IE920784A1 - Effluent treatment systems - Google Patents

Abstract

In an effluent treatment system, effluent to be treated passes initially through a primary stage (1) in which it undergoes primary settlement (13) and anaerobic treatment (14). The substantially liquid effluent is withdrawn from stage (1) by means of a balanced flow arrangement (5, 6) to provided a uniform rate of withdrawal of effluent from stage (1) for downstream treatment in subsequent stages of the system. Secondary treatment (21, 41) consists of a succession of aerobic treatment stages (22a-22f; 42a-42d, 42f). At least one nitrification sub-stage (47e) is also provided during secondary treatment (21, 41), sub-stage (47f) representing a de-nitrification sub-stage. The effluent then passes (48) to clarification and settlement stage (62) before entering a disinfectioon stage (64) by way of a filter (65). The treated effluent is withdrawn from stage (64) by a pump (66) for dispersal (67, 71, 72, 73) directly into the soil of an area of land. The system incorporates features (81-89; 91-94) for withdrawal of sludge and/or active biological matter entrained in liquid from sub-stages (62, 42f) for selective return and redirection to primary settlement stage (13) in the case of sludge and to one or more secondary treatment sub-stages (22a, 42a, 42c, 42f), in the case of active material entrained in liquid.

Description

This invention relates to effluent treatment systems. In particular, the invention relates to effluent treatment systems for use in situations where a conventional septic tank is either inadequate or unacceptable, but system demand does not justify a fullscale sewage treatment plant of traditional kind.

Irish Patent Application No. 507/89 of Biocycle Pty Limited provides water treatment apparatus providing for one-tank treatment of domestic sewage in substitution for a traditional septic tank. According to this patent application, there is provided a septic tank assembly having a primary outer tank with a cylindrical wall.

Within the primary outer tank, there is nested a second tank, also of cylindrical configuration. A dividing partition extends diametrically across each tank, to divided the two tanks up into four chambers which carry out, respectively, anaerobic, aerobic, clarification and disinfectant treatment steps. The arrangement includes an air pump and conduits for delivering air to the aerobic chamber, as well as a dispenser to discharge disinfectant material - 3 into the disinfection chamber in measured amounts. In the aeration chamber, where the aerobic treatment takes place, a medium to promote the growth of bacteria is suitably provided. This medium preferably consists of a plurality of partitioned corrugated sheets.

The invention of this patent application provides a compact and effective treatment unit especially suited to the processing and handling of domestic sewage. The system does not readily scale up to provide a plant suitable for small scale commercial and industrial use, such as for interpretative centres, club houses, for example, golf clubs, caravan parks, and the like. While it is possible to provide a multiplicity of individual units of the kind described by the above patent specification, to work in parallel, the economics of such an arrangement are however generally adverse.

It is accordingly an object of the present invention to provide an improved effluent treatment system suitable for relatively small scale industrial and/or commercial application of the kind identified above, in which the advantages of the unit of Application No. 507/89 are retained, but operating within a favourable technical and commercial configuration.

According to the invention, there is provided an effluent treatment system comprising: (a) at least one anaerobic primary treatment tank, (b) at least one compartmented treatment tank iii which at least one compartment contains a bacteria growth medium, and (c) at least one tank containing a settling chamber.

Preferably the system according to the invention comprises at least two compartmented treatment tanks. At least one of said at least two compartmented treatment tanks is suitably an aerobic treatment tank. Input of air to said aerobic treatment tank may be effected by discharge of air from air ducts located in the region of the base of the tank. At least one of said at least two - 4 compartmented treatment tanks may also a de-nitrification tank to which there is substantially no input of air.

In a further variant, a system according to the invention 5 may comprise at least two anaerobic primary treatment tanks.

Preferably, at least one anaerobic primary treatment tank comprises an internal baffle.

In a favoured arrangement, the system according to the 10 invention comprises means for returning sludge from said settling chamber to said at least one anaerobic primary treatment tank.

Said sludge returning means suitably comprises a sludge pump, and said sludge pump is preferably intermittently activatable to effect return of sludge from said settling chamber to said at least one anaerobic primary treatment tank.

