APPARATUS AND PROCESS FOR TREATING WASTE EFFLUENT

Abstract: A high rate multi-stages serial biological fluidised bed waste effluent treatment apparatus and process are provided. The apparatus comprises a series of chambers, interconnected, closed to the atmosphere and containing suspended biomass growth which treats waste effluent as it passes upwardly through each chamber. Successive chambers have increasing cross-sectional areas in order to reduce the upward flow velocity of the flow and so retain the growing particles within each stage for a sufficient period to effect purification of the pollutants. The respiring biomass requires a large supply of oxidant, e.g. oxygen, therefore the reactor, which is enclosed, will be kept under pressure, e.g. (3) to (5) bar, which will allow comparatively high concentration of oxygen to be dissolved without a problem due to effervescence. The apparatus can be adapted to treat any type of biodegradable waste effluent including industrial effluents.

Description: APPARATUS AND PROCESS FOR TREATING WASTE EFFLUENT This invention concerns effluent treatment apparatus and a process for treating waste effluents, and particularly but not exclusively apparatus and a process for treating waste water from a domestic or industrial source. A number of systems have been used previously for treating waste water. The majority of such systems have used aerobic biological treatment in which micro-organisms (biomass) are used to decompose the waste components of the water. One such system is a biological fluidised bed in which a slime growth (biomass) develops on the surface of inert media, usually micro sized particles approximately 0.50 to 2.00 mm in diameter. The particles are contained within a biological reactor unit, and are maintained in free suspension by a constant upward flow of the waste water to be treated (substrate) from which the micro organisms obtain their food and energy requirements. The biological energy requirement for such systems is achieved by the transfer of electrons from donors in the waste water (carbonaceous matter) to electron acceptors (oxidants) usually dissolved atmospheric or gaseous oxygen, injected into the waste water feed. In the absence of dissolved oxygen, an anoxic process can be used whereby nitrates are added as electron acceptors to reduce the pollution strength of the waste effluent. A distinct advantage claimed for the biological fluidised bed process over conventional aerobic biological methods of waste water treatment is the ability to maintain a very high concentration of active biomass in contact with the waste water to be treated per unit volume of reactor space. This enables a substantial reduction in the retention time for treatment also a reduction in the physical size and capital cost of effluent treatment units. However, owing to several major process operations and design problems the biological fluidised bed process has not been developed or commercialised to its full potential. These disadvantages can include the following: a) Treatment has normally been carried out in solo open top units arranged with a constant upward flow velocity. Oxygen essential for the process is only slightly soluble in water under normal atmospheric conditions (approximately I0 mg/l). Problems have been encountered in supplying adequate amounts of dissolved oxygen to keep pace with the high rate of respiration by the abundant quantities of biomass present. To overcome this problem some workers added oxygen to the inlet flow under high pressure, this caused secondary problems within open type reactors due to effervescence as the pressure decreased resulting in carry over and shearing of the biomass particles. b) As the biomass growth develops on the carrier media particles they become more buoyant and bulky and are discharged with the final treated effluent in large quantities; it being reported that on occasions the entire fluidised bed has been lost for this reason. c) Although several pilot scale units were tested during the I970's and early 1980's no full scale plant has been successfully developed and operated for the treatment of domestic waste water in the U.K. According to one aspect of the present invention there is provided apparatus for treating waste effluent comprising a plurality of chambers connected in series and adapted to hold a treatment media on which a biomass may be formed, means operative to supply waste effluent to the chambers to flow sequentially therethrough and to form a biomass therein characterised in that the chambers are closed to atmosphere, a downstream chamber has a cross-sectional area transverse to the direction of flow which is greater than the chamber upstream of it and means are provided for supplying an oxidant to one of the chambers. The chambers are preferably alignable such that in use the effluent flows upwardly therethrough. The chambers are preferably alignable substantially vertical in