AU754195B2

AU754195B2 - Method and installations for treating effluents in small communities

Info

Publication number: AU754195B2
Application number: AU51714/99A
Authority: AU
Inventors: Francois Virloget
Original assignee: Suez Lyonnaise des Eaux
Current assignee: Suez Lyonnaise des Eaux
Priority date: 1998-08-20
Filing date: 1999-08-11
Publication date: 2002-11-07
Anticipated expiration: 2019-08-11
Also published as: BR9913068A; FR2782508A1; ES2157876T1; DE69923778T2; CN1313836A; WO2000010927A1; ES2157876T3; CN1305784C; DE1112231T1; DE69923778D1; ID27782A; FR2782508B1; PT1112231E; ATE289280T1; EP1112231B1; EP1112231A1; AU5171499A

Abstract

The invention concerns a method for treating effluents in small communities, that is communities consisting of about 200 to 2000 inh.eq (inhabitant equivalent), characterised in that it consists in: carrying out a biological treatment of the effluent using a trickling filter eliminating matters suspended in the treated effluent, and, simultaneously performing a treatment of the sludge by filtering-composting on filters planted with reeds.

Description

Process and plants for the treatment of effluents from small communities The present invention generally relates to the treatment of effluents from what it is convenient to refer to as small communities, that is to say communities having from 500 to 2 000 le (inhabitant equivalent).

France has approximately 36 000 communes, 31 300 of which have more than 200 inhabitants and less than 2 000 inhabitants, which communes represent a population of the order of 15 000 000 inhabitants, constituting approximately 25% of the total population of France.

The total number of purification plants in France is approximately 12 000, and more than 60% have a size of less than 2 000 le.

These purification plants for small communities generally employ a biological treatment with activated sludge, although this technique is entirely unsuited to 20 purification plants of such a size, in particular 0because of the high capital cost and especially excessive operating costs. Furthermore, the efficiency of such plants is often mediocre. A person skilled in the art knows that the biological treatment of effluents with activated sludge must be reserved for the biggest plants in the context of discharge into a particularly sensitive environment.

The problem which has to be solved lies in the 0S** development of a technique suited to such small plants for financially acceptable operating costs. In particular, the objective is to achieve, for effluent treatment plants with a capacity of between 500 and 2 000 le, an operating cost which is reduced by 50 to with respect to that of plants employing a biological treatment with activated sludge.

In order to solve the abovementioned problem, the invention provides for the introduction of a novel treatment route which is inexpensive in terms of AJ capital and operating costs and which, of course, meets the discharge requirements of the decree of 21 June 2 1996 (Official Gazette of the French Republic of 9 August 1996) relating to facilities for the treatment of waste water from small communities, that is to say of 200 to 2 000 Ie. 12 kg BOD, and 120 kg BOD,/d) According to Art. 13 of this decree, the following performance is expected for a biological treatment: either a minimum efficiency of 60% with respect to the BOD s or the COD, or a maximum concentration in the treated effluent of 35 mg BOD/1 These requirements are, of course, met by the process and the plant which are subject-matters of the present invention.

Consequently, this invention firstly relates to a process for the treatment of effluents from small communities, that is to say of approximately 500 to 2 000 Ie (Inhabitant equivalent), employing filters planted with reeds, characterized in that it consists: in carrying out a biological treatment of the effluent using a trickling filter, and S* in removing the suspended matter in the effluent thus treated and simultaneously treating the sludge by filtration-composting on filters planted with reeds, 25 the latter preferably being Phragmites australis.

The invention also relates to a plant for the 000o purpose of the implementation of the process defined above, this plant being characterized in that it comprises: a trickling filter comprising at least one stage in which the effluent to be treated is received, and at least one filtration-composting compartment fed from the trickling filter, each of the said compartments comprising successive layers of filler materials and of sand and their upper surfaces being planted with reeds, in particular with Phragmites australis.

dSr4 As is understood, the discharge requirements mentioned in the decree of 21 June 1996 are observed by 3 the invention by employing a trickling filter, that is to say a treatment route of the fixed culture type with a low contact time, the feeding with effluents being carried out directly without passing into a preliminary clarification tank. The trickling filter technique, in its modern conception (absence of preliminary clarification tank, treatment route such as screening, "feeding-recirculation" pumping station, plastic-packed bed), makes possible an economical treatment of the effluents as a result of a low energy consumption (close to half that with activated sludge, for an equivalent performance). The capital cost remains advantageous for a treatment limited to removing pollution by carbon compounds.