According to another advantageous construction of the system according to the invention, said at least one tank containing the settling chamber may be partitioned to provide a first region defining said settling chamber and a second region defining a pre-discharge portion of said tank. Suitably, said settling chamber comprises substantially two-thirds of the internal volume of said tank.

In any variant of the system of the invention, communication may be effected between the tanks of the system by duct means commencing and terminating in tank regions such that dead spots in fluid flow are substantially minimised and a dynamic circulatory action is achieved.

At least two of the tanks of a system according to the invention are suitably sealed to the exterior environment and means are then provided enabling communication between said at least two tanks for transfer of gases present in the tanks above the liquid level within the tank system. - 5 According to a particular feature of an effluent treatment system according to the invention, a multiplicity of compartments of said at least one compartmented tank contain bacteria growth medium. In a favoured arrangement, all of the compartments of said at least one compartmented tank contain bacteria growth medium.

Said bacteria growth medium suitably comprises a plurality of partitioned corrugated sheets.

The invention also provides for any or all of the tanks of the system to be present either singly or in multiple. Thus not only may the system comprise two or more anaerobic primary treatment tanks, working in parallel, but multiple tanks for aerobic treatment or de-nitrification may also be provided, connected in parallel. In addition, two or more settling chamber tanks may also be provided, again to work in parallel.

An embodiment of the invention will now be described having regard to the accompanying drawings, in which: Figure 1 is a pictorial representation of an installation according to the invention, Figure 2 is a schematic cross-sectional top view of the system of Figure 1, showing the internal arrangements within the various tanks, Figure 3 is a schematic flow diagram showing the progression of the treatment stages carried out within the plant of Figures 1 and 2, Figure 4 is a detailed view of an air diffuser used in the aerobic treatment stage of the system of the invention, and Figure 5 is a side view of a Tee piece used for 35 intercommunication between the treatment chambers or tanks of the /f 920784 - 6 system of Figures 1 and 2.

As shown in Figure 1, a system 1 according to the invention comprises four tanks 2 to 5. Tank 1 is a primary treatment tank in which the effluent passes through an anaerobic stage. Tanks 3 and 4 provide first and second aerobic treatment stages, or alternatively, tank 4 may provide for de-nitrification, without input of air.

Finally, tank 5 provides a settling and discharge feature, from which sludge return to the first tank may also take place. Each tank is of substantially cylindrical configuration having a side wall6 and is closed at the top by a respective cover 7.

Referring now to Figure 2, primary anaerobic treatment tank has a main soil inlet 11, a transverse baffle 12 extending from side wall 6 of the tank across the greater part of a diameter of the tank, and an outlet 13. The inlet 11 and outlet 13 are located approximately 135° apart, and the transverse baffle 12 substantially bisects this angular separation, so as to divide the chamber defined by tank 2 into two haIf-chambers, communication between which takes place on the opposite side of the chamber from the 135° sector, so as to substantially maximise flow through the half-chambers and engender active biological processes within the material to be treated.

From outlet 13, liquids separated from solids in tank 2 flow to first aerobic treatment tank 3, entering through inlet 21. Tank is divided into two semi-cylindrical regions by a diametrical partition 22. A further sub-division into two concentric cylindrical regions is provided by an inner cylindrical partition 23, itself in turn also bisected into two semi-cylinders by the diametrical partition 22. Outer diametral partition portions 24a and 24b further sub-divide the sectoral cylindrical spaces between the tank wall 6 and the inner cylindrical partition 23 into smaller sectoral compartments. The end result of this internal construction is to define a plurality of compartments 25a to 25f through which the - 1 liquid to be treated flows in succession. The four outer compartments are sectoral portions of a generally annular configuration, while the inner compartments 25c and 25d are semi-cylindrical. Flow takes place between the respective compartments at points indicated by references 36a through 36e.

These flow communication locations are alternately at a high level or a low level from compartment to compartment, again so as to maximise turbulence of flow through the system and to minimise any inclination for the development of dead spots or stagnant eddies or vortices.

The succession of flow communication point levels is further described in connection with a subsequent Figure.

