Toilet system with reduced or eliminated flushing requirement, especially for transportation vehicles

A toilet system, especially for passenger transport vehicles, includes a toilet bowl connected via a suction valve and a waste collection pipe to a waste collection tank. Waste-contacting surfaces of the toilet system that come into contact with urine and fecal waste are coated with an adhesion-inhibiting or adhesion-reducing nanocoating. Thereby, the adhesion of waste to the toilet bowl and other components is significantly reduced, and the total flushing water demand can be substantially reduced or, preferably completely eliminated. An airflow flowing into the toilet bowl, induced by the vacuum suction through the suction valve, is sufficient to “flush” the waste material from the nanocoated waste-contacting surfaces. The toilet system provides a substantial reduction in the total system weight and in the required quantity of flushing water that must be carried in the vehicle, and thus makes the toilet system particularly applicable for passenger transport vehicles such as aircraft.

DETAILED DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS AND OF THE BEST MODE OF THE INVENTION FIG. 1 is a schematic representation of a toilet system 1 such as can be used in an aircraft A. The toilet system 1 comprises essentially at least one toilet bowl 2 that is connected via a waste water valve 3 to a waste collection pipe 4 . It is possible to connect a plurality of toilets located at various locations to the waste collection pipe 4 . The waste collection pipe 4 includes pipes, conduits, hoses, or lines that are used to convey waste material. The waste collection pipe 4 leads to a waste collection tank 5 in which the waste material and waste water are collected. A pressure differential between the toilet bowl 2 , which contains waste, and the waste collection tank 5 facilitates or effectuates the waste transport operation. The toilet system 1 is constructed therefor as a vacuum toilet system. A vacuum generator 6 generates the necessary negative pressure. When used in an aircraft, the vacuum toilet system 1 can also or alternatively take advantage of the predominating reduced external atmospheric pressure during flight to provide the pressure differential required for proper functioning of the vacuum toilet system 1 . The waste collection tank 5 is further connected to a tank drain valve 7 by means of which the collected waste water can be discharged as needed. A flushing liquid dispenser, which is a rinse or flush ring 8 in the example embodiments but may have any conventionally known arrangement of a flushing liquid dispenser, is provided on the toilet bowl 2 . Instead of the flush ring 8 , it is possible to use other liquid dispensing means, such as one or more individual water jets or nozzles arranged in the toilet bowl 2 . The flush liquid or water is guided from the flush ring 8 into the toilet bowl 2 and cleanses the toilet bowl 2 during a flushing operation. The flush water is drawn from a flush water tank 9 that is connected by a feed line 10 and a flush water valve 11 to the toilet bowl 2 (and particularly the flush ring 8 ) to be flushed or cleaned. A control unit 12 controls the actions of the waste water valve 3 and the flush water valve 11 , responsive to the actuation of a flush control button 12 A that can be depressed by a passenger who has used the toilet. After the toilet has been used, the flushing operation is initiated by the passenger by actuating the flush control button 12 A or other trigger device to convey the fecal materials or other waste material from the toilet into the waste collection tank 5 . The control unit 12 opens the flush water valve 11 and flush water is sprayed or guided into the toilet bowl 2 from the flush ring 8 (for example, by means of spray jets, which will keep the amount of flush water required for flushing as low as possible). The waste water, i.e., fecal material and flush water, collects by the force of gravity in a toilet drain 2 B of the toilet bowl 2 . The waste water valve 3 then opens for a brief time and the waste material that is collected in the toilet bowl 2 is conveyed out of the toilet bowl through the bowl outlet or drain 2 B, through the valve 3 and into the waste collection pipe 4 , and from there into the waste collection tank 5 by means of the pressure differential. An airflow A that flows into the toilet bowl, being induced by the just-mentioned pressure differential and suction out of the bowl through the drain 2 B, additionally “flushes” or “sweeps” the waste material out of the bowl 2 through the drain 2 B, as will be further described below. Flush water is necessary in conventional toilet systems in order to clean the toilet bowl 2 of any waste material that remains adhered to the inner surfaces of the toilet bowl 2 . In order to remove such waste or contamination with only a very small amount of flush water or even without flush water, a relevant surface area of