Patent Document

[0001]    The present invention relates to apparatus for the efficient treatment, namely wet composting of faeces, and to a method for such treatment. 
       BACKGROUND OF THE INVENTION 
       [0002]    In many developing countries the population does not have access to modern sewage systems for taking care of faeces. Instead, usually one simply digs a hole in the ground wherein people relieve themselves. Eventually the hole is covered and the faeces is left to undergo a natural breakdown. 
         [0003]    However, this usage inevitably causes certain sanitary problems that might be the cause of diseases. 
         [0004]    In many of these countries also the agriculture is not particularly developed. For example fertilizers being expensive are rarely used, and the availability of natural manure is not always good. 
         [0005]    With proper handling, human faeces could be use as fertilizer and would thereby contribute positively to agriculture. 
         [0006]    In EP 1 156 870 (Ahlström) there is disclosed a device and method for the treatment of contaminated media. It is based on a very efficient oxygenation by a rotary impeller device that creates a very vigorous suction and mixing of air into the contaminated media. 
       SUMMARY OF THE INVENTION 
       [0007]    In view of the above, the object of the present invention is to provide an apparatus and a method for treating human faeces that will in the first place eliminate the health problem caused by the presently used primitive latrines, and secondly will produce valuable fertilizer directly usable by farmers. 
         [0008]    This object is achieved in a first aspect with the apparatus as defined in claim  1 . 
         [0009]    In a second aspect the invention provides a method for treating faeces as defined in claim  20 . 
     
    
     
         [0010]    Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter and the accompanying drawings which are given by way of illustration only, and thus not to be considered limiting on the present invention, and wherein 
           [0011]      FIG. 1  illustrates schematically an implementation of the apparatus of the invention in a lavatory; 
           [0012]      FIG. 2  illustrates schematically an embodiment of an apparatus according to the invention; and 
           [0013]      FIG. 3  illustrates a cross-section of a rotary device used in the apparatus according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0014]      FIG. 1  schematically illustrates a lavatory  100  to be used by an individual household in e.g. a farmers village in a developing country, where there is no communal infrastructure, and wherein an apparatus  102  according to the invention (schematically shown) has been implemented. The lavatory would suitably be located near the house, such that the inhabitants will be able to easily access it on a frequent basis, thereby eliminating the need for digging latrine holes in the ground. A standard size of the apparatus could serve say 5-10 people. For ease of handling, the actual apparatus  102  will be placed on the ground, and the toilet room will be placed on top, thus requiring a staircase to gain access thereto. 
         [0015]    Of course the apparatus can be implemented to serve several households too, in which case the lavatory suitably would be located in the centre of a village. Depending on the size of the village there could of course be provided several lavatories. 
         [0016]    To the apparatus there will be coupled one or more toilets  104  suitably of a “mill” type, which is preferred because of its function to fragment the material. The apparatus according to the invention will treat the urine and faeces on a continuous basis and rapidly transform the faeces to virtually bacteria free harmless end products in the form of a nitrate-rich liquid phase and a phosphorous-rich slurry or semi-solid phase. These end products can be directly pumped or transported onto nearby fields to provide cheap fertilizer and thereby increase crops. 
         [0017]    The apparatus constitutes a self-contained system for taking care of faeces and treating it to produce cheap fertilizer thereby improving life for poor farmers in developing countries. 
         [0018]    Now the working and structure of the apparatus will be described in more detail with reference to  FIG. 2 . 
         [0019]    Thus, the apparatus comprises a housing or tank  200  wherein the treated faeces is stored temporarily before it is pumped or otherwise transported to the end use as fertilizer in the fields. 
         [0020]    Inside the tank  200  there is provided a process vessel  202 . The process vessel suitably has a circular cylindrical cross section. There is also an inlet tube  204  at the top of the vessel  202  through which faeces from a suitable toilet  206  will be fed into the process vessel  202 . 
         [0021]    Inside the process vessel  202  there is provided a member that is referred to as a guide collar  212 . This is a flange or rim running circumferentially along the inner wall  214  of the vessel  202  at a height above the bottom of the vessel  202  corresponding to about ⅔ to ¾ of the total height of the vessel  202 . This guide collar  212  extends horizontally inwards, i.e. radially, from the inner circumferential wall  214  so as to leave a central opening having a diameter that is between ⅓ and ⅘ of the diameter of the vessel  202  itself. Thus, the guide collar in a sense partitions the process vessel  202  in a lower  216  and an upper  218  compartment, respectively. 
         [0022]    Located in the centre of the vessel  202  there is a tube  220 . The tube  220  has an aperture  221  slightly lower that the level of the guide collar  212 . The tube  220  is drawn through the wall of the process vessel  202 , and further through the wall of the tank  200 . It is connected to the bottom  222  of the tank at  223  via a branch tube  224 . Thereby it will be possible to circulate the material located at the bottom of the tank  200  back into the process vessel  202  in a manner to be described. 
