WATER TREATMENT SYSTEM AND METHOD

Abstract

A water treatment system comprising a first reactor and a second reactor arranged to be placed in series in a body of water, the first and/or second reactor comprising at least one cell for housing biomedia. A mid-settling zone is provided between the first and second reactors for separating solids in the water. A method of treating water, the method comprising passing water to be treated through a first reactor and then a second reactor arranged in series in a body of water, the first and/or second reactors comprising at least one cell for housing biomedia, wherein the water is passed through a mid-settling zone between the first and second reactors before passing through the second reactor.

Claims

1. A water treatment system comprising a first reactor and a second reactor arranged to be placed in series in a body of water between an inlet of the body of water and an outlet of the body of water, the first and/or second reactor comprising at least one cell for housing biomedia, wherein there is provided a mid-settling zone between the first and second reactors for separating solids in the water.

2. The water treatment system of claim 1, further comprising one or more of an inlet settling zone upstream of the first reactor and an outlet settling zone downstream of the second reactor.

3. (canceled)

4. The water treatment system of claim 1, wherein the second reactor is arranged to be operated at a lower loading rate than the first reactor.

5. The water treatment system of claim 1, wherein the first reactor is adapted to operate at a loading rate of about 2.0 to about 6.0 g of soluble carbonaceous biochemical oxygen demand per effective surface area of biomedia per day (g sCBOD.sub.5/m.sup.2.Math.d).

6. The water treatment system of claim 1, wherein the second reactor is adapted to operate at a loading rate of about 0.5 to about 1.5 g of soluble carbonaceous biochemical oxygen demand per effective surface area of biomedia per day (g sCBOD.sub.5/m.sup.2.Math.d), or about 0.75 to about 1.25 g sCBOD.sub.5/m.sup.2.Math..

7. The water treatment system of claim 1, wherein the second reactor is arranged to operate at about 30-70% lower than the loading rate of the first reactor.

8. The water treatment system of claim 1, further comprising at least one baffle positioned across a flow path in the body of water and around the first and/or the second reactor for directing the water through the first and/or the second reactor.

9. The water treatment system of claim 1, further comprising an inlet settling zone upstream of the first reactor, the inlet settling zone having a hydraulic retention time of about 1.0 to about 3.0 days, or about 1.5 to about 2.5 days.

10. (canceled)

11. The water treatment system of claim 1, further comprising an outlet settling zone downstream of the second reactor, a hydraulic retention time of the outlet settling zone being about 0.5 to about 1.5 days.

12. (canceled)

13. The water treatment system of claim 1, wherein the mid-settling zone between the first and second reactors has a hydraulic retention time of about 1.0 to about 4.0 days, or about 1.5 to about 3.5 days.

14. The water treatment system of claim 1, wherein the mid-settling zone between the first and second reactors has an overflow rate of about 0.5 to about 2.0 m.sup.3/m.sup.2.Math.d.

15. (canceled)

16. The water treatment system of claim 1, wherein the body of water is a lagoon.

17. (canceled)

18. The water treatment system of claim 1, further comprising a filter at the outlet of the body of water.

19-20. (canceled)

21. The water treatment system of claim 1, wherein at least one of the first and/or second reactor comprise a plurality of cells arranged as an array, and the first and/or the second reactor are adapted to float in the body of water with the at least one cell immersed in the water.

22-38. (canceled)

39. The water treatment system of claim 1, further comprising biomedia housed within the at least one cell of the first and/or the second reactor, the biomedia comprising an unattached elongate thin film having a nest-like configuration in use and configured to be self-supporting within the water.

40-44. (canceled)

45. The water treatment system of claim 1, wherein the first and/or second reactor is modular.

46-89. (canceled)

90. The water treatment system of claim 1, wherein a hydraulic retention time of the system is less than 15 days or less than 10 days.

91. A water treatment system comprising a first reactor and a second reactor arranged to be placed in series in a body of water between an inlet of the body of water and an outlet of the body of water, the first and/or second reactor arranged to house biomedia, wherein the first reactor is arranged to operate at a higher loading rate than the second reactor.

92. A water treatment system comprising a first reactor and a second reactor arranged to be placed in series in a body of water between an inlet of the body of water and an outlet of the body of water, the first and/or second reactor arranged to house biomedia, a mid-settling zone between the first and second reactors for separating solids in the water, the first reactor being arranged to operate at a higher loading rate than the second reactor, the first and/or second reactor being adapted to float in the body of water, and the biomedia having a surface area of about 160 to about 330 m.sup.2 per m.sup.3 of water volume of the body of water.

93. The system of claim 1, further comprising a filter at the outlet of the body of water, wherein the filter is biomedia at a density of about 160 to about 330 m.sup.2 of biomedia per m.sup.3 of water.

