FIELD OF THE INVENTION This invention relates to a sensor apparatus for a grease trap for removing fats, oils and grease (hereinafter referred to as FOG) from waste water downstream of a washing facility, such as a sink in a commercial kitchen.

BACKGROUND OF THE INVENTION

Typically waste water drained from a sink in a commercial kitchen or catering facility contains grease in an emulsified state, as well as grease laden solids in suspension, typically in the form of foods wastes. Such contaminants can cause blockages in drainage systems and/or fouling of filtration systems or pumps within water treatment plants downstream of the drainage system.

Effluent from FOG contamination points in commercial kitchens typically originates from steam combination ovens, convection rotisserie ovens, pot sinks, pre-rinse sinks, dishwashers, canopies and the like. They have in common the use and application of hot water ranging in temperature from 40° C to 85° C for the purposes of dealing with FOG contamination, where FOG is washed away in the waste water stream from such devices.

For these reasons, depending on the country, it is often compulsory for commercial kitchen operations to fit some kind of interceptor device to collect the FOG before it enters the sewer, typically referred to as a "grease trap". Additionally where FOG is a concern in the local wastewater collection system, inspection programmes have been set up to ensure that these grease traps and/or interceptors are being maintained on a routine basis.

Known grease traps range in complexity from simple settling tanks, known as "passive" grease traps, that require periodic manual grease removal, to rather complex structural arrangements that provide for automatic skimming and collection of skimmed fats, oils and grease into external containers positioned adjacent the trap assembly, commonly referred to as "automated" grease traps.

Passive grease traps are, in essence, simply a settling tank having a wastewater inlet at one end and an outlet at an opposite end for connection to a drain. Often baffle plates are arranged within the tank to interrupt direct flow-through of wastewater between the inlet and the outlet. Periodically, an employee must manually skim the FOG that has accumulated at the surface of the wastewater. Automated grease traps include automatic skimmer arrangements, typically utilising a skimmer device, in the form of a disc, drum, endless belt or tube, mounted above the tank and connected to a drive arrangement to move the skimming device through the layer of FOG floating on the waste water within the tank of the grease trap. The skimming device collects FOG from the surface of the water in the tank and is subsequently cleaned by means providing a scraping or squeezing action on the skimming device, such as wiper blades, arranged to direct the collected FOG into a collection device before the skimming device passes back into the water. The collection device is typically a separate container or reservoir located on one side of the tank.

Known grease traps require a regular maintenance programme to be carried out to pump out such traps and refill with clean water. The European Standard EN 1825 calls for grease traps to be pumped monthly and preferentially fortnightly. In so far as grease traps contain some if not all of the entrained FOG and food wastes, these separate, with FOG having a specific gravity of less than 1 rising to the surface and food waste having a specific gravity greater than 1 sinking to the bottom.

Saturated fats, and animal fats in particular, are viscous above 40° C but may be prone to solidify below such temperature. They are emulsified in the hot water. Hot water is used to remove FOG and to leave crockery, cutlery and pots and pans free and clear of FOG. Most known automated grease traps are only effective when the temperature of the waste water in the grease trap is around 40° C to ensure that the FOG, in particular the more waxy components thereof, remain in viscous form and do not form a solid crust on top of the waste water. Therefore known automated grease traps often incorporate electrical heating elements within the grease trap. Such heating elements consume considerable electrical power and can cause a fire risk if overheating occurs or if the heating elements become exposed to the air. The size of a grease trap is typically determined by the time needed for the FOG to settle out from the waste water and is therefore based upon the required volume throughput of the grease trap. However, size constraints within kitchens produce a desire to keep the grease trap as small as possible. SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a sensor apparatus for a grease trap comprising a sensor body arranged to be submerged in effluent within a grease trap, said sensor body incorporating a plurality of first sensors adapted to distinguish between air, water and FOG, at predetermined vertical positions within the grease trap, in use, and a transmitter for wirelessly transmitting data from said plurality of first sensors, the apparatus further comprising a receiver receiving data from said plurality of first sensors and a processing means for monitoring operation of the grease trap in response to said date received from said plurality of sensors.

Preferably said plurality of first sensors are capable of distinguishing between air, water, FOG and an emulsion of water and FOG. Said plurality of first sensors may comprise capacitive sensors.

Preferably said sensor body contains a power supply for powering said plurality of first sensors and said transmitter. Said power supply may comprise one or more batteries. Preferably wherein said plurality of first sensors and said transmitter are encapsulated within said sensor body to protect them from effluent within the greasetrap while allowing the first sensors to determine the nature of the effluent. Said sensor body may further incorporate one or more second sensors for determining the temperature of the effluent within which the sensor body is immersed. Said sensor body may incorporate a plurality of said second sensors adapted to determine the temperature of the effluent at different vertical positions within the grease trap, in use.