the toilet bowl 2 according to the invention is coated with a special nanocoating 15 . The nanocoating 15 is applied to the complete inside surface of the toilet bowl 2 or at least in a waste-contacting surface area 2 A that comes into contact with the waste material, as indicated in FIGS. 1, 2 , and 5 . The structure and the mode of manufacturing the nanocoating 15 is shown in more detail in the FIGS. 3 to 5 and described in more detail below. The nanocoating 15 has adhesion-inhibiting or at least adhesion-reducing properties. The first example embodiment of the toilet system 1 , shown in FIG. 1 , uses a nano-coated toilet bowl 2 that requires a greatly reduced amount of water for cleaning or flushing, relative to conventional toilet bowls. This is achieved because the nanocoating 15 minimizes or prevents the adhesion of urine and fecal waste material onto the inner surfaces of the toilet bowl 2 , so that the above mentioned airflow A together with a minimal amount of flushing liquid and the effect of gravity are sufficient to remove the waste material from the bowl 2 out through the drain 2 B during a flushing operation. Thus, particularly for large capacity aircraft that fly long distances, the amount of water required for flushing toilets is substantially reduced. As a result, additional weight capacity is now available for additional passenger seats or for other measures that will increase the comfort of the passengers. Also, the waste collection tank 5 and the flush water tank 11 that are required can be made smaller, as they are now required to hold a lesser volume. This also results in a further reduction of weight. FIG. 2 shows a toilet system 20 according to a second example embodiment of the invention. In this embodiment, the toilet system 20 comprises a nano-coated toilet bowl 2 to which essentially no waste material at all can adhere. Thus, with the toilet bowl 2 according to this embodiment, rinsing or flushing liquid to flush or clean the surface of the toilet bowl 2 is completely unnecessary. Consequently, system components such as the flush ring 8 , the flush water tank 9 (or the fresh water feed line), the feed line 10 and the flush water valve 11 become superfluous and are thus not provided in the toilet system 20 . This is a substantial simplification of the overall toilet system 20 , which not only reduces the weight of the toilet system 20 , but also reduces the cost and effort of maintenance and repair. The toilet bowl 2 of the toilet system 20 is provided with a nanocoating 15 at least in the waste-contacting area 2 A shown in FIG. 5 . This is the area where waste material comes into contact with the surface of the toilet bowl 2 . Due to the elimination of the flush water valve 11 , maintenance measures for cleaning, decalcifying and replacing the seal elements of this valve 11 are also eliminated and the overall reliability of the system increases since leakages in the flush water circuit are also eliminated. Moreover, the advantages mentioned in connection with the toilet system 1 also apply to the toilet system 20 . The remaining system components of the toilet system 20 are identical with those of the toilet system 1 shown in FIG. 1 . The elimination of the flush water feed simplifies the system control and therefore the control unit 12 can also be simplified. With the elimination of the flush water circuit, only the opening and closing of the waste valve 3 is necessary to remove the collected waste material from the toilet bowl 2 . In other words, it is no longer necessary to actuate a flush water valve in proper coordination with the waste valve 3 . Instead, the waste material easily “slides” down from the nanocoated waste-contacting surfaces 2 A, so that the waste material is completely removed from the toilet bowl 2 by the combined effects of gravity and the induced airflow A, without needing any flushing liquid. Namely, the waste material is conveyed out of the toilet bowl 2 primarily by means of the suction created by the vacuum that exists within the toilet system, which in turn induces the airflow A into the toilet bowl as described above, when the suction waste valve 3 is opened. The airflow A is thereby caused to flow from the surrounding environment outside of the toilet bowl 2 , into the bowl 2 , and particularly directed downwardly along the nanocoated waste-contacting surfaces 2 A toward the outlet 2 B. Moreover, the downward force of gravity acts advantageously on the waste that falls onto the surface of the toilet bowl 2 because of the minimal adhesion properties of the nanocoating 15 provided on the waste-contacting surfaces 2 A of the toilet bowl 2 . After the waste material has been removed, the toilet bowl 2 is left in a clean condition without having to be flushed with liquid. As a further auxiliary alternative exemplified in FIG. 2 A, the toilet bowl 2 may be additionally equipped with airflow directing means to passively or actively direct an airflow forcefully along the waste-contacting