Abstract:
A waste water treatment system and method for use with a septic tank includes sequentially executing the steps of aerating waste water in the septic tank for a first period of time with an air diffuser, allowing the waste water to sediment for a second period of time, and pumping purified waste water out of the septic tank for a third period of time.

Description:
FIELD 
       [0001]    The present disclosure relates generally to a waste water treatment, and, more particularly, to system and method for effectively treating household waste water with aerobic bacteria. 
       BACKGROUND 
       [0002]    Conventionally, household waste water or sewage is treated with a septic tank before being released to ground. The septic tank is basically a large container buried in the ground near a house that collects and treats waste water. A first known system of this type in the United States was put into operation in 1876. Partitions in the septic tank, which improved the treatment effectiveness by regulating the flow of waste water, were added in 1905. At the turn of the twentieth century, the use of septic tanks became widespread. After the Second World War, it has become the primary system for waste water treatment in areas without sewer systems. 
         [0003]    The septic tank treats waste water fundamentally through a sedimentation process which involves separation of relatively heavy solid phase material from liquid in the waste water over time and with the effect of gravity. The effectiveness of the sedimentation process is determined by the flow rate of inflow waste water as well as the lack of whirling in the waste water. Lower flow rate, suppression of flow energy, evenly distributing inlets and high water level in the sedimentation tank can enhance the effectiveness of the sedimentation process. 
         [0004]    Another process occurring in the septic tank which leads to reduction in impurities in waste water is a floatation process. During the floatation process, air bubbles (gas) or buoyancy lifts hydrophobic suspensions, such as oils and fats, to the surface of the liquid, and form a layer of scum. Vegetative mold fungi may grow on the surface of the scum. 
         [0005]    As a result of the aforementioned sedimentation process, residues are deposited at a bottom of the septic tank after long setting time and activities of bacteria undergoing anaerobic stabilization (psychrophilic fermentation) at 8-12° C. 
         [0006]    In addition to the septic tank, a trickling drainage may be employed thereafter to further treat and evenly spread partially treated waste water over a large area of soil. Anaerobic bacteria, raw sewage and small particles can also accumulate in the trickling drainage. In order to maintain effectiveness of the trickling drainage, routinely, usually every three years, pumping out the residuals accumulated at a bottom of such trickling drainage is necessary. This adds cost and inconvenience for such anaerobic waste water treatment system. To overcome this problem, aerobic systems have been developed and in use throughout the United States for more than forty years. 
         [0007]    As the name implies, aerobic systems utilizes aerobic bacteria to treat waste water in septic tanks. Such systems use air blower to introduce air into the septic tank. Aerobic systems have many advantages over anaerobic ones. Many aerobic systems are capable of producing clear and odorless discharges that are less likely to contaminate ground water and greatly prolong the life of a secondary treatment system. The effluent produced by such aerobic system is of high enough quality that some States allow these types of clear and odorless discharges to be released directly to the ground surface through open pipes or spray irrigation. 
         [0008]    However, retrofitting an existing anaerobic septic tank into an effective aerobic one remains to be a challenge. For one thing, an existing septic tank often has an opening as small as twenty inches in diameter, which makes installing new equipment therein difficult. 
         [0009]    As such, it is desirable to provide a system that can be installed through a small opening and a method that can improve waste water treatment efficiency. 
       SUMMARY 
       [0010]    Disclosed and claimed herein is a waste water treatment system and method for use with a septic tank, the system and method include sequentially executing the steps of aerating waste water in the septic tank for a first period of time with an air diffuser, allowing the waste water to sediment for a second period of time, and pumping purified waste water out of the septic tank for a third period of time. 