Depending upon the restrictions of the natural environment, it is possible to envisage a nitrification treatment of the ammoniacal nitrogen by increasing the size of the trickling filter or by providing a second stage. Thus, the scale of the first stage must be defined, according to the invention, according to the discharge stipulations and the treatments for removal of pollution from the effluent to be carried out.

The effluents thus treated are subsequently freed from suspended matter by passing through 25 filtration compartments planted with reeds, in which is also carried out the treatment of the sludge by o rhizocomposting. It is also possible to count on an additional treatment of the effluents in the filtering o* core of the filtration compartments.

According to the present invention, the pretreatment of the effluents is restricted to a fine sieving (3 mm mesh) or a screening (6 mm mesh) which makes it possible to remove various types of waste. It is not necessary to employ a degritting-degreasing system, given that the particles (organic matter, including grease, sand) with a particle size smaller than the sieving or screening mesh have no effect on the treatment route (trickling filter filter- 2 rhizocomposting) 4 It may be indicated, as a nonlimiting implementational example, that a device produced according to the present invention comprises a first lift-recirculation station (equipped with two pumps, one of which is a spare) continually feeding the trickling filter. The latter is of the type with PVC plastic packing (cross current, specific surface area 165 m 2 /m 3 with a height of approximately 5 metres, the mean hydraulic load being of the order of 2 m/h. A partition is provided in this station in order to pump first and foremost the crude effluents to be treated, with an additional contribution of treated effluents in order to ensure the hydrodynamic conditions of the trickling filter.

The effluents treated on the trickling filter arrive at a second pumping station by overflow of the lift-recirculation station, this second pumping station, equipped with two pumps, one of which is a spare, exhibiting a differential volume sufficient to 20 allow batchwise feeding of the filtration-composting compartments (batches of 5 to 15 cm, over 10 to minutes).

According to this implementational example of the present invention, the treatment plant comprises 25 filtration-composting compartments, the latter numbering at least three. The surface area of these compartments is from 0.4 to 1 m 2 per Ie and the maximum surface area per unit is from 100 to 150 m 2 The feeding of the bed of one compartment corresponds to each batch. According to the present invention, the second pumping station is intended to be automatically controlled, in order to ensure feeding of all the filtration-composting compartments in rotation, with at least one compartment continuously at rest for a week.

By way of example, the filtration-composting compartments can be produced from pointed concrete boundary panels and piles exhibiting a height of approximately 2 metres (which results in a free height of 1.50 m) and a maximum width of 5 m, in order to 5 allow access for removing sludge. The foundation of the compartments is composed of a plastic sheet on which are positioned drains, in order to provide for the recovery of the treated effluents, in a layer of pebbles (h approximately 20 cm and particle size of the order of 30/80 mm). This layer of pebbles is covered successively with a layer of gravel (h approximately 10 cm) and with a layer of sand (h cm, washed sand devoid of fines) A biological treatment of the fixed culture type is carried out on the layer of sand and, with the mechanical effect of the filtration, it is possible to obtain a good purifying performance.

The surfaces of the filtration-composting 15 compartments are planted with reeds (Phragmites Saustralis), the intense root growth of which promotes the circulation of air and provides for composting of the sludge. Under normal operation, the dry content of Sothe sludge is approximately 12% and the veiling level 20 of the sludge in the compartments increases by 20 to *o 30 cm per year. After operating for approximately five years, it is necessary to provide for the extraction of the accumulated sludge (compost). After a period of rest of the order of one to two weeks, the compost is 25 extracted and is provisionally stored, for drying, on a neighbouring area of ground. After drying for several weeks, it is possible to obtain a fully stabilized product exhibiting a dry content of greater than The scale of the various components of 30 purification plants according to the present invention, for various sizes of plant, is given in Table 1 below by way of example.

