Abstract:
A system for treating wastewater having a treatment bed of particulate material, inflow distributing plumbing for applying wastewater from a wastewater supply source to upper part of the treatment bed. The wastewater percolates downwardly through the particulate material and is collected by outflow plumbing and conveyed out of the treatment bed. Preferably, the particulate material in the treatment bed is suitable for supporting aquatic plant life.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 U.S.C. §119(e) of prior U.S. Provisional Application No. 60/535,605 filed Jan. 9, 2004; which is hereby incorporated by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention has been created without the sponsorship or funding of any federally sponsored research or development program. 
     BACKGROUND OF THE INVENTION 
     The present invention is directed generally to a system for treating wastewaters such as landfill leachate, hazardous waste, domestic sewage, domestic sludge, industrial sludges, food processing wastewaters, urban runoff, aquaculture wastewaters, and petroleum residuals. The invention is directed more specifically to a wastewater treatment system that employs a physio-chemical, biological apparatus, commonly referred to as “artificial wetland” or “green system”. The use of “artificial wetlands” or “green systems” for wastewater treatment has been in practice for a long time. Over the past 50 years a multitude of variations to the technology have evolved. The applicant has obtained several U.S. patents for variation of the above-described technology (i.e., U.S. Pat. Nos. 4,995,969, 4,678,582, 4,368,120, and 4,276,164). 
     Conventional wastewater treatment systems rely on chemicals, and electrically driven motors and other mechanical apparatus. These elements add considerably to the cost of operating the treatment system. 
     Conventional wastewater treatment systems are also subject to climatic differences. In northern climates, bacterial action diminishes or ceases when air temperature drop significantly. Also plants used in the treatment systems either die or become dormant when air temperature is at or near freezing. 
     Another problem encountered in current wastewater treatment systems is that, over time, there is an accumulation of sludge in the flow components of the system which reduces the efficiency of the system and eventually causes the system to clog and fail. Even the most efficient systems fail to treat all of the wastewater. 
     What is needed is a wastewater treatment system that does not rely on chemicals, motor driven pumps or electric power. 
     What is also needed is a wastewater treatment system that provides substantially 100% treatment of the wastewater components. 
     What is further needed is a wastewater treatment system that essentially uses only sunlight and gravity as energy sources and can be used in areas where conventional wastewater treatment is neither possible nor practical. 
     What is still further needed is a wastewater treatment system that is economical for small as well as large applications. 
     What is also needed is a wastewater treatment system that biodegrades substantially all of the components in the wastewater, thereby eliminating the need for sludge disposal in landfills the production of effluent that can either be reused or returned to the environment without negative impacts. 
     BRIEF SUMMARY OF THE INVENTION 
     In general, the invention utilizes an “engineered” ecological system to treat a wide variety of wastewaters. Specially selected plants and growth mediums provide optimum conditions for aerobic and anaerobic bacterial to metabolize wastewater constituents. Lined basins approximately 1 meter in depth are constructed typically using PVC piping, stone, pea gravel and coarse sand as a growth media. Wastewater is introduced through the distribution network of PVC piping. The rate of percolation through the coarse sand is retarded using a control box. The control box insures an adequate detention time within the treatment unit so that intended physical, chemical and biological processes can occur. The treated effluent is collected by an underdrain system, and discharged into the control box where it can be monitored, and discharged or passed onto another treatment unit. Typically two or more treatment beds are operated in series or parallel to insure adequate detention times. Each treatment unit may utilize the same or different plants and growth mediums depending on design objectives. 
     Perpetual reed bed cells are seeded with various species of annelids (worms) to consume bio-solids. Hydraulic conductivity through the reed bed cells is maintained by using plants with an adventitious root structure. By combining perpetual reed bed cells with the treatment cells of the present invention, 100% of a wastewater stream can be effectively treated and then reused. 
     The invention resides in the combination of parts set forth in the specification and covered by the claims appended thereto. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The character of the invention, however, may best be understood by reference to one of its structural forms, as illustrated by the accompanying drawings, in which: 
         FIG. 1  is a longitudinal vertical cross section of a wastewater treatment system embodying the principles of the present invention; 
         FIG. 2  is a longitudinal vertical cross section of one of the treatment beds of the present invention; 
         FIG. 3  is a vertical cross-sectional view of a control box that forms part of the outflow device for the treatment bed; 
         FIG. 4  is a vertical cross section of a typical “perpetual treatment bed” for sludge treatment and decomposition; 
         FIG. 5  illustrates parallel and series connection options for roughing treatment beds and polishing treatment beds; and 