use. The chambers are preferably located substantially adjacent each other in use, at substantially but not necessarily the same height. The chambers are interconnected to each other by pipework or enclosed channels. The chambers are preferably constructed of suitable reinforced material which may include concrete, steel or high density plastics. The chambers are preferably constructed in circular, square or oblong cross sections but not necessarily so. Preferably a plurality of interconnecting chambers of at least two different cross-sectional areas may be provided. Automatic valve means may be provided in or beyond the last of said chambers for controlling the flow of effluent passing through and out of the said chambers and for regulating the pressure within the chambers. Means may be provided in or beyond the last of said chambers for washing the treatment media. The washing means may comprise scouring means which may use compressed air and filtered effluent for the scouring. Means may be provided for filtering the effluent. The filter means may comprise a media filter and means may be provided for cleaning the filter media by for example reverse flushing. The filter means are preferably carried out by passing the effluent through similar type media as is used within the process chambers. Outlet valve means may be provided in or near an upper part of one or more of the chambers to permit gases to be discharged therefrom and also samples to be taken of the contents of the or each chamber. Said outlet valve means may be automatically operated to discharge any gas which accumulates thereat. Outlet valve means may be provided in or near a lower part of one or more of the chambers to permit material to drain therefrom and also samples to be taken of the contents of the or each chamber. Means are preferably provided for supplying dissolved oxygen or bio- oxidant or a mixture of oxidant sources into the apparatus. Bio-oxidant supply means are preferably provided for a plurality of the chambers such that different conditions can be provided in different chambers. Sensor means may be provided in one or more of the chambers to sense the conditions therein. The or each sensor means may be connectable to either of the respective upper and lower valves and/or the oxygen supply means so as to cause automatic operation thereof upon detection of particular conditions. Means may be provided for recycling treated effluent into any chamber of the apparatus and preferably also to the upstream of said first chamber. According to another aspect of the present invention there is provided a process for treating waste effluent characterised by the steps of introducing a treatment media on which biomass may be formed into at least one of a plurality of chambers which are closed to the atmosphere, supplying an oxidant to at least one of the chambers passing effluent sequentially through the plurality of chambers, and decreasing the flow velocity of the effluent in a downstream chamber as compared with the flow velocity in an upstream chamber whereby to form biomass on the treatment media and to carry biomass coated media from an upstream chamber to a downstream chamber the biomass removing pollutants from the effluent during this process. The flow velocity of the effluent is preferably decreased at least twice. The effluent is preferably passed upwardly through the chambers. The effluent is preferably passed through the chambers under high pressure. Different biological conditions are preferable provided in at least some of the chambers. Dissolved oxygen or a bio-oxidant source is preferably supplied into at least some of the chambers and different rates of supply are preferably supplied into respective chambers as is required by the biological activity in the respective chambers. Waste gases may be removed from one or more of the chambers. The treated effluent is preferably settled to allow separation of heavy suspended solids. The treated effluent is preferably filtered and may be filtered subsequent to passing through said chambers or when passing from the final settlement chamber. A portion of the settled effluent passing from the final settlement chamber is preferably returned to the upstream of the first chamber to act as recycle water and for upward flow velocity regulation within the chambers. An embodiment of the present invention will now be described by way of example only with reference to the single figure No. I of the accompanying drawing which shows a schematic view of effluent treatment apparatus according to the invention. The effluent treatment apparatus comprises a high pressure flow control valve 27, a high pressure pump 4 and a waste water collection wet- well 2, six vertical aligned chambers 10, 12, 14, 16, 18, 20 connected together in sequence by the interconnecting pipes 26. The third and fourth chambers 14, 16 are of greater cross section area than the first and second chambers 10, 12. Likewise