GB1563106A - Purification of water used in vehicle washing equipment - Google Patents

Description

(54) PURIFICATION OF WATER USED IN VEHICLE WASHING EQUIPMENT (71) We, KIRTON ENGINEERING LIMITED, a British Company, of Leicester Road, Shepshed, Leicestershire, LE12 9EG, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to vehicle maintenance and has an an object the provision of a new and improved method of and apparatus for the recovery of water used in vehicle washing equipment.

In accordance with the present invention there is provided a method of treating the effluent water containing a bio-degradable detergent and solid matter from vehicle washing equipment of the kind in which the water containing the detergent is used in such a manner as to produce substantial aeration thereof, which method comprises forming a mixture of the aerated effluent water with a flocculating agent of the polymeric type, passing the mixture through a sedimentation zone and allowing flocculated solids to sediment within said zone during said passage to produce a stream of water of a reduced solids content and treating the water of reduced solids content with an adsorption agent.

A flocculating agent of the polymeric type, of which a well-known example is a polyacrylamide, is different in its behaviour from flocculating agents of the simple ionic type such as the alums. It produces comparatively large flocs and it is believed that the action depends upon providing mechanical bridging m addition to electrical bridging. Polymeric flocculating agents are used in a wide range of applications and the present invention is based upon the discovery that when applied to the highly aerated effluent water from vehicle washing equipment, the use of such a flocculating agent results in a considerable diminution of the content of biodegradable detergent. In one case where measurements were made it was found that the content of detergent was reduced from 46 to 6 parts by weight of detergent per million. It is suggested that some biological action involving organisms present in the soil normally accumulated by motor vehicles is involved in the mechanism and also that the hydrocarbon component inevitably present in the effluent may have an effect. Even so, the composition of the soil is clearly not highly critical, especially when averaged over a number of vehicles, the effect not being noticeably seasonal or dependent upon temperature or other weather conditions in which the soil has been accumulated.

The considerable reduction of the detergent content renders the water of reduced solids content suitable for re-use as wash water (with added detergent). More importantly, substantial removal of the residual detergent by adsorption, conveniently using a bed of activated carbon which also acts as a filter, is rendered feasible. The carbon-treated water is readily obtainable in such a detergent-free condition as to be usable in a rinsing step of the washing apparatus.

Vehicles are frequently polished with a wax-like material having cationic properties. The preferred biodegradable detergents are anionic and act with the cationic wax-like materials to form a stable colloidal precipitate in the effluent. This precipitate is difficult to coagulate, it does not flocculate in the presence of the liquid polymeric flocculating agent and it is not removed by a bed of activated carbon as aforesaid. It is however found to be readily removable from the effluent from the carbon bed by passage through a bed of diatomaceous earth.

The sedimentation effect is obtained with such ease that, in spite of the amount of water used per vehicle, the sedimentation zone may be of convenient dimensions and readily accommodated in an assembly also containing activated carbon and diatomaceous earth treatment devices, occupying an area small enough for practical purposes adjacent to the vehicle-wash site. In spite of the small area occupied by the unit, thorough treatment of the effluent is achieved. The only fresh water requiring to be added is that required to make up natural loss by evaporation, as residual water on vehicles and flung spray. No routine discharge to waste is required. Generally, with an outdoor washing equipment, water has to be discharged to waste only to allow for rain water collected on the site. The discharge can be to the surface of the site, no direct connection with a sewer system being necessary.

Further in accordance with the present invention there is provided a vehicle washing installation which comprises vehicle washing equipment using water containing a biodegradable detergent in such a manner as to produce substantial aeration of the water and providing an aerated effluent containing said detergent and solid matter, means for collecting the aerated effluent from the washing equipment, a source of liquid polymeric flocculating agent for addition to the collected aerated effluent, a sedimentation unit and one or more adsorption units for treating the water of reduced solids content obtained from the sedimentation unit. Preferably there are two adsorption units, one filled with activated carbon and the other with diatomaceous earth.

It is preferred to use a sedimentation unit containing a structure having walls which divide the flow of effluent into a number of shallow streams so that the sedimenting material is collected on the walls after travel only through a correspondingly reduced depth of liquid.

Having the walls inclined and running upwardly from the bottom to the top of the structure gives a simple arrangement. Complex inlet and outlet manifolds are avoidable by arranging for the structure to guide the flow of effluent upwardly through a containing tank which may be open at the top.

