WO2005033023A1

WO2005033023A1 - Sewage treatment

Info

Publication number: WO2005033023A1
Application number: PCT/GB2004/004208
Authority: WO
Inventors: Ian M. Wylie; Alan Higgs
Original assignee: Etac Limited
Priority date: 2003-10-02
Filing date: 2004-10-01
Publication date: 2005-04-14
Also published as: GB0323078D0

Abstract

A wastewater disposal unit is provided comprising an at least partly submersible container housing a plurality of treatment stages interconnected by pipes and conveyors, the plurality of treatment stages including an incinerator for disposing of sludge produced by the treatment stages and for providing thermal energy.

Description

Sewage Treatment

The present invention relates to a wastewater disposal unit and method, as well as to a container for such a unit and a method of constructing such a unit.

The process of urbanisation has driven the need to manage the difficult problem of sewage disposal. For over a century, this has been achieved by constructing and operating treatment plants, of increasing capacity and technical sophistication, on land sites relatively close to the populations they serve. Coastal populations have used the sea for disposal, with little treatment first.

A crucial set of environmental, land-use, water-resource, and demographic factors is now converging to force this traditional approach to be questioned, and in many cases replaced. This is particularly the case with treatment plants serving population centres bordering not just coasts, but also estuaries, lakes and large rivers. In response to these factors, major effluent handling and treatment programmes have been underway over the last few years at many such locations. This trend is set to increase, with the drive for improved water- related facilities now extending to many more countries across the world. But the solutions adopted by water companies or public authorities continue to be land-based (some have been contained within large underground chambers within the seafront of the communities they serve: but this option is restricted to suitable sea-front developments). The invention provides new-technology treatment facilities that deliver a more efficient service than conventional plants, and address environmental/amenity issues by housing these facilities in containers submerged offshore from the communities they serve. Each container, with its facilities, will be referred to as a 'unit'. Local drainage networks, storm-surge buffers and other onshore infrastructure link directly with these units through existing or purpose-built sea outfalls, and require no screening or other preprocessing of the flow before it is directed into the unit. The units generate little odour, and are for the most part invisible from land.

In addition to its amenity benefits, the invention provides a 'one pass' disposal service - i.e. all domestic or industrial waste-water is passed down the sea outfall into the offshore unit with no onshore pre-processing, where it is totally disposed-of without need for further onshore activities. Effluent may be either discharged into surrounding waters or pumped onshore as 'grey' water for irrigation or other purposes. Sludge resulting from this treatment is incinerated via a process which also generates energy to drive the unit's other processes. The unit is thus to some extent energy self-sufficient. The incineration process results in a small quantity of inert solid material which, after transfer ashore, can be used as road-fill or for similar purposes. Moreover, because of its modular design, the individual components of the unit can be altered or exchanged as technology progresses, without the need of redesigning the entire unit.

A first aspect of the invention provides a wastewater disposal unit comprising an at least partly submersible container housing a plurality of treatment stages interconnected by pipes and conveyors, the plurality of treatment stages including an incinerator for providing thermal energy. A second aspect of the invention provides a wastewater disposal unit comprising a container housing a plurality of treatment stages interconnected by pipes and conveyors, the plurality of treatment stages including an incinerator for providing thermal energy.

A third aspect of the invention provides a container for a wastewater disposal unit, the container being arranged to accept a first group of processing stages, the first group being any subset of a second group of processing, wherein the second group comprises more stages than the first group.

A fourth aspect of the invention provides a method of constructing a wastewater disposal unit comprising constructing a container arranged to accept a first group of processing stages, selecting a second group of processing stages from the first group and fitting the second group to the container.

A fifth aspect of the invention provides a method of operating a wastewater disposal unit comprising treating wastewater using a plurality of successive stages including separating sludge from the wastewater, dewatering the sludge and incinerating the sludge, whereby heat produced by incinerating the sludge is used to provide at least part of the power required to power the plurality of stages.

The invention can be put into practice in a number of ways. A specific embodiment of the invention is now described, by way of example only, with reference to the accompanying drawings, wherein Figure 1 shows a schematic cross-section through a unit embodying the invention; Figure 2 shows a plan view of a top level of the unit shown in Figure 1 ; Figure 3 shows the unit connected to onshore facilities.

In the specific embodiment shown in Figures 1 and 2, a waste disposal unit (1) comprises a container (2), for example made from concrete. At its upper extremity, the container defines a service platform (3) providing a trap door or other means of accessing the interior of the container. The service platform (3) may also house navigation and communication equipment, as well as solar panels and or wind turbines for generating at least part of the electric power required by the unit. At its lower extremity, the container provides a connector (4) for securing it to an anchorage for anchoring the container to the seabed. In the specific embodiment, the anchorage (6) comprises concrete pillars secured to the seabed, but other forms of anchoring the unit are envisaged, for example the unit could float semi-submerged in a fashion comparable to current oil and gas installations in the UK.