the fifth and sixth chambers 18, 20 are of greater cross- sectional area than the third and fourth chambers 14, 16. The final chamber 20 is connected to a settling and flow distribution chamber 40 which will be hereinafter described. The interconnecting pipework 26 entering the chambers 12-20 respectively at the lowest part. Each chamber 10-20 is fitted with an inlet flow distribution system 36 designed and fitted to disperse and distribute the incoming flow evenly in an upward direction over the cross-sectional area of the respective chamber. A valve 30 is provided adjacent the inlet into each of the chambers 10-20. The valve 30 is located at the lowermost part of the pipework 26 and permits material to be drained/removed from the apparatus and or samples to be taken. The interconnecting pipework 26 forming an outlet for each of the chambers 10-20 is provided at the uppermost part of the respective chambers 10-20 and connects downwardly to a respective inlet on the subsequent chambers 12-20. A further valve 32 is provided connecting into the uppermost part of the pipework 26 immediately downstream of the outlet from each of the chambers 10-20. Each valve 32 connects into gas extraction ducting 34. The valves 32 permit samples to be taken and also gas to be removed from the pipework 26. As the valves 32 are located at the uppermost part of the pipework 26 gases will automatically locate at this point. The valve 32 may be arranged to automatically bleed any gases accumulating thereat into ducting 34. Valve means 60 are provided for supplying an oxygen or other oxidant source such as dissolved atmospheric oxygen, dissolved oxygen gas, oxygen gas, dissolved nitrates, or other suitable bio-oxidant agents, or a combination of two or more of these components, into chambers 10 to 20. The pressure in the chambers is kept above atmospheric preferably between 3 to 5 bar. In certain instances oxygen supply means may be omitted from the sixth chamber 20. Sensors 62 may be provided for each of the chambers 10-20 to detect the conditions therein. The sensor signals may be transmitted via a control system 94 to the bio-oxidant supply 38 and/or units 60, 30, 32, 27 and 4 to automatically operate these as conditions dictate. The pipework 26 extending into settling tank chamber 40 connects to a centrally located flow baffle arrangement 42 which disperses the flow in a downward direction. The uppermost peripheral edge of the chamber 40 acts as a settled effluent overflow weir 44 discharging effluent into a surrounding channel 46 and pipework therefrom conveys a portion of the effluent to a media filter 70 and the remaining effluent to the waste water wet well inlet pumping sump 2 for recycle. Settling chamber 40 contains a lower sludge sump 48 in which settled solids accumulate. These solids can be withdrawn either mechanically, hydrostatically or pumped into a biomass/media washing and separation unit 50. Settled effluent for filtration passes from channel 46 into a media filter 70. The media filter 70 preferably contains similar filtering media as is used within chambers 10 to 20 and can be designed as an upflow or downflow conventional effluent filter. Backwash water from this filter is discharged along interconnecting pipework 72 to the media washing and separation unit 50. The biomass/media washing and separation unit 50 is fitted with a high pressure wash water supply 52 and a compressed air supply 54 discharging into a bottom baffled media washing zone 56 of this unit into 5 which the solids from sludge sump 48 and backwash water from the media filter 70 are also conveyed. The high pressure washwater supply 52 and the air supply 54 can also be used for washing the media in filter 70. The uppermost edge of unit 50 acts as an overflow weir 80 discharging waste supernatant liquor into a surrounding channel and 10 connecting pipework 82 which conveys the supernatant liquor to the inlet wet well 2. A number of decanting valves and pipework 84 are fitted to unit 50 which selectively allows supernatant liquor or waste biomass solids to be withdrawn from several levels and passed either to the inlet wet well 2 or 15 progressed for treatment and disposal elsewhere. Media coated biomass which enters zone 56 will undergo a rigorous compressed air and water scour after which the media is allowed to settle. The cleansed media can then be pumped via a media pump 58 for reuse to the first or any of chambers I0 to 20, or as make up media for filter 70. 