WO2020169962A1

WO2020169962A1 - Denitrifying downflow wastewater treatment apparatus and method

Info

Publication number: WO2020169962A1
Application number: PCT/GB2020/050388
Authority: WO
Inventors: David William Graham; Mui Choo JONG; Joshua Thomas BUNCE
Original assignee: University Of Newcastle Upon Tyne
Priority date: 2019-02-19
Filing date: 2020-02-19
Publication date: 2020-08-27
Also published as: GB201902248D0

Abstract

The invention relates to a downflow wastewater treatment apparatus. The apparatus comprises an aerobic reactor comprising at least one receptacle configured to retain sponge therein and configured to allow flow of wastewater therethrough. Each receptacle comprises a wall defining an airflow passage extending longitudinally through the receptacle to allow flow of air into the receptacle via the airflow passage.

Description

DENITRIFYING DOWNFLOW WASTEWATER TREATMENT APPARATUS AND

METHOD

The present invention relates to a denitrifying downflow wastewater treatment apparatus and method. In particular, but not exclusively, the present invention relates to a downflow wastewater treatment apparatus having an aerobic reactor including an airflow passage to allow flow of air into the reactor.

Effective wastewater treatment and community sanitation are critical to global health and environmental protection. However, many people still live without access to basic sanitation, which impacts infectious disease mortality and increases exposure to environmental antimicrobial resistance via contaminated water. The impact of water and waste borne antimicrobial resistance is most profound in emerging and developing countries because waste management is not proceeding as rapidly as urbanisation, leading to declining environmental quality as development occurs.

Problems tend to exist in expanding peri-urban environments because such locations often lack centralised sewage collection. As such, smaller, local-scale treatment options are needed to increase wastewater treatment coverage.

Denitrifying Downflow Hanging Sponge (DDHS) reactors are a low cost and low maintenance wastewater treatment option that is suitable for smaller or decentralised applications. DDHS systems can achieve high Chemical Oxygen Demand (COD), Ammonium-Nitrogen (NH4-N) and Total Nitrogen (TN) removals by using bipartite aerobic- anoxic sponge layers and a raw wastewater bypass to supply extra carbon to lower submerged layers to promote denitrification. Further, DDHS systems use minimal energy because they employ passive aeration and also provide design flexibility in the sponge core that can be customised to local conditions.

Examples of DDHS reactors are discussed in Bundy et al., Bioresource Technology, 2017, 226, 1-8 and in Jong et aL, Science of the Total Environment, 2018, 634, 1417-1423. Each of these papers disclose a DHS reactor in which the core design includes an upper sponge layer exposed to air and suspended above the water level allowing for passive aeration for nitrification, and a lower sponge layer partially submerged by effluent from the preceding aerobic layer, encouraging anoxic conditions for denitrification. However, the passive aeration within such systems are suboptimal for nitrification. Figure 1 illustrates an example DDHS reactor disclosed in Bundy et al. The reactor 100 includes an upper aerobic reactor 102 and a lower anoxic reactor 104. The upper aerobic reactor 102 includes a plurality of stacked containers 106 each housing sponge elements. The containers 106 include ventilation holes on the external surface and a gap 108 between containers to allow passive aeration. The lower anoxic reactor 104 is submerged below the water level 110 to encourage anoxic conditions for denitrification.

It would be useful to provide an improved denitrifying wastewater treatment apparatus that at least partially mitigates the problems discussed above.

According to a first aspect of the present invention there is provided a downflow

wastewater treatment apparatus comprising:

an aerobic reactor comprising at least one receptacle configured to retain sponge therein and configured to allow flow of wastewater therethrough;

wherein each receptacle comprises a wall defining an airflow passage extending longitudinally through the receptacle to allow flow of air into the receptacle via the airflow passage.

Suitably, the aerobic reactor comprises a plurality of receptacles.

Suitably, each receptacle is configured for placement adjacent another receptacle to form a receptacle column to allow flow of wastewater downwards through the receptacle column.

Suitably, wherein the wall is located substantially centrally within the receptacle such that the air flow passage extends substantially centrally through the receptacle.

Suitably, the aerobic reactor further comprises a distributor element configured to distribute wastewater substantially evenly throughout a cross-sectional area of the aerobic reactor.

Suitably, the distributor element comprises at least one arm configured to rotate about the airflow passage of the at least one receptacle for distributing wastewater substantially evenly throughout the at least one receptacle. Suitably, the at least one receptacle comprises a plurality of apertures sized to allow flow of air into the receptacle and flow of wastewater through the receptacle, whilst retaining sponge therein.

Suitably, at least one receptacle is formed from a wire mesh or a polymer mesh, or polymer basket. The receptacle may be constructed of materials including at least one of stainless steel, aluminium, polyamide, polycarbonate, polypropylene, or

Polyetheretherketone (PEEK), for example.

Suitably, the aerobic reactor further comprises an outer shell configured to enclose the at least one receptacle.

Suitably, the outer shell comprises a plurality of vents for allowing flow of air into the aerobic reactor.

Suitably, the apparatus further comprises an anoxic reactor fluidly coupled to the aerobic reactor downstream of the aerobic reactor.

According to a second aspect of the present invention there is provided a method of reducing the level of ammonia and organic pollutants in wastewater comprising passing wastewater through at least one sponge within the downflow wastewater treatment apparatus of the invention. Alternatively, or additionally, the method may reduce the level of bacteria in wastewater.

Suitably, bacterial loads including wastewater-borne pathogens and/or antimicrobial resistance genes may be removed from the wastewater.

