The present invention relates to waste management and more particularly to a self- contained system for treating and recycling waste water.

The invention has been developed particularly for utilisation in conjunction with toilet cubicles in railway carriages but may also find application for example in aircraft, ships or mobile homes, for mobile or temporary toilet facilities at construction sites, exhibitions, events or the like, or in other applications where there is a need to conserve water and/or access to a main sewer system is unavailable.

A typical present day railway carriage toilet cubicle is equipped with a tank of fresh water for toilet flushing and hand washing and a holding tank for the effluent. Typically the water tank must be replenished every one or two days and the effluent tank emptied and cleaned every two or three days. Servicing such an installation is therefore a frequent and labour intensive process and wasteful of water, and in one aspect the invention seeks to provide a system whereby the waste water can be effectively treated and recycled for both flushing and washing and which can be operated for substantially longer periods between scheduled maintenance.

Accordingly in one aspect the present invention resides in a self-contained system for treating waste water received from at least first and second utilisation apparatus, comprising at least a bioreactor, a reverse osmosis stage and an ion exchange stage, wherein a first stream of a first purity treated at least by said bioreactor is recycled through the first utilisation apparatus and a second stream of a higher purity treated at least by said bioreactor, reverse osmosis stage and ion exchange stage is recycled through the second utilisation apparatus.

The bioreactor in such a system is preferably an aerated membrane bioreactor.

Water treated by said bioreactor is preferably treated by ozone prior to said first stream passing to the first utilisation apparatus and said second stream passing to the reverse osmosis and ion exchange stages. As ozone can present a health hazard, excess from such treatment is preferably passed into the bioreactor, where it can be broken down, and this feature represents an independent aspect of the invention.

A possible alternative to the use of ozone for treatment subsequent to the bioreactor is nanofiltration.

Water treated by said bioreactor is also or alternatively treated by ultra violet light prior to said first stream passing to the first utilisation apparatus and said second stream passing to the reverse osmosis and ion exchange stages. Water of said second stream may also or alternatively be treated by ultra violet light subsequent to treatment by said reverse osmosis and ion exchange stages.

A problem that can occur with the operation of bioreactors, and particularly aerated bioreactors, is the production of foam in its headspace that, if uncontrolled, can escape through the vent which is typically provided to exhaust excess air and/or carbon dioxide or other gases produced by the biological reactions therein, and thus present a health hazard. In accordance with another independent aspect of the invention, therefore, the bioreactor is preferably provided with means for recirculating water therefrom into the headspace thereof in the form of a spray for suppressing foam therein.

In the case of a toilet cubicle installed in a railway carriage or elsewhere the first said stream can be recycled for toilet flushing, the first said utilisation apparatus being a toilet pan, while the second said stream can be recycled for hand washing, the second said utilisation apparatus being a wash basin.

These and other features of the invention will now be more particularly described, by way of example, with reference to the accompanying drawing which is a simplified schematic diagram of a system according to the invention utilised in conjunction with a toilet cubicle in a railway carriage.

With reference to the accompanying drawing a toilet pan is indicated at 1 and a wash basin at 2. The toilet pan is equipped with spray nozzles 3 which, when a flush switch (not shown) is pressed, are supplied by a pump 4 with water which has been treated and recycled as will be more particularly described hereinafter. Pressing the flush switch also causes a pump 5 to operate which draws the contents out of the pan 1 - this comprising water containing liquid and/or solid human waste and/or toilet tissue as the case may be. This pump is of a type which also macerates any solids and tissue, and it delivers the resultant mixture through a pipe 16 into an aerated membrane bioreactor (MBR) 6. The pan 1 is also equipped with sensors (not shown) which will initiate operation of the pump 5 in the event that its contents reach a specified volume.

