Abstract:
A waste treatment system grinds waste material into small pieces and soaks the pieces in a liquid disinfectant. The system includes a hopper, a grinder, a main solution tank, and an auger. Unprocessed waste material is dumped into the hopper. The hopper feeds the unprocessed waste material into the grinder. The grinder includes a rotor and anvil for grinding the unprocessed waste material. The ground material falls into the main solution tank where the ground material is wetted with the liquid disinfectant. The wetted waste is carried from the main solution tank by the auger and spends an additional two to three minutes of wetted time on the auger before entering a de-watering section. The total wetting time allows the waste material to be completely disinfected.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a device and method for treatment of waste and in particular to the treatment of infectious waste from a hospital.  
         [0002]     In the normal course of operation, hospitals generate a variety of waste which is not suitable for normal disposal. While some or most hospital waste may be harmless, it is difficult to distinguish such harmless waste from infectious waste. As a result, all of the waste from a hospital must be treated as if it may be harmful. Also, sensitivity to the handling of hospital waste has been raised as a result of AIDS and other health issues. Recently, the bird flu spread rapidly and initially was not well understood. As world travel has increased, so has the ability of infections, like the bird flu, to spread rapidly, and the need to contain outbreaks is greater than ever before. For all of these reasons, there is a need to deal properly with hospital waste.  
         [0003]     Common methods of treating hospital waste include systems having a steam autoclave or an ethylene oxide autoclave. U.S. Pat. No. 6,726,136 for “Waste treatment plant,” describes a system including an autoclave. Other systems include incinerators. Unfortunately, incinerators may be difficult to construct and operate, and may create environmental issues. Autoclaves may also be expensive and difficult to operate. Systems including autoclaves may also require additional steps to complete disinfecting waste.  
         [0004]     U.S. Pat. Nos. 5,425,925 and 5,656,248 for “Multi-stage infectious waste treatment system,” both assigned to the assignee of the present application, describe waste treatment systems which grind waste into small particle size, and then soak the waste in a volatile liquid disinfectant. Unfortunately, while the systems described in the &#39;925 and the &#39;248 patents successfully treat most hospital waste, some hospital waste has been found to contain material, such as titanium prosthetic joints, which may cause jamming. The &#39;925 and the &#39;248 patents are herein incorporated by reference.  
       BRIEF SUMMARY OF THE INVENTION  
       [0005]     The present invention addresses the above and other needs by providing a waste treatment system which grinds waste material into small pieces and soaks the pieces in a liquid disinfectant. The system includes a hopper, a grinder, a main solution tank, and an auger conveyer. Unprocessed waste material is dumped into the hopper. The hopper feeds the unprocessed waste material into the grinder. The grinder includes a rotor and anvil for grinding the unprocessed waste material. The ground material falls into the main solution tank where the ground material is wetted with the liquid disinfectant. The wetted waste is carried from the main solution tank by the auger, and spends an additional two to three minutes of wetted time on the auger conveyer before entering a de-watering section. The total wetting time allows the waste material to be completely disinfected.  
         [0006]     In accordance with one aspect of the invention, there is provided an apparatus for infectious waste treatment. The apparatus comprises a lift for lifting a waste container to a hopper, a hopper for receiving waste material from the waste container, a grinder for receiving the waste material directly from the hopper and grinding the waste material, a main solution tank for receiving and wetting the ground waste material, and an auger for carrying the wetted material from the main solution tank. The grinder comprises a rotor positioned below the hopper, an anvil in grinding cooperation with the rotor, and a sizing screen for controlling the size of the ground waste material. A liquid disinfectant is sprayed onto the ground waste material in the main solution tank, and a chopper pump circulates the liquid disinfectant.  
         [0007]     In accordance with another aspect of the invention, there is provided a method for treating hospital waste. The method includes pouring waste material into a hopper, providing the waste material to a grinder, grinding the waste material in the grinder, wetting the ground waste material with a liquid disinfectant, and carrying the wetted waste material on an auger for between two and three minutes. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0008]     The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein:  
         [0009]      FIG. 1  is a waste treatment system according to the present invention.  
         [0010]      FIG. 2A  shows a lift for lifting a waste container to dump waste material carried by the waste container into a hopper of the waste treatment system.  
         [0011]      FIG. 2B  shows the waste being dumped into the hopper.  
         [0012]      FIG. 3A  shows a side view of a grinder suitable for use with the waste treatment system.  