According to a third aspect of the present invention there is provided a use of the downflow wastewater treatment apparatus of the invention to reduce the level of ammonia in waste water, denitrify waste water or to reduce the level of antimicrobial resistance genes in waste water. Alternatively, or additionally, the method may reduce the level of organic pollutants or bacteria in the wastewater.

Suitably, the use may comprise reducing or removing bacterial loads including wastewater- borne pathogens and/or antimicrobial resistance genes from the wastewater. It will be appreciated that the method described herein may be performed using any of the apparatus described.

The apparatus provides an improved DDHS system compared to previously known systems.

The apparatus provides a wastewater sanitation system that does not require

infrastructure such as large-scale sewerage networks to operate, making it suitable for on site treatment.

Examples of the apparatus and method help to reduce the level of organic pollutants and ammonia in wastewater. Advantageously, the use of the aerobic reactor of the present invention efficiently reduces the level of ammonia and carbonaceous organic pollutants in the wastewater and where anoxic conditions are also provided reduction of the total nitrogen can be efficiently achieved.

Furthermore, the apparatus of the invention can also advantageously reduce the level of wastewater-borne pathogens and/or antimicrobial resistance genes.

The apparatus is relatively cheap to produce and maintain, making it suitable for use in less affluent areas, where waste sanitation is often not yet utilised.

The aerobic reactor may be particularly effective in relatively cold environments compared to known systems due to the improved aeration.

The apparatus and method can be particularly useful in rural areas or areas with little or poor electricity supply since little or no power is necessary for the apparatus to operate.

Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:

Fig. 1 shows a prior art denitrifying downflow hanging sponge system;

Fig. 2a shows an example of an aerobic reactor;

Fig. 2b illustrates a receptacle of the reactor of Fig. 2a;

Fig. 3 shows an example of an anoxic reactor;

Fig. 4 shows an example of a denitrifying downflow hanging sponge system including the aerobic reactor of Fig. 2 and the anoxic reactor of Fig. 3; Figs. 5 and 6 show an example plumbing layout of a denitrifying downflow hanging sponge system;

Figs. 7a and 7b show another example denitrifying downflow hanging sponge system;

Fig. 8 shows a side view of an aerobic reactor;

Fig. 9a shows a plan view of an anoxic reactor;

Fig. 9b shows a side view of the anoxic reactor of Fig. 9a;

Fig. 10a and 10b show an example distributer element;

Figure 11 shows the levels of antibiotic resistant genes (ARG) and mobile genetic elements (MGEs) at different stages in treatment process, for recirculation regime OP2;

Figure 12 shows the levels of antibiotic resistant genes (ARG) and mobile genetic elements (MGEs) at different stages in treatment process, for recirculation regime OP4; and Figure 12 shows the microbial analysis of communities in the two compartments (sponge layers 1 to 6 compartment 1 , sponge layers 7 to 1 1 compartment 2).

In the drawings like reference numerals refer to like parts.

Fig. 2a illustrates an aerobic reactor 200. The aerobic reactor includes at least one receptacle 210. Fig. 2b illustrates a receptacle 210 in further detail. In this example, the aerobic reactor 200 includes six receptacles. Each receptacle 210 retains at least one sponge 202 therein.

At least one sponge 202 is retained within the receptacle. In some examples the receptacle retains a plurality of sponges. The sponge may be formed from any material, for example polymer sponge, marine sponge, organic polymer (e.g. polyurethane), a ceramic or a metal. Aptly, the sponge is an open cell reticulated sponge. The use of sponge as the porous media helps to minimise weight of the apparatus and reduce the need for active aeration (e.g. via pumps). The material is aptly configured to capture bacteria.

Advantageously, a porous sponge provides a greater surface area to retain bacteria and support growth. These bacteria are utilised in the methods of the invention e.g. to reduce carbon sources from the waste water. For the avoidance of doubt, whilst the invention is illustrated with the use of a sponge any substance having a large surface area as a scaffold which can retain bacteria and support growth could be used.

The receptacle 210 is formed of at least one outer wall 208 proximate a base 212. The outer wall 208 and the base 212 define a volume for receiving the at least one sponge 202. In this example the receptacle is substantially cylindrical in shape. In other examples the receptacle 210 may have a substantially square, rectangular, hexagonal, octagonal or other polygonal cross-sectional shape. Aptly, each of the receptacles have substantially identical cross-sectional shapes and dimensions. The receptacles may each have substantially identical heights, or in some examples, one or more receptacle may have a different height to other receptacles.

In some examples the at least one sponge may occupy at least half of the volume defined by each receptacle. The sponge may include one single sponge element. In some examples the single sponge element may occupy at least half of the volume defined by the receptacle.

In other examples the receptacle may retain a plurality of sponges. The plurality of sponges may occupy at least half of the volume defined by each receptacle. By providing a plurality of relatively smaller sponges the sponge surface area is maximised and more effective aeration can occur. Aptly, each of the plurality of sponges may be configured for easy packing and to maximise surface area. For example, the sponges may be substantially cubed or cuboidal in shape.

The receptacle 210 further includes a wall 220 defining an airflow passage 230. The wall 220 defining the airflow passage 230 may be referred to herein as an“internal wall”. The internal wall 220 is located within the receptacle. The internal wall 220 extends

longitudinally through the receptacle to define the air flow passage 230. The airflow passage 230 extends longitudinally through the receptacle 210. The longitudinal extension of the air flow passage 230 allows the flow of air into the receptacle via the airflow passage 230. The arrows A in Fig. 2a illustrate flow of air through the system.

In this example the airflow passage is substantially cylindrical in shape. In other examples the airflow passage may have a square, rectangular, hexagonal, octagonal or any other polygonal cross-sectional shape. Aptly, the airflow passage has the same cross-sectional shape as the receptacle. Aptly, the internal wall is located substantially centrally within the receptacle such that the air flow passage extends substantially centrally through the receptacle. This can help to evenly aerate the sponge throughout the receptacle.