The container is provided with a wastewater inlet (8), a discharge (10) for treated water and an access pipe (12) for the removal of solid residues. A service shaft (14) communicates with the trap door provided on the service platform (3) to allow access to all levels of the container. In one particular embodiment, the container is cylindrical with a circumference of between twenty and thirty metres and thirty metres in elevation, having a service platform of eight metres diameter. In this embodiment, the service platform protrudes, at most, 4 metres above sea level, when the unit is installed. The interior of the container is divided into a number of levels, three in the specific embodiment, and arranged to accept a plurality of treatment stages a to f . A screening stage a is connected to the inlet (8) on the first level of the container and serves to extract untreatable objects from the flow of waste water. The screening stage has a first outlet for screened objects connected to a dewatering stage d by a conveyor (16). In one embodiment, the conveyor comprises an Auger feed. A second outlet for the screened water is connected to a primary treatment stage b by a pipe (18).

The primary stage b allows particles suspended in the wastewater to settle, thus separating them from the wastewater and provides further chemical treatment of the wastewater, for example using active carbon. The primary stage provides a first outlet for the settled particle, or sludge, and a second outlet for the treated wastewater. The first outlet is connected to the conveyor (16) by conveyor (20) and the second outlet is connected by pipe (22) to the inlet of a secondary stage c, which provides biological treatment of the wastewater. The secondary stage has a first outlet for solid residues of the biological treatment, connected to the dewatering stage d by yet a further conveyor (24). A second outlet for treated wastewater is connect to a tertiary stage f, which is adapted to remove remaining pathogens from the treated wastewater prior to discharge or reuse. The tertiary stage further comprises an outlet connected to the discharge (10).

The described arrangement may vary as new technologies and processes become available. The process configuration allows for this to occur. For embodiments that envisage returning treated wastewater back to shore, a pumping installation is provided between the outlet of the tertiary stage and the discharge (10), in order to create the outlet pressure required for pumping the treated wastewater back to shore. Alternatively, in other embodiments of the invention, pumping facilities for returning treated wastewater to the shore may be provided onshore or intermediately between the shore and the treatment unit.

The dewatering stage d has two inlet ports for sludge and other solids, connected to conveyors (16) and (24) and is arranged to substantially extract any remaining water from the incoming sludge and solids, for example by a combination of pressure and heat. A first outlet port for the dried sludge is connected to an incinerator e by a conveyor and a second outlet port for the water extracted from the sludge is connected to the tertiary stage f.

The incinerator e is arranged to receive dewatered sludge from the dewatering stage d via conveyor (26) and provides an outlet connected to the access pipe (12). In the embodiment shown in Figure 1, the access pipe (12) transverses the container and is thus accessible from the outside of the container. In an alternative embodiment, the access pipe protrudes in to the service shaft 14 and is thus accessible trough the service shaft via the trapdoor in the service platform 3. Furthermore, the incinerator may communicate with a storage facility that allows larger quantities of incineration residue to be stored than would be possible otherwise.

An exhaust for the emissions generated by the incinerator is provided via one or more dedicated exhaust pipes through either the access shaft (14) or access pipe (12), whereby emission to the environment may be reduced by pyrolitic scrubbing. The treatment stages may be vented through the exhaust pipes or through separate vents.

The incinerator is also arranged to provide thermal energy for the operation of the unit. Thermal energy is provided in the form of steam to those of the processing stages a-f that require input of thermal energy via steam conduits (not shown in the figures). In particular in one embodiment, the dewatering stage d is supplied with steam used for creating a vacuum used in the dewatering process. Sources of electrical energy may be provided on the unit, by providing solar panelling and/or wind- turbines on the service platform (3). Additional electrical energy may provided by connecting the unit to the onshore electricity grid for example by a sea cable. An additional steam generator may be fitted to the unit, driven either by electrical energy or by heat from the incinerator e. In one embodiment, a further source of electrical energy is provided by converting thermal energy from the incinerator to electrical energy, for example using a steam turbine driving a generator.

A controller is provided on the unit in order to co-ordinate the treatment stages and the transport of materials between the stages. The controller is in contact with a control station onshore via a data link, for example a radio frequency data link. However, the control mechanism of the unit comprises a collection of software routines and/or expert systems that allows the unit to control itself. The control post onshore serves principally for periodic monitoring of the functioning of the unit and for emergency interventions.

In one particular embodiment, the container (2) is pre-constructed with standard fittings and connections, allowing a range of commercially available processing stages to be fitted as a function of the design specifications of each unit. Thus the pre-constructed containers can be rapidly fitted with the processing stages that are best adapted for the purpose of the unit depending on such factors as the currently available technology, the scale of the installation to be serviced by the unit and cost considerations. Alternatively, the container may be designed around a specified set of processing stages, allowing to optimise the spatial layout, for example to minimise the footprint of the unit. The unit is installed offshore by towing it to its pre-prepared position and anchoring anchors (6) to the seabed. A typical location is 1-5 km offshore, for example. An assembled sewage system shown in Figure 3 whereby the unit is connected to the onshore drainage network (36) by a sea outfall pipe as indicated by arrow (30). Treated water is either discharged into the sea, as indicated by arrow 32 or pumped back onshore through an appropriate pipe, as indicated by the dashed arrow 34. The only installations required onshore are the control station, which also house a pumping station (38). A storm storage facility (40) for storing significant overflow, for example due to heavy rainfalls, may be provided where required. The rectangular area (42) indicates the area of land required for a comparable onshore installation.