20 Treated and filtered effluent is drained to a reservoir 90 for disposal or reuse as required. < The treatment process and apparatus is usable in the following manner. During start-up and commissioning chambers I0, 12 are partially filled with micro sized media particles to about 30 to 50 % by volume. The medium particles may be sand, fused alumina, garnet, anthracite or similar type biologically inert material, but it had been found preferable to use anthracite. The waste water to be treated preferably has an active biomass inoculant added to it during the first few days and is pumped via a variable output high pressure pump 4 from a waste water wet-well sump 2 into chamber I0 at a pre-set constant flow and pressure as controlled by pressure valve 27. The flow rate being sufficient to fluidise the media particles and maintaining a steady and constant upward flow velocity compatible with the density of the media being used. If anthracite is used the upward flow velocity will be approximately 90 meters per hour in chambers I0 and 12 but not necessarily so. It will be approximately 50 meters per hour in chambers 14 and 16 but not necessarily so. It will be approximately 35 meters per hour in chambers 18 and 20 but not necessarily so. The inoculant may comprise batches of mixed micro-organisms taken from a local waste water treatment plant or specially prepared batches of micro-organisms pre-adapted to degrade the particular components contained within the waste water. This latter inoculant type may be necessary where volatile organics or other anti-typical industrial materials are being treated in the waste water flow, or where industrial effluents are being treated alone by this process. Oxygen gas or other oxidant source is injected into the ingoing waste effluent flow and preferably controlled to allow a slight excess at all times during treatment. After a period depending on the strength and nature of the waste water and the presence or otherwise of an inoculant, a biomass growth will develop on the surface of the media particles contained in chambers I0 and 12. The rate of growth will be directly proportional to the strength of the 5 waste water pollutants and the oxidant usage. As growth develops the biomass covered media particles become less dense and the overall bulk volume of the media increases. As the particles continue to grow and become more buoyant they are slowly but progressively carried over in the liquid flow to chamber 14 and subsequently to 16. 10 Chambers 14 and 16 are of greater cross sectional area than I0 and 12. This means that the buoyant biomass coated particles flowing from chamber 12 will be contained within chambers 14 and 16 until their buoyancy increases further to a level where they again overcome the flow velocity restrictions and pass over to chambers 18 and 20. 15 Chambers 18 and 20 are of still larger cross sectional area than chambers 14 and 16 and the upward flow velocity is therefore proportionally reduced thus the biomass coated particles will be contained within chambers 18 and 20 until their buoyancy once more continues to increase to a density such that they are carried over in the outlet flow. 20 Chambers 18 and 20 are designed to provide sufficient biomass retention period to provide complete nitrification of any ammoniacal < compounds present in the waste water flow. Some endogenous respiration of the biomass will also take place in these chambers. The height and volume of the respective chambers are designed to allow sufficient retention period for the facultative micro-organisms contained therein to adapt and perform their particular activities. The types of biomass organisms vary through the chambers I0 to 20 according to the diminishing food supply and the flow velocities and zoning of micro biological activity takes place. The main stages being a growth phase chambers I0 and 12; a carbonaceous oxidation phase chambers 14 and 16; a nitrification and endogenous respiration phase chambers 18 and 20, but not necessarily so. Three stages have been described, however it may be necessary to increase the number of stages and their retention periods to deal with stronger or more complex waste waters. During this time oxygen or bio-oxidant is injected to each of the chambers 10-20 as is required. Sensors 32 may be supplied to automatically supply and control the required amount of oxygen or bio-oxidant to each chamber 10-20. An additional chamber not shown may be added in line with chambers 10-20 to which no oxygen or bio-oxidant is supplied to allow denitrification of any nitrates in the treated effluent from chamber 20 to take place. This could be important as there are currently stringent conditions concerning the discharge of nitrates to potable water abstraction sources. As the media coated biomass particles exit from chambers 10 and 12 replacement make-up media will be required which will be injected from a media store 96 or from the media washing process herein to be described. The treated effluent flowing from chamber 20 containing suspended biomass coated particles will pass along the interconnecting pipework 26 into settling chamber 40. The retention time of the flow within chamber 40 will allow the biomass coated media to settle and be collected, possibly with the help of mechanically operated floor scrapers not shown, into a lower sludge holding sump 48. The settled effluent from this tank overflowing