GB2456836A

GB2456836A - Method and reactor for the anaerobic and aerobic treatment of water

Info

Publication number: GB2456836A
Application number: GB0801518A
Authority: GB
Inventors: Jirachote Phattaranawik; Tor Ove Leiknes
Original assignee: NTNU Technology Transfer AS
Current assignee: NTNU Technology Transfer AS
Priority date: 2008-01-28
Filing date: 2008-01-28
Publication date: 2009-07-29
Anticipated expiration: 2028-01-28
Also published as: GB0801518D0; GB2456836B

Abstract

A reactor for the treatment of feedwater provides both an anoxic/anaerobic treatment and an aerobic treatment in a single reactor volume. The two reaction zones (31,32) are separated by a separator (4) being a hydrodynamic separator between the two reaction zones (31,32). The anoxic/anaerobic reaction is zone is arranged in a lower portion of the reactor and the aerobic zone is arranged in an upper portion. The reactor allows for an effluent having lower total suspended solid value, as well as presenting less sludge production and lower energy consumption due to reduced pumping costs and a simplified construction. A plurality of reactors may be arranged in parallel such that a modular treatment of feedwater is rendered possible which will allow for the easy replacement of any unit presenting a malfunction.

Description

METHOD AND REACTOR FOR THE TREATMENT OF WATER

The present invention relates to a method and a reactor for the treatment of water.

The present invention relates generally to a method for treating water wherein the water is arranged for being treated in a single reactor. The reactor is arranged for treating water both anoxially/anaerobically and aerobically within a single reactor volume. The preferred reactor is particularly well-adapted for treating industrial, municipal, agricultural or other wastewater. This entails that preferably the majority of the suspended solids should be removed from the feed-water, as well as removing as much as possible of any bacterial growth. This will result in less clogging problems within the reactor, less water and chemical use as well as facilitating maintenance of the reactor. The reduction in water and chemical use is of particular interest from an environmental point of view.

The preferred reactor is further arranged for reducing sludge production and thus reducing the needed post treatment of sludge. The preferred embodiments also reduce the energy requirements for treating water.

Biological reactors (or bioreactors) have been widely used to biodegrade organic or inorganic substances in municipal and industrial wastewaters in treatment systems.

Typically, there are two types of biological reactors commercially used: i) activated sludge reactors, and ii) biofilm reactors. Conventional designs for biological wastewater treatment systems using conventional activated sludge and biofilm reactors require a unit for sludge or particle separation to remove some suspended solid in the effluents from the reactors before the effluents are discharged to natural water reservoirs. The capital cost for the wastewater treatment systems would be lower if the particle separation unit was not needed. Recently, biological reactors have been applied with membrane filtration processes to produce treated water for water reclamation, clean water recycle, and drinking water processes. Microfiltration (MF) and ultrafiltration (UF) have been used with biological reactors in configurations of a submerged module unit and an external module unit.

Reverse osmosis CR0) membrane filtration units have then subsequently been used to treat the effluent from MF or UF units and to generate higher-quality effluent. As is clear, the use of MF and UF units have a cost, and it would be preferable if the use of such systems could be avoided.

However the fouling problems associated with treating wastewater directly in a RO plant would render the process inefficient at best due to the liquid viscosities and suspended solid concentrations of the effluents from conventional bioreactors being relatively high, and thus consequently causing serious problems of membrane fouling and clogging.

Periodic maintenance of conventional biological wastewater treatment systems results in additional cost and loss in clean effluent productivity. Moreover, aerobic biological reactors of activated sludge and biofilm for wastewater treatment systems necessitate extra management for sludge disposals and thus incur additional costs for the sludge handling system. The excess sludge from the aerobic biological reactor is required to be properly managed and adequately disposed of.

High suspended solid concentrations in the effluents, high viscosities in the effluents, and excess sludge management in the conventional aerobic biological reactors cause operational difficulties and incur extra capital costs of overall wastewater treatment systems and clean water production systems.

A large number of existing water treatment systems are already in use and known in the background art. Some of the most pertinent with respect to the present invention are described below.