In order to advance aerobic treatment, diffusers 27 provide for the dissemination of air bubbles into the liquid to be treated in each of the various compartments. Each compartment is also suitably charged or packed with bacteria growth medium, suitably in the form of blocks 28 comprising a plurality of partitioned corrugated sheets, such as are described in Patent Application No. 507/89. Discharge from aerobic treatment tank 3 takes place through outlet 29, from compartment 25f.

A further stage of aerobic treatment takes place in tank 4, which is essentially identical with tank 3 already described. Precisely the same reference numerals are used for the features of this tank as for those of tank 3, but in the series 31 to 39, as compared with 21 to 29. The sequence of high or low' in the flow communication locations between the successive compartments is however reversed as compared with the sequence of tank 3, as will be described in connection with Figure 3. The treated liquids leave tank 3 via outlet 39 and then pass into tank 5, where settling and final discharge takes place.

Liquids entering tank 5 through inlet 41 enter a clarification and settlement chamber 42 defined between a partition 43 and the wall 6 of tank 5. Partition 43 divides tank 5 into two - 8 regions, the chamber region 42 comprising substantially two-thirds of the internal volume of the tank and a final discharge region 44 occupying approximately one-third of the tank volume. Any solid matter remaining in the treated material at this stage settles out in chamber 42 and is returned to primary tank 2 by means of a sludge return line or conveyor 45. Preferably this return line includes a sludge pump or other sludge collection means, identified by references 46. Where return is accomplished by a sludge pump, suitably the sludge pump operates at intermittent intervals, such as for a short period during each day of system operation.

Following clarification and settling, the remaining fluid material passes into the discharge region 44 by way of a filter 47.

A discharge pump 48 then transfers the liquid, again on a intermittent basis, to an irrigation line 49, for disposal by spraying onto vegetable material, or by discharge into a suitable soak-away region.

Figure 3 is a schematic representation of the flow path of materials to be treated passing through the system of the invention, in which the tanks have as it were been rolled out to be represented as linear structures, rather than in terms of the circular or cylindrical arrangements shown in Figure 2. This representation is particularly advantageous in showing the sequence of movement of material to be treated through the aerobic treatment tanks 3 and 4. The alternating sequence of high and low transfer points between the successive compartments will be noted, as also the fact that the alternation of this sequence is reversed as between tanks 3 and 4.

At each input and discharge point to a respective tank, the feed or discharge line is suitably brought in at a point within the tank such that turbulence and biological action will be maximised and dead points or stagnant regions within the fluid flow minimised. In order to achieve this in for example the aerobic tanks 3 and 4, where the inlet points are located at a substantially central location in - 9 the walls of the initial compartments 25a and 35a, the inlet pipes may be carried down diagonally to a corner region of their respective compartment for discharge of liquid being transferred. Similar provisions may be made at discharge locations.

Figures 4 and 5 show in schematic form the air diffuser head 27 or 37 used in tanks 3 and 4 and also a Tee piece arrangement for use at the points of communication between the respective tanks. As shown in Figure 3, the diffuser head arrangement provides a downwardly extending air pipe 52, at the end of which a Tee piece arrangement terminates in bubble discharge features 53. Figure 5 shows a Tee piece arrangement for use at the various inlet and outlet connections, 21, 29, 31 and 39. Since the tanks are sealed against the external environment, a Tee piece 61 is provided at the upper end of each downwardly extending inlet or outlet pipe portion 62, the stub end of the Tee piece being open to the gas space above the liquid level within the respective tank. In this manner, any build up of gas pressure within one tank can be communicated to the other tanks of the system, and thereby any inhibition of fluid transfer is prevented.