the peripheral weir 44 into channel 46 and pipework therefore will preferanti ' laly flow to the inlet wet-well 2 in order to provide steady balanced upward flow velocities within chambers I0 to 20. During peak flows the effluent recycle will be at a minimum and during low night time dry weather flow this will be at a higher level. The process hydraυϋcs is designed to deal with up to three time normal dry weather flow. The remaining flow from channel 46 will pass to a media filter 70 herewith shown only for explanatory purpose as a down flow gravity filter. Filter 70 could also be designed as a conventional upflow or a pressure filter. It would be possible depending on the quality of the final treated effluent required, to distribute a portion of the effluent from chamber 20 without settlement direct to the media filter 70 for entrapment of the biomass particles and a portion to wet-well 2 for recirculation. The treatment process within the chambers 10 to 20 produce gaseous end products which may cause problems in the apparatus. Accordingly these gases are removed through the valves 32 into ducting 34. The valves 32 are preferably in the form of automatic gas release valves to provide automatic venting. The biomass particles can be withdrawn through any of the valves 30 when required and passed directly to chamber 50 for cleaning. There is thus described a process and apparatus for waste effluent treatment which provides a number of advantageous features. This system is very flexible and controllable thereby permitting for example high concentrations of dissolved oxygen to be introduced and held into different ones of the chambers. The system also permits different sources of oxidants to be supplied to different chambers. The ready removal of waste gases from the system is particularly advantageous as is the final filtration of treated effluent using the same type media as for biomass support within the chambers. The facility to wash the media and return it as make up to the process chambers is very economically advantageous. The use of different dimensional interconnected treatment zones allows different stages of micro-biological activity to take place in the most appropriate condition without undue loss of media in the treated effluent flow. This is a considerable and distinctive advance on previous systems. The ability to hold the upward flow velocity at constant but differing rate within each of the respective and sequential waste effluent treatment zones is a notable advance on previous methods and has largely contributed to the success of this invention. The biological treatment process is aerobic and entirely enclosed which will prevent the release of noxious odours normally associated with sewage treatment plants thus making the systems more environmentally acceptable than most other methods. In order to prove the efficacy of this treatment process a one year trial has been carried out using a large scale laboratory glass rig, having eight reactor tubes; 3 x 50mm diameter; 3 x 80 mm diameter and 2 x I00 mm diameter. The tubes arranged in series tubes were all 1,500 mm in height and interconnected with 40 mm tubes and "U" bends. After experimenting with many types of media, anthracite particles (2.0 to 2,5 mm dia.) were selected as considered most suitable for the trial in order to meet the upward flow velocities likely to be encountered in each of the treatment zones respectively. This proved to have been a good choice. The trial was carried out using screened but unsettled domestic sewage having a biochemical oxygen demand (B.O.D.) strength of approximately 320 mg/l. and producing a final treated filtered effluent quality of less than I0 mg/l B.O.D. and 5 mg/l suspended solids. These results equate to a treatment capacity of 9 kg B.O.D. removed per m3 of serial fluidised bed rector volume. This is much greater than most other aerobic biological waste water treatment systems; example a conventional activated sludge treatment plant will remove approximately only 0.8 kg B.O.D. per m3 capacity. The treatment micro-organisms identified in the final zone of the 100 mm diameter reactors were: Lionatus, Euplotes, Paramecium, Vorticella, Aspidisca and Nemotodes. All were present in an abundance with Vorticella, Paramecium and Nemotodes being the dominant types. The excess biomass sludge production discharged from the media washing plant is comparatively free from noxious odours and could be quickly processed into a marketable fertiliser or soil conditioner. When dried it has a consistent texture similar to dried activated sludge. It is to be understood that the described embodiment is by way of example only and various modifications may be made without departing from the scope of the invention. For example, a different number, type or design of chambers could be used. Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawing whether or not particular emphasis has been placed thereon.