         [0013]      FIG. 3B  shows a top view of the grinder.  
         [0014]      FIG. 3C  shows an end view of the grinder (note the grinder resides sideways in the waste treatment system.)  
         [0015]      FIG. 4  is a cross-sectional view of the grinder taken along line  4 - 4  of  FIG. 3B .  
         [0016]      FIG. 5  is a cross-sectional view of the grinder taken along line  5 - 5  of  FIG. 3B .  
         [0017]      FIG. 6A  is a side view of a main solution tank suitable for use with the waste treatment system.  
         [0018]      FIG. 6B  is a top view of the main solution tank.  
         [0019]      FIG. 7  is a cross-sectional view of the main solution tank taken along line  7 - 7  of  FIG. 6B .  
         [0020]      FIG. 8  is a second side view of the main solution tank (opposite side) showing a gas monitoring system, a chopper and recirculation pump, and a liquid disinfectant generator.  
         [0021]      FIG. 9  is a method of waste treatment according to the present invention.  
         [0022]     Corresponding reference characters indicate corresponding components throughout the several views of the drawings.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]     The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing one or more preferred embodiments of the invention. The scope of the invention should be determined with reference to the claims.  
         [0024]     A waste treatment system  10  according to the present invention is shown in  FIG. 1 . The waste treatment system  10  includes a cage  12 , hopper  14 , a grinder  16 , a main solution tank  18 , and an auger  20 . A hospital waste container  40  is placed into the cage  12  where a lift unit  42  lifts the container  40  and dumps hospital waste carried in the container  40  into the hopper  14  (see  FIGS. 2A and 2B ). The hopper  14  resides above the grinder  16  and feeds the waste into the grinder  16 . The grinder  16  grinds the waste, and the ground waste drops into the main solution tank  18  where the ground waste is wetted in a disinfectant liquid. The auger  20  lifts the wetted waste from the main solution tank  18  and completes the waste treatment. A radioactive material detector  13  resides in the cage  12 . When the radioactive material detector  13  detects radiation in the hospital waste, the waste treatment system  10  is turned off and an alarm is sounded. An example of a suitable radioactive material detector is Micro Bomb Detector made by Al NOTL Systems Inc. In Ontario, Canada.  
         [0025]     Continuing with  FIG. 1 , a pump  90  receives disinfectant liquid from the main solution tank  18  through a pump inlet line  92 , and returns the disinfectant liquid through a pump outlet line  94  through a manifold  104 . A drain line  100  is connected to the pump outlet line  94  through a drain valve  98 . A neutralizer tank  130  is connected to the drain line  100  at a neutralizer injector  130  for neutralizing the drained disinfectant liquid. The pump  90  is preferably a chopper pump, and is more preferably a high flow rate pump, and most preferably an approximately 200 Gallon Per Minute (GPM) pump. An example of a suitable 200 GPM pump is a model number HE3G6SEC-055 chopper pump manufactured by Vaughn Company in Montesano, Wash. In some cases, two separate pumps may be used to recycle the disinfectant liquid and to spray the disinfectant liquid onto the waste material. When two pumps are used, the pumps are preferably approximately 90 Gallon Per Minute (GPM) pumps.  
         [0026]     A continuous gas monitoring system  38  monitors the liquid disinfectant level in the main solution tank  18  and composition (i.e., strength) of the liquid disinfectant, and controls the generation of liquid disinfectant (see  FIG. 8 ). For example, chemicals may be introduced into a flow into the pump  90  at a chemical manifold  112  to generate liquid disinfectant. An example of a continuous gas monitoring system  38  is the system described in U.S. Pat. No. 5,269,832 for “Method and Apparatus for Continuously Measuring the Concentration of Chemicals in Solution.” The &#39;832 patent is herein incorporated by reference.  
         [0027]     The auger  20  is preferably a shaftless auger residing in an auger housing  21  supported by an auger strut  23  and is powered by an auger motor  22  which is preferably connected to the auger  20  through a gearbox  22   a . The auger  20  further includes a fluid trap  28  where the liquid disinfectant used to wet the ground waste is trapped and recirculated back into the main tank. A rotatable section  26  of the auger housing  21  may be rotationally positioned relative to the auger housing  21  at various rotations to adjust the position of a chute  24 . If the chute  24  is pointed down, the back pressure on the flow of the ground waste is minimized, and the amount of liquid disinfectant removed by the fluid trap  28  is minimized. As the chute  24  is rotated away from a pointed down position, the back pressure on the flow of the ground waste is increased, and the amount of liquid disinfectant removed by the fluid trap  28  is increased. If the chute  24  is rotated to an upward position, the back pressure on the flow of the ground waste is maximized, and the amount of liquid disinfectant removed by the fluid trap  28  is maximized.  