US-A-6132602 describes a vertical reactor for the treatment of wastewater. The publication describes the violent agitation and consequent distribution of biological matter within the wastewater to be treated in combination with a very large oxygenation of the wastewater. According to the publication the fine distribution of biological matter within the treatment section allows an increased contact area between the biological treatment agents and the heavily oxygenated wastewater. The treated water and biological material should then flow down externally to the main treatment element, whereupon the biological material should settle and be treated anaerobically in a sludge zone, and the wastewater be recycled. There are some major drawbacks to this design, one being that the finely distributed biological material will not easily settle into the sludge zone. One of the major objectives according to the publication is to distribute the biological material in such a manner that it does not agglomerate, thus it will prove difficult to adequately remove all suspended solids.

Accordingly there is need of a second settling zone, complicating the design. Furthermore, even a second

S

settling zone will not adequately remove all suspended solids, and further treatment of the effluent will be needed. This design further presents the disadvantage of having to bubble a large amount of air through the system, thus being energy intensive. Lastly, US-A-6132602 calls for installing a number of disc elements and channels into the reactor space, thus both increasing capital expenditure, and reducing the available reactor volume.

WO-A-94/16999 pertains to a secondary water treatment system wherein a single reactor is provided and wherein a plurality of reaction zones are situated. There are three main zones in this reactor, wherein the lowermost zone 9 is a sludge collecting zone, zone 10 is an anoxic settling zone, and zone 11 is a mixing and aeration zone through which the wastewater is pumped. Floating balls 17 are buoyant plastic balls on which bacterial media are to attach themselves. However the buoyant balls merely delimit the tank into three zones, wherein only the topmost area of the tank is the zone wherein the reaction takes place. The flow within the aerobic zone is directed downwardly, and the anaerobic activated sludge will not contribute to the treatment of the wastewater.

Furthermore, this reactor functions according to the air lift method, and is thus rather energy intensive. The effluent will also comprise quite a large amount of suspended solids due to the violent agitation of the was tewater.

EP-A-0428537 describes a process for the biological purification of wastewater by an activated sludge method, wherein the wastewater is contacted with micro-organisms in two treatment zones by being alternatingly introduced into

S

said treatment zones. However this method necessitates a subsequent treatment in a clarifying basin.

WO-A-91/11396 pertains to a system and method for the production of biofilm carriers and a subsequent treatment of was tewater thereby.

Review articles such as "Moving-medium biofilm reactors" by Rodgers and Zhan Reviews in Environmental Science and Biotechnology 2: 213-224 2003, and "Development of anaerobic sludge bed (ASB) reactor technologies for domestic wastewater treatment: motives and perspectives" by Kalago and Verstraete World Journal of Microbiology & Biotechnology 15:523-534, 1999, show some of the various approaches to wastewater treatment which are either in use or are beginning to be implemented. It is worth mentioning the Rotating Biological Contactors (RBC) and the Vertically Moving Biofilm Reactors discussed by Rodgers arid Zhan.

Both methodologies differ widely from the reactor as discussed in the present application. The authors further discuss the method known as Moving Bed Biofilm Reactors wherein use is made of carriers as discussed in Kalago and Verstraete discuss various methods for anaerobic treatment of wastewater but are less concerned with the aerobic post treatment of the resulting effluent.

Amongst the methods discussed are the use of upf low anaerobic sludge blanket reactor (UASB) as well as septic constructed upon the same principle, expanded granular sludge bed (EGSB), hydrolysis upf low sludge bed (HUSB) and variants thereupon. As is noted, there is a general need for a subsequent aerobic system for post-treatment of the ef fluent in order to effect nutrient and pathogen removal.

The post-treatment systems may be quite substantive and examples comprise facultative lagoons and oxidation ponds.

Goncalves et al in Water Science and Technology Volume 38, issues 8-9, 20 November 1998, pages 189-195 present a method for a two step treatment of wastewater using a combination of an Upf low Anaerobic Sludge Blanket (t.JASB) reactor and a submerged biofilter. The submerged biofilter is mainly a polishing step for the effluent after the wastewater has been treated in the UASB, and the described method illustrates the complexity of the background art systems. The submerged biofilter does not form a part of the UASB reactor, it will require separate sludge handling, and there is no circulation between the anaerobic process and the submerged biofilter.