In this example each receptacle 210 is configured for placement adjacent another receptacle 210 to form a receptacle column 214 to allow flow of wastewater downwards through the receptacle column 214. The receptacle may be configured in various ways for placement or stacking with an adjacent receptacle. For example, the receptacle may include at least one support element 216 for supporting an above adjacent receptacle. In this example, the receptacle 210 includes four support elements 216 arranged equidistant around the outer wall 208. The support elements 216 are arranged at a top end of the outer wall 208 distal to the base 212. As such, the support elements are configured to support the base of an above adjacent receptacle. In some examples adjacent receptacles 210 are releasably connected.

In this example the at least one receptacle has a plurality of apertures 206. In this example the at least one receptacle 210 includes a plurality of apertures 206. The apertures may be sized to allow flow of air into the receptacle and flow of wastewater through the receptacle, whilst retaining sponge within the receptacle. The one or more apertures 206 help to increase air circulation through the receptacle thereby improving passive aeration around the aerobic chamber.

The apertures may be formed in at least one of the outer wall 208, the internal wall 220, and the base 212. Aptly, each of the outer wall 208, internal wall 220 and the base 212 includes a plurality of apertures 206. For example, the apertures may be formed in any of the outer wall 208, internal wall 220 and the base 212 by drilling or punching holes therein. In other examples, at least one of the outer wall 208, internal wall 220, and the base 212 may be formed from a material having apertures, for example wire mesh, polymer mesh, or polymer basket.

In this example each receptacle 210 is configured for placement adjacent another receptacle to form a receptacle column to allow flow of wastewater downwards through the receptacle column.

In this example the receptacle 210 is formed of wire mesh. In other examples the receptacle 210 may be formed from any appropriate material for retaining sponge and allowing flow of waste water therethrough. That is the material is formed having apertures or holes of suitable size to allow flow of water therethrough, whilst sized suitably to prevent passage of sponge therethrough. Aptly the receptacle may be formed from a rigid plastic or a wire mesh or a polymer mesh, or polymer basket.

In this example the aerobic reactor 200 includes an outer shell (not shown in Fig. 2a). The outer shell is configured to enclose the receptacle column 214. In examples where the aerobic reactor comprises one or more receptacles 210 the outer shell is sized to enclose all of the one or more receptacles 210. The outer shell is described in more detail below with reference to Fig. 8.

In this example a clarifier 240 is provided below (i.e. at the bottom of) the aerobic reactor 200. The clarifier 240 may be situated below main body of the aerobic reactor 200 adjacent and below the lowermost receptacle 210. The clarifier 240 provides a settler for sludge management. The clarifier allows removal of solids from the wastewater by settling through hydraulic retention in the clarifier. The clarifier may aptly also capture biofilm that may become detached from the sponge media.

In this example the airflow passage 230 defined by the internal wall 220 of each receptacle extends the full height of the receptacle column. In other words, the airflow passage 230 extends from the base 212 of the lowermost receptacle (i.e. the receptacle at the bottom of the receptacle column 214) to the top of the uppermost receptacle (i.e. the receptacle at the top of the receptacle column 214). This allows for continuous airflow between receptacles of the aerobic reactor, thereby helping to improve aeration of the receptacles.

In some examples, the base 212 of each receptacle may extend transversely across the airflow passage 230. In this case, the base of each receptacle, in the region of the airflow passage may include a plurality of apertures or holes to allow continuous flow of air longitudinally through the airflow passage. In other examples, the base of each receptacle may include a single aperture in the region of the airflow passage to allow continuous longitudinal flow of air through the airflow passage. The single aperture may be sized and positioned to correspond to the size and position of the internal wall of the respective receptacle.

In this example the internal wall 220 is coupled to the base 212 of the receptacle. The internal wall 220 may be coupled to the base 212 of the receptacle via any suitable coupling element, for example adhesive, weld, or cable ties. Other suitable coupling elements or coupling means will be apparent to those skilled in the art and, for brevity, will not be described in detail. The internal wall 220 may be alternatively be releasably coupled to the receptacle 210.

The cross-sectional area of the airflow passage 230 (as defined by the internal wall 220) may be determined according to the cross-sectional area of the receptacle (as defined by the outer wall 208). For example, the cross-sectional area of the receptacle may be at least two times the cross-sectional area of the airflow passage. In other words, the ratio of the cross-sectional area of the airflow passage to the cross-sectional area of the receptacle may be equal to or less than 1 :2. For example, the ratio of the cross-sectional area of the airflow passage to the cross-sectional area of the receptacle may be from 1 :10 to 1 :2, or from 1 :8 to 1 :4, for example 1 :5. The ratio may be selected to optimise passive aeration through the receptacle. This may depend on the temperature difference between the inside and the outside of the reactor. For example, a larger temperature difference may result in a larger draft and so a smaller airflow passage may be needed.

In this example each receptacle is modular and may be separated from adjacent receptacles. The separation of the receptacles allows access to sponge in each receptacle within the aerobic reactor. This allows for replacement or cleaning of the sponge within the receptacle and eases maintenance. The receptacles can also be selectively replaced when needed. The modular configuration of the receptacles can also aid in transportation and set up of the reactor. For example, each receptacle may be handled separately during transportation rather than moving the whole receptacle column at once. Additionally, the number of receptacles within the receptacle column may be easily adjusted according to specific requirements and environmental factors, for example, which may affect the reactions in the aerobic reactor.

Fig. 3 shows an anoxic reactor 300. The anoxic reactor 300 may be fluidly coupled to the aerobic reactor 200. The anoxic reactor 300 may be fluidly coupled to the aerobic reactor 200 downstream of the aerobic reactor 200.