         [0011]    Other aspects, features, and techniques will be apparent to one skilled in the relevant art in view of the following detailed description of the embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The drawings accompanying and forming part of this specification are included to depict certain aspects of the present disclosure. A clearer conception of the present disclosure, and of the components and operation of systems provided with the present disclosure, will become more readily apparent by referring to the exemplary, and therefore non-limiting, embodiments illustrated in the drawings, wherein like reference numbers (if they occur in more than one view) designate the same elements. The present disclosure may be better understood by reference to one or more of these drawings in combination with the description presented herein. It should be noted that the features illustrated in the drawings are not necessarily drawn to scale. 
           [0013]      FIG. 1  schematically illustrates a waste water treatment system according to an embodiment of the present disclosure. 
           [0014]      FIG. 2  is a flowchart illustrating a waste water treatment method according to an embodiment of the present disclosure. 
       
    
    
     DESCRIPTION 
       [0015]    One aspect of the disclosure relates to transforming an existing anaerobic septic tank into aerobic one, and to implementing a novel sequential waste water treatment method. Embodiments of the present disclosure will be described hereinafter with reference to the attached drawings. 
         [0016]      FIG. 1  schematically illustrates a waste water treatment system  100  according to an embodiment of the present disclosure. The waste water treatment system  100  includes a septic tank  110 , an air diffuser  120 , an airlift pump (Mammoth pump)  130 , an air blower  140  and a timing controller  150 . In one embodiment, the septic tank  110  may be a pre-existing one buried in the ground near a house and originally built to operate primarily on anaerobic bacteria. The pre-existing septic tank  110  has one or more a small openings (not shown)—often less than 12 inches in diameter, on the top. The air diffuser  120  and the airlift pump  130  of the present disclosure can be installed in the septic tank  110  through these openings. In other embodiments, the septic tank  110  may be a newly built one including the same feature elements as described above. 
         [0017]    Referring again to  FIG. 1 , the septic tank  110  has an inlet  115  near a top thereof for household waste water  113  to flow into the septic tank  110 . The air diffuser  120  is weighted, of either a plate type or a pipe type, and placed at a bottom of the septic tank  110  for dispersing air bubbles  124  into the waste water  113 . Ideally, the air diffuser  120  is placed at the bottom and near a center of the septic tank  110 . For a good result, the air diffuser  120  should be located no more than thirty five percent of the distance from the center of the septic tank  110 , and no more than four inches above the bottom of the septic tank  110 . It is also desirable for the diffuser  120  to cover a large area. However, the size of the air diffuser  120  is limited by the size of openings of a pre-existing septic tank  110 . In embodiments, more than one air diffusers can be installed in the septic tank  110 . 
         [0018]    Referring again to  FIG. 1 , air is blown to the air diffuser  120  by the air blower  140  through a valve  142  and a hose  145  under the control of the timing controller  150 . In one embodiment, the air blower  140  and the valve  142  are conveniently placed outside of the septic tank  110 , and the hose  145  is of a flexible type and one half inch in diameter. 
         [0019]    Referring again to  FIG. 1 , the airlift pump  130  has an inlet  132  below a waste water surface, and an outlet  135  leads to outside of the septic tank  110 . The airlift pump  130  is placed in such a way that a bottom part of the airlift pump  130  is located not less than four inches from the bottom of the septic tank  110 , and a top part of the airlift pump  130  is not less than four inches above the level of the outlet  135 . The top part of the airlift pump  130  include a deflector  138  which functions as an air barrier designed to not allow untreated waste water to escape the septic tank  110  through the outlet  135 . In addition, a height of the inlet  132  of the airlift pump  130  is also important, which can be determined based on a level of the waste water  113  so that only purified waste water without uncleaned particles is picked up by the airlift pump  130 . In one embodiment, the inlet  132  is located at a height equal to approximately two third of a distance from the bottom of the septic tank  110  to the outlet  135 . 
         [0020]    Although  FIG. 1  shows only one airlift pump  130  is installed in the septic tank  110 , in case of large discharge volume, multiple airlift pumps can be installed in the same septic tank  110 . With the effectiveness of the presently disclosed waste water treatment system  100 , effluent from the outlet  135  can generally be directly discharged to surrounding ground. However, the outlet  135  can also be connected to a secondary treatment system (not shown) such as a trickling drainage before releasing treated waste water to the ground. 