         [0028]     A lift  42  for lifting a waste container  40  to dump waste into the hopper  14  of the waste treatment system  10  is shown in  FIG. 2A . Grasping arms  48  are attached to a lift trolley  46  which travels on tracks  44 .  FIG. 2B  shows the waste container  40  grasped and lifted by the grasping arms  48 , and the waste being dumped into the hopper  14 . A filter system  49  is connected to the hopper  14  by a filter hose  49   a . The filter system  49  includes a fan to draw air from the hopper  14 , and preferably includes a High Efficiency Particle Arresting (HEPA) filter.  
         [0029]     A side view of a grinder  16  suitable for use with the waste treatment system  10  is shown in  FIG. 3A , a top view of the grinder  16  is shown in  FIG. 3B , and an end view of the grinder (note the grinder resides sideways in the waste treatment system) is shown in  FIG. 3C . The grinder  16  includes a rotor  50  having teeth  51 . An anvil  52  cooperates with the rotor  50  to grind the waste material. Power is provided to the rotor by a grinder motor  62 . A fluid coupling  60  connects the motor  62  to a belt  58 . The belt  58  connects the fluid coupling  60  to a hub  56  on a grinder gear box  54 , and the gear box  54  contains gears connecting the hub  56  to the rotor  50 .  
         [0030]     A cross-sectional view of the grinder  16  taken along line  4 - 4  of  FIG. 3B  is shown in  FIG. 4 . The rotor  50 , teeth  51 , and anvil  52  are fed by a ram  64 , which is preferably a hydraulic ram connected to hydraulics  68 . The ram  64  moves toward and away from the rotor  50  as shown by arrow  66 . The ram  64  is controlled to provide efficient operation of the rotor  50  and anvil  52 , for example, if the ram  66  senses high resistance to motion toward the rotor  50 , the speed of the ram  66  is reduced, and if the ram  66  senses low resistance to motion toward the rotor  50 , the speed of the ram  66  is increased. A sizing screen  79  resides under the rotor  50 , thereby limiting the maximum size of ground waste material which may fall into the main solution tank  18 . The sizing screen  79  may be selected with a hole size to control the size of the ground material, the holes are preferably between approximately ½ inch diameter and approximately three inch diameter.  
         [0031]     A cross-sectional view of the gearbox  54  taken along line  5 - 5  of  FIG. 3B  is shown in  FIG. 5 . The rotor  50  and gearbox  54  are mounted to the grinder  16  to allow motion  86  of the rotor  50  and gearbox  54  if force is exerted on the rotor  50  by the anvil  52 , thus moving the rotor  50  away from the anvil  52 . If the motion  86  is sufficient, a switch  88  turns the motor  62  off to avoid damage to the grinder  16 .  
         [0032]     A side view of the main solution tank  18  suitable for use with the waste treatment system  10  is shown in  FIG. 6A , a top view of the main solution tank  18  is shown in  FIG. 6B . A cross-sectional view of the main solution tank  18  taken along line  7 - 7  of  FIG. 6B  is shown in  FIG. 7 . An auger screw  72  extends though the main solution tank  18  and is cupped by an auger floor  74  which is preferably an auger screen extending under approximately half of the circumference of the auger screw  72 . The liquid disinfectant resides in a lower portion  18   a  of the main solution tank  18  with a static fluid level  78   a . Additionally, while the waste treatment system  10  is in operation, the liquid disinfectant resides at a dynamic level  78   b  above the auger floor  74  in a wetting portion  18   c  of the main solution tank  18 . The dynamic liquid level  78   b  is maintained in equilibrium by the cooperation of pumping the liquid disinfectant into an upper portion  18   b  of the main solution tank  18  and the liquid disinfectant draining through the auger floor  74  into the lower portion  18   a  of the main solution tank.  