The anoxic reactor 300 is configured to retain sponge within the anoxic reactor and is configured to allow flow of water therethrough. Advantageously, the use of an anoxic reactor in accordance with the invention can reduce the level of total nitrogen in the wastewater as bacteria on the sponge with convert NO₃ to N₂ to utilise the oxygen.

In this example the anoxic reactor 300 includes five receptacles 302. In other examples, the anoxic reactor 300 may include one or more receptacles. The one or more receptacles 302 are filled with one or more sponge or a plurality of sponge elements. That is, the one or more sponge or plurality of sponge elements substantially fills each receptacle 302 of the anoxic reactor 300. In other examples, the one or more sponge or plurality of sponge elements may occupy at least 70% or at least 80% or at least 90% of the volume of the receptacle. The one or more sponge or plurality of sponge elements may be configured similarly to those described above in relation to Figs. 2a and 2b, so for brevity, will not be described again in detail. The anoxic reactor 300 is formed of at least one receptacle 302. The receptacle 302 includes at least one outer wall 308 proximate a base 312. The base 312 is configured to allow passage of fluid therethrough whilst retaining sponge therein. For example, the base 312 may include a plurality apertures or holes to allow passage of fluid therethrough. The apertures or holes may be sized to prevent passage of the sponge therethrough. For example, the base 312 may be formed from a wire or polymer mesh.

The outer wall 308 of the receptacles 302 of the anoxic reactor are substantially gas impermeable. In this way, the outer wall 308 helps to prevent diffusion of air into the anoxic reactor 300, thereby maintaining the relatively anoxic environment. In other examples, rather than gas impermeable outer walls, the receptacles of the anoxic reactor may be enclosed in an outer shell for preventing diffusion of gas into the anoxic reactor.

In this example the receptacles 302 are substantially cylindrical in shape. In other examples the receptacles 302 may have a substantially, square, rectangular, hexagonal, octagonal or other polygonal cross-sectional shape. Aptly, each of the receptacles have substantially identical cross-sectional shapes and dimensions. The receptacles 302 may each have substantially identical heights, or in some examples, one or more receptacles 302 may have a different height to other receptacles 302.

Each receptacle is configured to retain at least one sponge 304. In this example each drum 302 retains a plurality of sponges 304. In some examples the at least one sponge 304 is a different sponge material to the sponge retained by the receptacle 210 of the aerobic reactor 200. In this example the sponge 304 is the same sponge material as the sponge retained by the receptacle 210.

The volume of sponge in the aerobic reactor to volume of sponge in the anoxic chamber, herein“the aerobic-anoxic ratio”, may be selected according to ammonia and dissolved oxygen concentrations in the wastewater entering the aerobic reactor, the desired concentration of total nitrogen in the effluent discharged from the anoxic reactor, and the temperature differential between the inside of the reactor and the ambient air. For example, the aerobic-anoxic ratio, by sponge volume, may be from 1 :9 to 1 :3, or aptly from 1 :5 to 1 :7. Larger ratios (e.g., 1 :9) result in a relatively greater hydraulic retention time through the anoxic section. Fig. 4 shows an example of a denitrifying downflow hanging sponge (DDHS) system 400 including the aerobic reactor of Fig. 2 and the anoxic reactor of Fig. 3. The anoxic reactor 420 is fluidly coupled to the aerobic reactor 410 downstream of the aerobic reactor 410 via a fluid flow conduit 416. That is, the fluid flow conduit 416 fluidly couples an outlet of the aerobic reactor 410 to an inlet of the anoxic reactor 420. The outlet of the aerobic reactor 410 is located at a lower end of the aerobic reactor, in the region of the lowermost receptacle of the aerobic reactor. The inlet of the anoxic reactor 420 is located at an upper end of the anoxic reactor in the region of the uppermost receptacle of the anoxic reactor.

The DDHS system 400 further includes a container 402 for retaining the wastewater. The container 402 is fluidly coupled to the aerobic reactor 410 via an influent connection conduit 406. The influent connection conduit fluidly couples the container 402 to at inlet of the aerobic reactor 410. The inlet of the aerobic reactor 410 is located at an upper portion of the aerobic reactor 410 in the region of the uppermost aerobic reactor receptacle, such that the wastewater enters the aerobic reactor at the uppermost receptacle of the receptacle column. In use, the wastewater passes from the container 402 to the aerobic reactor 410 via the influent connection conduit 406 and passes through the aerobic reactor 410 from the uppermost receptacle to the lowermost receptacle via gravity. In some examples, one or more pumps may aid the passage of wastewater through the aerobic reactor 410.

In use, as wastewater passes through the aerobic reactor 410 the oxygen will react with the ammonia and the ammonia is oxygenated to nitrates. Hence, advantageously the level of ammonia is reduced. Furthermore, the bacterial colonies on the sponge will remove other organic matter utilising carbon as a food source. Furthermore, the bacteria may utilise and thereby remove other pollutants from the waste water. The airflow passage 230 and the apertures in the receptacles help to maintain an aerobic environment to help facilitate the oxygenation of ammonia.