Good results are obtained using a structure in the form of a set of spaced-apart plates, preferably corrugated plates with the corrugations running in the direction of the flow.

Improved results are obtained using a cellular structure formed of cell walls which define therebetween a set of channels for the passage of the streams of effluent, said channels having a cross-sectional shape such that they narrow in the downwards direction. For compactness of construction the cross-sectional shape of the channels may be such that the channels together form a close-packed array, a square or other rhombic cross-sectional shape being convenient and preferred. A rhombus narrows in the directions of its diagonals.

The rhombic, or other, cellular structure is preferably formed of a set of plate members mounted together and having a surface configuration such that each plate provides cell walls for a row of cells. A regular zig-zag configuration would give truly rhombic channels. It is desirable in practice to secure the plate members together and for this purpose they may be provided with mating flats. These flats give the channels a cross-sectional shape which is strictly hexagonal rather than truly rhombic. The width of the flats may however, in practice, be trivial.

In a convenient construction the plate members may be formed of glass-fibre reinforced plastic material and secured together by a cold cure adhesive to form the cellular structure.

It is found that improved results are obtainable by distributing the flocculating agent in the effluent in a manner such as to minimise turbulence in the mixture. The chain length of the flocculating agent may be such that the molecular weight is of the order of 30 million and it is believed that turbulence can break the chains and so reduce the efficacy of the bridging effect.

A convenient arrangement is to feed the effluent through a conduit having discharge ports and a configuration such that the discharge ports communicate with an inlet part of the sedimentation unit at distributed positions. The flocculating agent is advantageously fed to the conduit at a number of positions between the discharge ports, thereby providing evenness of the feeding of the flocculating agent to the inlet part.

The following description in which reference is made to the accompanying diagrammatic drawings is given in order to illustrate the invention. In the drawings: Fig. 1 shows a vehicle wash station, Fig. 2 is a diagrammatic cross section of an effluent treatment apparatus installed at the wash station, Fig. 3 shows a modification of the apparatus of Fig. 2, Fig. 4 shows a further modification of part of the apparatus, said modification incorporating a cellular structure, Figs. 5 and 6 show parts of the cellular structure of Fig. 4 in further detail.

Fig. 7 shows another modification of the apparatus said modification having an improved arrangement for mixing the flocculating agent with the effluent, and Fig. 8 shows part of the arrangement of Fig. 7 in further detail.

Referring to Fig. 1, a vehicle 1 is shown standing in a washing position upon a concrete pad 2 formed in a manner known to collect wash and rinse water and lead it to an underground reservoir 3 via a coarse filter compartment 4 which retains coarse matter such as stones, paper or cigarette ends. A washing device is indicated at 5. This washing device may be of any suitable type, the type preferred being of the kind having three rotary mops, one for each side of the vehicle and one for the top, and control apparatus for moving the mops along the vehicle from one end to the other whilst following its contours. The mops, which are fed with wash or rinse water, have very long strips of flexible material, e.g. woven cotton fabric, which extend by centrifugal action to contact the vehicle in an adaptable manner.

Used water, usually a mixture of wash and rinse water from several vehicles, is pumped from reservoir 3 through line A (Fig. 1) by a pump 6 (Fig. 2) to the inlet part 7 of the treatment apparatus. Adjacent to inlet part 7 is a metering device 8 for dispensing a liquid polyacrylamide flocculating agent from a supply tank 129. Part of the used water is passed to device 8 by means not shown, to receive a controlled proportion of the flocculating agent, and thence to inlet part 7.

The water passes through sedimentation compartment 11 and is delivered with a reduced solids content over an adjustable weir 12 into a tank 13. Water for washing purposes may be pumped from tank 13 back to the washing device 5, via line B.

Water of substantially detergent-free quality for rinsing purposes is obtained by pumping water from the bottom of tank 13 by pump 19 via line 20 and through a pressure filter 21 containing granular activated carbon for delivery via line 22 to rinse water tank 23 from which it may be pumped via line B. Tank 23 has an overflow 24 leading to waste. Line B is connected with tank 13 or tank 23 by solenoid valves as required.

Provision is made for back-washing carbon bed 21 by operating valves 26. Line 27 conveys the wash water to inlet part 7 for recycling.