         [0023]    Another branch  226  of the tube  220  extends upwards and opens  227  at a level above the top level in the tank  200 . This provides overflow protection in the event that the tank should be completely filled. 
         [0024]    At a level above half of the height of tank  200  there is provided a drainage  228  for NO 3 -rich supernatant. This liquid can be used directly as a fertilizer by pumping it into the fields. There is also provided at a lower level a drainage  229  for phosphorous-rich sludge collecting at the bottom of the tank  200 . This material can also be used directly as fertilizer. At the top of that tank  200  there is also provided a vent  230  for CO 2  and other gases from inside the tank. 
         [0025]    There is also provided an overflow feed tube  231  which ascertains that treated material continuously will be fed into the storage tank  200 . This overflow feed tube is located at a level such that there is formed a head space H above the liquid inside the process vessel  202 . The normal level inside the process vessel  202  is indicated with a broken line in  FIG. 2 . 
         [0026]    The key component of the apparatus is a rotary impeller device  300  of a similar construction to that of the device mentioned in the Background section. The impeller  300  is positioned substantially within the upper portion of the process vessel  202 , i.e. at a position above the level of the guide collar  212 . However, it preferably extends slightly below the collar. The impeller  300  is driven by a motor  232  the speed of which can be controlled to at least two different speeds. The impeller  300  is connected to the motor via a shaft  234  which is hollow for the purpose of supplying air to the process vessel  202 . The motor  232  is suitably an electric motor, but in cases where electricity is not available, diesel engines or other types of combustion engines could be used instead. It is also conceivable to use solar power or wind power to generate the required electric energy, which can be stored in batteries. 
         [0027]    The impeller  300  is similar in construction to the device disclosed and claimed in EP 1 156 870, but with some modifications to render it suitable for the purpose of the present invention. The details of the impeller will now be described separately below with reference to  FIG. 3 . 
         [0028]    Thus, the impeller, generally indicated with reference numeral  300  in  FIG. 3 , is suitably made of stainless steel (although other resistant materials such as various types of plastics are equally possible), and comprises two distinct portions; an upper compartment  301   a  and a lower compartment  301   b  separated by a partition plate  302 . A driving shaft  304  is attached to the partition plate  302  in the centre thereof. The shaft is hollow to enable ambient air to be drawn into the lower compartment  301   b  via a hole  306  in the partition plate  302 . 
         [0029]    The upper compartment  301   a  is formed by a truncated cone  303   a  having the narrower part thereof facing upwards such as to leave an annular opening  305  around the centrally located shaft  304 . The truncated cone  303   a  is preferably welded to the partition plate  302 . There are provided openings  308  in the wall of the upper compartment  301   a . These are circumferentially spaced along the periphery of the compartment wall, preferably near the partition plate  302 , most preferred such that the lower edge of the openings is flush with the partition plate. Suitably there are four such openings, although two or three or five or more openings are possible. The purpose and function of the upper compartment will be described below in connection with the description of the operation of the apparatus according to the invention. 
         [0030]    The lower compartment  301   b  is also formed by a truncated cone  303   b  having the narrower part thereof facing downwards. This truncated cone  303   b  is attached to the bottom side of the partition plate  302  via impeller blades  307 , distributed evenly along the periphery of the cone  303   b . The impeller blades form spacers between the cone  303   b  and the partition plate  302 , so as to provide a peripheral opening for liquid to pass out from the compartment  301   b  during the treatment. Preferably there are six impeller blades, although this number is not critical. There could be four or five or even seven up to ten or more blades. The width of the “slit” formed between the truncated cone  303   b  and the partition plate typically could be 15 mm if the diameter of the entire impeller is 150 mm. The slit width will vary with size of the impeller, and thus a large diameter will yield a correspondingly larger slit width. 
         [0031]    At the periphery of the opening at the narrow end of the truncated cone, there is collar  310 , also in the form of a truncated cone but arranged such that it widens downwards, i.e. it has an opposite orientation compared to the cone forming the lower compartment  301   b.    
         [0032]    The height of this “collar cone”  310  from its wider opening up the joint with the larger compartment forming cone is preferably about 30% of the height of the larger cone, but can vary from 25 to 35%, but could be substantially larger without departing from the inventive idea or negatively impart the function. The lower circumference of this collar cone  310  is located slightly below the level of the guide collar  212 . 
         [0033]    Furthermore, and an important feature, is that the cone angles α of the cone forming the compartment  301   b  and the collar cone  310  should be the same. Suitably this angle α is about 60° but can vary within certain limits such as 65 to 75°, or 60 to 80°. 
