GB2505507A

GB2505507A - Ballast water treatment system with a UV radiation source

Info

Publication number: GB2505507A
Application number: GB1215699.8A
Authority: GB
Inventors: Andrew William Clark; Stephen David Larner
Original assignee: Hanovia Ltd
Current assignee: Hanovia Ltd
Priority date: 2012-09-03
Filing date: 2012-09-03
Publication date: 2014-03-05
Also published as: GB201215699D0; WO2014033478A1

Abstract

A ballast water treatment system comprises a chamber 1 for the UV treatment of ballast water in said chamber, a UV source 7 located in said chamber to irradiate said ballast water and a sensor 9 configured to measure the intensity of the UV radiation irradiating said ballast water. The sensor is located at a pre-determined distance from the UV source, said predetermined distance being within 20% of the point where the relationship between D and S/Q has a minimum dependence on the transmittance of the ballast water, where D is the UV dose provided to the ballast water, S is the intensity of radiation measured at the sensor located at the predetermined distance and Q is the flow rate of ballast water through the chamber.

Description

I

Ballast Water Treatment The present invention is concerned with the field of treatment of ship ballast water.

More specifically, the present invention is concerned with a meLhod and apparatus for disinfecting ship ballast water using UV radiation.

The use of water as ballast on ships is essential in order to maintain the stability of the ship throughout the voyage. When a ship is lightened, for example by lack of cargo or consumption of fuel, water can be pumped on board to compensate. When the load is increased this water is released. This often happens in a different geographical location. This transfer of water carries organisms, including bacteria and microbes, from one ecosystem to another. The transferred species can become invasive, and harmful to native species. In this way the use of sea water as ballast can have a harmful effect on some ecosystems.

In order to prevent this, systems for managing ballast water on board ships have been brought into use. These include filtration systems, which remove larger organisms, and disinfection systems, which inactivate or kill smaller organisms such as bacteria and microbes. One of the methods of disinfection used is UV treatment of the water, where UV irradiation of the water kills or removes the reproductive capacity of micro-organisms. UV sterilisation processes involve water flowing through a chamber that is exposed to UV radiation, usually from a mercury vapour lamp In many such systems the water is circulated several times in order to ensure disinfection.

As awareness of the problem has grown, guidelines for the management of ballast water have been set. These ensure that ships use a ballast water management system to meet a standard based on agreed numbers of organisms per unit of volume. These regulations are being phased in gradually for ships constructed before the guidelines, and enforced for ships newly constructed. This has resulted in a growing need for on board ballast water management systems which can monitor whether the water treatment is above a minimum standard.

However, most methods of accurately estimating the UV dose require measurement of the transmittance of the water. This is particularly problematic when monitoring ballast water as the transmittance of the water can vary considerably dependent on the location where the ballast water was taken into the ship. A large variance in the transmittance can have a dramatic effect of the disinfection performance of the system.

It is therefore important to be able to calculate the disinfection performance accurately under conditions where transmittance is changing to ensure the ballast water is being disinfected to the required level.

A UV ballast water system can be supplied with a transmittance monitor, and the transmittance of the ballast water being treated can be measured and then used by the UV control system to calculate the UV dose being delivered However! such monitors are expensive and are not suited to the intermittent use that they will receive is used in a marine environment.

The present invention addresses the above problems, and in a first aspect provides a ballast water treatment system, said system comprising a chamber for the UV treatment of ballast water in said chamber, a UV source located in said chamber to irradiate said ballast water and a sensor configured to measure the intensity of the UV radiation irradiating said ballast water, the sensor being located at a pre-determined distance from the UV source, wherein the predetermined distance is within 20% of the point where the relationship between ID and SI Q has a minimum dependence on the transmittance of the ballast water, where D is the UV dose provided to the ballast water! s is the intensity of radiation measured at the sensor located at the predetermined distance and 0 is the flow rate-A system in accordance with an embodiment of the present invention allows an accurate dose to be calculated without the need for measuring a transmittance value, even though the dose varies with transmittance changes. Thus, removing the requirement to use a transmittance monitor in order to calculate an accurate dose.

In embodiments of the above system, a sensor is provided to measure the intensity of the UV radiation at a distance from the (JV source. The actual delivered dose is determined by the design of the chamber, the flow rate, the transmittance and the amount of UV light emitted into the water. At this distance, it is possible to accurately calculate the dose that the UV system is delivering to the ballast water without knowing the transmittance of the ballast water being treated. This is explained in Wright, Harold, et al. (2002) Critical Aspects of UV Dose Delivery Monitoring" Annual Conference Proceedings American Water Works Association, which shows that if the UV sensor is positioned at this distance, an accurate dose can be calculated without a transmittance value if the dose equation has a polynomial form dependent on terms where the measured UV intensity is divided by the flow.