The wash basin 2 is equipped with a conventional water dispensing unit 7 which includes a hand proximity sensor 8, water heater 9, mixing valve 10, spray nozzle 11 and pump 12 with filter 12A. This is also supplied with recycled water but which has been treated to a higher degree of purity than the flush water for the toilet pan 1 , as will be more particularly described hereinafter. The effluent from the basin, typically comprising water, soap and hand washings, passes to a sump 13 equipped with a level sensor 14 connected so that the pump 5 is also operated when a full sump is signalled. The wash basin effluent is therefore also delivered into the MBR 6. The sump 13 also has a vent/overflow pipe 56 leading to an outlet over the railway track.

The tank of the MBR is partitioned as indicated at 15 into a smaller, essentially anoxic zone (to the right of the partition as viewed) and a larger essentially aerobic zone (to the left of the partition as viewed). These zones are in partial communication, however, though perforations 15A at a chosen level in the partition and also due to the level of water in the tank normally being maintained above the height of the partition. The anoxic zone encourages microbiological denitrification, to produce ammonia and nitrogen gas, and provides some balance to the nitrification which takes place in the aerobic zone. It also provides a zone within the tank where any dense solids, e.g. from extraneous material which may have been deposited or lost in the pan 1 or basin 2 and passed through the macerating pump 5, can settle out, the opening into the tank from the waste inlet pipe 16 being positioned to allow any such solids to drop into this zone.

The aerobic zone of the bioreactor tank is equipped with an air diffuser 17 fed through a pipe 30 by blowers 18,19, and a membrane pack 20. When the MBR is initially commissioned, a quantity of activated sludge is introduced containing the bacteria required to sustain the microbiological treatment of the waste from the pan 1 and basin 2, and its tank is filled with water. In use, the air from diffuser 17 provides the conditions to promote biological oxidation of the waste, causes continuous recirculation of the water in the tank, and prevents settlement of the suspended and flocculated organic matter, cellulose and bacteria. The rate of aeration can be controlled in the illustrated embodiment by switching between the two blowers to provide a higher rate (from blower 18) during normal service of the carriage when the toilet cubicle is likely to be used and a lower rate (from blower 19) sufficient to maintain the process in the reactor during intervening periods (e.g. out of service periods at night or otherwise).

The basic microbiological process which takes place in the aerobic zone of the MBR is the breaking down of long chain organics in the human waste and soap into shorter chain organics, carbon dioxide and water, and the formation of nitrogen, phosphorus and sulphur products which in an aerated system will form nitrates, sulphates and phosphates. Salts will also be present from the original waste. Carbon dioxide produced by this process together with excess air, and nitrogen from the anoxic zone, is vented through a pipe 21 which opens over the railway track. Cellulose from the toilet tissue will remain in suspension and will largely be removed from the MBR when the latter is pumped out as will be described hereinafter.

One problem which can occur with bioreactors of this kind is that some of the bacterial strains produce a mucous which, due to the aeration in the tank, leads to the production of foam in its headspace. If uncontrolled this foam can escape through the vent pipe 21 and present a potential health hazard. The MBR 6 is accordingly equipped with foam sensors (conductivity cells) 22 in the headspace which, when foam is detected at the level of the sensors, activate a pump 23 to draw water out of the tank and recirculate it through a spray nozzle 24 in the headspace to douse and thereby suppress the foam. If necessary an antifoaming agent can also be inducted into the flow through the pipe 25 which carries this recirculating water.