surfaces 2 A of the toilet bowl 2 . In the example of FIG. 2 A, an air jet arrangement with air jets 27 is provided instead of the water spraying flush ring 8 of FIG. 1 , so that one or more directed air jets blow downward along the inner surfaces of the bowl to assist in moving any remaining waste material down into the toilet drain 2 B. For example, such air jets 27 may be driven actively by a source of pressurized air, or passively from the room air outside of the toilet bowl due to the airflow induced into the bowl upon opening the suction waste valve 3 . The air jets 27 may optionally be formed by air-directing configurations on the bottom of a toilet seat provided on the toilet bowl. As a further optional component, the toilet may be equipped with a cover or lid 28 , which selectively covers the bowl 2 in the usual fashion and/or also enhances the passive flow of outside air through the air jets. For this purpose, the cover 28 may optionally be adapted to close the top opening of the bowl sufficiently tightly to cause at least most of the induced airflow A to enter the bowl through the air jets 27 , if the cover 28 is closed before actuating the suction waste valve 3 . FIGS. 3 and 4 illustrate to what extent a nanocoating will reduce the wetting angle of a liquid or waste droplet 13 on the surface 14 of a toilet bowl 2 . FIG. 3 shows a conventional surface 14 ′ without a coating or, for example, with a PTFE-coated toilet bowl. A droplet 13 of water or urine or feces is located on the surface 14 of the toilet bowl 2 . The wetting angle 13 A is relatively large (e.g. 65°) in the conventional toilet bowl 2 and thus the droplet 13 can adhere to the surface 14 ′. FIG. 4 illustrates a wetting angle 13 B of a droplet 13 on the surface 14 of a toilet bowl 2 that is coated with a nanocoating 15 according to the invention. As can be seen, the wetting angle 13 B on the nano-coated toilet bowl 2 is much smaller than that of the uncoated toilet bowl shown in FIG. 3 , and, as a result, the droplet 13 will have a significantly reduced wetting adhesion on the surface and will glide or roll over the surface of the nano-coated toilet bowl 2 much more easily, simply under the force of gravity. For example the wetting angle 13 B may be in a range from 0° to 25°, or preferably 0° to 10°. The nanocoating 15 is produced by means of nano-technology and is applied to the surface 14 . The nanocoating 15 has a coating thickness in the nanometer range, e.g. less than 10 nanometers, or preferably less than 5 nanometers. Nanotechnology provides ordered surfaces with a low surface energy, such that when such a surface is wetted by a droplet, the wetting angle 13 B approaches 0°, thereby providing a best possible achievable anti-adhesion coating. This anti-adhesion nanocoating 15 inhibits or at least substantially reduces the adhesion of the droplet 13 of water or urine or particles of fecal matter to the surfaces of the toilet bowl 2 and/or other components of the toilet systems shown in FIGS. 1 and 2 that are coated with the nanocoating 15 . The droplets 13 fall under the force of gravity into the drain 2 B of the toilet bowl 2 , which is also preferably coated, and are then suctioned off by the effect of the vacuum via the waste collection pipe 4 into the waste collection tank 5 . FIG. 5 shows a detail of the toilet bowl 2 according to the invention and FIG. 5A shows a much enlarged sectional view of the nanocoating 15 on the surface of the toilet bowl 2 . Preferably, the base material or structural substrate 2 ′ of the toilet bowl 2 is made of stainless steel, in view of its corrosion-inhibiting properties, and its ductility or lack of brittleness. Synthetic materials, e.g. plastics, however, may also be used for the toilet bowl 2 and for other components of the toilet system. In the embodiment shown in FIGS. 5 and 5 A, the substrate 2 ′ of the toilet bowl 2 is first coated with a base coating 16 . The base coating 16 may be necessary in some cases, for example, when it is difficult to apply the nanocoating 15 directly to the base material or substrate of the toilet bowl for lack of adequate adhesion or because the roughness is too great. In such cases the nanocoating 15 can be produced with better results when applied to the intermediate base coating 16 . In a preferred embodiment, the surface of the toilet bowl to be coated is first pretreated before the base coating 16 or the nanocoating 15 is applied. The surface is first subjected to a grinding and polishing process in order to obtain a surface roughness in the range of less than 100 nm and a mean roughness in the range of less than 10 nm. Subsequently, the surface is cleaned with an organic solvent and/or by an ultrasound cleaning process. The application of the nanocoating 15 to the toilet bowl 2 will now be described in greater detail. Preferably, metals or elements of the fourth major group of the periodic system, or alternatively and more particularly Cr, Ti, Mn, Ni, Ta, Al, V, W, Co, Be, Zr, Hf, Nb, Mo, C, Si, Ge