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0S 0O 0 BASIC DATA Nominal Ie 200 500 1 000 1 500 2 000 capacity Daily m 3 /d 30 75 150 225 300 throughput BOD, nd Raw kg/d 12 30 60 90 120 water

DISCHARGE

OBJECTIVE

BOD, ad2 dis- mg/l 35 35 35 35 charge targeted (trickling filter outlet) FINE SIEVING (type Aquagard 3 mm) Waste production kg/year 438 1 095 2 190 3 285 4 380

RECIRCULATION

PUMPING STATION Throughput m 3 /h 8.0 20 40 60 per unit Pump number u 2.0 2.0 2.0 2.0 TRICKLING FILTER Filter 87 87 87 87 87 efficiency (ad2 Raw water) Expanded surface area to be m 2 2 600 6 600 13 000 20 000 26 000 provided Diameter m 3.2 4.1 5.1 6.2 6.4 Minimum throughput of the re- m 3 /h 8.0 20 40 60 circulation pump Production of kg SS/d 13.4 33.5 66.9 100.4 133.9 nonstabilized sludge SECONDARY LIFT

STATION

Throughput for pumping to the m 3 /h 15 38 56 56 56 compartments

FILTRATION,

RHIZOCOMPOSTING

Rhizocomposting compartment u 3 3 4 6 8 number Surface area per unit of the com- m 2 30 74 112 112 112 partments Compost m 3 /year 16 40 79 119 159 production I I I 1 _1_1 0 0 0000

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0@ S. S 7- As regards the use of space, the total surface areas which have to be employed, on the one hand in the previous techniques and on the other hand in a plant according to the present invention employing a trickling filter combined with filtrationrhizocomposting compartments, are shown in Table 2 below. In this table, "DG" denotes a draining grating, for example as defined in FR-A-2 754 191.

Table 2 Capacity le 200 500 1. 000 1 500 2 000 Buried filters m 2 500 1 175 2 300 3 425 4 550 Infiltration m 2 750 1 725 3 350 4 975 6 600 Percolation Natural m 2 4 500 11 250 22 500 33 750 45 000 lagooning Trickling filters m 2 300 750 1 500 2 250 3 000 Clarif DG Activated sludge Clarif m 2 200 500 1 000 1 500 2 000 DG Filters planted with reeds, two m 2 600 1 500 3 000 4 500 6 000 stages_____ Trickling filter Mn 2 140 350 700 1 050 1 400 Rhizocomposting filter___ It clearly emerges, on examining this Table 2, that the technique provided by the invention occupies 15 very little space, which gives it a significant advantage in comparison with the other techniques, in particular in comparison with lagooning and with any technique in which filtration is involved in the treatment of the effluents.

Table 3 allows the capital costs of the plants according to the invention to be compared with those of the plants according to the other treatment routes. The values shown in Table 3 correspond to relative costs Sexpressed with respect to the most expensive scenario, arbitrarily assessed at 1 000.

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0000 0, *0 0 0 *000 00 00 -8- Table 3 Capacity 200 le 500 l e 1 000 le 1 500 le 2 000 le Buried 1 000 847 f ilters 1 Natural 840 445 290 245 230 lagooning Infiltration 735 460 260 200 185 Percolation Trickling 795 380 290 245 230 filters Clarif DG Silo Activated 655 410 320 275 260 sludge Clarif DG +4 Silo Filters planted 550 380 275 245 230 with reeds (2 stages) Trickling 520 320 260 230 215 filter Rhizocomposting filter The price ratios mentioned above are given by 5 way of indication, with the objective of observing the abovementioned standards, apart from the lagooning technique (specific standard on samples of the prefiltered discharge) As regards the activated sludge technique, reference is made to a treatment of the prolonged aeration type. For plants with a capacity of less than 500 le, no account is taken of dynamic thickening (for example "IDG" or other similar techniques).