At intervals a pump 26 is operated to draw water out of the bioreactor tank through the membrane pack 20 and deliver it through a pipe 31 to a permeate tank 27. In this respect both the bioreactor tank and permeate tank are fitted with pairs of contents level sensors 28 and 29 respectively and the pump 26 is operated whenever the level within the bioreactor tank goes "high" or the level within the permeate tank goes "low"; (operation of the pump 26 will however be inhibited if the level in the bioreactor tank goes "low" or if the level in the permeate tank goes "high" except when the level in the bioreactor tank is itself "high"). The effective pore size of the membranes in the pack 20 is typically 0.1 μm or less so they will filter out from the flow to the tank 27 any particulates greater than this size, bacteria and viruses. The aeration within the bioreactor tank induces a flow of water across the surfaces of the membranes which helps to prevent clogging of their pores. The permeate from the MBR 6 is treated with ozone in tank 27. In this respect pressurised air from the pneumatic system typically provided on railway carriages is passed through a filter 32 and optionally through an oxygen concentrator (not shown) to a corona discharge ozone generator 33. The ozone from generator 33 passes through a pipe 34 to a diffuser 35 in the tank 27. The ozone bleaches out tannins and other colour forming organics which may pass through the MBR and also has an antiseptic effect, resisting the regrowth of bacteria in the permeate within the tank 27. The tank is also fitted with a source 36 of ultra violet light (254nm), which also resists bacterial regrowth and removes dissolved ozone. The water produced by these treatments is substantially colourless, odourless and bacteria-free and, while not of potable quality, is suitable for recycling as flush water for the toilet pan 1. In this respect the outlet pipe 37 from the tank 27 has a first branch 37A in which the pump 4 is situated and through which water is supplied to the spray nozzles 3 when demanded. The tank 27 is also equipped with an overflow pipe 38 leading to an outlet over the railway tack.

It is important that excess ozone in the headspace of the tank 27 is removed from the system as it might otherwise present a health hazard. The solution adopted to this in the present invention is to use the MBR 6 as a sink for such ozone. To this end a branch 39 is taken from the air supply to the ozone generator 33 and passes through a Venturi 40 which draws excess ozone from the headspace of the tank 27 through a pipe 41 and into the air stream, with which it is delivered through a pipe 42 and diffuser 43 into the MBR, where the ozone breaks down by oxidation of organic material in the sludge.

It is also important that the ozone is fully dissipated from the water led out of the tank 27 as it may otherwise render ineffective the reverse osmosis filter to be described hereinafter, or in other words that the water has had sufficient dwell time since ozonisation before being passed to the reverse osmosis filter. For this purpose the tank 27 may optionally be partitioned into, say, two or three zones or two or three distinct tanks linked by suitable valves, with ozone being supplied only to the first one (or two in the case of a three zone/tank system) and the feed to the reverse osmosis filter only being taken from the last one.

In any event, the outlet pipe 37 from the permeate tank(s) 27 has a second branch 37B leading to a pump 44 and a spiral wound reverse osmosis filter 45. When the pump 44 runs, water from the tank(s) 27 is passed under pressure to the membrane of the filter 45, which is selected for brackish water and filters down to a size of typically O.OOOδμm, removing divalent salts and any remaining organics. This filter will not, however, remove very small molecules such as nitrates, nitrites and ammonia, so its product is passed through a pipe 46 to an ion exchange resin filter 47, while the concentrate from the reverse osmosis filter 45 is recirculated through a pipe 48 to the permeate tank(s) 27. The filter 47 has a mixed bed including a strong anion resin (chloride form) which targets nitrate and nitrite ions and replaces them with chloride ions in a 1 to 1 ratio, and a strong cation resin (sodium form) which targets ammonium ions and replaces them with sodium ions in a 1 to 1 ratio.

The water produced from this stage is stored in a tank 49 where it is kept disinfected by ultra violet light (254nm) from a source 50. It is of potable quality and hence safe to recycle as hand wash water for the basin 2, where it might also be drunk, being supplied to the latter through a pipe 51 when demanded by operation of the pump 12.

The hand wash water tank 49 is fitted with a contents level sensor 52 and a vent/overflow pipe 53 leading to an outlet over the railway track. The aim is always to keep this tank full and the pump 44 is controlled in response to the sensor 52 to pass permeate from the tank(s) 27 through the filters 45 and 47 and into the tank 49 whenever its level falls below that set by the sensor 52.