The dose that a UV system delivers is dependent on the design of the reactor, the flow rate, the transmittance and the amount or UV light emitted into the water. There are a number of different interpretations and ways to calculate dose D, but it is generally accepted that the Reduction Equivalent Dose (RED) is the only accurate indication of the disinfection performance of a UV system The RED can be measured using biodosimetric testing or modelled by using Computational Fluid Dynamics (CFD).

Whichever is used, it is important that the UV system controller calculates an accurate delivered RED dose i.e. is as close as possible to the real dose being delivered. By positioning the sensor at this distance the influence of the transmittance on the relationship between the dose and the value S/Q is at a minimum and preferably the transmittance has no influence on the relationship between the dose and the value 6/0.

As the sensor moves away from the point distance, it is possible to calculate the error on the calculated dose resulting from changes in transmittance. To ensure that the calculated dose does not exceed the actual delivered dose, the calculated dose equation can be modified basically to provide a worst case calculated dose which would always by lower than the delivered dose over the range of transrnittances that the system would be expected to see in use. The actual distance will depend on the reactor design.

In one embodiment, the sensor is positioned at the exact point where the relationship between the dose and 610 has its minimum dependence on the transmittance of the ballast water, the ideal position. However, some variation in this position is allowable which will still allow a fairly accurate dose to be calculated. In one embodiment! the sensor position may be varied within 20% of the ideal position, in a further embodiment, to within 10%, in a yet further embodiment to within 5% In use, it is safer to use the 3/0 measurement to underestimate the dose. Therefore, in an embodiment the sensor is provided within a range from -10% to 20% of the ideal position, where a sign indicates that the sensor is closer to the source than the ideal position. The percentages are measured in terms of the distance of the sensor from the lamp.

In an embodiment, at distances shorter than the pre-determined distance, the caLculated dose will increase faster than the deLivered dose as the transmittance of the ballast water increases and at longer distances than the predetermined distance the calculated dose will decrease faster than the delivered dose as the transmittance increases, the minimum dependency being where the relationship between the calculated dose and the delivered dose remains the same as transmittance changes.

The system is used to treat ballast water which, typically, has a transmittance ranging from 25% to 98% over a 10mm distance.

Generally, the UV source will be an elongate UV source. In some embodiments, it is located parallel to the direction of fLuid flow through the UV chamber in others it is located perpendicular to the direction of fluid flow through the UV chamber.

The water may pass through the system vertically or horizontally. Space is at a premium in marine vessels and often a system which is conligured such that the water will vertically enter the reaction vessel can be more easily filled into the space available.

The ballast water treatment system may further comprise a filter configured to fitter the ballast water before it enters the chamber for UV treatment. The filter may be a backwashing filter. Generally, the water will be filtered when it is first taken onto the vessel and before it enters the UV chamber. When the water is to be discharged, it will generally not re-enter the filtration process and will just be treated by UV.

In some embodiments, the system further comprises a control system, said control system comprising an input receiving data from the sensor and an input of the flow rate of ballast water through the tJV chamber, the controller being adapted to divide the input from the sensor by the flow rate. In a further embodiment, the system further comprises a memory in communication with said controller, the controller being adapted to calculate a value indicative of a dose from the input from the sensor divided by the flow rate, the controller being further adapted to compare the value indicative of a dose with a pre-determined dose value in said memory. The system may further comprise an indicator, said indicator being configured to indicate it said value indicative if a dose is acceptable or not acceptable, wherein an acceptable value is a value greater than that of the predetermined dose value. The indicator may by a physical indicator on the system or close to the system, for example a green light to indicate that the dose is above an acceptable level and a red light to indicate when the dose has dropped. In further embodiments, the indicator may be a signal sent to a remote monitoring facility either located on the ship or off the ship, for example, the signal could be sent to the ship's managing company or it could be sent to the local port authority.

In a further embodiment, the control system is configured to reduce the flow rate of the water through the system until the dose reaches the acceptable value. For example, the control system may control a valve to adjust the flow rate.

