JP2002518163A - Aeration pond wastewater treatment system and method - Google Patents

Abstract

SUMMARY A four-pond wastewater treatment method for controlling algae and ammonia in an effluent stream is disclosed. A plurality of opaque module cover casings (80, 81, 82, 83) float on the surface of some or all of the aeration ponds, sedimentation basins, and clarification ponds to shield sunlight, thereby increasing algal growth and solids. Control the suspension. To increase the nutrient enrichment of ammonia, the attached growth biomedium is submerged in an aeration pond.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION

The present invention relates to a process for returning sanitary and non-sanitary wastewater to the environment. In particular, the present invention relates to a four-pond wastewater treatment system and a method for controlling biological oxygen demand, solid suspension and ammonia in an effluent within acceptable limits. The solid suspension is
Some are controlled by limiting algae growth using opaque floating module covers on the surfaces of aerated sedimentation and clarification ponds. Ammonia nutrient enrichment is enhanced in an aerated pond using a submerged adherent growth biomedium to support vegetatively enriched microorganisms under the module cover.

[0002]

BACKGROUND OF THE INVENTION

In a wastewater treatment system, a plurality of floating module foam cores tied together, each housed in a durable membrane, to shield sunlight and prevent algae growth in aerated ponds To cover an aerated pond. It has also been known to provide such a casing on the surface of a settling basin. Characteristics of such a treatment system are a biological oxygen demand of about 10 mg / L,
It was believed to produce a mg / L solid suspension and about 2 mg / L ammonia.
It was thought that such a sun-shielding system would allow for nutrient enrichment even in cold climates. The characteristics of systems using a floating module sunlight cover have not always met expectations, especially with respect to the enrichment of ammonia in cold climates. "Cold climate" means 2 to 10 mg / L for at least part of the year
Means a location characterized by an average ambient temperature sufficiently low that the ammonia emission concentration, preferably 5-10 mg / L, is not substantially harmful to the aquatic flora and fauna species contaminating said aqueous environment. .

[0003] It has also been known to sediment adherent growth biomedium in aerated tanks to increase the growth of nutrient-rich microorganisms. For example, US Patent No. 5,399,266 to Hasegawa describes a method for treating wastewater using a microbial medium. This medium includes a central strut, in which polyvinylidene chloride fibers and acrylic fibers woven in a 1: 1 ratio have removed more nitrogen from the wastewater than similar media containing only polyvinylidene chloride. .

Further, in order to control the growth of algae in an aerated tank, a light transmissive heat retaining cover placed on a shaded natural large aquatic plant such as a duckweed,
It was known to combine the use of sedimentation activated bioweb substrates. In this prior art system, the known problem of duckweed being blown to one side of an open pond or swamp was solved by providing a greenhouse enclosure for a wastewater treatment tank.

[0005] There is still a need for outdoor wastewater treatment systems and processes to control algae growth and provide sufficient nutrient enrichment in cold climates. Surprisingly,
Applicants have found that the combination of the use of a sunscreen cover and a settling biomedia in an outdoor wastewater treatment process provides unexpectedly superior properties with respect to BOD, solid suspension and ammonia removal.

[0006]

Summary of the Invention

The present invention is a process for treating sanitary and non-sanitary wastewater in a four-pond system in the order of an aerated pond, an aeration pond, a sedimentation pond and a purification pond.
A plurality of floating module casings tied together cover substantially the entire surface of the aerated pond in order to significantly reduce, if not prevent, the growth of algae in the aerated pond by shielding from sunlight. The through opening in the cover is preferably adapted for a pair of spaced floating aerators. Preferably, the floating module casing covers substantially all of the sedimentation and clarification ponds. To increase the growth of nutrient-enriched microorganisms in the aeration pond, the attached growth biomedium may be submerged in the aeration pond.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION In accordance with the process of the present invention, raw wastewater 1 is treated in a four-pond wastewater treatment process to return to the environment. Raw wastewater may contain sanitary components as well as non-sanitary or industrial components such as refrigeration system debris and laboratory chemical effluents.