94. The system of claim 1, wherein the inlet is upstream of the first reactor and the outlet is downstream of the second reactor.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0099] Further aspects and advantages of the present invention will become better understood with reference to the description in association with the following in which:

[0100] FIG. 1 is a schematic representation of a water treatment system comprising reactors and at least one settling zone according to an embodiment of the present disclosure;

[0101] FIG. 2 is a schematic representation of a water treatment system when used in a lagoon, according to another embodiment of the present disclosure, the water treatment system comprising reactors having at least one cell and at least one settling zone;

[0102] FIG. 3 shows the water treatment system of FIG. 2 in which the cells are visible;

[0103] FIG. 4 shows the water treatment system of FIGS. 2 and 3 in which the direction of water flow through the system is indicated with arrows;

[0104] FIG. 5 shows one embodiment of a reactor which may be used with the method and system of the present disclosure, the reactor having a buoyant structure and at least one cell;

[0105] FIG. 6 shows one embodiment of a cell which may be used with the method and system of the present disclosure; and

[0106] FIG. 7 shows an expanded view of the cell of FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

[0107] The present invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including”, “comprising”, or “having”, “containing”, “involving” and variations thereof herein, is meant to encompass the items listed thereafter as well as, optionally, additional items.

[0108] Furthermore, although an embodiment of the present invention described below with reference to FIGS. 2-7 describes a wastewater treatment system and method in a lagoon, the present invention can equally be used in or applied to any body of water or any combinations of bodies of water. Furthermore, discrete tanks could be provided as the body of water to delineate water treatment zones. The method and the system of the present disclosure can be applied to treating wastewater discharged from residential, commercial or community wastewater systems, as well as any liquid containing impurities in the present or in any other technical fields, such as industrial or agri-food wastewater. For this reason, expressions such as “waste water”, and “septic” and the like should not be taken to limit the scope of the present invention and should be taken to include all other kinds of liquids or technical applications with which the present invention may be used and could be useful.

[0109] Moreover, in the context of the present invention, the expressions “wastewater”, “water to be treated” and any other equivalent expression known in the art used to designate a substance displaying liquid-like features which may be contaminated or polluted or require cleaning in any other way, as well as any other equivalent expressions and/or compound words thereof, may be used interchangeably. Furthermore, expressions such as “polluted” and “contaminated” for example, may also be used interchangeably in the context of the present description.

[0110] In addition, although one embodiment of the present invention as illustrated in the accompanying drawings comprises various mechanical components, such as actuated ball valves, blowers, fine bubble diffusers, etc., and although one embodiment of the present invention as shown consists of certain geometrical configurations and arrangements, not all of these components, geometries and/or arrangements are essential to the present disclosure and thus should not be taken in their restrictive sense, i.e. should not be taken as to limit the scope of the present invention. It is to be understood, as also apparent to a person skilled in the art, that other suitable components and co-operations thereinbetween, as well as other suitable geometrical configurations and arrangements may be used in the wastewater treatment system and method according to the present invention, as will be briefly explained hereinafter, without departing from the scope of the invention. In the following description, the same numerical references refer to similar elements.

[0111] Referring to FIG. 1, there is shown a schematic representation of a water treatment system 10, according to an embodiment of the present disclosure, comprising a first reactor 12 and a second reactor 14 arranged to be placed in series in a body of water 16 having an inlet 18 and an outlet 20, the first and/or second reactor 12, 14 arranged to house biomedia 22 (shown in FIG. 7) for converting biomass. The water treatment system 10 comprises a mid-settling zone 24 between the first and second reactors 12, 14. By means of this arrangement, water to be treated flows through the first reactor 12, then the mid-settling zone 24, followed by the second reactor 14. Optionally, the water treatment system 10 further comprises an inlet settling zone 26 for primary clarification, sludge storage and/or retaining decantable (settleable) solids from raw sewage. Optionally, the water treatment system 10 further comprises an outlet settling zone 28 for final clarification and sludge storage zone at the outlet. In certain embodiments, a filter (not shown) is also provided at the outlet 20.

[0112] According to another embodiment which is illustrated in FIGS. 2-4, the body of water 16 comprises a lagoon having an inlet 18 and an outlet 20. In this embodiment, the lagoon has two basins in fluid communication with one another although the system 10 of the present disclosure can be adapted to be incorporated into any type of body of water or any combinations of different bodies of water, with any configuration. The embodiment of FIGS. 2-4 comprises (i) an inlet settling zone 26 upstream of the first reactor 12 and downstream of the inlet 18, (ii) a mid-settling zone 24 inbetween the first and second reactors 12, 14, and (iii) an outlet settling zone 28 downstream of the second reactor 14 and upstream of the outlet 28. The reactors 12, 14 and the settling zones 24, 26, 28 are positioned in series. There is no recirculation of water in this embodiment of the system 10.