Claims: CLAIMS 1. Apparatus for treating waste effluent comprising a plurality of chambers (I0, 12, 14, 16, 18, 20) connected in series and adapted to hold a treatment media on which a biomass may be formed, means operative to supply waste effluent to the chambers to flow sequentially therethrough and to form a biomass therein characterised in that the chambers are closed to atmosphere, a downstream chamber (14, 16) has a cross-sectional area transverse to the direction of flow which is greater than the chamber upstream (10, 12) of it and means (60) are provided for supplying an oxidant to one of the chambers. 2. Apparatus as claimed in claim I, in which each chamber (I0, 12, 14, 16, 18, 20) is elongate and is disposed with its elongate axis upright. 3 Apparatus as claimed in claim I or 2, in which each chamber (I0, 12, 14, 16, 18,20) has a circular, oblong, or square cross-section. 4. Apparatus as claimed in claim I, 2 or 3, in which valve means (27) are provided for controlling the flow of effluent. 5. Apparatus as claimed in claim 4, in which the valve means (27) are disposed in or downstream of the most downstream chamber for controlling the flow of effluent through the chambers (I0, 12, 14, 16, 18, 20). 6. Apparatus as claimed in claim 5, in which the valve means (27) are automatically operable. 7. Apparatus as claimed in any preceding claim, in which washing means (50) are provided for washing the treatment media. 8. Apparatus as claimed in any preceding claim, in which the washing means comprise scouring means. 9. Apparatus as claimed in claim 8, in which filter means (70) are provided for filtering the effluent. 10. Apparatus as claimed in claim 9, in which the filter means (70) comprise a media filter. 11. Apparatus as claimed in claim 9 or 10, in which means (50, 72) are provided for cleaning the filter means (70). 12. Apparatus as claimed in any preceding claim, in which outlet valve means (32) are provided in one of the chambers (10, 12, 14, 16, 18, 20) to enable gases to be vented from that chamber and/or samples to be taken of the chamber content. 13. Apparatus as claimed in any preceding claim, in which outlet valve means (30) are provided in one of the chambers (I0, 12, 14, 16, 18, 20) to enable material to be drained therefrom and/or samples to be taken of the chamber contents. 14. Apparatus as claimed in any preceding claim, in which sensor means (62) are provided in one or more of the chambers to sense conditions therein. 15. Apparatus as claimed in claim 12, or 13, in which sensor means (62) are provided associated with the outlet valve means (30, 32) operative to actuate the valve means on sensing particular conditions. 16. Apparatus as claimed in any preceding claim, in which means are provided for recycling treated effluent. 17. Apparatus as claimed in any preceding claim, in which settling means (40) are provided comprising a settling chamber for settling out and removal of suspended biomass solids. 18. Apparatus as claimed in any preceding claim, in which means are provided for subjecting the effluent to an anoxic treatment where denitrification of nitrate is effected. 19. A process for treating waste effluent characterised by the steps of introducing a treatment media on which biomass may be formed into at least one of a plurality of chambers (10, 12, 14, 16, 18, 20) which are closed to the atmosphere, supplying an oxidant to at least one of the chambers (10, 12, 14, 16, 18, 20) passing effluent sequentially through the plurality of chambers, and decreasing the flow velocity of the effluent in a downstream chamber (14, 16) as compared with the flow velocity in an upstream chamber (I0, 12) whereby to form biomass on the treatment media and to carry biomass coated media from an upstream chamber to a downstream chamber the biomass removing pollutants from the effluent during this process. 20. A process as claimed in claim 19, in which different biological treatment phases and zones are created in the chambers (10, 12, 14, 16, 18, 20) by passing the effluent at different velocities in the chambers whilst maintaining a constant flow of effluent for the development of biomass. 21. A process as claimed in claim 19 or 20, in which the concentration of oxygen dissolved in the effluent flow is increased or decreased in proportion to the pressure produced in the chambers and as required by the respiring biomass at the respective chamber (10, 12, 14, 16, 18, 20). 22. A process as claimed in claim 19, 20 or 21 in which the effluent is subjected to an anoxic treatment in which no oxidant is supplied and denitrification of nitrate takes place. 23. A process as claimed in any of claims 19 to 22, in which the treated effluent is passed to a settling chamber (40) for settling out and removal of suspended biomass solids. 24. A process as claimed in any of claims 19 to 23, in which the treated effluent is passed to a media filter (70) for filtering out suspended biomass solids. 25. A process as claimed in any of claims 19 to 24, in which treated effluent is recycled to augment effluent inflow during periods of low flow and to maintain the required flow velocity through the chambers compatible with treatment requirement. 26. A process as claimed in any of claims 19 to 25, in which treatment parameters are sensed during treatment and employed to control the process, the treatment parameters comprising one or more of flow rate, pressure, media level and bio-oxidant concentration. 27. A process as claimed in any of claims 19 to 26, in which excess waste gases produced during treatment are automatically vented. 28. A process as claimed in any of claims 19 to 27 in which any biomass coated media carried through the chambers is separated and washed and returned to the apparatus.

Inventors: MONAGHAN WALLACE, MONAGHAN, WALLACE
Applicants: MONAGHAM JENNIFER, MONAGHAN WALLACE, MONAGHAM, JENNIFER, MONAGHAN, WALLACE
Application year: 1995
Main classification: C02F3
IPC codes: C02F3