Sedimentation compartment 11 is provided in its upper portion with a series of nine mutually parallel plates 28 inclined at 35C from the horizontal. These plates are formed from corrugated polyvinyl chloride sheeting of the type used for roofing purposes. The bottom of the sedimentation compartment is constituted by two sloping bottom walls 29 and 30. Water entering the compartment at inlet part 7 passes downwardly under a baffle 31 and rises up between plates 28 at a low linear rate of flow. Flocculated soil is deposited on the plates and eventually falls into the bottom 32 of the compartment where it forms a sludge which is cleared periodically through sludge cock 33, e.g. into a visiting tanker at intervals of a few weeks.

Weir 12 is set at such height that the top ends of plates 28 are always submerged. It maintains a substantially uniform distribution of flow across the width of the tank.

The shape of the bottom 32 of the sedimentation compartment leaves a space 34 for housing the pumps 6 and 19 as shown in Fig. 2. Pump 6 draws soiled water directly via lineA from reservoir 3 and delivers it by a pipe 35 to a transverse distributor pipe 36 which feeds it to inlet part 7.

Pump 6 is brought into operation by a float switch 37 when the level of treated water in tank 13 falls. The rate of pumping is such that satisfactory sedimentation is obtained in the compartment 11. This rate may be substantially less than the rate at which water is collected in reservoir 3. Reservoir 3 serves as a buffer store and removes any need for short term synchronisation of the water treatment with the washing and rinsing of vehicles provided that tanks 13 and 23 are sufficiently large.

Using the commercially available liquid polymeric flocculating agents of the polyacrylamide type in an amount of 5 ml. per 10 gallons (Imperial), satisfactory treatment of water containing suspended solids in an amount of up to 500 parts by weight per million is obtained with a plate area of 6 square feet per gallon per minute of water treated.

The modified apparatus of Fig. 3 has a pump 36 which draws carbon-bed treated water from tank 23 via line 37 and passes it via line 38 and a pressure filter 39 which it leaves via line 40 to enter a further tank 41 provided with an overflow 22'. Pressure filter 39 is filled with a bed of diatomaceous earth which effectively removes any colloidal precipitate derived from cationic wax-like polishing material as aforesaid. The quality of the pre-treated water passed through the diatomaceous earth bed is such that the bed has a usefully long life before re-charging is required.

Fig. 4 shows a modification of the effluent treatment apparatus. A tank 101 shaped as shown, is divided by a weir 102 to form a treatment section and a treated water receiving section 103 from which treated water may be withdrawn via outlet 104 for treatment in an adsorption apparatus (not shown). The water level in the treatment section is determined by the height of the weir 102. Water to be treated is fed at 105 into a receiving section 106 defined by a baffle 107 the top edge 108 of which projects above the water level and the bottom edge 109 of which is clear of sloping base part 110 of the tank. The water passes downwardly in section 106 and flows through upwardly extending channels in a cellular structure 111 arranged as shown.

Cellular structure 111 is formed from plate members of glass fibre reinforced plastic material formed by the wet lay up method. Part of structure 111 is shown in transverse cross-section in Fig. 5. As will be seen the plates are configured to provide generally square channels 112 therebetween. The plates are joined together by a cold-cure resinous adhesive and are formed with narrow flats 113 to provide mating surfaces. As will be seen, the channels converge in the direction of the arrows 114 of Fig. 2. The direction of these arrows is shown at 114' in Fig. 1. As the water ascends through the channels the soil settles in the lowermost (flattened) corners of the channels and eventually descends in the corners, (in the opposite direction from the liquid flow) to accumulate in the bottom of the tank at 115 from which it may be withdrawn periodically via sludge cock 116.

Satisfactory descent of the sludge depends upon having the channels smooth in the regions of their lowermost corners. For this reason the plates are produced using male and female moulds, and they are positioned in the cellular structure with the surfaces formed in contact with the moulds facing upwardly.

With car wash water to which has been added a polymeric flocculating agent, a cellular structure arranged as shown can give a settling rate of more than twice the rate obtained with a cellular structure having square channels of similar size but oriented with their sides, rather than their corners, lowermost.

Fig. 6 is an enlarged elevation of the cellular structure 111. The plates are formed without mitred edges, so that the surfaces with which the channels 112 communicate have a stepped configuration.