According to a first aspect of the present invention, there is provided a reactor for the biological treatment of feedwater, said reactor comprising: one or more feedwater inlets; one or more sludge outlets; one or more effluent outlets; and, at least an anoxic/anaerobic reaction zone and an aerobic reaction zone; wherein: said one or more feedwater inlets are arranged generally at a lower portion of said reactor for furnishing feedwater to the reactor, said one or more sludge outlets are arranged at a lower portion of said reactor for the removal of sludge from said reactor, said one or more effluent outlets are arranged at an upper portion of said reactor for the removal of treated effluent from the reactor, said anoxic/anaerobic reaction zone is arranged in a lower portion of said reactor and said aerobic reaction zone is arranged in an upper portion of said reactor, and said reaction zones are at least

S

partially separated by a separator arranged for separating the upper aerobic reaction zone and the lower anoxic/anaerobic reaction zone, such that feedwater provided to the reactor can be subjected to both an aerobic and an anoxic/anaerobic treatment process within a single reactor volume.

According to a second aspect of the present invention, there is provided a method for treating a feedwater stream wherein said feedwater stream is furnished to a reactor through one or more feedwater inlets, sludge is removed from one or more sludge outlets, and effluent is removed from one or more effluent outlets, wherein said reactor comprises a plurality of reaction zones, said reaction zones comprising an anoxic/anaerobic reaction zone in a lower portion of said reactor, and an aerobic reaction zone arranged in an upper portion of said reactor, wherein: said feedwater is passed through said lower anoxic/anaerobic reaction zone, wherein said feedwater flows past a separator arranged for separating said anoxic/anaerobic reaction zone from said aerobic reaction zone, wherein said feedwater flows into said aerobic reaction zone for aerobic biological treatment therein, wherein resulting biological matter from said aerobic biological treatment settles down to said lower anoxic/ariaerobic reaction zone, and wherein said biological matter is subjected to an anoxic/anaerobic reaction such that said biological material is treated, whereby said feedwater is subjected to both an anoxic/anaerobic treatment and an aerobic treatment within a single reactor volume.

The invention further comprises the use of said reactor for the treatment of both municipal and industrial wastewater, as well as for the recycling of process water.

The preferred embodiments handle at least some of the problems resulting from high suspended solid and sludge production in the feedwater treatment systems and minimize the costs of operation and maintenance in biological feedwater treatment systems.

The preferred embodiment provides a biological reactor designed to control the suspended solid and sludge production and to produce an effluent having a relatively low concentration of suspended solids.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawing, in which: Figure 1 shows schematically an example of a reactor according to an embodiment of the present invention.

Briefly, the preferred reactor has a feedwater inlet 1 comprising a subsequent feedwater flow distributor 11, a sludge outlet 21, an effluent outlet 22, a lower anoxic/anaerobic reaction zone 31 comprising activated sludge and/or biofilm carriers 51, an upper aerobic reaction zone 32 comprising biofilm carriers 52, a separator 4, upper and lower screens 6 for delimiting the upper reaction zone 32, a bubble diffusion device 7 for releasing gas to the upper aerobic reaction zone 32 and a recycle line 8 for use in some of the embodiments of the invention. The flow direction of the feedwater has been indicated, as has the angle e for the separator 4. The flow directions have been indicated in order to show some of the flow patterns within the reactor.

The preferred embodiment of the present invention provides a reactor wherein the reactor volume allows an anoxic/anaerobic treatment as well as an anaerobic treatment of feedwater to take place within said volume.

The reactor comprises inlets 1 for the feedwater to be treated, and respective outlets 22,23 for effluent and sludge. The inlets 1 for feedwater are arranged at the lower end of the reactor such that the feedwater passes through the sludge or biological carriers 51 arranged therein. This is an advantage as the feedwater will provide carbon to the anoxic/anaerobic reaction zone 31.

The feedwater will as a consequence first be treated within the lower anoxic/anaerobic reaction zone 31.

In an embodiment, the feedwater is distributed through a feedwater flow distributor 11 such that the feedwater flow is well distributed before flowing through the lower anoxic/anaerobic reaction zone 31. This will allow for a good distribution of carbon in embodiments wherein the feedwater comprises carbon which will be consumed by the anoxic/anaerobic biological material within the lower reaction zone 31.

The lower anoxic/anaerobic reaction zone 31 may comprise an activated sludge, biofilm carriers 51 or other biological agents for the anoxic/anaerobic treatment of the feedwater as well as for the stabilization of sludge and settling biomass from the upper aerobic reaction zone 32.

In an embodiment, there may be arranged a mixture of an activated sludge and biofilm carriers 51 for the anoxic/anaerobic treatment of the feedwater and sludge.