In furiher embodiments, a marine vessel is provided, the marine vessel comprising a ballast tank and a connection between said ballast tank and an external port of said marine vessel such that ballast water may be ejected from said ballast tank through said external port to the sea, the vessel further comprising a baLlast water treatment system as described above said ballast water treatment system being located to receive water from the ballast tank and output treated water through the said external port.

In a second aspect, the present invention provides a method of locating a sensor in a ballast water treatment system, said system comprising a chamber for the UV treatment of ballast water in said chamber, a UV source located in said chamber to irradiate said ballast water and a sensor configured to measure the intensity of the UV radiation irradiating said ballast water, said method comprising: collecting or calculating RED data for a plurality of different doses, flow rates and for a plurality of different transmittances of water for said chamber; obtaining a plurality of readings from said sensor for a plurality of different transmittances of the ballast water and different powers of said UV source or flow rates, said data being collected at different sensor positions; and selecting said sensor position where the RED equation used to calculate the dose on the ship uses term(s) that include the sensor output divided by the flow rate such that the calculated dose and delivered dose have minimum difference independent of the transmittance of the ballast water.

In further embodiments, the position of the sensor can be determined by mathematical S modelling.

The present invention will now be described with reference to the following figures in which: Figure 1 is a schematic of a ballast water treatment system in accordance with an embodiment of the present invention; Figure 2 is a schematic of a ballast water treatment system in accordance with a yet further embodiment of the present invention; and Figure 3 is a schematic of a ballast water treatment system in accordance with a further embodiment, comprising a filter.

Figure 1 is a schematic of a system for the UV treatment of ballast water in accordance with an embodiment of the present invention. Water enters the UV treatment chamber 1 through inlet 3 on one side of chamber 1. The water flows through the chamber 1 and it exits through the outlet 5, which in this embodiment is provided on a different side of the chamber Ito the inlet 3.

Located in the chamber is at least one UV source 7. The UV source is elongate and is, in this embodiment, positioned, such that it is arranged perpendicular to the flow of the ballast water through the chamber 1. Chambers with the lamps perpendicular to the flow allow the chamber to be positioned in line with the pipe. This avoids the need for so-called elbows etc in the piping. This allows a more compact installation and space is always limited on a ship. The perpendicular arrangement also has another advantaged in that it also allows the same chamber to be used with either vertical or horizontal flow, so if a ship has headroom but limited floor area, vertical flow can be used.

Although it is possible to use lamps which are arranged parallel to the flow, such a chamber is more limited in the orientations in which it can be arranged, since the lamps can only be used horizontally as medium pressure lamps do not start reliably when vertical.

The UV source 7 typically emits UV radiation at the germicidal wavelength. An example of such a source is a low pressure mercury vapour lamp, which emits light at 254nm or a medium pressure mercury vapour lamp UV source that emits radiation across the UVC spectrum.

In some embodiments, the source is housed in a quartz sleeve. In further embodiments, there is provided a mechanism for wiping the surface of the sleeve, in order to ensure it is clean and not limiting the intensity of the UV radiation. Although just one source 7 is shown, more than one source may be provided. Figure 1 is a simplified figure. In an actual system, the source will be mounted to a side wall of the chamber 1 so that it can be externally powered.

A sensor 9 is provided mounted to a wall of the chamber 1. The sensor measures the intensity of the radiation which is emitted by the source 7. The sensor is provided at a distance "d" shown by arrow 11.

In an embodiment, the UV system will be provided with a controller (not shown) which is configured to monitor the dose which is being supplied by the UV system.

The log inactivation reduction equivalent dose (RED) can be determined as a function of the flow rate through the reactor. The RED may be determined by a biodosimetric approach or by using computational fluid dynamics.

In some embodLments, it is desirable to configure the UV system such that there is a dose set point in which case the reactor is known to be in compliance with a required RED when the UV intensity measured by the UV sensor is greater than a required value which is defined in terms of function of the flow rate of the ballast water through the reactor.

The relationship between RED, UV intensity measured by the sensor (S) and flow rate (Q) varies with the transmittance and also the distance d".

By plotting the RED against 5/0, if the UV sensor is located relatively close to the lamps, the relationship between RED and 8/0 will change in proportion to the transmittance. However, if the UV sensor is located relatively far from the lamps! the relationship between RED and 5/Q changes in inverse proportion with transmittance.

Therefore1 there is a point at which the dependency changes from being proportional to inversely proportional i.e. there is a point where the transmittance does not materially affect the relationship between RED and 5/0.

