Abstract:
A method and equipment are disclosed for tertiary sewage treatment by naturally-occurring microorganisms after the sewage has passed from a septic tank or other primary treatment device. Tertiary treatment occurs within enclosed, controlled conditions in a recirculation tank housing a recirculating spray system and a filter bed. The recirculation process is controlled by a timer and a timer float responding to the wastewater level in the recirculation tank. A mixing zone is provided in a bottom portion of the recirculation tank.

Description:
This application claims the benefit of U.S. Provisional Application Ser. No. 60/062,286, filed Oct. 17, 1997, entitled “Home Wastewater Treatment Plant”. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to methods and equipment for tertiary sewage treatment by naturally-occurring microorganisms after the sewage has passed from a septic tank or other primary treatment device. 
     2. Description of the Prior Art 
     Various sewage treatment systems are known for treating the waste stream from small communities, housing developments and single family units. With the establishment of state and federal guidelines, the need has become more acute for a system to handle sewage disposal needs where traditional methods do not work. 
     Septic tanks are the most commonly used means of treating sewage from a single source. They employ anaerobic bacteria for the primary decomposition of sewage, separating some solid wastes from liquid. The liquid waste streams from septic tanks are often discharged directly to the entry of a subsurface drain field. The remainder of wastewater treatment occurs in the soil. However, many sites and many soil types are unable to accomplish this process in a manner that meets applicable guidelines. 
     Tertiary treatment systems employ processes in which anaerobic decomposition is followed by aerobic decomposition. Tertiary systems lessen the burden on the land, as soils are no longer being called upon to treat wastewater. 
     A secondary treatment method wherein aerobic processes are augmented, for example, by a flow of gas through the material to be treated, is known from U.S. Pat. No. 3,202,285. It has also been proposed to use a gravel bed in secondary treatment, as set forth in U.S. Pat. Nos. 3,057,796 and 4,293,421. 
     U.S. Pat. No. 5,597,477 contains a description of a sewage effluent disposal system comprising a primary sewage treatment tank and an effluent holding tank. A float switch controls the pumping of effluent from the effluent holding tank. Secondary treatment is accomplished by passing the effluent through a sparger as it enters the secondary treatment tank, or by adding disinfectant as the effluent passes through the sparger. The secondary treatment tank does not contain a filtration bed. 
     It is an object of the present invention to provide a wastewater treatment system in which tertiary treatment occurs in enclosed, controlled conditions rather than in surrounding soils, so that the invention can be used where soils are marginal or cannot be used with other systems. 
     The tertiary treatment recirculation process may be controlled by a timer and a pump float responding to the wastewater level in the recirculation tank, thus providing an automated control system. 
     Another object of the invention is to provide a wastewater treatment system as described in the preceding paragraphs in which the effluent is safe and environmentally acceptable. Yet another object of the invention is to provide a durable wastewater treatment system, requiring minimal maintenance, and in which repair and regeneration are readily accomplished. 
     SUMMARY OF THE INVENTION 
     Accordingly, I have invented a system for the tertiary treatment of sewage, comprising a septic tank, which catches the solid component of sewage and houses the primary step of the wastewater treatment process. The heavy solids settle to the bottom of the tank, and the lighter solid material floats to the top. Both solid components largely decompose into liquids and gases in the anaerobic conditions present in the primary treatment step. Relatively clear effluent from the middle level of the septic tank flows into a bottom mixing zone of a recirculation tank. A pump moves effluent from the bottom zone to the top zone of the recirculation tank, where it is distributed over a sand filter located in the top zone, for example, by a spray grid. The effluent trickles through the filter medium where it is treated aerobically and anaerobically by naturally occurring microorganisms. The treated effluent is stored in the bottom zone where it is mixed with incoming septic tank effluent. The effluent is discharged either by gravity or a small discharge pump after which it may be subjected to disinfection. 
     A complete understanding of the invention will be obtained from the following description when taken in connection with the accompanying drawing figures wherein like reference characters identified like parts throughout. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of the wastewater treatment system of the present invention; 
     FIG. 2 is an overhead view of a septic tank, according to the invention; 
     FIG. 3 is a section view of the septic tank of FIG. 2; 
     FIG. 4 is a section view of a recirculation tank, according to the invention; and 
     FIG. 5 is an overhead view of the recirculation tank of FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, one or more septic tanks  10 , positioned below ground level, accept raw sewage and carry out primary or anaerobic processing of the sewage. Septic tanks  10  are connected to a recirculation tank  30 , also preferably below ground level. Recirculation tank  30  carries out mixing and storage of clarified effluent received from septic tanks  10 . After mixing or dilution processing, effluent exits the recirculation tank  30  through one or more outlet lines  86  to optional disinfection device  87 . 