The reaction mechanisms of the lower anoxic/anaerobic reaction zone 31 are well known in the art, and will as such not be described in detail in the present specification. There are various treatment mechanisms which may be used such as an anoxic/anaerobic denitrification of the sludge within the lower reaction zone 31. Using a denitrification process, the carbon comprised in the feedwater will as mentioned above serve as a carbon source for the reaction.

The lower reaction zone 31 is thus arranged for digesting and collecting excess sludge settling from an upper reaction zone 32 of the reactor. The residence time of the sludge within the lower reaction zone 31 may be controlled by periodic or continuous sludge purging through the sludge outlet 21 and may be adapted such that there is sufficient time for the stabilization of the sludge. This will result in a lower sludge volume and thus further to a reduced sludge volume, resulting in lower post-treatment costs associated with the treatment of the sludge.

After having passed through the anoxic/anaerobic reaction zone 31, the feedwater passes a separator 4, wherein the separator 4 has a variety of functions including keeping the lower anoxic/anaerobic reaction zone 31 separate from the upper aerobic reaction zone 32, preventing diffusion of oxygen from the upper aerobic reaction zone 32 to the lower anoxic/anaerobic reaction zone 31, as well as for directing biological material settling from the upper reaction zone 32 towards the lower reaction zone 31. -1].-

Above the separator 4 there is arranged the previously mentioned upper aerobic reaction zone 32, wherein the feedwater undergoes an aerobic biological treatment. The feedwater treatment within the upper aerobic reaction zone 32 comprises a biological treatment of the feedwater by biological material arranged within the reaction zone 32.

The aerobic reaction zone 32 may comprise a plurality of aerated biofilm carriers 52 being kept in place using coarse screens 6, a fluidized bed comprising biofilm carriers, a fixed bed comprising carriers, or any other suitable method for carrying biofilm, all of which should be considered to lie within the scope of the present invention. The biofilm carriers as such are known from the art. As the treatment of the feedwater within the upper reaction zone 32 takes place, biofilm will grow on the biofilm carriers 52. The resulting biofilm will after having reached a sufficient size fall or be sheared off the carriers 52 and the now free floating biological material will settle towards the lower section of the reactor. The separator 4 is arranged for directing the settling biological material towards the lower anoxic/anaerobic reaction zone 31 wherein the biological material will become part of the sludge comprised therein.

The microbial processes within the lower anoxic/anaerobic reaction zone 31 may in an euibodiment comprise a denitrification process. This will result in nitrate and nitrites in the feedwater being reduced to form gaseous nitrogen. Other biological anoxicfanaerobic reaction processes may evidently occur within the lower reaction zone 31. Other examples may comprise the

S

biological degradation of micro-organic pollutants which are often a problem in water treatment processes.

The microbial processes within the upper aerobic reaction zone 32 may in an embodiment comprise the nitrification of compounds within the feedwater such that ammonia NH3 reacts to form nitrite and nitrate. Other biological aerobic reaction processes may evidently occur within the upper reaction zone 32.

The volumetric proportions of the lower and upper reaction zones 31,32 to each other may be chosen freely according to the feedwater composition and the desired reaction and effluent quality.

After having passed through the upper reaction zone 32, the feedwater has thus undergone both an anoxic/anaerobic reaction and an aerobic reaction within a single reactor volume.

For aerating the upper aerobic reaction zone 32, a bubble diffuser 7 is arranged for releasing oxygen comprising bubbles such that the biological oxygen demand of the feedwater is met and the aerobic reaction may take place. The bubble diffuser 7 may have any adapted constitution and a plurality of examples is given in the art. The bubble diffuser 7 may in an embodiment release bubbles having a rather small diameter, being thus arranged for not having a too great shearing effect upon the biofilm comprised within the upper reaction zone 32. If needed the bubble diffuser 7 should also periodically be able to provide a larger amount of bubbles such that the biofilm carriers within the upper may slough off excess biofilm growth.

The bubbling of air through the upper reaction zone 32 will further result in a mixing of the upper reaction zone 32, ensuring that there is a circulation of fluid within the reaction zone 32, allowing mixing to take place. This is of importance to ensure that the reactor volume is used in an efficient mariner.

The separator 4 serves a plurality of functions as mentioned above. The shape of the separator is of some importance to ensure that it will perform the various functions in an adequate manner. The preferred separator has an upwardly tapered shape such that biological material does not accumulate on the upper surface of said reactor.