[0113] The settling zones 24, 26, 28 are portions of the body of water 16 in which particulate matter such as sludge and scum can settle, for example by sedimentation, and be stored. Additional means of settling solid and particulate matter are also possible such as by filtering, screening or flotation. The inlet settling zone 26 of this embodiment, allows primary clarification and sludge storage for retaining settleable solids such as raw solids from raw sewage thereby allowing soluble matter to be treated by the first reactor 12. The mid-settling zone 24 is for settling and storing particulate matter leaving the first reactor 12. The outlet settling zone 28 is for settling the secondary particulate matter generated by the second reactor 14 which may avoid the need for a clarifying reactor or separate sludge removal. The reactors 12, 14 comprise at least one cell 32 for housing biomedia 22. Biomedia 22 is also known as a bacteria growth device or biofilm support media, has surfaces for bacteria to attach and grow on for converting biomass.

[0114] The reactors 12, 14 for use with embodiments of the present system and method can take any form. One embodiment of the reactors 12,14 is illustrated in FIGS. 2, 3, 5, 6 and 7, although it will be clear that other forms or types of reactors are possible. In this embodiment, each reactor 12, 14 is adapted to float in the body of water 16 by means of a buoyant structure 30 for supporting the cells 32 for suspension in the body of water. In other words, in this embodiment of the present system, the reactors 12, 14 have a two-part construction comprising the buoyant structure 30 and the cells 32. The cells 32 can be removeably attached to the buoyant structure 30. In this embodiment, the buoyant structure 30 comprises a first set of hollow pipes 34 connected to a second set of hollow pipes 36 which carry gas to gas diffusers 38 contained at a distal end of the cells 32. The first and second sets of pipes 34, 36 form a grid formation or a frame defining a plurality of openings 40. Each opening 40 defined by the frame may be considered a unit of the buoyant structure, and each buoyant structure unit is arranged to support one cell 32. Each unit may be quadrilateral, such as square or rectangular. In this way, the cells 32 can be arranged as an array and, in use, substantially immersed in the body of water as an array. The array of cells can be any configuration.

[0115] In this embodiment, the first set of hollow pipes 34 provide the predominant buoyancy of the buoyant structure, and the second set of hollow pipes 36 provide additional buoyancy. The first set of hollow pipes 34 have a wider diameter (about 10 inches in this embodiment) than the second set 36, have sealed ends and, in use, will sit partially in the water, whereas the second set of hollow pipes 36 are arranged above the first set of hollow pipes 34 when assembled and are used as aeration lines. It will be appreciated that any other configuration of the buoyant structure 30 is also possible which provides buoyancy to the cells. Connectors 42 are provided for connecting the first and second sets of hollow pipes 34, 36 to one another at approximately 90 degrees to each other. The connectors 42 comprise two faces, a bottom face comprising a first saddle which is sized and shaped for receiving a portion of pipe from the first set of hollow pipes 34, and a top face comprising a second saddle which is sized and shaped for receiving a portion of pipe from the second set of hollow pipes 36, the first and second saddles being arranged at right angles to one another. The second set of hollow pipes 36 can have male alignment studs that fit into female holes located on the connector to facilitate the construction of the buoyant structure 30. The saddles comprise two arms extending from a curved base. The first set of hollow pipes 34 may be manufactured with the connectors 42 preinstalled before delivery to the site for ease of installation. It will be appreciated that any other type or form of connector can be used.

[0116] The hollow pipes 34, 36 may comprise high density polyethylene (HDPE) or polyvinyl chloride, although it will be apparent to a skilled person that they can be made of any other material which can float or be made to float in the body of water and which has sufficient flexibility to mechanically withstand turbulence in the body of water, as well as removal and installation steps into/out of the body of water. Installation can be modular and comprises pulling or pushing the buoyant structure 30 into the water from the shore followed by attachment of the cells 32. It will be appreciated that the installation which may require considerable ‘bend’ of the hollow pipes due to a height difference between the shore and the water level. The buoyant structure offers flexibility to resist breakage under stress, such as waves or ice and installation/removal, but also allows enough rigidity to maintain the cells 32 in a substantially vertical configuration during aeration.

[0117] Each reactor 12, 14 also comprises at least one cover or covers 44 for covering the grid units of the buoyant structure 30. The covers 44 may comprise tiles which can be removeably attached to the buoyant structure 30 by means of the hollow pipe connectors 42, or any other separate connecting means (not shown). In the embodiment of FIGS. 5-7, the covers are attached to the buoyant structure by means of the connectors in which the arms of the second saddle extend sufficiently from the base to be received in slots in the cover 44. A rubber O-ring around the top of the connectors 42 is one way of attaching the cover 44 and which can provide enough elasticity to adapt to the movement of the buoyant structure 30. The cover 44 may also include openings 46 across its surface to facilitate anchoring during lifting operations. Excess air flow from the gas diffuser 38 can be evacuated in the periphery of the covers 44 to prevent the formation of ice stalagmites during cold weather. Air is forced to evacuate against warmer air lines thus limiting ice formation. The covers 44 can also function as a flooring for providing safe above water walkway access to the reactor and/or the cells for ease of maintenance or repair. The buoyant structure 30 together with the covers 44 are raft-like. As the covers 44 extend over the cells 32 in use, they also provide a protection over the cells 32 and the water being treated. For example, the covers 44 may reduce or block UV light exposure to prevent undesirable biogrowth. Furthermore, the covers 44 may be arranged to absorb solar radiation to transfer heat to the water, to maintain the temperature of the water or to prevent ice formation. For example, the covers 44 may be formed of a dark colour to absorb solar radiation.