Therefore, if the sensor is placed at this point, the RED varies with 5/0 with no or little dependence on transmittance. The dependence of the relationship between RED and S/Q varies with transmittance along the distance from which the sensor is placed from the source. Therefore, the sensor is placed at the minimum of the variation with transmittance against distance from the source.

The position of the sensor will be determined when the UV chamber is originally validated before it is sent to a customer. Typically, a plurality of readings from said sensor for a plurality of different transmittances of the ballast water and different powers of said IN source will be collected at different sensor positions. Then a plurality of readings of the dose for a plurality of different flow rates, source powers and transmittances will be determined. The sensor position will be selected where the sensor output divided by the flow rate has a minimum dependency on the transmittance of the ballast water.

Typically, the RED for a plurality of different values of S/Q will be determined for a number of different transmittances at a plurality of different values of "d". In an embodiment, "di' will be selected by trial and error. If from the data, the RED plotted against 8/0 varies in a proportional manner with "d" then a larger i'd" must be selected until there is no variation of RED against S/Q with transmittance.

In the above embodiment, once the position of the sensor has been set, the system may be provided with a controller which collects the intensity data supplied by the sensor and divides it by the flow rate through the system. If the sensor is correctly located, the transmittance does not need to be monitored and thus the system may be configured to indicate that the correct dose is applied if the value of SIQ translates to an RED value which is equal to or above a setpoint.

Once the position has been determined for a particular chamber and source arrangement, the sensor can be used in that position for all identical chambers. There is no need to calculate the position of the sensor every time a chamber is manufactured.

The flow rate in the above embodiment may be measured by a flow rate sensor either within the chamber 1 or close to the inlet or outlet of the chamber, or anywhere En the treatment system.

In the embodiment of figure 1, a single UV source is shown. In the embodiment of figure 2 a plurality of UV sources 21 are shown. To avoid an unnecessary repetition like reference numerals will be used to denote like features.

In figure 2, the plurality of sources 21 are arranged in a symmetric configuration about a central axis. However, asymmetric arrangements may also be used.

The sensor 9 is positioned so that it is facing one of the lamps 13. In an embodiment! the sensor is a narrow angled sensor. In one embodiment, such a sensor has a opening of 165 degrees or less. In a further embodiment, a narrow angled sensor with an opening of 50 degrees or less is used. Currently! in the industry, there are two industry standard sensors used! one has a nominal opening angle of 40 degrees and the other is 160 degrees.

Using a narrow angled sensor allows the radiation from one light source to be collected. Where multiple sources are used, such an arrangement can give a more accurate value of S/Q for calculating the dose.

In the embodiment, of figure 2, 6 lamps are shown, but this is just an example, in practice a plurality of lamps may comprise 2 or more lamps.

In a further embodiment as shown in figure 3, the system further comprises a filtration stage 21. In an embodiment, the filtration stage is provided by a back-washing filter.

Details of this will not be provided here. When the ballast water is first taken onto the ship, the water enters through inlet pipe 23 and passes through valve 24 which directs the water into backwashing filter 21. The valve 24 can either connect the inlet pipe 23 to the backwashing filter 21 or it can direct the water to along cross pipe 27 to valve 26 which is connected to outlet pipe 26. Depending on the setting of the valves 24 and 26, the ballast water can bypass the backwashing filter 21 or pass through the S backwashing filter 21.

The water passes through the backwashing filter 21 and then exits through outlet pipe 25. Outlet pipe 25 has a valve 26 which allows the water to leave the backwashing filter 21 and the water passes inlet of the UV treatment chamber 1.

The water is then stored on the ship as ballast. When the ballast water is to be discharged from the ship, it only passes through the UV treatment chamber and does not need to pass through the backwashing filter 21. Therefore, valves 24 and 26 are set so that the water can pass between inlet pipe 23 and outlet pipe 25 and bypassing the filter 21.

In an embodiment, the system of figure 3 may also be provided with a controller 31.

The controller is connected to the output of the sensor 9 and can also flow meter 33.

The flow meter 33 is shown on the inlet to the chamber 1, but may be placed at any position which allows the flow rate of ballast water through the chamber ito be accurately measured. The controller is configured to measured 5/0. The controller also has a memory which stores an acceptable Sf0 value or a set point value.

In a further embodiment, the controller is configured to raise an alarm if the measured s/a value falls below the acceptable 5/0 value. In a yet further embodiment, the controller 31 is configured to control at least one valve in the system which allows the controller 31 to control the flow rate in the system such that the acceptable S/Q value can be achieved. For example, if the measured Sf0 value falls below the set point value, the controller can reduce the flow rate until the 8/0 value increases to the leveL of the set point. Thus, automatic control of the dose supplied by the chamber can be achieved.

