FR2747671A1 - Treating waste water in lagoons of floating macrophytes - Google Patents

Abstract

Treating waste water in a lagoon of floating macrophytes comprises: (a) passing effluent for treatment through a battery of decanter-digesters (dd and DD); (b) passing the effluent into one of a number of arms of parallel horizontal lagoons (A to D), each of which operates independently and which ends have overflows leading to a drainage canal that sets the liquid level, and (c) plants can be pushed over the overflow by a hydraulic system towards a collection point.

Description

 This purification process by lagooning with floating macrophyx filters, usable in tropical climate, uses plants to absorb pollution and reoxygenate the water of the effluent. The mature plants are extracted from knitted sweaters.

The effluent (or wastewater) first passes through a decanter-digester, characterized inter alia by its retention time (vanable from a few hours to a few Days) Heavy particles are deposited there at the bottom, organic matter is there transformed into mlcroparticles suspended in water under the action of anaerobic bacteria and fermentation. The effluent is then discharged into the lagoon. Floating plants are grown there.

 On leaving the lagoon, the effluent still undergoes the anaerobic action of the treatment started in the decanter-digester. The microparticles in suspension are captured in the roots of plants. In contact with the surface of the water, the leaves irradiated by the sun produce oxygen (photosynthesis). Water oxygenates on contact with the leaves.

This oxygenation promotes the proliferation of aerobic bacteria which mineralize the microparticles on which they feed, thus making them assimilable by plants.

 As the effluent advances in the lagoon, oxygenation increases, reinforcing the aerobic action of the treatment at the same time as the anaerobic action decreases. At a certain level of oxygenation, protozoa and small microphagous animals appear which feed on bacteria and viruses, some of which are pathogenic, which have reached this point.

 Plants during this time absorb almost all of the pollution entering the lagoon. When they reach maturity, they must be harvested so that others, in the growth phase, can develop by capturing their share of pollution. The plants remaining in the lagoon will ensure the reproduction and therefore the renewal of the filters.

 To date, to my knowledge, there are two types of construction of lagoons operating with this process.

 Fig. I - A series of narrow and shallow tubs (represented here 4 in number) are arranged in series. Each bin is at a higher level than the one that follows it. The effluent is pretreated in a Dd decanter-digester. The plants are harvested manually from the banks of the tanks. The flow rate of effluent admitted and the cross section of the slice of water in the tanks define the speed of the effluent.

If this speed exceeds a certain value, it is incompatible with the development of plants. This very efficient system is therefore limited to a few thousand equivalent inhabitants. However, it offers two advantages thanks to the narrowness of the tanks:
- possibility of harvesting manually or mechanically from the banks.

 - absence of preferential passages.

 Fig. 2 - Two switchable lagoons are fed in turn through a settling tank-digester. Harvesting can be automated thanks to the use of small plants passing through the weirs at the end of the lagoon, or mechanically with equipment allowing access to the middle of the lagoon far from the banks. This material is necessarily heavy and expensive.

 This system allows the realization of large stations. Preferential crossings may occur. It is necessary to create a mixing of the effluent in the lagoon.

The purification is continued in a lagoon with rooted plants.

 The devices which are the subject of this request are intended to remedy certain drawbacks of the systems described above.

 They make it possible to save space by avoiding the doubling of the surface of the lagoon in the case of FIG. 2 where the two lagoons operate alternately to allow maintenance interventions. They also reduce the area occupied in the case of FIG. 1 by reducing the number of dikes separating the tanks: an arm of length equal to all the tanks will replace them. By multiplying the arms, we will multiply the capacity of the station. By widening the arms, we will decrease the number of dikes. The space saving can be considerable. In the case of FIG. 1, if you need to work on a tank or a settler-digester, you stop the station. The devices, described below, allow the normal operation of the station in the event of intervention for its maintenance.

They will reduce the number of elevation changes, which decreases the power required to lift the effluent. They allow easy harvesting, both manual and mechanical.
Indeed, the problem of harvesting can be considered as solved If we manage to bring the plants to a precise point in the system at the end of treatment. It is one of the objects of the invention.

 The station will operate by gravity requiring no machinery except, possibly, a recycling pump to reinforce the hunting device described below.

 These devices will give great flexibility of use in tropical climates where a dry season succeeds a rainy season. In the dry season, a certain number of arms will be closed to maintain a sufficient level in the others, the station possibly being able to operate without discharge of water if the evaporation is strong.

 In the following description, the word lagoon designates all of the arms of a treatment plant.