         [0021]    As shown in  FIG. 1 , the airlift pump  130  receives air also from the air blower  140  though the valve  142  and a hose  147  which is, for instance, one half inch in diameter. The valve  142  functions to direct air flow to either the hose  145  or the hose  147 , or stop the air flow altogether. Although, as shown in  FIG. 1 , the air blower  140  in combination with the valve  142  is exemplarily used for supplying air to either the air diffuser  120  or the airlift pump  130 , two separately controlled air blowers can be used to individually supply air to the air diffuser  120  and the airlift pump  130 . 
         [0022]    According to embodiments of the present disclosure, the timing controller  150  controls the waste water treatment system  100  to perform aeration, sedimentation and outflow operations sequentially as depicted in  FIG. 2 . The timing controller  150  may be implemented with a timer equipped state machine or by a computer. 
         [0023]      FIG. 2  is a flowchart illustrating a waste water treatment method according to an embodiment of the present disclosure, which sequentially circulating among three processing steps: aeration step  210 , sedimentation step  220  and outflow step  230 . During the aeration step  210 , the air blower  140  is turned on and the valve  142  is switched to a position to allow air to flow only to the air diffuser  120 . Introducing air into the septic tank  110  produces an activated sludge in the septic tank  110 . The activated sludge forms a living suspension of heterotrophic bacteria and protozoa in the waste water  113 . The living suspension carries out oxidation of organic compounds that causes nitrification and denitrification of the substance in the waste water  113 . During the aeration step  210 , bio-sorption and reduction of selected pollutants by microorganisms may also occur. Duration (t 1 ) of the aeration step  210  is predetermined and stored in and executed by the timing controller  150 . Alternatively, the duration t 1  can be dynamically adjusted by the timing controller based on conditions of the waste water  113 , which can be measured by sensors installed in the septic tank  110 . In one embodiment, the duration t 1  is set at between 5 to 30 minutes. 
         [0024]    During the sedimentation step  220  which is subsequent to the aeration step  210 , the air blower  140  is shut off, so that aeration of the waste water  113  is substantially stopped. During this period, sludge in the waste water  113  is allowed to settle onto the bottom, and purified waste water in the form of resembling water floats to the top of the septic tank  110 . Duration (t 2 ) of the sedimentation step  220  can also be predetermined and stored in and executed by the timing controller  150 . In one embodiment, the duration t 2  is set at 90 minutes. In an embodiment, the duration t 2  should not be less than 60 minutes or exceed 120 minutes. In an alternative embodiment, a sensor may be placed in the septic tank  110  that measures the cleanliness of the purified waste water from time to time, and sends the cleanliness information to the timing controller  150  for determining the sedimentation duration (t 2 ). 
         [0025]    During the outflow step  230  which is subsequent to the sedimentation step  220 , the air blower  140  is turned on and the valve  142  is switched to a position to allow air to flow only to the airlift pump  130  through the hose  147 . As a result, purified waste water is pumped out of the septic tank  110  by the airlift pump  130  through the outlet  135 . Duration (t 3 ) of the outflow step  230  can be predetermined as well and stored in and executed by the timing controller  150 . In one embodiment the duration t 3  is set at 10 minutes. Alternatively, a sensor may be used to detect the level of the purified waste water in the septic tank  110 , and sends the level information to the timing controller  150  for determining the start and stop of the outflow step  230 . 
         [0026]    As shown in  FIG. 2 , once the outflow step  230  is finished, the waste water treatment method completes a full cycle and can go back to the aeration step  210  to start a new cycle. Preferably, during a twenty four hour period, at least three such full cycles are run, but the number of such full cycles should not exceed six. 
         [0027]    While this disclosure has been particularly shown and described with references to exemplary embodiments thereof, it shall be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit of the claimed embodiments.