In the modification shown in Figs. 7 and 8 weir 1 08a is shaped as shown to provide a wide space at the top of compartment 106a for the accommodation of a distributor 170 supplied via pipe 171 with flocculating agent from a metering pump P of the piston type and with effluent via a pipe 172 (Fig. 8).

The distributor is formed, as shown in Fig. 8, of four lengths 173 of wide diameter perforate tubing formed with large discharge ports and connected as shown by three elbows 174 and a tee-piece 175 to form a square. Pipe 171 feeds in the flocculating agent via branch 176 to the tee-piece, via branches 177 to two of the elbows and itself terminates in a feeding connection 178 with the third elbow. In this way, mixing of the flocculating agent with the effluent is obtained in an improved manner. The tendency of shearing forces to break the long chain structure of the flocculating agent, and so reduce its efficiency is minimised.

Polymeric flocculating agents of the polyacrylamide and other types have polar groups distributed along the chain length which normally corresponds with a molecular weight of at least 100,000. Such polar groups may be acidic groups giving the flocculating agent anionic properties, or basic groups giving cationic properties. For example an anionic agent may be produced by co-polymerising acrylamide and acrylic acid or by the partial hydrolysis of polyacrylamide homopolymer.

A cationic agent is obtainable by copolymerising acrylamide with a quaternary ammonium acrylamide or polyacrylamide.

Other flocculating agents may be prepared by chemical modification of other linear polymers such as polymers of the nylon or alkyd type during or after polymerisation.

Various polymeric flocculating agents are available commercially under various trade names. In many cases the manufacturers do not reveal their constitution but the most suitable for present purposes, viz. the efficiency of removal of the detergent during the flocculation and sedimentation steps is readily ascertainable by simple routine experiment. Important trade names in the field are Decapol*, Magnafloc*, Nalfloc*, Purifloc*, Malcolyte, Catfloc and Superfloc*. The words indicated by asterisks are registered Trade Marks.

Test results which have been obtained using apparatus as described herein are given in the following table. In the Table SS represents suspended solids, BOD represents biological oxygen demand, COD represents chemical oxygen demand (all in milligrams per litre), AD and CD represent anionic detergent and cationic detergent respectively.

Water after Water after Effluent from flocculation adsorption by Polymer Type Car Wash & sedimentation carbon bed Cationic Polyacrylamide SS 2326 18 5 BOD 2500 60 25 COD 3780 100 32 AD 46 6 0.6 Cationic Polyacrylamide SS 2642 24 7 BOD 2420 54 21 COD 3450 90 28 CD 54 7 0.5 Anionic Polyacrylamide SS 2987 27 6 BOD 2340 45 17 COD 2950 84 25 AD 75 8 0.7 Polyamide SS 3254 36 8 BOD 2870 45 20 COD 3570 95 30 AD 38 5 0.4 Polyalkylene Imine SS 3480 32 8 BOD 2530 80 30 COD 4200 120 40 AD 65 10 1

Claims (34)

WHAT WE CLAIM IS:

1. A method of treating effluent water containing a bio-degradable detergent and solid matter from vehicle washing equipment in which the water containing the detergent is used in such a manner as to produce substantial aeration thereof, which method comprises forming a mixture of the aerated effluent water with a flocculating agent of the polymeric type, passing the mixture through a sedimentation zone and allowing flocculated solids to sediment within said zone during said passage to produce a stream of water of a reduced solids content and treating the water of reduced solids content with an adsorption agent.

2. A method according to claim 1 in which the flocculating agent is a polyacrylamide.

3. A method according to either of claims 1 or 2 in which the adsorption agent is activated carbon.

4. A method according to any one of claims 1 to 3 in which part of the water of reduced solids content is re-used, with added detergent, as wash water.

5. A method according to any one of claims 1 to 4 in which water is passed through a bed of diatomaceous earth after its treatment with the adsorption agent.

6. A method according to any one of claims 1 to 5 in which the sedimentation zone contains a structure having walls which divide the flow of mixture into a number of shallow streams.

7. A method according to claim 6 in which the walls are inclined and run upwardly from the bottom to the top of the structure.

8. A method according to either of claims 6 or 7 in which the structure is arranged to guide the flow of mixture upwardly through a containing tank.