The lagoon (Fig. 3) is divided into n arms in parallel (here 4 in number for simplicity) located on the same level. Two decanter-disgestors Ddl and Dd2 receive the effluent through a distributor r. The effluent gathered in r 'feeds the different arms. In case of intervention on Ddl, for example, we will form V1 and V3. Valves V2, V4, V5, V6,
V7, and V8 will remain open. The retention time of the decanter-digesters, even divided by two, will allow the station to function correctly, the case being planned from the design. Similarly, the closing of an arm will have an incidence all the more reduced the greater the number n of arms.

 The station could be carried out on a clay embankment.

 The watertightness of the settling tanks must be ensured by a geomembrane (not shown in Fig. 4). The water level in each arm will be fixed by a weir.

 Fig. 5 represents a lagoon identical to that of FIG. 3. The effluent enters a distributor from where it is divided towards the decanter-digesters ddl and dd2 of small width and height, whose role is to retain a maximum of decanted sands in the form of muddy deposit and accumulated light materials in a floating crust. The retention of these elements in ddl and dd2 will avoid too frequent interventions on Ddl and Dd2 made difficult because of their large height and width. Closing a series of decanter-digesters (DOF and DOF for example) allows, as in the previous case, correct operation of the station. Similarly, the closing of an arm will have only a small impact on the operation of the assembly.

Fig. 6 is a diagram of elevation differences. Blen that having one more elevation gain than in the previous case (Fig. 3), the total elevation will be more reduced for a large width station the elevation (Fig. 4) from r to Ddl and Dd2 is conditioned by the slope to give to the connecting pipes and to the length of these connections. The
Fig. 5 shows that the length of the links is not conditioned by the importance of the station.

 In Fig. 7, the decanter-digesters are equal in number to the arms. Each settling tank is in series with an arm.

 In this device, the distribution is on a single stage. The total drop will be lower than in the two previous cases. The length occupied by the station will be greater for equivalent retention times of the settler-digesters.

 Fig. 8 is the elevation diagram.

 Fig; 11 shows in its upper part another arrangement of the settling tanks. The effluent arrives in the distributor r where it is divided into ddl and dd2 of shallow depth and height, therefore easy to drain. The effluent is grouped in r 'from which it leaves towards the settling tanks-digesters arranged at the entrance of each arm which they supply, DDA for arm A, DDB for arm B, etc. The closure of ddl or dd2 makes the loss of retention time negligible compared to that of all the settler-digesters in operation: ddl (or dd2) + DDA + DDB etc ...

 Fig. 9 shows a device with wide arms which can be closed by doors in the narrow part of the funnel to isolate them. The arms A, B and C are shown closed by the doors pl, p2 and p3. They must be maneuverable manually by two men. They will not exceed 5m in length and their height will be approximately Im. They will be described later in the appendix to this request.

 The length of the door must not be less than 1/3 of the width of the arm it closes. The angle a, formed by the edge of the funnel and the bank must not exceed 30 (Fig. 9). For arms wider than 15m, you will need 2 (Fig. 11), 3 (Fig. 13) or 4 (Fig 12) doors per arm or more if necessary.

 Fig. 12 shows a device allowing maximum passage for the plants. Concrete studs serve as supports for the doors. Fig. 10 is an enlarged partial longitudinal section of the arm D of FIG. 9. It shows the rising profile of the bottom of the funnel and the position of the plants in the water. The height (hc) of the water in the channel is about half that (h) in the arm. This low height facilitates the drainage of plants in the canal. The end of the arm and the channel are concreted to resist the current which has become significant from the upstream ramp (see below).

 Fig. 14 shows the end of the first five arms of a lagoon which has n.

Each arm is terminated by two funnels corresponding to two doors. A device for hunting plants, by acceleration of the current, consisting of cylindrical PVC or concrete pipes is shown in dotted lines. The collecting pipe 1T 'crosses all of the arms. It is closed at the ends. Each of the ramps, close to the outlet of the arm, is isolated by a valve (V3 and V4, Fig. 15, for arms C and D). These valves are placed at the bottom of concrete boxes between two arms (Fig. 15, 16 and 17). The optional valve 5 is shown in dotted lines (Fig. 15).

 An upstream ramp located at the last 1 / 5th of the length of each arm is isolated by a valve (V1 and V2 for C and D, Fig. 15). Arms A and B are shown empty of plants (Fig. 14). The doors of arms A, B, D, E and following not shown, are closed.

The doors of C are open. All upstream valves are closed except Vi for C.

All downstream valves are open except V3 for C (Fig. 15). All the arms are supplied with effluent which has no other outlet than the end of C. The levels in the arms A, B, D, E and the following tend to increase. Any drop will cause a flow towards the upstream ramp of C through the collector TT 'in stages each time it receives the effluent from an arm. The pressure drops follow an increase consequent upon this acceleration.