     Referring to FIGS. 2 and 3, inspection cover  12  allows access to the septic tank&#39;s inlet line  14  at its point of entry to the septic tank. The inlet line  14 , which delivers raw sewage to the septic tank, is typically positioned towards the top of the septic tank. Cleanout cover  16  allows the removal of accumulated solids from the septic tank. Access riser  18 , capped by vented carbon lid  20  and constructed so that there is a minimum of six inches from the top of the riser to grade, allows access to effluent filter  22  and septic tank outlet line  24 , positioned opposite inlet line  14 . Septic tank outlet line  24  is also positioned to allow passage of the relatively clear effluent from the middle level of the septic tank. Effluent filter  22  prevents solids from passing through septic tank outlet line  24 , while allowing the passage of liquids. 
     As set forth in FIG. 4, clarified effluent from the septic tank enters recirculation tank  30  through inlet line  32 . Flexible seal  34  secures inlet line  32  to recirculation tank  30 . The clarified effluent flows downward, then through communicating inlets  36  joining the two filter chambers  39  of recirculation tank  30 , then through slotted pipe  40  and upper inlet  42 , or through lower inlet  44  to pump chamber  46 . Recirculation pump  48  and discharge pump  50 , located within pump chamber  46 , are controlled by low water float  52 , timer float  54 , discharge pump float  56  and high water float  58  electrically connected through junction box  60  to control panel  62  containing timer  64 . Optionally, the pump chamber may contain an ultraviolet disinfecting unit or an ozonator to treat the clarified effluent as it enters the recirculating process, or prior to final discharge. 
     Low water float  52  in the down position switches off power to all pumps in the event of an extreme low-water level. Timer float  54  activates or deactivates the recirculating process controlled by timer  64 . Discharge pump float  56  in the up position activates discharge pump  50 ; in the down position, discharge pump float  56  deactivates discharge pump  50 . In the up position, discharge pump float  50  also overrides timer  64  to initiate continuous recirculation. High water float  58  activates an alarm in the event of a high effluent level. This alarm can take the form of various types of indicators, and can be placed in a location remote from the recirculating tank, such as in the user&#39;s residence. 
     Timer  64  is activated when timer float  54  is up. The clarified effluent is then pumped intermittently by recirculation pump  48  through feed pipe  66  and valves  70  to heads  72 , positioned above a sand bed  74 . Pipe  66  is secured to recirculation tank  30  by flexible seal  68 . The spray heads may be helical spray nozzles or another spray diffusion system, such as a conventional brass building sprinkler system spray head, dispersing the liquid into a fine spray to increase the oxygen content of the sprayed effluent and to maximize spray coverage onto the surface of sand bed  74 . Effective operation of the spray heads has been found to occur with an orifice demand of 3 gallons per minute at a clarified effluent pressure of 10-15 PSI. 
     The sprayed effluent passes through sand bed  74 , gravel bed  76  and stone bed  78 . The sand bed contains, for example, sand with a particle size between 1.5 mm and 2.5 mm, with a uniform coefficiency of less than 2. The gravel bed  76  contains, for example, gravel at a size of ⅜″-½″, and stone bed  78  contains, for example, stone at a size of 1½″. Exemplary thicknesses are as follows: sand bed  74  2′0″, gravel bed  76  8″, and stone bed  78  1′4″. As the effluent passes through the sand bed, gravel bed and stone bed, it is treated by the naturally-occurring microorganisms populating the filter. In the event of plugging of the sand bed, overflow lines  82  act as a bypass. At the bottom of recirculation tank  30 , the filtered effluent mixes with the clarified effluent entering through inlet line  32 . Mixing is accomplished by hydraulic displacement. Infiltrators or a leaching type chamber  84  partially supports stone bed  78  and partially encloses a mixing zone  85  at the bottom of recirculation tank  30  in which the mixing of filtered effluent and clarified effluent can occur. The mixing zone comprises the infiltrators  84  and the stone bed  78  and serves as a holding volume A typical infiltrator or leaching chamber  84  is made from HDPE plastic, has a solid top and a louver configuration on its sides through which effluent passes. 
     Overflow line valves  80  may be opened to provide a direct infusion of oxygenated recirculated effluent if there is a buildup of flocculant in mixing zone  85  or spray heads  72 . 
     Discharge pump  50  is connected to one or more outlet lines  86  secured to recirculation tank  30  by flexible seals  88 . Effluent treated in recirculation tank  30  is discharged to a drip field or to disinfection device  87 . Chlorine-containing compounds and exposure to ultraviolet light can be used to disinfect the discharged effluent. Disinfected effluent may meet applicable standards for discharge to a stream or other body of water, or for irrigation use. 
     In FIG. 5, access openings  90  and  92  to pump chamber  46  are shown. These openings allow service, repair and replacement of pump, float and control components. Inspection lids  94  allow access to spray heads  72  for servicing. 
     It will be readily appreciated by those skilled in the art that modifications may be made to the invention without departing from the concepts disclosed in the foregoing description. Such modifications are to be considered as included within the following claims unless the claims, by their language, expressly state otherwise. Accordingly, the particular embodiments described in detail herein are illustrative only and are not limiting to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.