In one embodiment there may be provided a first sensor body incorporating a plurality of said first sensors and a transmitter for transmitting data therefrom to said receiver and a second sensor body incorporating a plurality of said first sensors and a transmitter for transmitting data therefrom to said receiver, said first and second sensor bodies being mounted on a support frame adapted to be located within a grease trap such that the first sensor body is located in an upper region of said grease trap, in use, and said second sensor body is located in a lower region of said grease trap, in use. The support frame may be adapted to adjust the distance between said first and second sensor bodies to adjust the height of the first sensor body.

The processing means may be adapted to control a skimming device for removing FOG from the grease trap as a function of the data received from said plurality of first sensors.

According to a further aspect of the present invention there is provided a grease trap for removing FOG from waste water comprising a tank having at least one waste water inlet for passing waste water into an inlet region of the tank, at least one waste water outlet for draining waste water from an outlet region of the tank, and a sensor apparatus in accordance with the first aspect of the present invention, wherein said sensor body of said sensor apparatus is located within the tank such that said plurality of first sensors can detect the presence of air, water and FOG are predetermined heights within the tank to determine the thickness of the layer of FOG in the tank and the transition between water and FOG within the tank.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which :-

Figure 1 is schematic sectional view of a grease trap incorporating a sensor apparatus in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

As illustrated in the drawing, a grease trap 2 in accordance with a first embodiment of the present invention comprises a substantially rectangular tank 4 having a waste water inlet 6 at one end and a waste water outlet 8 at an opposite. Baffles 10,12 are located adjacent the inlet 6 and outlet 8 under which water must pass to enter a central settlement region "S" of the tank. A skimming device may be mounted in the tank for removing FOG that settles out on top of the waste water in the tank 4. In one embodiment, the skimming device may comprise an elongate drum having a surface coated with or formed from a hydrophobic and oleophilic material, the drum being mounted in the tank 4 to be partially submerged in waste water held in the tank 4 when in use, the drum being rotatable, under the action of a motor, to rotate to collect FOG from the surface of the waste water, a scraper being used to remove FOG from the drum and deliver it into a suitable collection vessel. However, the use of other types of skimming devices is envisaged. A pair of sensor arrays 20,22 are mounted within the tank 4 to be submerged with the effluent contained therein. The sensor arrays are mounted on a support frame 24 to locate the two sensor arrays in vertical orientation adjacent lower and upper regions of the tank 4 respectively. The support frame 24 may be adjustable to facilitate adjustment of the height of the sensor arrays 20,22 within the tank 4, in particular the upper sensor array 20.

Each sensor array 20,22 comprises a plurality of vertically spaced capacitive sensors 30 adapted to determine the identity of the fluid adjacent and surrounding the respective sensor based upon the specific gravity of said fluid. Each sensor is calibrated to distinguish between air, water, FOG and emulsified FOG, as will be described below in more detail. Each sensor array 20,22 also incorporates one or more temperature sensors for determining the temperature of the fluid within which it is immersed. In one embodiment each sensor array may incorporate a plurality of vertically spaced temperature sensors to form a vertical temperature profile of the effluent in the tank 4.

Knowledge of the temperature of the effluent can also be used to control the operation of a skimming device (i.e. so that a skimming operation takes place when the temperature of the effluent is above a predetermined level).

Each sensor array 20,22 also includes a transmitter for transmitting data from the sensors incorporated therein. Each sensor array comprises a self-contained unit that is powered from a small, sealed internal battery pack with an estimated life of 5-10 years.

Each sensor array 20,22 may comprise a PCB upon which the sensors and other components are mounted, said PCB being encapsulated, for example within a resin sensor body coated with a rubber (e.g. EPDM) outer sheath, to allow the sensor arrays to be fitted within the tank 4 of the grease trap 2, at least partially submerged within the effluent contained therein, in order to monitor the composition of the effluent in the tank 4 over a predetermined vertical range. The specific tank contents that the sensors of the sensor arrays can differentiate are air, water, FOG, tallows and oils having a specific gravity of less than that of water and temperature. FOG, tallows and oils having a specific gravity of less than that of water describe the layer of fats, oils and grease that have a lower SG than water and thus tend to gravitate upwards. However when agitated, these will mix with the water resulting in emulsification down to some depth below the water surface, with a concentration gradient for the FOG in the water changing from high concentration near the surface to lower concentrations at increasing depth below the surface. The emulsification process is affected by a number of factors including temperature, detergents, velocity of the influent and the varying specific gravities of FOG, tallows and oils.