From the aerobic reactor 410, the wastewater passes through an optional clarifier 440 to the anoxic chamber 420 via the fluid flow conduit 416. The wastewater may enter the clarifier from the base of the aerobic reactor and the wastewater may fill the clarifier. The wastewater may flow from the clarifier by an outlet at the top of the clarifier and below the aerobic reactor. Solids within the wastewater sink under gravity to the bottom of the clarifier and can be removed by a tap. The fluid flow conduit 416 is therefore coupled to a lower end of the aerobic reactor or an outlet at the top of the clarifier 440. A first end of the fluid flow conduit 416 in this example is fluidly coupled to the outlet of the clarifier 440. In other examples, the first end of the fluid flow conduit may be fluidly coupled to an outlet at the lowermost receptacle of the aerobic reactor 410. A second end of the fluid flow conduit 416 is fluidly coupled to an inlet at the upper portion (or uppermost receptacle) of the anoxic reactor 420. In this way, waste water may flow through the anoxic reactor by gravity from the uppermost receptacle to the lowermost receptacle. In some examples, a pump may optionally be used to aid transport of wastewater through the anoxic reactor 420.

In use, as wastewater passes through the anoxic reactor the level of readily available oxygen for utilisation by aerobic bacteria decreases. Therefore, the bacteria break down nitrates in the waste water to obtain a source of oxygen to support survival and growth. Thus nitrates are deoxygenated to nitrogen which is then released into the environment. Hence, the apparatus of the invention may efficiently reduce or even eliminate nitrogen from the waste water. Furthermore, the present invention has surprisingly found that such apparatus is particularly effective at reducing antimicrobial resistance genes from the waste water. This aligns with an increased desire to tackle antimicrobial resistance to reduce the use of antibiotics.

In this example an influent bypass conduit 404 fluidly couples the container 402 directly to the anoxic reactor 420. The wastewater may therefore bypass the aerobic reactor 410 and flow directly to the anoxic reactor 420. This can help to supply extra carbon to the anoxic reactor to help promote denitrification.

A recirculation conduit 414 fluidly couples the outlet of the anoxic reactor 420 to the inlet of the aerobic reactor 410. Once the wastewater passes through the anoxic chamber 420, the wastewater then may enter the recirculation conduit 414 which fluidly connects the outlet of the anoxic reactor 420 to the inlet of the aerobic reactor 410 to repeat the denitrification process.

An effluent conduit 412 is fluidly coupled to the outlet of the anoxic reactor 420. The effluent conduit may be coupled to a treated water tank 408 or may be configured to discharge the treated water back into the environment (e.g. a river, lake or reservoir). Once the wastewater is sufficiently treated (e.g. to comply with regulations) to remove ammonia or total nitrogen and organic pollutants to the desired level the water may exit the DDHS system 400 via the effluent conduit 412. For example, this may be after one or more cycles through the aerobic and anoxic reactors. The final effluent may be considered denitrified and effectively‘clean’ water. Figs. 5 and 6 show an example plumbing layout of a denitrifying downflow hanging sponge system of Fig. 4. Many elements are identical to those described in relation to Fig. 4, so for brevity will not be described again in detail.

Fig. 5 illustrates an additional outlet conduit 450 coupled to a lower portion of the clarifier. The outlet conduit 450 may include a valve or cap to selectively allow waste to exit the clarifier via the outlet conduit 450. The waste may include at least one of sediment, particles, or sludge, that has separated from the wastewater.

As shown in Fig. 5, the system also includes a distributor element 1000 located at the uppermost portion of the aerobic reactor 410. The distributor element 1000 is configured to distribute wastewater substantially evenly throughout a cross-sectional area of the aerobic reactor 410. The distributor element 1000 is described in further detail below, with reference to Figs. 10a and 10b.

Fig. 6 illustrates the direction of flow of wastewater through the system as indicated by arrows 600_a-i. As illustrated, the wastewater enters the system at entry point 610, and is optionally pumped into the container 402 by a first pump 602. Suitable pumps for pumping water will be known to those skilled in the art, so will not be described in detail. In other examples, pumps may be omitted, for example where the flow of water can be encouraged by other means, e.g. gravity.

As illustrated in Fig. 6, a second pump 606 may be coupled to the influent connection conduit 406 for pumping fluid from the container 402 to the aerobic reactor 410. A third pump 604 may be coupled to the influent bypass conduit 404 for pumping fluid from the container 402 directly to the anoxic reactor 420. A fourth pump 608 may be coupled to the recirculation conduit 414 for pumping fluid from the anoxic reactor 420 to the inlet of the aerobic reactor 410.

Any of the first to fourth pumps may be omitted where flow of water can be encouraged by other means. Similarly, additional pumps may be used if appropriate. For example, an additional pump may be couple to the conduit 416 fluidly coupling the aerobic reactor 410 to the anoxic reactor 420. Also, a further pump may be coupled to the effluent conduit 412.

Figs. 7a and 7b show alternative three dimensional views of an example arrangement of a DDHS system 700. In this example, the DDHS system 700 additionally includes a supporting framework 702. The supporting framework 702 may optionally be utilised to attach a netting (not shown) to prevent insects, arachnids and the like from entering the aerobic reactor 710.

In the example DDHS system 700 shown in Fig. 7a the aerobic reactor 710 is situated on a platform 704 at a raised height compared to the anoxic reactor 710. The anoxic reactor 720 may also be situated on a platform 706, which may be placed on the ground or may also be elevated.

The platform 704 and surface 706 prevent the DDHS system 700 from directly contacting the ground. This may help prevent contamination from microbes or the like found in soil and or on the ground.

Fig. 8 shows a side view of an aerobic reactor 800. In this example the outer shell 802 encloses the receptacle column (e.g. the receptacle column 214 of Fig. 2a). In this example the outer shell 802 includes a plurality of vents 804. The vents 804 may be distributed substantially evenly throughout the height of the outer shell 802 to help aid air flow into the whole receptacle column. Similarly, the vents may be distributed substantially evenly around the circumference of the outer shell to help aid air flow around the receptacle column. In this example, a first series of vents are distributed longitudinally along a first portion of the outer shell 802 and a second series of vents (not shown) are distributed longitudinally along a second portion of the outer shell 802 opposite to the first portion.