         [0033]     Continuing with  FIG. 7 , a first nozzle  80   a  provides a flow of the liquid disinfectant into the lower portion  18   a  of the main solution tank to provide circulation of the liquid disinfectant, a second nozzle  80   b  provides a flow of the liquid disinfectant into the upper portion  18   b  of the auger end of the main solution tank  18 , a third nozzle  80   c  provides a flow of the liquid disinfectant into the upper portion  18   b  of the main solution tank  18  near the auger end of the main solution tank  18  (i.e., where the auger  20  enters the main solution tank  18 ), and a fourth nozzle  80   d  is positioned opposite the auger end of the main solution tank  18  and provides a flow of the liquid disinfectant directed towards the auger screw  72 .  
         [0034]     A bubble tank assembly  128  is partially submerged in the disinfectant liquid below the static fluid level  78   a  and to preferably within approximately one half inch of the bottom of the main solution tank  18 , and is further described in  FIG. 8 . A gas sample tube  129  resides in the main solution tank  18  and has a lower end above the static fluid level  78   a , and preferably between approximately six inches and approximately eight inches above the static fluid level  78   a.    
         [0035]     A second side view of the main solution tank  18  (an opposite side view from  FIG. 1  or  7 ) showing the continuous gas monitoring system  38 , the pump  90 , and liquid disinfectant generator elements are shown in  FIG. 8 . The pump  90  draws the liquid disinfectant from the lower portion  18   a  of the main solution tank  18  through the inlet line  92  and returns the liquid disinfectant to the nozzles  80   a ,  80   b ,  80   c , and  80   e  (see  FIG. 7 ) through nozzles lines  96   a ,  96   b ,  96   c , and  96   e  respectively connected to the circulation pump  90  by the outlet line  94  through the manifold  104 . The drain valve  98  is also connected to the outlet line  94 , and a drain line  100  is connected to the drain valve  98  to allow convenient draining of the main solution tank  18 . A neutralizer tank  130  is connected to a neutralizer nozzle  132  in the drain line  100  by a neutralizer line  134 . The neutralizer neutralizes the disinfectant liquid, and is preferably sodium sulfite.  
         [0036]     The continuous gas monitoring system  38  measures the liquid disinfectant depth and concentration using the bubble tank assembly  128  and the gas sample tube  129  (also see  FIG. 7 ). The continuous gas monitoring system  38  provides control signals over a control cable  122  to valves or pumps  16   a ,  116   b ,  116   c , and  116   d  to control a flow of liquid disinfectant precursors from chemical tanks  114   a ,  114   b ,  114   c , and  114   d  to a second manifold  112 . The liquid disinfectant precursors preferably comprise an approximately 12 percent industrial clorox bleach (i.e., sodium hypochlorite), an approximately 12 percent to approximately 50 percent citric acid solution, an approximately 25 percent sodium chlorite solution as precursors for chlorine dioxide, and an anti-form agent.  
         [0037]     The continuous gas monitoring system  38  includes a continuous gas monitoring device which uses a diaphragm pump to provide the gas flow received through the gas sample tube  129  to a sensor. The sensor&#39;s electrical output is sent through a sensor circuit board to a digital panel meter which processes the sensor output and produces a digital readout in Parts Per Million (PPM) of the chemical levels in the liquid disinfectant. The continuous gas monitoring system  38  compares the measured gas level to the preset alarm levels and activates alarm indicators when gas levels exceed user set levels. If low gas levels are detected, a signal is sent to the liquid disinfectant generator to generate additional chlorine dioxide. If the liquid disinfectant is low, water is added to the systems. The continuous gas monitoring system  38  further includes data logging for recording data including chemical levels, fluid level, maintaining level, and kill ratio.  
         [0038]     The static liquid level  78   a  (see  FIG. 7 ) of the liquid disinfectant in the main solution tank  18  is measured using the bubble tank assembly  128  (see  FIG. 7 ). The bubble tank assembly  128  comprises a six-inch cylinder sealed at the top with a one half inch tube protruding through the top of the seal and extending one half-inch past the bottom of the cylinder. A second one half-inch tube extends just through the seal into the top of the cylinder. The bubble tank assembly  128  is submerged in the liquid disinfectant in the main solution tank  18  to a depth wherein the longer tube is approximately one half-inch from the bottom of the main solution tank  18 . Low-volume air is injected through the longer tube and the resulting pressure inside the cylinder is measured and converted to a measurement of depth of the liquid disinfectant in the main solution tank  18 .  