In use of the system of the invention, the soil enters the primary tank 2. Separation of solid matter takes place, but the build-up of solid matter within this tank is relatively slow, because of the highly active biological processes taking place within the system. Fluid material advances to the treatment tank’s 3 and 4, where the presence of the biological medium 28, 38 ensures a very active progression of the purification processes, this being further advanced by the convoluted flow path and the general turbulence of flow through these tanks. Treated fluid then enters the clarification and settlement chamber 42, where any remaining solids are deposited. The sludge conveyor provides for return of any such solids to the primary tank 2. The accumulation of solids in the clarification region 42 is however relatively modest, and intermittent and short-term operation of the sludge conveyor is quite - ίο sufficient to achieve the desired result of keeping chamber 42 substantially clear of sludge. The quality of final liquid output from the system is very high and is accepted by the competent Standards Authorities as appropriate for disposal by soakage or spray onto vegetation.

As an alternative to the sludge pump, a Venturi type arrangement may be provided. Suitably, the tanks are approximately 2.2 metres in diameter, but this dimension is not to be regarded as limiting. The nested partition arrangement described in respect of tanks 3 and 4 is also in no way limiting, and alternative arrangements may be provided, within the parameters of the invention.

The second aerobic treatment tank of Figure 2, tank 4, may also be adapted for de-nitrification, by having no air input to the material to be treated. In tank 5, the final settlement and discharge tank, the filter between the two regions of the tank may be adapted to provide water of substantially drinking water quality at the final exit from the system. This arrangement may serve as an alternative to the irrigation or soakage arrangement previously described. In the case of irrigation, discharge of effluent by by spray over suitable plants enables speedy evaporation of the material. With this arrangement, a disposal rate of up to 5 litres per square metre per day is acceptable.

Any or all of the tanks of the system may also be doubled-up, by providing two tanks operating in parallel, to enhance the capacity of the system. The capabilities of the system may be still further raised by placing three, four or more tanks in side by side multiple operation, again connected in parallel.

Claims (5)

1. An effluent treatment system comprising: (a) at least one anaerobic primary treatment tank, 5 (b) at least one compartmented treatment tank in which at least one compartment contains a bacteria growth medium, and (c) at least one tank containing a settling chamber.

2. A system according to Claim 1 comprising at least two 10 compartmented treatment tanks.

3. A system according to Claim 2, wherein at least one of said at least two compartmented treatment tanks is an aerobic treatment tank.

4. A system according to Claim 3, wherein input of air to said aerobic treatment tank is effected by discharge of air from air ducts located in the region of the base of the tank. 20 5. A system according to any of Claims 2 to 4, wherein at least one of said at least two compartmented treatment tanks is a de-nitrification tank to which there is substantially no input of air 6. A system according to any preceding claim comprising at 25 least two anaerobic primary treatment tanks. 7. A system according to any preceding claim, wherein said at least one anaerobic primary treatment tank comprises an internal baffle. 8. A system according to any preceding claim, comprising means for returning sludge from said settling chamber to said at least one anaerobic primary treatment tank. 35 9. A system according to Claim 8, wherein said sludge returning •Ε 920784 - 12 means comprises a sludge pump. 10. A system according to Claim 9, wherein said sludge pump is intermittently activatable to effect return of sludge from said 5 settling chamber to said at least one anaerobic primary treatment tank. 11. A system according to any preceding claim, wherein said at least one tank containing the settling chamber is partitioned to 10 provide a first region defining said settling chamber and a second region defining a pre-discharge portion of said tank. 12. A system according to Claim 11, wherein said settling chamber comprises substantially two-thirds of the internal volume of 15 said tank. 13. A system according to any preceding claim, wherein communication is effected between the tanks of the system by duct means commencing and terminating in tank regions such that dead spots 20 in fluid flow are substantially minimised and a dynamic circulatory action is achieved. 14. A system according to any preceding claim, wherein at least two of the tanks are sealed to the exterior environment and means are 25 provided enabling communication between said at least two tanks for transfer of gases present in the tanks above the liquid level within the tank system. 15. A system according to any preceding claim, wherein a 30 multiplicity of compartments of said at least one compartmented tank contain bacteria growth medium. 16. A system according to any preceding claim, wherein all of the compartments of said at least one compartmented tank contain 35 bacteria growth medium. - 13 17. A system according to any preceding claim, wherein said bacteria growth medium comprises a plurality of partitioned corrugated sheets.

5. 18. An effluent treatment system substantially as described herein with reference to and as shown in the accompanying drawings