The angle of inclination of the separator 4 may be varied according to the size of bioflocs settling down from the upper reaction zone 32 and according to the flow regime which is to occur around the separator 4. The separator 4 may for example have an angle between about 200 to about 70°. The separator 4 should also hinder the movement of anoxic/anaerobic sludge into the aerobic reaction zone 32.

If the sludge comprised in the lower reaction zone 31 is entrained into the upper aerobic reaction zone, the reactor will evidently function less well. The separator 4 should thus be of a size and shape to hinder such sludge movement.

Correspondingly, the separator 4 should hinder the oxygen diffusion from being too large from the upper aerobic reaction zone 32 down into the lower anoxic/anaerobic reaction zone 31. There will evidently be some flow down towards the lower reaction zone 31, thus providing oxygen to the anoxic/anaerobic zone. However, due to the shape of

S

the separator 4, the oxygen diffusion will be reduced.

Thus the separator 4 will function as a hydrodynamic separator between the lower and upper reaction zones 31,32, as an oxygen diffusion control, and as a sludge trap.

Amongst the various shapes that may be envisaged for the separator 4 are upwardly tapered roof-like shapes or upwardly cones or the like. However, any suitable separator geometry should be considered as being within the scope of the invention. The separator 4 will in an embodiment be arranged about a centre axis of the reactor, although it may also be arranged in closer proximity to a first wall than a second.

Given the functioning of the reactor wherein the mixing of the different reaction zones 3 should be reduced, it is furthermore clear that a relatively low superficial velocity of liquid upf low should be used. The superficial velocity of the liquid upf low is preferably within about 0.001 cm/mm and 3.5 cm/mm, although higher flow velocities may be envisaged.

One should furthermore aim to reduce the amount of biological material in the effluent, as this will with the preferred embodiment probably be the major source of total suspended solids in the effluent. Having a too high flow velocity or having a too violent bubbling action could result in a rising value of total suspended solid in the effluent by entrainment of biological material from the biofilm carriers.

The flow pattern within the reactor is in reality somewhat more complicated than the simple throughput of water from the lower portion of the reactor to the effluent

S

outlet at the upper portion of the reactor. There will be backinixing due to the settling movement of the biological material, there will be a complex flow pattern around the separator wherein feedwater having flowed past the separator 4 will pass close to the reactor wall, and return water from the upper portion of the reactor will pass along the separator plates down into the lower reaction zone 31.

There will be mixing within both the upper 32 and lower 31 reaction zones as well. This mixing and return flow within the reactor will result in the feedwater passing from the lower reaction zone 31 to the upper reaction zone 32 a number of times before exiting the reactor as treated effluent. If needed, a recycle line 8 may further be arranged such that the effluent is recycled back to the feedwater inlet 1 for further treatment. The percentage of effluent to be recycled may be varied according to need and according to the desired treatment degree of the feedwater.

Measurements of, amongst others, ammonia content and oxygen demand may be among the parameters influencing the degree of recycling.

There has been mention throughout of the upper and lower reaction zones 3, as is shown in Figure 1 of the present application. Although being shown as being mainly vertical, it is evident that the reactor as such may be inclined as long as there is sufficient vertical reactor inclination to allow the biological material from the upper reaction zone 32 to settle into the lower reaction zone 31.

In order for constructing an inclined reactor such as described above it is evident that the separator 4 should also be modified in order for adapting to the modified reactor lay out.

The reactor as described may be run in batch mode or continuous mode according to the operational specifications of the feedwater treatment.

Thus the present invention describes both a reactor as such, and a method for treating feedwater such that it may later be treated to produce water of high standards, suitable for tertiary treatment, or further to comply with drinking water standards.

The reactor according to the preferred embodiment has been verified experimentally in a laboratory-scale biological reactor to evaluate the degree of suspended solid control and sludge production reduction. The biological reactor and the separator were constructed from high-grade transparent acrylics. A biofilm carrier made of HDPE was filled in the upper chamber with the filling fractions for the biofilm carrier of approximately 50% of the chamber volumes giving effective specific surface areas of 250 m2/m3. The biofilm carriers were shaped as short cylinders having internal crosses and external wavy fins.