Conductivity sensors 54 and 55 are provided in the pipework respectively upstream and downstream of the reverse osmosis filter 45 and are used to check that there is a higher salt concentration in the water on the upstream than the downstream side. Failure to maintain this relationship indicates that the filter 45 may have failed "open" and an alarm condition will be signalled accordingly.,

It will be appreciated that with each usage of the toilet 1 the total volume of material within the system will increase. Consequently when its capacity has been reached any excess will be lost by overflow of permeate through the pipe 38 from the tank(s) 27. It is arranged that any loss to the environment from the system occurs from the permeate tank(s) 27 in preference to loss from the bioreactor tank 6 or the hand wash water tank 49 by virtue of the control protocol whereby the pump 26 is operated whenever a high contents level is sensed in the bioreactor tank and the pump 44 is stopped whenever the hand wash water tank is full. From time to time it is required to remove accumulated sludge from the MBR 6. For this purpose pipes 57 and 58 extend down to the bottom of its tank, on opposite sides of the partition 15. These pipes unite outside the MBR and lead to pump-out valves 59 which are externally accessible on opposite sides of the carriage. An external pump and collection tank is connected to one or other of the valves 59 and, with the valve 64 in the pipe 57 open, operated to draw out the contents of the MBR tank through the pipes 57 and 58. Once the level of sludge in the tank has reached the bottom of the perforations 15A the compartment to the right of the partition 15 as viewed will empty more quickly than the compartment to the left due to its smaller volume. Once the right hand compartment has emptied of sludge air will be drawn through the pipe 57 and this will effectively prevent further sludge being drawn through the pipe 58. At the end of the pumping-out process, therefore, a defined quantity of sludge will be left in the tank which will be sufficient to maintain the necessary microbiological action of the MBR when refilled with water. In the event that it becomes necessary to empty the MBR completely (eg a "freeze drain") the valve 64 can be closed after emptying the right hand compartment to enable the remaining sludge to be pumped out from the left hand compartment through pipe 58.

Refilling of the MBR tank after pump-out is achieved by connecting an external water supply to one or other of two fill valves 60 which are externally accessible on opposite sides of the carriage. These connect to a fill pipe 61 which supplies the MBR tank through a float valve 62. A normally-closed pressure relief valve 63 also connects the fill pipe 61 to the vent pipe 21. Consequently when the tank has been filled to the level of the float valve 62 and the latter closes, the valve 63 is caused to open by the applied water pressure and diverts the water supply to the vent pipe 21 , the resultant escape of water to the track signalling to the operator that the tank is now full.

It is of note that a proportion of the concentrate from the reverse osmosis filter 45 that is recirculated to the permeate tank(s) 27 will be lost with any overflow from the latter, and another proportion that is recirculated from the tank(s) 27 with flush water for the toilet pan 1 and into the MBR 6 will be lost when the latter is pumped out.

By way of example an experimental system of the kind described with reference to the accompanying drawing has been constructed to handle up to 15 uses per hour, each typically comprising 0.35 litre deposited waste together with a 0.6 litre toilet flush and 0.25 litre hand wash supply. The whole system comprising MBR 6, tanks 27 and 49 ozone generator 33, filters 45 and 47 and associated pipework, pumps and blowers (that is to say excluding the pan 1 , basin 2, unit 7, sump 13 and the pump-out and fill connections) fits within a space envelope measuring 0.8m x 0.8m x 2.0m (height) and has been found to perform effectively with a basic maintenance cycle of only once per month, such including pumping out and refilling the MBR with 300 litres of fresh water, and in-situ cleaning of the reverse osmosis filter membrane. Other maintenance tasks such as in-situ cleaning of the MBR membrane pack and regeneration of the ion exchange resins can take place at more extended intervals.

Although described above with only a single toilet pan 1 and wash basin 2, a common system of sufficient capacity may be provided to serve two or more such cubicles simultaneously.