         [0039]     In an exemplar embodiment, the continuous gas monitoring system  38  includes an electrical control panel, a pump control box, and an operator console. The electrical control panel comprises a PLC control unit, variable frequency drives for the grinder and auger, motor starters for fan and pump, 120VAC and 24VDC control voltage supplies. The pump control box comprises chemical pumps, chemical concentration, reservoir tank water level and air pressure controls, and a three light stack alarm annunciator. The operator console comprising a six inch touchscreen Human Machine Interface (HMI) operator interface display, Start-Stop and Emergency Stop control operators, waste bin color detectors and weight scale. The hydraulic unit control box comprises hydraulic unit controls and position sensors junction terminal blocks.  
         [0040]     All system functions are completely automatic controlled by a Programmable Logic Controller (PLC) unit and the HMI display. All the operator needs to do is load the waste bin in the bin cage and press the start button on the operator console. The system will start functioning in a pre-programmed sequence. The complete process is monitored for time, water level, and chemical concentration by the PLC unit. Should any operating parameters deviate from normal, treatment is automatically halted and the control panel alerts an operator. The operation of the system can be monitored on the HMI display as explained below.  
         [0041]     Before powering the system for the first time, the following checking steps are performed. Ensure all power cords are securely fastened (cord plugs preferably have a guide notch to prevent wrong connection of the plug to the receptacle, if a cord is unplugged, ensure that the system power is turned off, and re-plug). Check hydraulic unit oil level is normal. Ensure chemical containers are connected and are at least 30 percent full. Check for water leakages in the system. And lastly, ensure a water supply is present.  
         [0042]     The waste treatment system  10  may be started by executing the following steps. Turn power on at the electrical panel (the 120VAC and 24VDC power indicator lights that are on the right side of the panel should light.) Make sure there is no alarm message on the HMI display and the 3-stack light is green. Check that the bin lift is at the extreme down position. If alarm messages are present, bring the lift down manually by using the touch buttons on the HMI display. Load the waste bin in the bin cage and make sure the cage door is firmly closed. Make sure that the E-Stop push button is released. If the green lamp on the operator console is not on, then press the Reset button. The green lamp should then turn on. And lastly, press the start button. The system will now start to run in the following sequence based on the color of the waste bin, Red=Medical waste, Grey=Cafeteria (non medical) waste. The HMI display will indicate the operating mode. If the mode must be set manually, the mode can be set on the HMI display Mode select page. The operation of the system may also be monitored on the HMI display as explained below.  
         [0043]     An operating sequence for the waste treatment system  10  comprises the following steps. The lift will lift the waste bin and empty the contents in to the hopper (there is a 5 sec delay at the top emptying position). The shredder, auger and HEPA fan will start running. If in Medical mode, the circulation pumps will start running. The lift will lower the waste bin. The hopper door will close. If in Medical mode, the chlorine dioxide generator will start pumping chemicals into the system based on the chemical concentration set point adjusted on the chemical concentration controller. The shredder will continue to run based on the pre-programmed cycle time. The cycle time maybe longer if there are hard substances in the waste. After the cycle time is over the system will stop.  
         [0044]     The system will stop during the normal running cycle under the following conditions: water level is low or high; chemical level is low; air pressure is low; any one of the motors fault (overloading or other electrical problems); and E-Stop or Stop push button is pressed. The system will start running the cycle from the beginning when the alarm conditions are cleared and Start button is pressed.  
         [0045]     Alarms are indicated by a bell flashing in the upper-right corner of the display when an alarm is activated. To go to the alarms screen, the alarm button on the lower right corner of all the display screens is touched. Alarms are presented in an alarm list with predefined alarm texts. The alarm list contains the latest alarms and is arranged in alarm group order according to definition, so that the latest alarms are shown at the top of the list. The number of times the alarm has been generated (if selected), the status of the alarm, the time it was activated, became inactive or was acknowledged, is shown for every alarm. Touching the acknowledge button accepts an alarm. If the alarm condition is already cleared, then the alarm message line will disappear after acknowledgment. If the alarm condition still exists, the message line will continue to display.  
         [0046]     A method of waste treatment according to the present invention is described in  FIG. 9 . The method includes the steps of pouring waste material into a hopper at  200 , providing the waste material from the hopper directly to a grinder at  202 , grinding the waste material in the grinder at  204 , wetting the ground waste material with a liquid disinfectant at  206 , and carrying the wetted waste material on an auger for between two and three minutes at  208 .  
         [0047]     While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.