[0008] The solid material in the raw wastewater is sieved and, if necessary, a conventional screen mill 50.
The size is reduced mechanically using. The wastewater feed 2 is first supplied to the equalization pond 10 before being released as a process effluent into a natural water environment such as a river.
Then, it is sent to the aeration pond 20, the sedimentation pond 30, and the purification pond 40.

[0009] Each of these treatment ponds (10, 20, 30, 40) will preferably have generally sloping sidewalls and a substantially flat centrally located pond bottom. Preferably,
These ponds are lined with viscosity. The shape of each pond is not important, but they are generally rectangular in shape. For example, the equalizing pond, the aeration pond and the sedimentation pond may have a rectangular shape, while the purification tank may have a triangular shape. The size and depth of each pond will be determined based on the nominal flow capacity of the system. The nominal flow capacity can be, for example, 0.15 MGD (million gallons / day). Aeration ponds, sedimentation basins and clarification ponds are intended to be maintained at substantially constant liquid levels, while equalization ponds provide about 50,000 to about 120,000 gallons for accumulation and mixing of wastewater feedstock 2. Perturbation and composition of water load, varying with volume or biological oxygen demand (BOD)
It is intended to attenuate the changes in and prevent these changes from affecting the aeration pond. The bottom 21 of the substantially flat central portion of the aeration pond is, for example, approximately 30 feet × 100
Feet and has a nominal depth of 10 feet. The particular size or geometry of the various ponds should not be considered as limiting the scope of the invention.

[0010] Both the equalizing pond and the aeration pond are preferably a pair of spaced-apart floating aerators, such as suction jet aerators, generally located at diagonal corners of a substantially flat central pond bottom. An aerator 22 will be included.

[0011] Raw effluent 1 does not prevent, if not prevent, the growth of the desired carbonaceous and nutrient-enriched microorganisms in the aeration pond, but at least at a sufficiently high level (eg, 0.
(05 to 0.1 mg / L or more). Thus, the equalization pond is dechlorinated, for example, by the addition of sodium bisulfate, reducing the chlorine level to a level below which microbial growth in the aeration pond is adversely affected. For example, the addition of sodium hydrogen sulfate 3 may be used to reduce the chlorine concentration in the equalization pond to 0.05 mg / L or less, preferably to about 0.01 mg / L or less. The dechlorinating agent is added, for example, to the suction port of a lift pump that transports wastewater from the equalization pond to the aeration pond while recirculating (not shown) a portion of the pump discharge to the equalization pond. What is necessary is just to add to an equalization pond by any conventional method. The remainder of the pumping effluent carries the equalization pond effluent 4 to the aeration pond.

[0012] To enhance the growth of the vegetatively enriched bacteria in the aeration pond, one or more frames supporting the adherent growing biomedium are located at a central pond bottom 21 approximately intermediate between the aeration pond aerators. Is done. Preferably, the frame is made of an inert lightweight material such as aluminum or polyvinyl chloride. This frame is submerged in bio media,
Actually, it can be of any size as long as it is not placed so close to the aerator that it collides with the water flow and is rocked. For example, four 10 ft x 10 ft aluminum frames are placed in the middle 30 ft x 100 ft center pond of clay-lined middle between two aerators located at two diagonal corners of the pond bottom. You only need to install it. The aeration pond 20 is shown schematically in FIG. 1 and is not drawn to scale. Preferably, the frame has channels and foot pads (not shown) for stability.

[0013] The frame supports a rack of adherent growth biomedium. A variety of different types of biomedia are known, for example, as disclosed in US Pat. No. 4,165,281. A preferred type is a fiber loop-type biomedium 70 comprising fibers 71 bonded to a central strut 72, as shown in FIG. The most preferred type is the RINGLACE ™ brand adherent growth biomedia manufactured by Ringlace Products Inc. of Portland, Oregon. RINGLACE ™ biomedium is made of 100 micron diameter polyvinylidene chloride fibers woven into strands. The biomedium includes a flexible loop extending from the strand. Nutrient-rich microorganisms are supported in this loop. The strands define openings approximately 3 inches apart and allow oxygenated wastewater to flow freely throughout the frame across the openings.

