the flow control device (8), which consists of at least one basin (6) comprising outward discharge means constituted on the one hand, an evacuation (13) with controlled flow at most equal to the aforesaid determined value (Q _ma χ) and, on the other hand, a safety overflow (14) arranged at a level ( h + h ') higher.

2.- Installation according to claim 1, characterized in that the level (h) of the controlled flow discharge (13) and the upper level (h + h ') of the overflow (14) of the basin define between them a retention volume (Vr).

3.- Installation according to one of claims 1 or 2 characterized in that said determined value (Qmax) is equal to the maximum flow rate in dry weather existing at its inlet (A).

4.- Installation according to one of claims 1 to 3 characterized in that the cumulative area of the reed-type filter (1) and the lagoon (5) is less than 6.5 m ² for 60 grams of pollution received per day, on average in dry weather, this pollution being expressed in biological oxygen demand over 5 days (BOD5).

5.- Installation according to one of the preceding claims, characterized in that the flow control device (8) consists of a vortex type regulator.

6.- Installation according to one of the preceding claims, characterized in that the evacuation (13) controlled flow is connected to a vortex type regulator.

7.- Installation according to one of the preceding claims, characterized in that the reed-type filter (1) comprises at least two basins adapted to be traversed alternately by the flow (Qtr).

8. A process for treating effluents collected by a sewerage network of a unitary nature, characterized in that it comprises the steps of: controlling the incident flow rate (Q) admitted at the inlet of an installation so, when the latter exceeds a given value (Q _max ), to separate it into two flow rates, namely a through flow (Q _tr ) and a surplus flow (Q _e ) beyond said given value (Q _max ), to process the through flow ( Q _t ) by means of a reed type filter (8),

- treat, in a lagoon (5), the through flow (Q _t ) from the reed type filter (8), and the excess flow (Q _e ) when the incident flow (Q) exceeds said given value (Q _ma χ), reject the two combined rates with an output rate at most equal to said given value (Q _ma χ) •