Following agitation, the FOG layer will, under the action of gravity, reduce in depth and increase in concentration near the surface. The primary purpose of the upper sensor array 20 is to monitor the concentration and depth of this FOG layer on the surface of the water. The second or lower sensor array 22 can be used to determine the level or heavier contaminants, including food waste and sludge, that settle out within the bottom of the tank 4.

The capacitive sensors 30 of the sensor arrays 20,22 are sufficiently sensitive to permit the measurement of FOG concentration so that the sensors 30 can determine if the FOG retained in the tank and above a particular depth is at an appropriate concentration to warrant extraction from the tank for further processing Each sensor array 20,22 continuously reports its measurements by means of an inbuilt wireless transmitter, such as a Bluetooth radio beacon, that may be received by any correctly configured receiver 40.

The sensor apparatus can determine the level of water in the tank 4 and the depth of FOG worth recovering from the tank as well as the level of solids collected in the bottom of the tank, thus enabling service personal to be alerted when servicing of the grease trap 2 is required and/or controlling the operation of a skimming device to automatically periodically remove collected FOG from the tank. The sensor apparatus can retain a record of tank level activity in a memory that can be retrieved by a service engineer for historic analysis of the performance of the product to which the sensor is attached. Such data can also be used to determine how much FOG is collected in the tank and removed in a servicing stage/automated FOG removal stage (by a skimming device) to monitor and/or control FOG disposal.

A control circuit associated with each sensor 30 of each sensor array 20,22 may measure a change in capacitance of the respective sensor 30 to determine the nature of the fluid adjacent the respective sensor. FOGs, air, water, and emulsified FOGs each have a different density which translates to a different capacitance as sensed by each sensor 30.

Submerging the sensors 30 within the effluent in the tank (albeit protected by encapsulation in a resin) such that the sensors 30 are surrounded by the effluent, enables each sensor to give a very distinctly different response to each fluid and permits accurate identification of the type of fluid adjacent each sensor as a function of the sensor output value (measured capacitance). The output of each sensor 30 may comprise a number between 0 and 65535, with low numbers typical of air and high numbers typical of water.

To calibrate each sensor array may involve several stages: a. In a preferred embodiment, each sensor array may incorporate fifteen capacitive sensors arranged at vertically spaced locations along the sensor body of each vertically oriented sensor array. Each sensor 30 may naturally output a different value for air. Therefore the first step in calibration is to take account of these offset values so that each sensor 30, once initially calibrated, outputs the same value for air. This step may be completed during factory programming and setup of each sensor array.

b. The boundaries between sensor output that represents air and that which represents emulsified oil or pure oil or water must then be established. When a capacitive sensor is located on an exterior wall of a grease trap the identification of boundaries between air, water, FOG and emulsified FOG is very difficult because there are so many external factors that can lead to errors. However, it has been found that locating the capacitive sensors within the tank, submerged in the effluent contained therein, enables that the boundary values to remain fairly fixed, even when temperature changes.

c. The impact of temperature on these boundary values must be determined so that the correct boundary value can be applied for any given temperature. Once calibrated, this adjustment can be achieved by the inbuilt temperature sensors of each sensor array. A programmable controller (PLC) 50 may be provided for monitoring and controlling the operation of the grease trap 2 as a function of the data received from the sensor arrays 20,22 via the receiver 40. The controller may be programmed to control and monitor remotely the status of the grease trap and, optionally, of a skimmer device fitted thereto.

The controller 50 may supports a windows application within which a user can define the logical set of rules by which each output state is determined based on a set of input voltages and currents.

The controller 50 may include a connection to the Internet by means of one of a number of connection protocols and may include telemetry connection protocols to wireless sensory products within its environment by means of sub-GHz radio and BLE.

Each sensor array 20,22, with its built in transmitted and internal power supply, can be immersed in the effluent in the tank without any need for external connections or wires. By immersing the sensors within the effluent in the tank, problems associated with prior art sensors mounted externally of the tank, such as the need to make a good contact with the wall of the tank, are avoided.

While in the embodiment described above, two sensor arrays 20,22 are provided vertically spaced from one another, it is envisaged that only a single elongate sensor array may be used extending vertically through just an upper portion of the tank or along the full height of the tank.

The invention is not limited to the embodiment(s) described herein but can be amended or modified without departing from the scope of the present invention.