[0118] As best seen in FIG. 5, the buoyant structure 30 also includes a handrail 48 around the perimeter of the first and/or second reactor 12, 14 as a safety feature and which can also provide a support or housing for additional components to the reactor such as a power/gas/electrical supply. The handrail 48 also supports an air manifold and an electrical ball valve controlling air feed to the gas diffuser 38 for biofilm thickness control. One part of the buoyant structure 30 may be in the form of a walkway 50 only extending from the grid to provide access from land to the cells 32. The walkway may have no cells suspended therefrom.

[0119] The buoyant structure 30 may be constructed on site or provided pre-made as a dock or a raft. The first and/or the second reactor 12, 14 can be installed into the body of water by initially placing the buoyant structure 30 on the water, then attaching the cells 32 to the buoyant structure 30 by passing them through the grid openings 40. Once the cells 32 have been positioned and secured, the covers 44 may be fitted. The modular construction of the reactors and/or water treatment system enables its retrofitting into any size or shape body of water. Removal of the cells for maintenance is also simple and can be performed without skilled labour. For example, the cells can be lifted vertically through the buoyant structure openings, or be released from the buoyant structure and allowed to float horizontally.

[0120] Turning now to the construction of the cells in one embodiment, each cell 32 comprises one or more cell units 52 or cell segments for varying the length of the cells. Each cell unit 52 comprises a water permeable wall 53 (FIG. 7) for retaining the biomedia 22 within the cell supported by vertical support struts 54. FIGS. 6 and 7 illustrate a cell 32 comprising three units 52 although any number of units is possible. The cell units 52 of one cell 32 are separated vertically by a unit or segment divider 56 which also space apart the vertical struts 54 and impart a cylindrical shape to the cells 32. The segment divider 56 can be made of any material such as a polymer or concrete. In one embodiment, the segment divider 56 is non-buoyant (has a density less than that of water) to provide additional stability to the cell 32. The cells 32 can be adapted to be any size or shape. Within the most distal part of at least one cell unit in a cell, there is provided the gas diffuser 38. The gas diffuser 38 can also serve as the segment divider. The water permeable walls 53 are flexible and comprise a mesh or a net having openings sufficiently small to retain the biomedia 22 within the cell. In one embodiment, the cell 32 comprises the self-distributing self-supporting biomedia and the cell is attached to the cover of the buoyant structure to facilitate removal of the entire cell for maintenance by simply lifting the cover. In another embodiment, only the biomedia 22 or the mesh 53 is attached to the cover 44 of the buoyant structure 30 and can be removed by lifting the cover 44.

[0121] In the embodiment of FIGS. 1-3, each cell 32 is attached to the buoyant structure 30 by means of the covers 44. The vertical support struts 54 of the top cell unit are received into corresponding openings (not shown) in the cover 44 and secured by means of conventional connectors such as bolts and wing nuts. It will be appreciated that any means of securing the cell to the cover is included within the scope of the present disclosure. Each cell 32 is secured to the cover in a non-detachable or detachable manner. As the connection between the cover 44 and the buoyant structure 30 is detachable, the cells can be removed from the reactor by disconnecting the cover 44 from the buoyant structure and lifting the cover with the cell attached. In an alternative embodiment (not shown), each cell 32 is detachably attached to the buoyant structure 30 and not to the cover 44.

[0122] The cells 32 are modular in that cell units 52 can be stacked one on top of another to increase their total length. For example, each cell may have a one metre length. It has been found by the inventors that a length of about one metre prevents compaction of the biomedia 22 contained therein and imparts to the cell 32 a manageable weight for removeable and maintenance purposes taking into account the additional weight of a fully loaded biomedia with biofilm. The cage-like structure of each cell 32 also helps to minimize or reduce the weight of the structure as well as allowing for the movement of water in and out of the cells 32. The modularity of each cell 32 enables the provision of biomedia 22 throughout a depth of a body of water, even bodies of water with varying depth. Cell segments 52 can be detached from one another by removing connectors such as bolts or screws from the top of the struts 54 of each segment 52 and leaving the bottom segment divider 56 or gas diffuser 38 in the case of the last segment to retain the biomedia 22 in a basket type embodiment. This feature facilitates installation or removal of deep cells, especially when the biomedia is colonised with heavy biomass.