         [0034]    Now the operation of the apparatus according to the invention will be described with reference to  FIGS. 1-3 . 
         [0035]    The apparatus according to the present invention can be run in two modes. A first “treatment mode” in which freshly collected faeces is treated, and a second “maintenance mode”, in which material is treated that has been stored long enough that unwanted odours have started to develop. Also, unwanted bacterial growth can be inhibited by this second mode operation. 
         [0036]    The first mode will now be described. 
         [0037]    When the toilets  206  are used, faeces will be fed via the inlet tube  204  and into the process vessel  202 . Initially of course the system is empty, and the treatment of the material will not begin until the process vessel is filled to the set level, defined by the position of the overflow feed tube  231 . 
         [0038]    At this point in time, i.e. when the process vessel is adequately filled, the motor  232  will be started to initiate stirring of the faeces by means of the impeller  300 . Once the system is up and running the motor will run continuously. In the first mode the speed of rotation of the impeller is in the order of 750 rpm but can be up to about 1000 rpm. This will cause the material inside the vessel  202  to rotate forming a vortex. At this speed the liquid or semi-liquid material located at or near the walls in the process vessel, in the region below the guide collar  212 , will be drawn upwards and into the impeller  300 . The collar cone  310 , by virtue of its cone shape, will support the flow into the impeller to render the transport more efficient. 
         [0039]    The guide collar  212  will effectively function as a partition wall between the upper and lower part of the process vessel, thereby preventing material that has been treated inside the impeller to mix too rapidly with untreated material below the collar  212 . Eventually of course the material will in some sense be “homogeneous”, and only when new material is fed into the system an inhomogeneous situation occurs and the process of oxygenation will become operative. 
         [0040]    Due to the construction of the impeller  300  with its truncated cone configuration, there will be created a suction due to the formation of a vortex inside the lower compartment  301   b  of the impeller  300 . Thereby, air from the environment will be sucked in through the hollow shaft, and also liquid will be sucked in through the collar cone  310  at the lower end of the impeller. 
         [0041]    In the extreme conditions inside compartment  301   b  there will a very efficient oxygenation of the faeces material, and a rapid nitrification process will take place thereby eliminating ammonia formation, and also killing of bacteria will be very rapid. 
         [0042]    The upper part of the impeller  300 , i.e. the compartment  301   a , will have dual functions. 
         [0043]    First of all it will cause a suction into the upper opening  305 , such that newly introduced faeces will very rapidly enter there into and mix with air that is also sucked in from the head space H in the vessel  202 . The material will then be thrown out through the peripheral openings  308  and back into the upper portion  218  in the vessel  202 . 
         [0044]    During running of the impeller, proteins and other biological material in the faeces will cause heavy foaming. However, due to the construction of the impeller with an upper portion  218  as described above, foam that is generated will be drawn in from the surface of the media in the vessel and disintegrate in the process of passing through the upper compartment  301   a . Thus, use of anti-foaming agents, common in sewage treatment systems is eliminated. 
         [0045]    Now the second mode of operation will be described. 
         [0046]    When the system has been run for a while, and if the treated material has been stored in the tank  200  for more than say 24 hours inevitably there will be e.g. H 2 S generated together with other unwanted gases, such as ammonia, and as mentioned above, bacterial growth may have reached an unwanted level. 
         [0047]    In order to stop this unwanted process, the material from the tank  200  can be recirculated into the process vessel for further treatment. This is achieved by increasing the speed of rotation of the impeller  300  to about 1500 rpm. This will cause the vortex formed by the impeller at the lower opening to be more directed and actually essentially focussed to the tube  220  and down into it through the opening  221 . As can be seen in  FIG. 2 , the tube  220  extends via the branch  224  to the bottom of tank  200 . Thus the suction caused by the impeller  300  in this second mode of operation will transport material from the bottom of the tank  200  back into the process vessel  202 , where it will undergo the same treatment again as it already once have undergone. 
         [0048]    The second mode of operation can be triggered by sensors (not shown) capable of detecting e.g. H 2 S and ammonia, and when the level has reached a threshold level the second mode of operation will be initiated. 
         [0049]    Alternatively, the second mode could be subject to time control, i.e. the system will automatically go into second mode at certain time intervals. 
         [0050]    In a preferred embodiment, the second mode of operation will be the idle mode, i.e. the first mode will be triggered to become operative when fresh faeces has been fed into the process vessel. 
         [0051]    Although the invention has been described with reference to use by humans, the apparatus is suitable for use also with animal dung and excrements, provided the viscosity thereof is suitable for stirring as contemplated using the rotary device disclosed herein.

Technology Category: 4