Waste Recycling System

The present invention relates to a waste recycling system. More particularly the invention relates to a system for use in recycling putrescible waste material.

Schemes for recycling of household waste materials are becoming more sophisticated, especially as people become better educated about the environmental benefits and more amenable to taking appropriate steps within their homes. Consequently, household waste recycling schemes have evolved, in which the householder separates the waste into different categories, such as glass, paper/cardboard, metal etc. However, there ^• remains a problem with waste that contains moisture and putrescible matter. Such matter contains substances that can have a value, for example for use as fertilisers. However, in most domestic wastes the moisture content is too high for the material to be of sufficient value to be worth recovering unless it is dried first. Also, the decay of such material tends to be malodorous, and the presence of moisture in the matter prolongs the decay period.

It is an object of the present invention to provide a waste material recycling system that alleviates the aforementioned problems.

According to the present invention there is provided a waste recycling system comprising: a porous bio-degradable container for holding waste material that includes putrescible waste material; an enclosure at least partially surrounding and covering the container; sensor means for monitoring a moisture content related to a moisture level in the container; air moving means for drawing air through the enclosure to remove moisture from the container; and control means, responsive to the sensor means, for controlling the air moving means.

It is an advantage that the system is provided with a porous container, which acts as a wick to take up moisture from the putrescible material by capillary action. However, to extend the usefulness of this process the moisture is

removed by drawing air through the enclosure to dry the container. This means that the container should never reach a completely saturated condition in which it is unable to take up any more moisture from the putrescible material. Drying out the putrescible material significantly increases the rate and degree of decay, leaving an inert dry residue that can be easily disposed of. Also, by drawing air past the container odorous vapours can be easily removed.

In a preferred embodiment, the air moving means comprises one or more fans. Preferably, the fans are powered from a self-contained power unit. The self-contained power unit may comprise photovoltaic means, for example an array of photovoltaic cells, for generating power from daylight. The self- contained power unit may also comprise a battery. An advantage of this ^■ configuration is that the system can operate as a stand-alone unit without the need to be connected to a mains power supply. Also, the life of the battery is prolonged by the photovoltaic cells (PV array). For example, the battery may be used to power the system at night-time and the PV array in daylight.

In a preferred embodiment, the porous bio-degradable container comprises cardboard. It is an advantage that the container itself can be made from readily available recycled materials. To avoid the possibility of the cardboard container collapsing and spilling its contents, means may be provided for supporting the container. In embodiments of the invention, the support means comprises a wire mesh or basket.

In a preferred embodiment, the sensor means is disposed within the enclosure close to the container. The sensor means may comprise one or more capacitative sensors. Preferably, the control means is operable to compare a capacitance of the capacitative sensor with a reference capacitance.

An embodiment of the invention will now be described with reference to the accompanying drawings, wherein:

Figure 1 is an elevation in cross-section of a putrescible waste recycling system; and

Figure 2 is a schematic circuit diagram of a control system for the putrescible waste recycling system of Figure 1.

Referring to Figure 1 a household waste recycling system includes a unit 10 for processing of putrescible waste matter. The unit 10 would typically be situated outside a domestic residence along with receptacles for recyclable waste, such as paper, glass etc. The unit 10 includes an enclosure 12 having a door 14 through which a container 18 containing putrescible waste material 16 can be inserted. The putrescible waste material 16 is made up of matter that cannot readily be separated for recycling purposes and includes ^■ biodegradable and moisture-containing matter such as waste foodstuffs and the like. The container 18 is made of a porous biodegradable material, for example cardboard. The container 18 is supported in a wire mesh basket 20.

The enclosure 12 has a top region 22, inside which is an air duct 24. A fan 26 blows air from inside the enclosure 12 into the duct 24 and out through a filter 28. Power to and control of the fan is provided from a power and control circuit 29 that includes an array 30 of photovoltaic (PV) cells and a battery 32. A moisture sensor 31 is disposed in the unit 10 close to the container 18. The moisture sensor 31 is, typically, a capicitative sensor having a dielectric material that takes up or loses water according to the moisture content of the surrounding air. A variation in the moisture content of the dielectric material alters the capacitance of the moisture sensor 31. The moisture sensor 31 is linked to and forms part of the electrical circuit that makes up the power and control circuit 29.

Referring to Figure 2, the power and control unit 29 includes the PV array 30 and the battery 32. Voltage outputs from both the PV array 30 and the battery 32 are coupled to a boost converter 34, which is arranged to provide a steady

d.c. voltage output (say 12 volts). This power output is used to drive the fan 26 when the control circuit requires it to do so.

The power and control circuit 29 also includes an oscillator 36, which provides ■ an a.c. voltage across a resistor 38 and the moisture sensor 31 , which is a capacitative sensor, as described above. As a result, the voltage across the capacitative moisture sensor 31 varies in dependence on its capacitance. The a.c. voltage provided by the oscillator 36 is also applied across a reference resistor 40 and a reference capacitor 42 having a fixed capacitance. As a result the voltage across the reference capacitor provides a predetermined steady reference voltage. This reference voltage can be set by adjustment of the resistance of the reference resistor 40, which is a variable resistor.

The voltages across the capacitative moisture sensor 31 and the reference capacitor 42 are provided as inputs to a comparator 44. Accordingly, when the voltage across the capacitative moisture sensor 31 exceeds a threshold (determined by the reference capacitor), the comparator 44 will provide an output signal to an interface controller 46. The interface controller 46 is configured to switch a voltage supply to the fan 26 when it receives the output signal from the comparator 44. The interface controller 46 also causes an LED 48 to be lit when the fan 26 is on. A reverse diode 50 is provided in a circuit in parallel with the fan 26 as a safety feature to ensure that a reverse polarity voltage will not cause damage to the fan 26.

■ In use, when putrescible material 16 is loaded into the enclosure 12 of the unit 10, moisture in the putrescible material 16 will be taken up by the porous cardboard of the container 18 due to capillary action. Also, the moisture content of the air inside the enclosure 12 will start to rise. This moisture level will cause the capacitance of the moisture sensor to change (due to the change in moisture content of the sensor's dielectric material). When the moisture level sensed rises above the predetermined point set by the reference capacitor 42 and resistor 40, the control and power circuit 29 will

start the fan 26. The fan 26 will blow air from inside the enclosure 12 out through the duct 24 and filter 28, to be replaced by fresh air from outside the enclosure 12. The air currents will have the effect of drying the cardboard of the container 18. When the moisture content.detected by the moisture sensor 31 falls below the threshold, the fan will be switched off.

The PV array 30 and the battery 32 are arranged such that when the PV array is exposed to light, the voltage generated can be used to drive the fan (when required to do so) or to charge the battery 32 when the fan is not running. ■ When not exposed to light (e.g. at night) the power to drive the fan 26 is taken from the battery 32.