[0123] Turning now to the biomedia 22, any device which can support bacterial or biofilm growth to increase biomass concentration and to biologically consume impurities contained in the body of water within one of the reactors 12, 14 can be used. Biomedia with a high surface area to volume ratio is preferred. Incorporating such a biomedia within embodiments of the present disclosure increases sludge retention time when compared to what is possible in the majority of lagoon wastewater treatment systems, apparatuses and methods known in the art. For example, the large surface area to volume ratio of the biomedia may enable the oxidation of the toxic concentrations of ammonia/nitrite/nitrate where it was not previously possible in a lagoon.

[0124] In one embodiment, the biomedia comprises one or more elongate thin films or strips which can be loosely bundled up or intertwined in an unbound, nest-like configuration, the film or strip having surfaces for bacteria to attach and grow on. A suitable biomedia has been described previously in WO 03/027031 and WO2009033291, the contents of which are incorporated herein in their entirety. The biomedia is made of a non-toxic and non-biodegradable material. The biomedia comprises a material having a density close to that of water so that advantageously the biomedia can remain submerged and suspended within the body of water. The material of the biomedia may be selected from the group consisting of acrylonitrile butadiene styrene (ABS), polyvinyl chloride (PVC), high-density polyethylene, polypropylene or any other plastic that can be heated, extruded, molded, milled, cast and/or made in a way that will allow them to form strips which can be loosely packed together. Each strip of the biomedia 22 should be constructed and arranged so as to not compress or collapse or disintegrate over time and/or stop the flow of water passing therethrough.

[0125] With regard to the dimensional features of the biomedia 22, in certain embodiments these strips are preferably as thin as possible while being structurally sound and rigid at the same time. The rigidity is, among other factors, provided by the nature of the material used as well as the cross-sectional area of the strip. Each strip should be made of a suitable material and suitable dimensions such that it has sufficient structural integrity to not collapse on itself in order to not restrict passage of water between the strips.

[0126] In one embodiment, each strip is made of ABS although other materials can also be used. In one embodiment, each strip has a substantially rectangular cross-sectional area, a thickness of about 0.2 mm and a width of about 3.0 mm. The biomedia 22 can provide a surface area of up to about 330 m.sup.2 per m.sup.3 of biomedia volume, or about 165 m.sup.2 of biomedia per m.sup.3 of water.

[0127] In use, the biomedia 22 can occupy less than about 1.6% of the volume of water being treated. As the elongate strip biomedia can self-distribute in the water, it can provide an adequate distribution of bacteria in the volume of water being treated to therefore not require additional mixing. The biomedia is also sufficiently rigid to prevent its subsidence even under the maximal weight of bacteria. The bundled yet unbound structure of the biomedia also favors the shedding (sloughing) of excess sludge through movement of the elongate strip against itself or other strips. Also, the bundled configuration of the biomass does not clog, unlike biomedia of the prior art, therefore minimizing or avoiding the need for maintenance. Advantageously, embodiments of the present system utilizing such a fixed well distributed biomass do not require mixing of the body of water (e.g. aeration) thus requiring less energy than a fluidized process such as an aerated lagoon or a moving bed bioreactor.

[0128] Biofilm can reach a thickness of about 1 cm, and the sloughing of excess biofilm to maintain an ideal biofilm thickness can be helped by gas bubbles working only a couple of minutes each hour. The second set of hollow pipes 36 in the buoyant structure 30 comprises air lines 58. All air lines 58 connect to a manifold where one line out of two is closed by an electric ball valve or a similar timer controllable device. The gas diffusers 38 comprise a coarse bubble diffuser 60 and a fine bubble diffuser 62. The coarse bubble diffuser 60 is fed gas via the second set of hollow pipes 36 through a gas line, and the fine bubble diffuser 62 is fed gas via another adjacent hollow pipe 36 using another gas line. The gas bubble generation may be continuous or intermittent and be coordinated in a regular schedule depending on the rate of biofilm accumulation. In one embodiment, the fine bubble diffuser 62 provides a constant stream of fine bubbles for oxygenation of the biomedia, whereas the coarse bubble diffuser 60 is only switched on for a few minutes per hour for promoting sloughing. Therefore, the coarse bubble diffuser 60 has a timing control whereas the fine bubble diffuser has no timing control. In preferred embodiments, the gas lines feeding the bubble diffusers have a structure and/or are made from a material which resists compression by water and/or ice. For example, reinforced rubber tubing may be used such as rubber pipes reinforced with a helical polyethylene. In one embodiment, the coarse bubble diffuser 60 has a separate high-pressure compressor for supplying air than the fine bubble diffuser 62.