In this example, the outer shell is a singular unit. That is, the outer shell is a single unitary shell. In other examples, the outer shell may be modular. For example, the outer shell may include a plurality of outer shell module that couple together to form the outer shell. For example, the outer shell may include two or more outer shell modules that stack together vertically to form the outer shell. Aptly, the number of outer shell modules may be equal to the number of receptacles in the aerobic reactor. This can help to ease transportation and assembly of the reactor due to smaller component dimensions. In addition, this can help improve ease of maintenance since each outer shell module can be individually removed to access the receptacle column housed therein.

The outer shell 802 can help to regulate humidity within the aerobic reactor as well as controlling or reducing evaporation of wastewater within. The outer shell also allows for controlled aeration via the vents 802. As such, excessive aeration can be prevented, which can help prevent poisoning of bacteria within the reactor due to over aeration.

Section A of the aerobic reactor 800 is a clarifying section 810. The clarifying section 810 may be shaped to encourage sediment to flow downwardly and towards the centre where an outlet conduit (for example, outlet conduit 450 of Fig. 5) may be located. In this example, the clarifying section is frustoconical in shape. It will be appreciated that the clarifier may have any other suitable shape for directing the flow of sediment to an outlet conduit.

Fig. 9a shows a plan view of an anoxic reactor Fig. 9b shows a side view of the anoxic reactor of Fig. 9a. The plan view of the anoxic reactor 920 shows the anoxic reactor lid 910.

In this example the anoxic reactor lid 910 includes a peripheral lip 918. The anoxic reactor lid 910 includes three apertures (or inlets) 902, 904, 908 for connecting the various flow conduits to the anoxic reactor. At least one aperture may be configured to allow gas release from the anoxic reactor (e.g. via a one-way gas release valve). At least one aperture may be configured to allow flow of wastewater into the anoxic reactor from the aerobic reactor. The third optional aperture may be configured to allow flow of wastewater into the anoxic chamber from an influent wastewater holding tank (e.g. the container 402 described in relation to Fig. 4). In other examples, the anoxic reactor lid may include a single inlet aperture for connecting all relevant conduits to the anoxic reactor.

The anoxic reactor illustrated in Fig. 9b may include at least one peripheral flange 916 that extends annularly around the circumference or perimeter of the anoxic chamber. In this example the peripheral flange corresponds to the peripheral lip 918 of the anoxic chamber lid 910. When mated together the lip 918 and flange 916 may form an airtight seal. The lip 918 may be fastened to the flange 916, for example by bolts 906.

In some examples the lip 918 and/or flange 916 may include an annular seal, for example a rubber seal or other sealing means.

Figs. 10a and 10b illustrate an example of a distributer element 1000. A distributer element 1000 may be coupled to the aerobic reactor to distribute the wastewater substantially evenly throughout the cross-sectional area of the aerobic reactor. Dispersion of the water throughout the reactor ensures the water is distributed more evenly throughout the reactor to optimise aeration and distribution throughout the scaffold (e.g. the sponge) supporting the bacteria which remove organic pollutants etc.

The distributer element 1000 may rotate about the airflow passage of the at least one receptacle to thereby distribute wastewater substantially evenly throughout the at least one receptacle. The distributer element 1000 includes a central portion that is configured to cover the airflow passage to prevent wastewater bypassing the sponge in the receptacles and passing instead through the airflow passage.

The distributer element 1000 includes at least one arm 1010. In this example the distributer element includes six arms. In this example the six arms 1010 are arranged equidistant from one another.

In this example, each arm 1010 includes at least one aperture 1020. This may improve aeration to the waste water. In this example each arm includes four apertures 1020.

At the centre of the distributer element 1000 there may be a hollow columnar member 1030. Wastewater may be pumped or provided to the top of the distributer element through the hollow columnar member 1030 and may be evenly distributed along each distributer arm 1010 to be evenly distributed via the apertures throughout the aerobic reactor. Rotation of the distributer element helps to ensure even distribution throughout the reactor. Furthermore, pumping the influent to the aerobic reactor under pressure (e.g. via an electric pump) may further help to distribute the wastewater evenly to each distributer arm.

Each arm has a supporting connection 1040 attaching the apex of the hollow columnar member 1030 to the distal end of the arm. In this example the supporting connection may be formed from wire or yarn for example.

The hollow columnar member 1030 may aptly be arranged over the airflow passage in the receptacles such that wastewater is prevented from entering the airflow passage by the distributor element.

Various modifications to the detailed arrangements as described above are possible. Although the aerobic reactor in the example described above includes six receptacles, the aerobic reactor may include at least one or a plurality of receptacles. For example, the aerobic reactor may include 2 receptacles, from 2 to 12 receptacles, for example from 3 to 10 receptacles, or for example from 5 to 8 receptacles.

The at least one sponge or the plurality of sponges may occupy at least half, or at least 60% or at least 70% or at least 80% of the volume defined by each receptacle.

Although in the example described above the receptacle 210 includes four support elements 216 arranged equidistant around the outer wall 208, the receptacle may include any plurality of support elements arranged around the outer wall 208 at the end distal from the base. In other examples, the support element may include a single flange extending inwardly from the outer wall at the end of the outer wall distal from the base. Aptly, the flange may extend inwardly around the whole perimeter or circumference of the outer wall. As such, the flange is configured to support the base of an above adjacent receptacle.

Although in the example described above the aerobic-anoxic ratio is described as from 1 :9 to 1 :3, other examples may include different ratios. The aerobic-anoxic ratio may be determined according to the average external temperature variance where the DDHS system is to be utilised.