The air flowrate for aeration in the biofilm chamber was 1 L/min. The biofilm chamber was enclosed by perforated plates with 5 mm diameter holes arranged for retaining the carriers. The anaerobic activated sludge was filled in the lower chamber. The total suspended solid concentrations of the anaerobic activated sludge were in a range of 6.2-8.7 g/L with solid retention time (SRT) of 21 days. The effective volumes of the biofilm chamber and anaerobic activated sludge zone were about 1.6 L and about 2.2 L respectively. The biofilm zone and anaerobic activated zone chamber theoretically contributed approximately 33% and 66% to the overall hydraulic retention time respectively. The liquid flow of wastewater spent more hydraulic retention time in the chamber of anaerobic activated sludge. The superficial liquid velocities in the vertical biological reactor ranged from about 0.05 to about 0.1 cm/mm. The dividing plate used had a roof-like shape with a 38° angle slope to a horizontal line. The gaps between the dividing plate edges and the reactor walls were 7mm.

The experiment was aimed at investigating the strategy to control the suspended solid concentrations. The effect of liquid upflow velocities and the hydraulic retention times (HRT) on the suspended solid concentrations was determined. Municipal was tewater from the Trondheim community used was pre-treated by a gravity settler, and then the overflow from the settler was pumped to the biological reactor. A MasterFiex computerized peristaltic pump with speed control of �0.25% was used to control the flowrate of the wastewater. National Instrument DAQ card USB 6210 and LabVIEW 8.2 were used for experimental data collections.

The effect of liquid upflow velocities and hydraulic retention times (HRT) on effluent quality from the vertical biological reactor was investigated. The total suspended solid (TSS) concentrations and residual organic characteristics in the effluent from the biological reactor are dependent on the liquid upf low velocities. Low superficial liquid upf low velocities used were 0.099 cm/mm at HRT of 5.2 h and 0.062 cm/rain at HRT of 8.3 h. Table 1 shows the average characteristics of wastewater and effluents from the vertical biological reactor at HRTs of 5.2 and 8.3 hours. The concentration of total suspended

S

solid, FCOD, and turbidity in the effluents at HRT of 8.3 h was significantly lower than that at HRT of 5.2 h. At HRT of 8.3 h or the upf low velocity of 0.062 cm/mm, average TSS concentration was reduced to 14. 3 mg/L which was very low compared to typical effluents at approximately 200 mg/L for the biofilni reactant and 350 mg/L for activated sludge biological reactor with a particle settler. Removal of colour, DOC, ammonia, total nitrogen, and t.JV adsorbances in the effluents at HRT of 5.2 and 8.3 h were relatively similar. High removal rates of suspended solids and turbidities were achieved at HRT of 8.3 hours which were 87.5% and 92% for suspended solid rejection and turbidity rejection by the biological reactor respectively. The effluent from the reactor at HRT of 8.3 hours was much clearer than that at HRT of 5.2 hours. Reduction in conductivity in Table 1 shows that the anaerobic part mainly removed inorganic salts in the wastewater influent.

SUVA @ 254 and 436 rim in the effluent at HRT of 8.3 hours were different from those in the influent and those in the effluent at HRT of 5.2 hours. Increases in SUVA referred to some molecular changes of organic substances after biodegradations in the biological reactor.

Table 1. Average characteristics of influent wastewater and removal rates in effluents from the vertical biological reactor at 5.2 and 8.3 hours HRT Effluent from the bioreactor Influent ____________________________________ Characteristics to the HRT at 5.2 h HRT at 8.3 h bioreac tor _____________________________________ Value % Removal Value % Removal