or Sn, or compounds with these elements are used to make the nanocoating 15 . It is possible to use compounds with a metallic bonding property, in particular carbides such as MC as well as secondary carbides M 2 C, M 3 C, M 6 C, M 7 C, M 23 C 6 , whereby M designates a metal or an intermetallic metal group. It is furthermore possible to use nitrides of the structure MN or borides of the structure MB, whereby, again, the M stands for a metal. Alternatively, it is possible to produce the nanocoating 15 from a compound having a covalent bonding property such as, for example B 4 C, SiC, BN, Si 3 N 4 or MOS 2 . In a further alternative, the nanocoating 15 can be made from a composition having an ionic bonding property, such as, for example Al 2 O 3 or ZrO 2 or BeO. In a further embodiment the nanocoating 15 can be made from a sialon composition, i.e., an alloy of silicon nitride and aluminum oxide, or from polymers. The nanocoating, also referred to as “thin films” or “ultra thin films”, can be produced by classic cathodic, or vapor deposition or sputtering methods, or by means of resistance heating through vacuum assisted processes. The demands on the production of a coating by means of nanotechnology are characterized by atomically precise boundaries and by controlling the deposition of layers that are each only one atom thick. For the most part, applied vacuum methods are based either on molecular beam epitaxy (MBE) or deposition from a gas phase. Possible methods of production are, for example: cathodic sputtering; ionic implantation; sputter techniques (plasma beam source, magnetron sputtering, radio frequency diode sputtering); gas phase deposition (chemical vapor deposition—CVD, atomic layer epitaxy—ALE, and chemical beam epitaxy—CBE); plasma assisted chemical vapor deposition—PACVD; and physical vapor deposition—PVD. As a further alternative, an anti-adhesion coating can be formed on the basis of inorganic-organic nanocompositions with a low surface energy. Such a coating can be formed by generally known coating techniques, such as dipping immersion, spray coating, or centrifugal spin coating or the like, followed by curing or hardening of the coating layer by UV-radiation and/or thermal heating, whereby the resulting nanoparticles of the coating achieve the desired anti-adhesion properties. When producing the nanocoating 15 according to the possible methods, it is essential that the nanocoating is formed rather soft and non-brittle, as this will prevent parts of the nanocoating 15 from peeling from the toilet bowl 2 . The magnetron sputter technique is the preferred method of producing the nanocoating 15 . This technique, which is generally known to the person of ordinary skill in the art, belongs to the group of methods referred to as cathodic sputtering. According to this method, the coating is applied in a vacuum and a solid base is coated with metallic or non-metallic layers. The coating material on the cathodes is atomized or sputtered by bombardment of the material with gas ions in a gas atmosphere. The material is then deposited on the toilet bowl substrate surface as a coating. The ions ensure that the upper atomic layers from the coating material are converted by impulse exchange into the gaseous state. The coating material, now in a gaseous state, is then deposited on the surface to be coated. The thermal stress on the toilet bowl substrate to be coated is relatively low when this magnetron sputtering technique is used. It is currently possible to attain a coating diameter of up to 150 mm, with a coating rate of 0.1 to 1 mm/min when using a double ring magnetron source. According to the invention, the nanocoating 15 is to be applied to rather large surface areas of the toilet bowl, and optionally other portions of the toilet system. Preferably, the whole inner surface of the toilet bowl 2 is to be coated. Application of the nanocoating 15 to the toilet bowl 2 has been described in greater detail above. It is possible, of course, to apply the nanocoating 15 using suitable application methods to other components of the toilet system that come into contact with fecal material or other waste material. It is within the scope of the invention, for example, to coat the interior of the waste collection pipe 4 , or at least portions of the waste collection pipe 4 such as branching areas, in order to reduce as much as possible the effort involved with cleaning and maintaining the toilet system. Although the invention has been described with reference to specific example embodiments, it will be appreciated that it is intended to cover all modifications and equivalents within the scope of the appended claims. It should also be understood that the present disclosure includes all possible combinations of any individual features recited in any of the appended claims. The term toilet bowl herein includes all possible types and configurations of toilets including sit-down toilets, crouching-type toilets, urinals, etc.