In operation, a continuous flow of wastewater is pumped from the control and pumping station (38) to the unit 1, with all usual buffering (apart from large overflows absorbed by the storm storage facility (40) performed by the unit under control of the unit's controller. Wastewater arriving at the unit via sea outfall (30) and inlet (8) first arrives at the screening stage a, which removes any objects not suitable for further treatment. Removed objects are transported to the dewatering stage d by conveyor (16). The screened wastewater then flows through pipe (18) to the primary stage b, where the wastewater is settled. The settled sludge is transported to the dewatering stage d by conveyors (20) and (16) while the treated wastewater continues to secondary stage c, where it is treated biologically. Any further solid residues are transported to dewatering stage d by conveyor (22) and the treated water enters the tertiary stage f for microbiological filtering. From the tertiary stage f, the treated wastewater is either discharged into the sea via discharge (10), or pumped back to shore to be used as grey water, for example for irrigation or sanitary purposes. All solid residues from the various treatment stages is collected as sludge in the dewatering stage d, where any residual water is substantially removed. The residual water extracted from the sludge is fed to the tertiary stage f, while the dried sludge is transported to the incinerator e for incineration. The thermal energy produced by the incineration process is used directly in the form of steam to drive the dewatering stage d, and may also be converted to electrical energy, for example by a generator driven by a steam turbine.

As a by-product of incineration, a small amount of inert solid materials is produced, which remains inside the incineration stage or in separate storage compartment, until it is periodically transferred to shore (e.g. for use as road- fill) by ship. In one embodiment, the residues are removed from the incinerator by connecting a custom-made connection tube from a transport ship to the access pipe (12) provided on the container wall, as shown in Figure 1. In an alternative embodiment, the connection tube can be connected to the access pipe through the trapdoor in the service platform (3) and via the access shaft (14).

It will be evident to the skilled person that the invention is not restricted to the specific embodiment and alternatives described above, but that it may be put into practice by rearrangement, selection or juxtaposition of the individual features.

In particular, the invention is not limited to any particular dimensions of the unit, internal layout of the unit, number of levels inside the unit, the arrangement of the treatment stages inside the unit or any particular substance for the connections between the treatment stage. Equally, the container may be constructed of any suitable material, fore example steel or fibreglass.

Depending on the local requirements of each site, some of the treatment stages may be omitted, or others added, without departing from the invention.

The size of sewage system that can be served can be increased by connecting multiple units to the sewage system. The multiple units may be monitored by a single control station, or, alternatively, by a number of control stations. Finally, the unit may be installed in any suitable place, for example lakes, rivers or quarries, or indeed underground.

Claims

1. A wastewater disposal unit comprising an at least partly submersible container housing a plurality of interconnected treatment stages, the plurality of treatment stages including an incinerator for providing thermal energy.

2. A unit as claimed in claim 1, the plurality of treatment stages comprising a dewatering stage.

3. A unit as claimed in claim 2 further comprising a steam generator driven, in operation, by thermal energy produced by the incinerator.

4. A unit as claimed in claim 3, whereby the dewatering stage is at least partially driven by the steam generator.

5. A unit as claimed in any of the preceding claims, further comprising a service platform aπ-anged, when the unit is installed in a body of water, to protrude above the level of water.

6. A unit as claimed in claim 5, wherein the platform comprises a solar panel for generating electrical power.

7. A unit as claimed in claim 5, wherein the platform comprises a wind turbine for generating electrical power.

8. A wastewater disposal unit comprising a container housing a plurality of interconnected treatment stages, the plurality of treatment stages including an incinerator for providing thermal energy.

9. A unit as claimed in claim 8 comprising a dewatering stage.

10. A unit as claimed in claim 9 further comprising a steam generator driven, in operation, by thermal energy produced by the incinerator.

11. A unit as claimed in claim 10, whereby the dewatering stage is at least partially driven by the steam generator.

12. A container for a wastewater disposal unit, the container being arranged to accept a first group of treatment stages, the first group being any subset of a second group of treatment stages, wherein the second group comprises more stages than the first group.

13. A method of constructing a wastewater disposal unit comprising constructing a container arranged to accept a first group of treatment stages, selecting a second group of treatment stages from the first group and fitting the second group to the container.

14. A method of operating a wastewater disposal unit comprising treating wastewater using a plurality of successive treatment stages including separating sludge from the wastewater, dewatering the sludge and incinerating the sludge, whereby heat produced by incinerating the sludge is used to provide at least part of the power required to power the plurality of stages.

15. A method as claimed in claim 14, comprising converting the heat to steam.

16. A method as claimed in claim 14, whereby at least part of the heat is produced in the form of steam.

17. A method as claimed in claim 15 or 16 comprising using the steam to dewater the sludge.

18. A wastewater disposal unit, container or method of constructing or operating a wastewater disposal unit substantially as described herein with reference to the accompanying drawings.