Although described above as frustoconical, the clarifying section may be any other suitable shape, including cylindrical, conical, tetrahedron. In some examples the base of the clarifying section may be larger than the end distal to the base, in other examples the base may be smaller than the end distal to the base.

The anoxic chamber lid may have more or less apertures than described above dependent on the flow paths to and from the anoxic reactor. For example, some variants of the DDHS system may not include the aerobic bypass conduit, thereby requiring fewer apertures in both the anoxic reactor and the waste water container.

Although in the example described above the airflow passage extends longitudinally through the whole receptacle column, in other examples, the airflow passage may extend longitudinally only part way through the receptacle column. For example, in one or more of the receptacles, the internal wall may be omitted such that there is no airflow passage in that receptacle. For example, the airflow passage may only extend through the upper receptacles, and the lower receptacles, for example the bottom two receptacles may not include an airflow passage.

In some examples, the one or more of the receptacles of the aerobic reactor may include a plurality of airflow passages. For example, the receptacle may include two or more internal walls defining two or more airflow passages extending longitudinally through the receptacle.

Although the system described above includes both an aerobic reactor and an anoxic reactor, in some examples, the aerobic reactor alone can efficiently reduce the level of ammonia in wastewater and is particularly suitable for use in cold environments.

Although in the example shown above, the anoxic reactor is provided separately to the aerobic reactor, in some examples the aerobic and anoxic reactors may be provided in a single column. That is the aerobic reactor may be provided above the anoxic reactor and enclosed within a single outer shell. The outer shell in the aerobic reactor may include vents similarly to those described above to allow for passive aeration of the aerobic reactor.

In addition to the components of the DDHS system described above, the system may additionally include one or more settling tanks positioned and fluidly coupled to the system upstream of the container 402. The settling tanks may include a grit chamber configured to remove heavier components, for example sand or gravel, from the waste water. The waste water may then pass through a further settling tanks, which may be configured to remove finer particles from the wastewater before it is passed to the aerobic reactor. In some examples, the container 402 may be configured as a settling tank. By removing solids from the waste water in settling tanks, this reduces the build up of material within the aerobic reactor, particularly in the region of the inlet and the distributer element. In some examples the clarifier may include an outlet to remove sediment build up from the reactor.

In one aspect, the present invention provides a method of reducing the level of ammonia, bacteria and/or organic pollutants in wastewater comprising passing wastewater through at least one sponge within the downflow wastewater treatment apparatus of the invention. Organic pollutants include any carbon source. For example, it includes manure or sewage.

Suitably, the level of organic pollutants (carbon sources) may be reduced by up to 85% of total Chemical Oxygen Demand (COD) and 45-59% of soluble COD. When the methods utilise an anoxic reactor, it has been advantageously found that the total nitrogen reduction from waste water can be enhanced from below 10% TN removal with one aerobic reactor, to achieve 52% removal.

The methods described herein are particularly useful for removing a proportion of bacteria from the wastewater. In other words, the bacterial load present in the wastewater may be reduced or removed during the method. The bacteria may be pathogenic bacteria, commensals or a mixture thereof. The bacteria may be enteric bacteria. The bacteria may comprise antimicrobial resistance genes (e.g. they may have antimicrobial resistance).

Suitably, the methods of invention may result in a one or two log reduction in total bacterial abundance in the waste water.

In one example, bacterial loads present in the waste water (including wastewater-borne pathogens and/or antimicrobial resistance genes) may be reduced or removed from the wastewater. Likewise, mobile genetic elements may be reduced or removed.

Suitably, the methods of invention may result in a one or two log reduction in total antimicrobial resistance gene abundance in the waste water. The percentage of recycling of anoxic effluent can readily be optimised by the skilled person to maximise removal of antimicrobial resistance genes. For example, a percentage recycling of anoxic effluent of 10 to 30% or 15 to 25% or approximately 20% may achieve good results. Some

antimicrobial resistance genes may be more readily removed from the wastewater. For example, the number of Extended Spectrum Beta Lactamase (ESBL) and carbapenem- resistant bacteria may be reduced by greater than a two or three log reduction, suggesting the system may advantageously remove enteric bacteria which prevalently carry these genes.

In another aspect, the present invention provides a use of the downflow wastewater treatment apparatus of the invention to reduce the level of ammonia in waste water, denitrify waste water or to reduce the level of antimicrobial resistance genes in waste water. Field results showed 57 - 72% reduction of ammonia, 37 - 52% reduction of total nitrogen and up to 98% reduction of antimicrobial resistance genes level in waste water.

In the examples described above the receptacles are easily replaceable or removed for maintenance. This allows for easier replacement or cleaning of the sponge within the receptacle. Also, transport and assembly of the reactor at the desired location is easier since the reactor may be transported in relatively smaller component receptacle parts. This may be particularly advantageous for harder to access rural areas, for example.

Furthermore, the modular nature of the receptacles in both the aerobic and anoxic reactors allows for greater flexibility in configuring the reactors for optimal performance according to the specific environment in which it is located. For example, the number of receptacles in each reactor can be chosen to adapt the aerobic-anoxic ratio to optimise performance according to temperature and humidity of the surrounding environment.

The distributor element helps to evenly disperse wastewater throughout the receptacle thereby ensuring an even distribution across all of the sponge contained within the receptacle.

The airflow passage provides an additional dimension for aeration of the aerobic chamber compared to previously known systems. This helps to optimise the aerobic environment thereby facilitating oxygenation of ammonia to nitrates and encouraging bacterial growth and thereby removal of organic pollutants.

The invention is exemplified by the following non-limiting examples.