         FIGS. 6 and 7  illustrates typical root cross section of the plants in the treatment beds of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 1 and 2 , the wastewater treatment system of the present invention, generally indicated by the reference numeral  10 , is shown as having a wastewater supply source which may be in the form of a settling tank or storage container such as tanks  12 . Treatment units or beds, generally indicated by the reference numerals  14  and  16 , are operatively connected to the tanks  12  by an inflow control device, generally indicated by the reference numeral  17 . Each treatment unit  14  and  16  is comprised of a natural or synthetic liner  18  which fits the contour of a depression in perimeter dikes  19  and treatment unit bottom  21 . Inside the liner is a system of perforated collection pipes  20  that conducts the treated effluent to a control box  22  via a connecting pipe  23 , see  FIG. 3 . The control box  22  contains a “tower” of vertically spaced overflow T&#39;s  24  with caps  26  that can be used to control the level of water within the treatment unit  14  and constitutes a first outflow control device that is operatively connected to the distribution pipes of the polishing bed  16  via an outlet connecting pipe  25 . A similar control box  22  is operatively connected to the collection pipes of the polishing bed  16  and constitutes part of a second outflow control device. The perforated collection pipes  20  are surrounded by a stone layer  28 , typically using stones 2cm-5 cm in diameter. The stone drain layer  28  insures unrestricted entrance of the percolated wastewater effluent into pipes  20 . Above the stone drain layer  28  is, preferably, a layer  30  of pea gravel with a particle diameter of 0.5 cm-1.0 cm. The pea gravel layer  30  supports a growth media  32  above and it insures that finer particles from the growth media  32  do not enter the stone drain layer  28  below. The pea gravel layer  30  is typically 5-10 cm in depth. The growth media  32  can be comprised of any number of substances including but not limited to coarse sand, peat mass, rock wool, coconut fiber, corn husks, rice shells, African palm shells, African palm fiber, sun flow seed pods, sun flower seed shells, coffee bean shells, shredded plastic, crushed glass, and a variety of other materials that possess desirable surface areas and hydraulic conductivity. Typically the growth media depth equals the plant root penetration depth (i.e. 60-80 cm). Near the top of the growth media  32  is a network distribution of perforated pipes  34 . Spacing for the network of distribution pipe is generally half that of the network of collection pipes  20  (i.e. 1.5 m-2 m, and 3 m-4 m respectively). Each perforated distribution pipe  34  is surrounded by a zone  35  of stones 2 cm to 5 cm in diameter. This is generally the same size stone as that used in the stone drain layer  28 . Each zone  35  is generally 0.5 m-1 m in width. This insures a uniform distribution of wastewater into the growth media  32 . As with the collection pipes  20 , the distribution pipes  34  are covered with a 5 cm-10 cm layer  36  of pea gravel with a particle diameter of 0.5 cm-1.0 cm. A 5 cm growth media layer  38  is used to cover the entire treatment unit  14 . Selected plants  40  are then introduced into the growth media layers  32  and  38  in a manner that insures viable propagation for the species selected. 
     Plants with economic value are preferred because they can be harvested and sold (e.g. Giant Bulrush, Bamboo, Phragmites). Other plants can also be used for treatment and as animal forage (e.g. Reed Canary Grass). In some cases, the treatment vegetation selected can be used for human consumption (e.g. bamboo shoots, Sweet Basil, and rice). 
     The polishing bed  16  is normally constructed identical to the roughing bed  14 , but for special applications, the growth media and plant species may be modified. The distribution pipes of the roughing bed  16  are typically connected directly to an outlet collecting pipe  25  of the control box  22  of the roughing bed  14 . Under certain circumstances it may be desirable to construct the roughing bed  14  and the polishing bed  16  so that they can be operated in series or parallel.  FIG. 5  illustrates the general piping and valving configuration for that option. 
     Referring to  FIG. 5 , there is shown a roughing bed  64  and a polishing bed  66  for receiving wastewater from a pair of parallel settling tanks  58  and  70 . Valves  72  and  73  control flow of wastewater into the settling tanks  68  and  70 , respectively to a pipe  78  that is connected to the roughing bed  64 . A pipe  80  connects the control box of the roughing bed  64  to the polishing bed  66 . A pipe  81  conducts the treated wastewater from the control box of the polishing bed  66 . Flow of wastewater into the roughing bed  64  is controlled by a valve  82  in pipe  78 . Pipe  80  contains a valve  84  for controlling flow of wastewater from the roughing bed  64  to the polishing bed  66 . 
     A bypass pipe  86  operatively connects pipe  78  to pipe  80 . A valve  88  in pipe  86  selectively directs flow of wastewater from pipe  70  to pipe  80 . A second bypass pipe  90  connects the control box of the roughing bed  64  directly to pipe  81 . A valve  84  is located in bypass pipe  90  for selectively controlling the flow of wastewater through the pipe  90 . 
     In the series mode of operation valves  88  and  92  are closed and valves  82  and  84  are open. In the parallel made of operation, the valves  82 ,  88  and  92  are open and the valve  84  is closed. 
     Normally the roughing beds  14  and the polishing beds  16  are constructed in a way that provides equal surface area and depth. The surface area occupied by each treatment unit  14  and  16  is determined by several design equations unique to the treatment units of the present invention. A first order kinetic model is used to determine the required treatment time 
               t   _     =       1   k     ⁢   ln   ⁢       C   o       C   t               
where:
         t=treatment time (days)   k=kinetic rate constant (days −1 )   C 0 =influent concentration (mg/L)   C 1 =desired effluent concentration (mg/L)       
     Although the biochemical oxygen demand (BOD 5 ) is the basis for most treatment system designs, the same first order model can be used to determine treatment times for other wastewater parameters (e.g. COD, TOC, nutrients, heavy metals etc.). A kinetic rate constant of 1.2 days −1  has been established for domestic wastewater BOD 5  reduction in a treatment system of the present invention, but the value can vary depending on climate (i.e. temperature ranges). Larger or smaller rate constants may be appropriate for other wastewaters like landfill leachate. 
     Based on the desired effluent concentration (C 1 ) and the strength of the influent (C 0 ) (Equation 1) can be solved for the needed detention time (typically in days). 
     Equation 2 is then used to determine the land area or treatment area needed.
 