S

Chemical oxygen demand -COD (mg 273.4 89.7 67.2 56.1 79.5 02 / L) ___________ ______ __________ ______ __________ Filtered chemical oxygen demand -135.2 52.4 61.2 27.6 79.6 FCOD (mg 02/L) _____ _________ _____ _________ Total suspended solid -TSS 114.7 46.1 59.8 14.3 87.5 (mg / L) ___________ _____ __________ ______ __________ Total organic 73.6 27.2 63.0 19.9 73.0 carbon-TOC (mg/L) Dissolved organic carbon -DOC 42.4 17.8 58.0 13.1 69.1 (rng / L) ____________ ______ __________ ______ __________ Turbidity (NTU) 89.3 19.6 78.1 7.1 92.0 N-NH3 (mg/L) 29.7 22.5 24.2 21.2 28.6 Total nitrogen 41.3 34.2 17.2 28.6 30.8 UV absorption at 254 run -42.2 28.6 32.2 27.3 35.3 (rn-i) _____________ _______ ____________ _______ ____________ UV absorption at 436 run -2.1 1.8 14.3 1.6 23.8 (rn-i) Specific liv absorption at 254 0 99 1 6 -2 0 -rim -SUVA@254 run (L/m.rng) __________ _____ _________ _____ _________ Specific UV absorption at 436 0 050 0 101 -0 122 -urn -SUVA@436 run (L/m.rng) __________ _____ _________ _____ _________ Conductivity 1016 804 -781 -(u.S/cm) ___________ _____ __________ _____ __________ pH 7.34 8.15 -8. 29 - Colour (mg Pt/L) -56.4 -47.1 -With the reactor of the preferred embodiment, the sludge production will be lower than for comparable methods according to the background art. This is of importance as sludge handling to render the resulting sludge disposable is costly. There will furthermore be less need for sludge pumping as the sludge from the upper reaction zone 32 will simply settle down into the lower reaction zone and form part of the sludge comprised therein. The design of the reactor will allow for longer sludge residence time, further reducing the produced sludge volume, and thus reduce the cost of sludge handling.

Due to the flow pattern of the reactor wherein the flow is mainly upwardly directed, the feedwater first passing through the lower anoxic/anaerobic reaction zone, the resulting effluent from the reactor will have a lower total suspended solid than in comparable methods of the background art. This allows for a plurality of benefits amongst which are less problems with clogging in the aerobic reaction zone 32, evidently less total suspended solids in the effluent which may necessitate further treatment of the effluent and particularly that there will be less need for aeration of the aerobic reaction zone 32.

As a major proportion of the energy costs associated with feedwater handling is due to the need for pumping air for meeting the biological oxygen demand of the feedwater, the savings upon using a reactor according to the preferred embodiment are substantial. Further benefits of the present reactor include less water and chemical use upon treatment of the feedwater. This is of particular interest from the environmental point of view.

The reactor is of particular interest when applied to industrial or municipal wastewater handling. The feedwater volumes that are required to be treated in such applications are very large and thus there is a major incentive to reduce all costs associated with handling such feedwaters. Other applications include treating specific drinking water applications, or the treatment of feedwater from agriculture or marine culture applications.

A plurality of reactors according to the present invention may be arranged in parallel such that a feedwater plant may treat large volumes of feedwater. A modular arrangement presents a number of advantages allowing for ease of inspection and replacement of malfunctioning elements. in the embodiment wherein the reactors are arranged mainly vertically this may allow for a feedwater plant having a small footprint, thus further reducing the capital costs of the plant.

The reactor as such may be used for the biological treatment of any feedwater such as for instance municipal and industrial wastewaters. The biological composition of both the sludge comprised within the lower reaction zone 31 and the composition of the upper reaction zone 32 is largely adaptable to adjust to the treatment needs of a variety of wastewater compositions.

Embodiments of the present invention have been described with particular reference to the examples illustrated. However, it will be appreciated that variations and modifications may be made to the examples described within the scope of the present invention.

Claims

1. A reactor for the biological treatment of feedwater, said reactor comprising: one or more feedwater inlets; one or more sludge outlets; one or more effluent outlets; and, at least an anoxic/anaerobic reaction zone and an aerobic reaction zone; wherein: said one or more feedwater inlets are arranged generally at a lower portion of said reactor for furnishing feedwater to the reactor, said one or more sludge outlets are arranged at a lower portion of said reactor for the removal of sludge from said reactor, said one or more effluent outlets are arranged at an upper portion of said reactor for the removal of treated effluent from the reactor, said anoxic/anaerobic reaction zone is arranged in a lower portion of said reactor and said aerobic reaction zone is arranged in an upper portion of said reactor, and said reaction zones are at least partially separated by a separator arranged for separating the upper aerobic reaction zone and the lower anoxic/anaerobic reaction zone, such that feedwater provided to the reactor can be subjected to both an aerobic and an anoxic/anaerobic treatment process within a single reactor volume.

2. A reactor according to claim 1, wherein the lower anoxic/anaerobic reaction zone is arranged for the digestion and/or stabilisation of sludge.

3. A reactor according to claim 1, wherein said lower anoxic/anaerobic reaction zone comprises an activated sludge for the anoxic/anaerobic digestion of biological material from the upper aerobic reaction zone.