Examples

The inventors have tested the downflow wastewater treatment apparatus described herein to determine their ability to remove antibiotic resistance bacteria (ARB) and genes (ARG) from wastewater. They have shown that the apparatus described herein can remove between 90 and 99% of both ARGs and mobile genetic elements (MGEs) from wastewater (see Figures 11 and 12), which is in the removal range one finds in large, more expensive wastewater treatment technologies. MGEs are genetic elements that allow bacteria to share ARGs between each other and are a measure of how readily ARGs can be transmitted in a location; a key trait for reducing antibiotic resistance spread in the environment.

The data shown in Figures 11 and 12 relates to two embodiments of the downflow wastewater treatment apparatus described herein (referred to as OP2 and OP4 herein), comprising an aerobic reactor (referred to as“compartment 1”) and an anoxic reactor (referred to as“compartment 2”) described herein. OP2 and OP4 represent two different recirculation regimes for operating the downflow wastewater treatment apparatus that achieve very high ARG removal rates, especially when recirculation is performed from the bottom of the anoxic reactor of the apparatus. It is also noteworthy that OP2 and OP4 reduce all classes of measured antibiotic resistance, including Beta_Lactam resistance, which reflects over 50% of the antibiotics used in hospitals. ARB removal rates are about 10 times higher than ARG removal rates, which means resistant bacteria are removed even more effectively than resistance genes.

OP2 is where the effluent from the bottom of compartment 1 (aerobic reactor) is returned to the top of compartment 1 (aerobic reactor). This means that the aerobic effluent is recirculated in the system and does not cross oxygen free effluent from compartment 2 (anoxic reactor) to the top of compartment 1 (aerobic reactor).

OP4 is where the effluent from the bottom of compartment 2 (anoxic reactor) is returned to the top of compartment 1 (aerobic reactor). This means that the oxygen-free effluent is recirculated instead, which means that the wastewater passes through the whole system twice, meaning the contact times are slightly longer.

Very similar results to those shown in Figure 11 have also been seen in pilot studies which scale up the process (data not shown). These pilot studies use the OP2 configuration that balances and co-optimises nitrogen and ARG-removal, which was considered the better option for most applications. These results confirm that the ability to remove nitrogen, ARGs and ARBs is not affected by scale, meaning successful scale-up to full scale is possible.

Parallel to pilot scale work, molecular microbial analysis of communities in the two compartments (aerobic reactor (“compartment 1”) and anoxic reactor (“compartment 2”)) showed that the key microbial reactions related to nitrogen removal, primarily occur in the bottom sponge layers of compartment 1 (see Figure 13). This is evidenced by increasing concentrations of ammonia oxidizing bacteria (AOB) in bottom of compartment 1 of reactor R-S20, which has the same recirculation design to the pilot plant. The figure also shows the same enrichment of AOB does occur when this recirculation is not employed, confirming that nitrogen removal is enhanced by the apparatus design. This data allows the depth of the compartment 1 to be optimised, creating more consistent nitrogen removal.

The data in Figure 13 was generated using an OP2 configuration that balances and co optimises nitrogen and ARG-removal. It is noted that an OP4 configuration could also be used as the alternative if one wanted to optimise ARG removal. Throughout the description and claims of this specification, the words“comprise” and “contain” and variations of them mean“including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise. Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

Claims

1. A downflow wastewater treatment apparatus comprising:

2. A downflow wastewater treatment apparatus according to claim 1 , wherein the aerobic reactor comprises a plurality of receptacles.

3. A downflow wastewater treatment apparatus according to claim 2, wherein each receptacle is configured for placement adjacent another receptacle to form a receptacle column to allow flow of wastewater downwards through the receptacle column.

4. A downflow wastewater treatment apparatus according to any preceding claim, wherein the wall is located substantially centrally within the receptacle such that the air flow passage extends substantially centrally through the receptacle.

5. A downflow wastewater treatment apparatus according to any preceding claim, wherein the aerobic reactor further comprises a distributor element configured to distribute wastewater substantially evenly throughout a cross-sectional area of the aerobic reactor.

6. A downflow wastewater treatment apparatus according to claim 5, wherein the distributor element comprises at least one arm configured to rotate about the airflow passage of the at least one receptacle for distributing wastewater substantially evenly throughout the at least one receptacle.

7. A downflow wastewater treatment apparatus according to any preceding claim, wherein the at least one receptacle comprises a plurality of apertures sized to allow flow of air into the receptacle and flow of wastewater through the receptacle, whilst retaining sponge therein.

8. A downflow wastewater treatment apparatus according to any preceding claim, wherein at least one receptacle is formed from a wire mesh or a polymer mesh, or polymer basket.

9. A downflow wastewater treatment apparatus according to any preceding claim, wherein the aerobic reactor further comprises an outer shell configured to enclose the at least one receptacle.

10. A downflow wastewater treatment apparatus according to according to claim 9, wherein the outer shell comprises a plurality of vents for allowing flow of air into the aerobic reactor.

11. A downflow wastewater treatment apparatus according to any preceding claim, further comprising an anoxic reactor fluidly coupled to the aerobic reactor downstream of the aerobic reactor.

12. A method of reducing the level of ammonia, bacteria and/or organic pollutants in wastewater comprising passing wastewater through at least one sponge within the downflow wastewater treatment apparatus of any one of claims 1 to 11.

13. A method according to claim 12, wherein bacterial loads including wastewater- borne pathogens and/or antimicrobial resistance genes are reduced or removed from the wastewater.

14. Use of the downflow wastewater treatment apparatus of any one of claims 1 to 11 to reduce the level of ammonia in wastewater, denitrify waste water, reduce the level of organic pollutants in wastewater, or reduce the level of bacteria in wastewater.

15. The use of claim 14, comprising reducing or removing bacterial loads including wastewater-borne pathogens and/or antimicrobial resistance genes from the wastewater.