9. A method according to any one of claims 6 to 8 in which the structure is in the form of a set of spaced-apart plates.

10. A method according to claim 9 in which the plates are corrugated with the corrugations running in the direction of flow of the mixture.

11. A method according to any one of claims 6 to 8 in which the structure is formed of cell walls which define therebetween a set of channels for the passage of the streams, said channels having a cross-sectional shape such that they narrow in the downwards direction.

12. A method according to claim 11 in which the channels together form a close-packed array. A

13. A method according to either of claims 11 or 12 in which the channels are of substantially rhombic cross-sectional shape.

14. A method according to any one of claims 11 to 13 in which the cellular structure is formed of a set of plate members mounted together and having a surface configuration such that each plate member provides cell walls for a row of cells.

15. A method according to any one of claims 1 to 14 in which the mixture is fed through a conduit having discharge ports and in a configuration such that the discharge ports communicate with an inlet part of the sedimentation unit, containing the sedimentation zone, in distributed positions.

16. A method according to claim 15 in which the flocculating agent is fed to the conduit at a number of positions between the discharge ports.

17. A method according to either of claims 15 or 16 in which the conduit is formed to a square configuration with the discharge ports directed inwardly.

18. A method according to any one of claims 1 to 17 in which the effluent is collected prior to treatment in a reservoir from which it is pumped for treatment, the rate of pumping being less than the rate at which the effluent is collected in the washing of a vehicle.

19. A vehicle washing installation which comprises vehicle washing equipment using water containing a biodegradable detergent in such a manner as to produce substantial aeration of the water and providing an aerated effluent containing said detergent and solid matter, means for collecting the aerated effluent from the washing equipment, a source of liquid polymeric flocculating agent for addition to the collected aerated effluent, a sedimentation unit and one or more adsorption units for treating the water of reduced solids content obtained from the sedimentation unit.

20. An apparatus according to claim 19 in which the sedimentation unit contains a structure having walls which divide the flow of mixture into a number of shallow streams.

21. An apparatus according to claim 20 in which the walls are inclined and run upwardly from the bottom to the top of the structure.

22. An apparatus according to either of claims 19 or 20 in which the structure is arranged to guide the flow of mixture upwardly through a containing tank.

23. An apparatus according to any one of claims 20 to 22 in which the structure is in the form of a set of spaced-apart plates.

24. An apparatus according to claim 23 in which the plates are corrugated with the corrugations running in the direction of flow of the mixture.

25. An apparatus according to any one of claims 20 to 22 in which the structure is formed of cell walls which define therebetween a set of channels for the passage of the streams, said channels having a cross-sectional shape such that they narrow in the downwards direction.

26. An apparatus according to claim 25 in which the channels together form a closepacked array.

27. An apparatus according to either of claims 25 or 26 in which the channels are of substantially rhombic cross-sectional shape.

28. An apparatus according to any one of claims 25 to 27 in which the cellular structure is formed of a set of plate members mounted together and having a surface configuration such that each plate member provides cell walls for a row of cells.

29. An apparatus according to any one of claims 20 to 28 provided with a conduit for the mixture of flocculating agent and the effluent, said conduit having discharge ports and a configuration such that the discharge ports communicate with an inlet to the sedimentation unit, containing the sedimentation zone, in distributed positions.

30. An apparatus according to claim 29 having means for feeding the flocculating agent to the conduit at a number of positions between the discharge ports.

31. An apparatus according to either of claims 29 or 30 in which the conduit is formed to a square configuration with the discharge ports directed inwardly.

32. An apparatus according to any one of claims 20 to 31 in which the effluent is collected prior to treatment in a reservoir from which it is pumped for treatment, the rate of pumping being less than the rate at which the effluent is collected in the washing of a vehicle.

33. An apparatus for treating the effluent water containing a bio-degradable detergent and solid matter from vehicle washing equipment of the kind in which the water containing the detergent is used in such a manner as to produce substantial aeration thereof, substantially as hereinbefore described and illustrated by reference to Figs. 1 to 3, of the accompanying drawings.

34. An apparatus for treating the effluent water containing a bio-degradable detergent and solid matter from vehicle washing equipment of the kind in which the water containing the detergent is used in such a manner as to produce substantial aeration thereof, substantially as hereinbefore described and illustrated by reference to Figs. 4 to 6 or Figs. 7 and 8 of the accompanying drawings.