4. A reactor according to any of claims 1 to 3, wherein said upper aerobic reaction zone comprises aerobic biofilm carriers, wherein said aerobic biofilm carriers are arranged for bearing biological films arranged for the treatment of feedwater provided to the reactor.

5. A reactor according to claim 4, wherein said aerobic biofilm carriers are arranged for releasing biological material in a generally downwards direction upon the completion of a growth cycle on the aerobic biofilm carriers.

6. A reactor according to claim 5, wherein said aerobic biofilm carriers are arranged to be fluidized within the upper aerobic reaction zone.

7. A reactor according to claim 6, wherein said aerobic biofilm carriers are arranged for being fixed within the upper aerobic reaction zone.

8. A reactor according to any of claims 1 to 7, wherein a bubble diffuser is arranged for providing oxygen to said aerobic reaction zone.

9. A reactor according to claim 8, wherein said bubble diffuser is arranged for releasing bubbles having a small diameter.

10. A reactor according to any of claims 1 to 9, wherein said separator is arranged for allowing the passage of biological matter from the upper aerobic reaction zone to the lower anoxic/anaerobic reaction zone.

11. A reactor according to any of claims 1 to 10, wherein said separator has a generally upwardly tapered shape.

12. A reactor according to any of claims 1 to 11, wherein a recirculation line is arranged for recirculation of at least a portion of effluent from the upper portion of the reactor to the lower portion of the reactor.

13. A method for treating a feedwater stream wherein said feedwater stream is furnished to a reactor through one or more feedwater inlets, sludge is removed from one or more sludge outlets, and effluent is removed from one or more effluent outlets, wherein said reactor comprises a plurality of reaction zones, said reaction zones comprising an anoxic/anaerobic reaction zone in a lower portion of said reactor, and an aerobic reaction zone arranged in an upper portion of said reactor, wherein: said feedwater is passed through said lower anoxic/anaerobic reaction zone, wherein said feedwater flows past a separator arranged for separating said anoxic/anaerobic reaction zone from said aerobic reaction zone, wherein said feedwater flows into said aerobic reaction zone for aerobic biological treatment therein, wherein resulting biological matter from said aerobic biological treatment settles down to said lower anoxic/anaerobic reaction zone, and wherein said biological matter is subjected to an anoxic/anaerobic reaction such that said biological material is treated, whereby said feedwater is subjected to both an anoxic/anaerobic treatment and an aerobic treatment within a single reactor volume.

14. A method according to claim 13, wherein said biological treatment comprises a nitrification process in the aerobic reaction zone and a denitrification process in the anoxic/anaerobic reaction zone.

15. A method according to claim 14, wherein carbon in said feedwater is used as a carbon source for the denitrification process within said anoxic/anaerobic reaction zone.

16. A method according to any of claims 13 to 15, wherein the residence time of sludge in said lower anoxic/anaerobic reaction zone is sufficient for sludge stabilization and compression to be initiated such that the resulting sludge volume is reduced.

17. A method according to any of claims 13 to 16, wherein a bubble diffuser provides an oxygen-comprising gas stream to said aerobic reaction zone such that at least a portion of the oxygen demand of said aerobic reaction zone is met.

18. A method according to claim 17, wherein said bubble diffuser releases bubbles having a small diameter.

19. A method according to claim 17 or claim 18, wherein the upwards movement of the bubbles agitates the upper reaction zone and provide an impulse for the upwardly directed flow of feedwater.

20. A method according to any of claims 13 to 19, wherein aerobic biofilm carriers carry biological films for the treatment of said feedwater.

21. A method according to claim 20, wherein said aerobic biofilm carriers are circulated within the upper aerobic reaction zone.

22. A method according to any of claims 13 to 21, wherein said superficial liquid upflow velocity within said anoxic/anaerobic reaction zone lies within the range of about 0.0005 cm/s to about 4 cm/s.

23. A method according to any of claims 13 to 22, wherein at least a portion of said effluent stream is recycled for a further treatment within said reactor.

25. Use of a reactor according to any of claims 1 to 12 for the treatment of a municipal wastewater stream.

26. Use of a reactor according to any of claims 1 to 12 for the treatment of an industrial wastewater stream.

27. A reactor for the biological treatment of feedwater, substantially in accordance with any of the examples as hereinbefore described with reference to and as illustrated by the accompanying drawing.

28. A method for treating a feedwater stream, substantially in accordance with any of the examples as hereinbefore described with reference to and as illustrated by the accompanying drawing.