[0129] Gas bubbles for biofilm control are generated by the gas bubble diffusers 38 (aerators) in conventional manner. The coarse bubble aerator has several leveled openings at the bottom of an air space to evenly distribute bubbles. In one embodiment, the gas is air, however any other gas may be used, such as nitrogen or oxygen for example. In the illustrated embodiment, there are eight (8) aerator ⅛″ openings. The gas bubble diffusers 38 are present at the bottom of each cell 32 as gas bubbles will rise through the water as a column of bubbles.

[0130] The gas bubble diffusers 38 also enable control of aeration conditions to provide aerobic and/or anoxic zones within the same reactor 12, 14. This means that nitrogen may also be eliminated with biological denitrification together with lowering biological oxygen demand (BOD) all within the same reactor.

[0131] In another embodiment, the coarse bubble diffusers are open pipes. Furthermore, the coarse bubble diffusers need not be present at the bottom of each cell 32 depending on the amount of sloughing required. For example, there may be a single course bubble diffuser provided at the bottom of a column of cell units.

[0132] Referring back to the system 10 of FIGS. 2-4, an embodiment of the system comprises at least one baffle 64 positioned across or around the first and/or the second reactor 12, 14 for preventing water flow around the first and/or the second reactor 12, 14. The baffles 64 are made of a flexible, water impermeable material such as a polymer or a rubber. In the case of baffles 64 which extend across the reactor, at least one baffle opening 66 is provided for allowing water to flow into the reactor. The baffles 66 are anchored to the bottom and sides of the lagoon such as by ballasting by a chain and are attached to the first set of hollow pipes 34 of the floating structure 30 using cables or cord. They provide a physical barrier to the flow of water causing the water to flow into the reactors 12, 14 and not around them. Holes in the baffles allow passage from one zone to another of the treatment chain. The height of the holes can be adjusted to optimize biomass separation. For instance, holes at the outlet of a clarification and storage zone can be located at the bottom to benefit from sludge blanket filtering accumulating near the exit. They can also be located in the middle to retain sludge at the bottom and scum at the top. Overflow from the top of the deflector wall can be desirable in situations where no scum is expected.

[0133] An embodiment of the system 10 also comprises deflector walls 68 (FIG. 4) positioned between the cells 32 to direct the flow of water through the first and/or second reactors 12, 14. In the example of FIG. 4, the deflector walls 68 are arranged to cause substantially a plug-flow effect of water flow through the cells 32. By plug-flow is meant that the concentration of the water varies along the water path through the reactor i.e. there is a concentration gradient through the path. Plug-flow conditions can generate a faster growth rate of the bacteria on the biomedia (theoretically about 3.9 times faster than that of a completely mix reactor for a first order kinetic). The deflector walls 68 are arranged to create long narrow channels. In one embodiment the channels are at least 2 m wide and 33 m long. In FIG. 4, it can be seen that the deflector walls 68 divide the reactor into two to maximise the distance through the reactor. The deflector walls 68 can provide any configuration of water path through the reactor, whether straight or tortuous depending on the load of the water being treated and the configuration of the body of water. The reactors 12, 14 can be positioned such that the reactor inlets and outlets are located in a way to maximize the path of a particle with respect to adjacent clarification and storage zones. In this respect, the reactors 12, 14 have an impermeable outer wall for retaining water within, and only allowing water flow in and out of the reactor inlet and outlet, respectively.

[0134] In another embodiment, a filter (not shown) is provided around the final outlet 20 of the lagoon. The filter can be a bundle of biomedia as described above, within a net and having a density in the water of about 330 m.sup.2 of biomedia per m.sup.3 of water.

[0135] According to embodiments of the present disclosure, the second reactor 14 does not need to handle the same amount of load as the first reactor 12 in order to meet target specifications. In fact, in certain embodiments, the second reactor 14 is arranged to handle a lower loading than the first reactor 12. The second reactor 14 may be arranged to operate at about 30-70%, about 40-60%, or about half the loading rate compared to the first reactor 12. Fermentation and hydrolysis of sludge can reduce sludge volume and slightly increase organic soluble matter flowing through the first reactor. Operating the first reactor 12 at a high soluble biological oxygen demand (BOD) loading rate can produce biomass with good settling characteristics. By “high soluble BOD loading rate” means higher than about 2.0 g sCBOD.sub.5/m.sup.2 of biomedia per day. In certain embodiments, the first reactor 12 is adapted such that approximately half the BOD is oxidized to carbon dioxide by the first reactor 12.