 Q·t=L   2   ·f   (Equation 2)
 
where:
         Q=design flow rate (L 3 /d)   t=required treatment time (d)   L 2 =required treatment system area (L 2 )   H=treatment system depth (m)   f=growth media porosity (unitless but typically 0.35-0.40)       

     Because Q, t, H, and f are fixed by the wastewater flow, its constituents, and treatment system design parameters, (Equation 2) can be solved for the required treatment area (L 2 ). This area may range from several m 2  for a single family dwelling to hundreds of hectares for a large city. In most climates for domestic sewage an area of 2 m 2 /capita is sufficient to reduce BOD 5  from 300 mg/l to less than 5 mg/l (i.e. a 98% reduction). 
     In addition to reducing the quantitative aspects of wastewater (e.g. BOD−CO 2 +H 2 O), treatment system units can also convert contaminant species from one form to another. This is primarily due to the unique array of aerobic and anaerobic microsites within the treatment unit.  FIGS. 6 and 7  illustrate how oxygen rich zones around plant roots  43  and plant root hairs facilitate aerobic chemical and microbial processes in aerobic zone  44 , while a short distance away in anaerobic zone  46 , the growth media may be totally anaerobic with associated anaerobic processes occurring. As an example, nitrification of ammonia to nitrite and nitrate can occurs in the aerobic zone  44 
 
(NH 4 +O 2 +Nitrosomonas→NO+O 2 +Nitrobacter→NO 3   2 ).
 
     While denitrification of NO 3   2  to N 2 O and N 2  can be simultaneously occurring just a few mm away in the anaerobic zone  46 
 
(NO 3   2 +denitrifying bacteria→N 2 O+N 2 ).
 