The collector 1T 'as well as the connections to the upstream and downstream ramps will be dimensioned so that the maximum drop does not bring the water level above the banks under the worst possible conditions. The flow of liquid in the mouths of the ramps must be equitably distributed on the discharge, so it is necessary to proceed to successive symmetrical Y-shaped dislslons. The number of mouths will therefore be 2 or 4 or 8 or 16 etc. The total section of the pipes, after each division must be equal to that of the pipe which feeds it.

Sharp elbows should be avoided (Fig. 14 is only a schematic diagram).

 The water collected downstream of the n arms except C, will exit through the upstream ramp of C, accelerating the current whose speed will be n times that of C before the upstream ramp, facilitating the drainage of plants in the end of the arm, the funnels and the channel to the outlet.

 For example, if the speed of the current in each arm is 30rn / day after stabilization of the levels, the narrowing of the funnel 1/3 of the width of the arm, the ascent of the bottom hc = 1/2 h (Fig. 10 ) and n = 10 arms, we will have at the narrow passage of the funnel a speed ve = 30m / day x 3 x2 x 10 = 1,800m / day.

 To maintain this speed in the channel, it is necessary to maintain its height at the passage to the doors and its width equal to the entire width of the doors of each arm.

 If one of the funnels is blocked, the other can be closed to speed up the flow. In case of failure, you can close V1 and open V3 to bring the flush closer to the stopper.

 We can also use an effluent recycling pump at the outlet of the channel to reinforce the current in Tut '. Finally, it is quite simply possible to open manually, the water height in the canal being less than 0.5m, it allows passage on foot.

 The arm D is shown in FIG. 14 ready for harvest. To collect it, we open the doors of this arm, we open V2 (Fig. 15), we open V3, we close V1, we close V4, we close the doors of C.

 We can thus successively harvest 1 / 5th of the plants of each arm. In the closed arm C, the downstream part of which has been emptied of its plants, the current abruptly decreases to regain its initial value. The plants will slowly descend to the downstream ramp, and the arm can be harvested again when the time comes.

 Fig. 15 shows an enlarged section of FIG. 16 according to a, b, c, d.

 Fig. 16 shows a right view along b, d.

 Fig. 17 shows a front view along c, d.

 It should be noted that it is possible to harvest two arms at the same time on the same lagoon by closing a median valve placed directly on TT 'We can then use the two ends of the channel for harvesting, the level of the lagoon then being fixed by two weirs.

Claims (10)

 1) Device intended for the treatment of waste water by lagooning with floating macrophyte filters characterized by a battery of settling tanks-digesters, characterized by the division of the lagoon into n horizontal parallel arms, of the same level operating independently, interconnected at their downstream end by a plant drainage channel towards one of its ends where there is a weir which fixes the general level of the lagoon and by a hydraulic system for flushing the plants towards the harvest point.  2) Device according to claim I characterized by a battery of two decantersdigesters in parallel supplied by a distributor r. These settlersZigesters can independently or together, feed the different arms of the lagoon through a distributor r '(Fig. 3).  3) Device according to claim I characterized by a battery of four settler-digesters arranged in two parallel series operating together or in isolation. The ddl and dd2 decanter-digesters are reduced in width and depth compared to Ddl, and Dd2 (Fig. 5).  4) Device according to claim I characterized by a battery of decantersdigesters supplied by a distributor. Each decanter-digester is in series with the arm it supplies (Fig. 7).  5) Device according to claim I characterized by a battery of decantersdigesters including two dof, and dd2 of shallow depth and height, supplied by a distributor r, operate in parallel or separately. They group the effluent in a distributor r 'which redistributes them to the different settling tanks-digesters placed in the extension of the arms which they supply respectively (Fig. 11).  6) Device according to claim I characterized by the closing of the arms by a door (Fig. 9), two doors (Fig. 11), three doors (Fig. 13), four doors (Fig. 12) or more if necessary, on each arm.  7) Device according to claim 6 characterized in that one fixes the level of the lagoon by a single weir placed at one end of the channel which interconnects the arms downstream of the doors.  8) Device according to claim 6 characterized in that the flow of all the arms of the lagoon passes in a single arm, from a level determined in its length to evacuate the plants to the point of harvest. All the arms of the lagoon can be harvested in turn by a set of doors and valves. This device includes the arms doors giving access to the canal, a collecting pipe crossing all the arms of the lagoon (Fig. 14). A downstream ramp located near the outlet of each arm is connected to the collector and can be isolated from it by a valve. An upstream ramp located at the level of the arm from which the plants are to be harvested is connected to the collector and can be isolated from it by a valve.  9) Device according to claim 8 characterized by the addition of a pump outside an arm located at the edge of the lagoon, the pump recycling the water after the weir in rF 'to strengthen the current in the arm harvest.  10) Device according to 8 characterized by the separation of the lagoon in two by simply closing a valve on the collector rF 'to collect two arms at the same time by the two ends of the channel.