[0136] The second settling zone 24 can allow the retention of approximately another quarter of influent BOD through settling of up to about 75% of suspended solids almost entirely composed of biomass generated from soluble CBOD.sub.5 from the first reactor 12. Again, fermentation and hydrolysis are likely to take place in the accumulated sludge at the bottom of the water body. The second reactor 14 is adapted to be operated at lower organic load to produce a high quality effluent. A lower surface loading of the biomedia can provide better contact time of soluble and particulate substrates with the biofilm. Entrapment of finer particles in the biofilm and advanced conversion of soluble substrates can lead to low CBOD.sub.5 concentration. Settling characteristics of biomass detaching from the second reactor may be lower than in the first settling zone, but a low overflow rate in the final settling zone and final filtration of effluent through dense biomedia upstream of the outlet may result in a concentration below about 15 mg/l for both BOD.sub.5 and TSS even at temperatures as low as about 0.5° C. In certain embodiments, at temperatures above about 8° C., full nitrification may be possible depending on the loading rates and nitrogen removal if anoxic zones are created. When the temperature of the water falls below 8° C., the autotrophic biomass growth slows while decay continues but the accumulated autotrophic biomass during the warmer months allows partial nitrification down to near freezing conditions. The first and the second reactors 12, 14 may be adapted to achieve a 5 day hydraulic retention time (HRT) system to achieve required effluent levels. Compare this with a traditional aerated lagoon, where typically a 15-60 day HRT is required in order to meet regulations (see e.g. KRANTZBERG, G. (2010). Advances in water quality control. Scientific Research Publishing, USA).

[0137] Embodiments of the present disclosure can reduce the HRT down to about 5 days. In other words, embodiments of the present method and system do not require long hydraulic retention times. Embodiments of the present method and system have a HRT of less than 15 days, less than 10 days, less than 9 days, less than 8 days, less than 7 days, less than 6 days, or less than 5 days. In this way, loading can be increased by at least two-fold. Hydraulic retention time, can be understood to mean the measure of the average length of time that a soluble compound of wastewater remains in a bioreactor system. Hydraulic retention time is calculated by dividing the system volume by the wastewater flow rate (see e.g. Federation of Canadian Municipalities and National Research Council (FCMNRC), 2004. Optimization of Lagoon Operation. https://www.fcm.ca/Documents/reports/Infraguide/Optimization_of Lagoon_Operations_EN.pdf).

[0138] In one embodiment, the first reactor 12 is adapted to operate at a loading rate of about 2.0 to about 6.0 g of soluble carbonaceous biochemical oxygen demand per effective surface area of biomedia per day (sCBOD.sub.5/m.sup.2.Math.d), or about 2.5 g sCBOD.sub.5/m.sup.2.Math.d. The second reactor 14 is adapted to operate at a loading rate of about 0.5 to about 1.5 g of soluble CBOD.sub.5/m.sup.2.Math.d, about 0.75 to about 1.25 g of soluble CBOD.sub.5/m.sup.2.Math.d, or about 1.25 g of soluble CBOD.sub.5/m.sup.2.Math.d.

[0139] In one embodiment, the inlet settling zone 26 is adapted to have a hydraulic retention time of about 1.0 to about 3.0 days, about 1.5 to about 2.5 days, or about 2 days, and/or an overflow rate of about 0.5 and 2.0 m.sup.3/m.sup.2 of mirror surface of body of water, per day.

[0140] In one embodiment, the outlet settling zone 28 is adapted to have a hydraulic retention time of about 0.5 to about 1.5 days, or about 1 day, and/or an overflow rate of between about 0.5 and about 3.0 or about 0.5 and about 2.0 m.sup.3/m.sup.2 of mirror surface of body of water per day.

[0141] In one embodiment, the settling zone 24 between the first and second reactors 12, 14 is adapted to have a hydraulic retention time of about 1.0 to about 4.0 days, about 1.5 to about 3.5 days, about 2 to about 3 days, about 2.5 days, and/or an overflow rate of about 0.5 to about 2.0 m.sup.3/m.sup.2.Math.d.

[0142] Referring now to an embodiment of a method of treating water, the method comprises passing water to be treated through the first and second reactors 12, 14 arranged in series in the lagoon of the system 10 described above, wherein the water is passed through the mid-settling zone 24 between the first and second reactors 12, 14 before passing through the second reactor 14. In a preferred embodiment, the water to be treated is additionally passed through the inlet settling zone 26 which is upstream of the first reactor 12 and/or the outlet settling zone 28 which is downstream of the second reactor 14. The treated water is discharged as treated effluent from the second reactor 14 and/or the outlet settling zone 28.

[0143] The method may comprise creating aerobic and anoxic areas within the same reactor. In one embodiment, an aerobic area is created by bubbling oxygen-containing gas using the gas diffusers 38 in cells 32 in a first portion of the array of cells 32 whilst cells in a second portion of the array remain anoxic by keeping the diffusers turned off. Alternatively, the reactors may be aerated in any other way. In certain embodiments, the settling zones are non-aerated, by turning off aeration of the lagoon for example.

[0144] Advantageously, embodiments of the present system and method do not require recirculation of the wastewater. In other words, treated water is not fed back to the first reactor after leaving the second reactor. By means of certain embodiments and aspects of the present disclosure, some problems associated with recirculation, such as reduction of clarification zone capacity and efficiency, can be minimised or avoided.