     Similar transformation processes can anaerobically convert organic ring compounds like benzene to straight chain hydrocarbons that are much easier for aerobic bacteria to convert into carbon dioxide and water. 
     Unlike conventional wastewater treatment systems, the apparatus of the present invention uses no chemicals, no motors, no electricity and it has no moving parts. It relies totally on the sun, gravity, wetland plants, bacteria, and a growth media to achieve the desired effluent quality. Because all of the treatment is accomplished below ground level, surface features are conducive to the creation of ecology parks, recreation areas, and self-educational nature trails. Although wastewater treatment is the primary objective, economic considerations usually include a selection of plants with resale value, and the production of clean water that can be reused for industrial processes, irrigation, aquaculture or even drinking. An additional benefit of “below ground” treatment is that the technology is much less sensitive to climatic difference than other systems. In northern climates when air temperatures drop to well below freezing, bacterial heat production in the growth media maintains an above freezing environment. The growth media itself also serves as insulation. In addition, to naturally occurring materials like coarse sand a wide variety of other media can be used effectively. These include but are not limited to, peat moss, rockwool, shredded plastics, crushed glass, coffee bean shells, rice shells, coconut fiber, corn husks, African palm shells, and the shells of sun flower seeds. Unlike other systems, the technology, also provides 100% treatment of the wastewater components. After separation of solids using conventional settling tanks, sludge residuals are removed and treated using “perpetual reed beds”. The liquid fraction of the wastewater undergoes transformations in the roughing and polishing beds that include aerobic microbial breakdown near plant root surfaces and anaerobic microbial breakdown a short distance away from the roots (see  FIGS. 6 and 7 ). Additionally, there are aerobic and anaerobic chemical processes occurring throughout the growth media matrix. Heavy metals are oxidized and precipitated while others “exchange” on growth media surfaces. Plants absorb wastewater nutrients and other organic materials. The media itself is an excellent sieve or filter, and typically reduces suspended solids concentrations to one or two mg/l. During summer months, the high rate of plant evapotranspiration can reduce effluent flows to near zero. 
     Referring to  FIG. 4 , sludge treatment is accomplished using a perpetual reed bed that relies on microbial decay and annelidic consumption (i.e. worms) to biodegrade the sludge at a rate essentially equal to that being applied. As such, there is not measurable accumulation of sludge within the treatment cells once the annelid population has established itself. The perpetual reed bed shown in  FIG. 4  is generally indicated by the reference numeral  48  and includes a 15 to 20 cm base  50  of 2-5 cm drain stone. A 15-20 cm layer  52  of 1 mm-2 mm coarse sand is located above the base  50 . A 5 cm layer  45  of 0.5-1 cm pea stone is located between layers  52  and base  50 . Decades of stored sludge  56  is located above the layer  52  and contains worms  58  and the roots  60  of phragmites reeds  62 . Perforated drain pipes  51  are located in the base  50  of drain stone. 
     A special application of the technology when used for landfill leachate treatment can include the combustion of waste methane gas to heat greenhouses that can be operated year round even in temperate climates. The use of this greenhouse gas (i.e. methane) to produce heat and carbon dioxide not only enhances leachate treatment and plant growth, but it also eliminates the large economic and environmental costs associated with trucking and treating leachate at municipal wastewater plants. When one considers that post landfill closure leachate treatment is usually required for 30-50 years, the economic savings are substantial. 
     In areas of the world where wastewater for irrigation is limited, the use of the treatment system of the present invention can greatly reduce the demand on potable water supplies by farmers. The extremely high quality effluent which can be controlled to retain its nutrients like nitrogen, phosphorus and potassium represents an excellent irrigation source. In other applications it can be recycled into municipal drinking water sources by percolation back into the groundwater. The extremely low concentration of suspended solids and turbidity make effluent from the treatment system of the present invention an excellent candidate for ultra violet disinfection, thereby reducing public health concerns regarding bacteria and virus contamination of groundwater. By eliminating the need for costly and “environmentally unfriendly” electricity, the technology also offers and excellent long-term solution for wastewater treatment in developing countries. 
     It is obvious that minor changes may be made in the form, construction and operation of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form here in shown and described, but it is desired to include all such forms as intellectual property that come within the scope claimed.