It clearly emerges from Table 3 that the technique introduced by the present invention is particularly advantageous for plants of less than or equal to 1 000 lIe in size. Furthermore, it should be noted that the cost of the land was not taken into consideration in these cost evaluations, which may prove to be a determining parameter in the choice of a solution which will be adopted. In this respect, the technique according to the present invention has decisive advantages in the case of a high price of MINI land.

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0£* 0 00.0 00* 00 0 00 0 9 Table 4 below allows the operating costs of purification plants of different capacities according to the present invention to be compared with those of purification plants of the same capacity according to the previous techniques. The approximate operating costs per year and per inhabitant equivalent (expressed as a ratio with respect to the highest operating cost) are given in Table 4.

Table 4 Capacity 200 Ie 500 Ie 1 000 Ie 1 500 Ie 2 000 Ie Activated 1.00 0.70 0.44 0.39 0.34 sludge Trickling 0.66 0.43 0.26 0.22 0.19 filter Rhizofilter Natural 0.36 0.20 0.17 0.15 0.14 lagooning Infiltration 0.32 0.23 0.21 0.20 0.19 Percolation Filters planted 0.23 0.16 0.15 0.14 0.13 with reeds (2 stages) Trickling filter Rhizo- 0.44 0.21 0.17 0.13 0.11 composting filter It clearly emerges from reading the preceding description that the invention introduces a process and a plant for the treatment of effluents with an 15 optimized scale which makes it possible to reduce the capital and operating costs, while benefiting from the advantages of each of the treatment stations (trickling filter and rhizocomposting filters), this being particularly true as regards the second station, in which the filtration of the effluents originating from the trickling filter and the composting of the sludge phase are simultaneously provided.

The process and the device which are a subjectmatter of this invention make it possible to obtain a stabilized and non-fermentable sludge which is convenient to employ, in particular in carrying out 10 backfilling operations, in agricultural applications, and the like.

Of course, it remains that the present invention is not limited to the implementational examples described and/or represented here but that it encompasses all the alternative forms thereof coming within the scope of the invention as defined by the claims.

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Claims

1. Process for the treatment of effluents from communities of 500 to 2000 le (inhabitant equivalent), by employing filters planted with reeds, wherein it comprises: carrying out a biological treatment of the effluent using a trickling filter, and removing the suspended matter in the effluent thus treated and simultaneously treating the sludge by filtration-composting on filters planted with Phragmites australis.

2. Plant for the implementation of the process according to claim 1, wherein it comprises: a trickling filter comprising at least one stage in which the effluent to be treated is received, and at least one filtration-composting compartment fed from the trickling filter, each of the said compartments comprising successive layers of filler materials and of sand and 15 their upper surfaces being planted with Phragmites australis.

3. Plant according to claim 2, wherein the dimensions of the trickling filter are determined according to the treatments for removal of pollution from the effluent to be carried out.

4. Plant according to claim 2, wherein it comprises at least three filtration-composting compartments.

Plant according to either one of claims 2 and 4, wherein the maximum surface area per unit of each of the filtration compartments is of the order of 100 to 150 m 2

6. Plant according to any one of claims 2, 4 and 5, wherein the surface area of the filtration-composting compartments is from approximately 0.4 to 1 m 2 per le. P:\OPER\Jgc\2386790cms 196 doc-16O8/02 -12-

7. Plant according to any one of claims 2 to 6, wherein automatic control is additionally provided in order to ensure feeding of the filtration-composting compartments in rotation.

8. Device according to any one of claims 2 to 7, wherein it comprises a means for the pre-treatment of the effluents before they are passed onto the trickling filter for the purpose of removing waste.

9. Device according to claim 8, wherein the said means is composed of a sieving :system having a mesh size of the order of 3 mm.

Device according to claim 8, wherein the said means is composed of a screening system exhibiting a mesh size of the order of 6 mm.

11. Device substantially as hereinbefore described with reference to the examples DATED this 16th day of August, 2002 Suez-Lyonnaise Des Eaux 20 by DAVIES COLLISON CAVE Patent Attorneys for the Applicant