Claims

CLAIMS1. A ballast water treatment system, said system comprising a chamber for the UV treatment of ballast water in said chamber, a UVsource located in said chaniberto irradiate said ballast water and a sensor configured to measure the intensity of the UV radiation irradiating said ballast water, the sensor being located at a pre-determined distance from the UV source1 wherein the predetermined distance is within 20% of the point where the relationship between D and S/C has a minimum dependence on the transmittance of the ballast water, where D is the UV dose provided to the ballast water1 S is the intensity of radiation measured at the sensor located at the predetermined distance and Q is the flow rate.
2. A ballast water treatment system according to claim 1, further comprising a filter configured to filter the ballast water before it enters the chamber for UV treatment.
3. A ballast water treatment system according to claim 1, wherein at distances shorter than the pre-determined distance, the relationship between D and SIC varies proportionally with the transmittance of the ballast water and at longer distances than the predetermined distance the relationship between D and S/C varies inverse proportionally with the transmittance, the minimum dependency being at the cross over from the proportional dependency on transmittance to the inverse proportional dependency on transmittance.
4. A ballast water treatment system according to any preceding claim, wherein the predetermined distance is within 10% of the point where the minimum dependence on transmittance occurs.
5. A ballast water treatment system according to any preceding claim, wherein the ballast water has a transmittance ranging from 25% to 98% over a 10mm distance of ballast water.
6. A ballast water treatment system according to any preceding claim, wherein said UV source is an elongate UV source and is located parallel to the direction of fluid flow through the UV chamber.
7. A ballast water treatment system according to any of claims 1 to 5, wherein said UV source is an elongate UV source and is located perpendicular to the direction of fluid flow through the UV chamber.
8. A ballast water treatment system according to any preceding claim, comprising a plurality of UV sources.
9. A ballast water treatment system according to claim 8, wherein the said sensor is positioned such that it is directed towards one of the UV sources.
10. A ballast water treatment system according to claim 9, wherein a narrow angle sensor is used.
11. A ballast water treatment system according to claim 2, wherein said filter is a backwashing filter.
12. A ballast water treatment system according to claim 2, comprising a bypass channel for said filter and a valve, said valve being configured to direct ballast water being taken on by a ship through said filter and then said treatment chamber1 said valve being configured to direct ballast water to be discharged by said ship through said bypass channel and into said treatment chamber.
13. A ballast water treatment system, further comprising a control system, said control system comprising an input receiving data from the sensor and an input of the flow rate of ballast water through the UV chamber, the controller being adapted to divide the input from the sensor by the flow rate.
14. A ballast water treatment system according to claim 13, further comprising a memory, said controller being adapted to calculate a value indicative of a dose from the input from the sensor divided by the flow rate, the controller being further adapted to compare the value indicative of a dose with a pre-determined dose value in said memory.
15. A ballast water treatment system according to claim 14, further comprising an indicator, said indicator being configured to indicate if said value is acceptable or not acceptable, wherein an acceptable value is a value greater than that of the predetermined dose value.
16. A ballast water treatment system according to either of claims 14 or 15, further comprising a valve, said valve being operable by said controller to control the flow rate of water through said chamber to modify the value indicative of a dose to be equal to or greater than the predetermined dose value.
17. A marine vessel comprising a ballast tank and a connection between said ballast tank and an external port of said marine vessel such that ballast water may be ejected from said ballast tank through said external port to the sea, the vessel further comprising a ballast water treatment system according to any preceding claim, said ballast water treatment system being located to receive water from the ballast tank and output treated water through the said external port.
15. A method of locating a sensor in a ballast water treatment system, said system comprising a chamber for the UV treatment of ballast water in said chamber, a UV source located in said chamber to irradiale said ballast water and a sensor configured to measure the intensity of the UV radiation irradiating said ballast water, said method comprising: obtaining a plurality of readings from said sensor for a plurality of different transmittances of the ballast water and different powers of said UV source, said data being collected at different sensor positions; determining a plurality of readings of dose for a plurality of different flow rates, source powers and transmittances selecting said sensor position where the sensor output divided by the flow rate has a minimum dependency on the transmittance of the ballast water.
19. A method according to claim 16, wherein the dose is determined using computational fluid dynamic techniques.
20. A ballast water treatment system as substantially hereinbefore described with reference to any of the accompanying figures.