[0145] Identification of equivalent systems and methods are well within the skill of the ordinary practitioner and would require no more than routine experimentation, in light of the teachings of the present disclosure.

[0146] Variations and modifications will occur to those of skill in the art after reviewing this disclosure. The disclosed features may be implemented, in any combination and subcombinations (including multiple dependent combinations and subcombinations), with one or more other features described herein. The various features described or illustrated above, including any components thereof, may be combined or integrated in other systems. Moreover, certain features may be omitted or not implemented. Examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the scope of the information disclosed herein. For example, it will be appreciated that any other reactor can be used in the present system and method. The reactors need not be buoyant. The at least one cell of the reactor can take any form or shape. The biomedia need not be a thin film as described but may also take any other form or shape. All references cited herein are incorporated by reference in their entirety and made part of this application.

[0147] Practice of the disclosure will be still more fully understood from the following examples, which are presented herein for illustration only and should not be construed as limiting the disclosure in any way.

Examples

[0148] The following examples are illustrative of the wide range of applicability of the present invention and are not intended to limit its scope. Modifications and variations can be made therein without departing from the spirit and scope of the invention. Although any method and material similar or equivalent to those described herein can be used in the practice for testing of the present invention, the preferred methods and materials are described.

Example 1—Water Treatment System and Method

[0149] A pilot study was conducted of a water treatment system in a body of water, the system having a water treatment chain comprising an inlet settling zone followed by a first reactor followed by a mid-settling zone, followed by a second reactor, followed by an outlet settling zone. The body of water comprised a limited access 20 foot sea container containing the reactors and settling zones. The inlet settling zone had a hydraulic retention time of about 1.5 day and an overflow rate of about 1.1 m.sup.3/m.sup.2.Math.d. The first reactor comprised 2 cells operating at a load of about 1.4 g sCBOD.sub.5/m.sup.2.Math.d. The mid-settling zone had a hydraulic retention time of about 1 day and an overflow rate of about 1.7 m.sup.3/m.sup.2.Math.d. The second reactor comprised 1 cell operating at a load of about 0.4 g sCBOD.sub.5/m.sup.2.Math.d. The outlet settling zone had the same design as the mid-settling zone. The different zones were separated by fiber glass deflectors. The body of water was fed with municipal wastewater through an inlet and treated water collected through an outlet. The cells of the first and second reactors comprised fine and coarse bubble diffusers. The cells contained the thin elongate unattached biomedia strips described above. The fine bubble diffusers were switched on continuously and the coarse bubble diffusers were activated for 3 minutes per hour.

[0150] Preliminary testing of the final effluent after less than 10 months of treatment time showed an average CBOD.sub.5 and TSS concentration of 5.2 mg/l and 6.5 mg/l respectively. The nitrification rate was 89% and nitrogen removal was 27% with no optimisation of the aeration levels. Since nitrification is influenced by water temperature, ammonia removal the results can be separated in two distinct periods. During the winter season (December 21 to March 20) the nitrification rate was 76%. For the period outside the winter season, the nitrification rate was 96%.

Example 2—Lagoon Water Treatment System and Method

[0151] A full scale study was conducted of a water treatment system in a body of water, the system having a water treatment chain comprising an inlet settling zone followed by a first reactor followed by a mid-settling zone, followed by a second reactor, followed by an outlet settling zone. The body of water comprised about one third of an existing lagoon containing the reactors and settling zones. The inlet settling zone had a hydraulic retention time of about 1.8 day and an overflow rate of about 1.9 m.sup.3/m.sup.2.Math.d. The first reactor comprised 10 cells operating at a load of about 3.9 g sCBOD.sub.5/m.sup.2.Math.d. The mid-settling zone had the same design as the inlet settling zone. The second reactor comprised 5 cells operating at a load of about 0.9 g sCBOD5/m2.Math.d. The outlet settling zone had the same design as the inlet settling zone and the mid-settling zone. The different zones were separated by polyester curtains. The body of water was fed with municipal wastewater through an inlet and the treated water was collected through an outlet. The cells of the first and second reactors comprised fine and coarse bubble diffusers. The cells contained the thin elongate unattached biomedia strips described above. The fine bubble diffusers were switched on continuously and the coarse bubble diffusers were activated for 3 minutes per hour. Preliminary testing of the final effluent after less than 9 months of treatment time showed an average CBOD.sub.5 and TSS concentration of 9.1 mg/l and 6.3 mg/l respectively. Nitrification did not take place during this period since the system was installed at the end of the month of September when water temperature was too cold to allow a sufficient autotrophic biomass growth.

[0152] It should be appreciated that the invention is not limited to the particular embodiments described and illustrated herein but includes all modifications and variations falling within the scope of the invention as defined in the appended claims.