Algal growth is substantially reduced and, in fact, prevented by shielding sunlight from irradiating one or more of the aeration ponds, sedimentation ponds, and clarification ponds. Preferably, sunlight is shielded from all three ponds. For any desired pond, natural sunlight is deprived by many possible means. On its surface, several floating module casings
Opaque cover assembly 8 assembled by connecting 81, 82, 83 together
Floating zero blocks sunlight. The cover system is available from Industrial Environmental Concepts, Inc. of Minneapolis, Missouri.
(Industrial Environmental Concepts, Inc.). The sun may be shielded by a translucent fabric suspended on the surface of the pond. Preferred fabrics shield and / or filter sunlight by varying factors such as weave, thread density, color, and polarization component. Thus, in a preferred embodiment, the means of shading the pond allow for adjustment of the shade by changing the cover or by retracting the cover so that the entire surface of the pond is not covered.

The shape of each casing is generally rectangular, approximately 8 feet wide and 40 feet long. As shown in FIG. 3, each casing is constructed of an upper member 84 and a lower member 85 that are heat fused together at a seam 85 along an edge 86 of the casing. The upper and lower members have a buoyant thickness 2 to provide buoyancy to the casing.
An inch foam core is sealed and housed. Preferably, the foam is a polystyrene foam. This core is most preferably FORMULAR® 250 brand polystyrene foam, available from Owens Corning Corporation. The membrane is a permeation resistant 40 mil thick high density polyethylene.

[0016] Casing edges 86 of adjacent casings are overlapped and secured together by a securing system to form an overlap joint. Two such fixation systems are shown in FIGS. The fixation system of FIG. 3 includes a series of spaced holes 88. Once the edge holes 88 of two adjacent casings are vertically aligned, the securing member 90 is removed from each of the aligned pairs until the band retaining member 91 on the securing member 90 prevents further passage of the securing member 90. Insert from under the hole 88. Preferably, the securing member includes a circular band 92 of membrane material at one end to which the retaining member is attached. For reasons that will become apparent in the next paragraph, the retaining member 91 is designed to be raised against the underside of the overlapped casing edge 86, thereby preventing the band from being removed throughout the hole 88. Have been.

When the band is in the correct position, a 1/4 inch diameter polyvinyl chloride coated stainless steel cable 100 made from a 1/8 inch diameter stainless steel aircraft cable (not separately shown) is attached to the center of the band. Screwed into the opening. This cable is
It is screwed through all the bands in the aligned holes of the casing and fixed at each end to concrete piles 110 (FIG. 4) outside the perimeter of the pond. This cable allows the casing to rise and descend with slight changes in the liquid level, while keeping the casing stable down in the wind.

The edge holes may be spaced apart from each other at regular intervals of, for example, about 3 feet. The surface of the pond absorbs oxygen through the overlapping joints, vents gas, drains rain and meltwater into the pond through the overlapping joints, and collects water on the casing surface, submerging the entire casing below liquid level. As such, each film edge is not intentionally fixed to an adjacent film edge. Thus, the pond can "breathe" through the overlap joint.

This casing is substantially opaque to sunlight. The cover, during the day,
It virtually blocks all light energy that would otherwise reach the surface of the pond. Thus, the floating module cover substantially limits and preferably substantially prevents the growth of photosynthetic algae in a pond equipped with a cover system.

In general, due to the insulation value R of the foam core, preferably a polystyrene foam core, the installation of such a floating cover makes it possible to transfer heat from the pond to the environment, especially during cold ambient climatic conditions. It appears that loss is significantly reduced. Depending on the number of polystyrene cores wrapped in the membrane, the casing can have an adiabatic R-value of 8-30. Preferably, the casing should have an R-value of 8 to 12 to at least partially insulate the pond liquid from ambient atmospheric conditions.

The aeration ponds are preferably aerated regardless of the presence of a floating cover over the entire pond surface. The cover has a through-opening 120 (FIG. 1) in the cover structure, the opening being adapted to place a floating aerator therein.

The process stream flows from the aeration pond to the sedimentation basin and then from the sedimentation basin to the clarification pond. One, and preferably both, of the sedimentation basin and the clarification pond also include a substantially opaque cover constructed of a floating module casing and covering substantially the entire surface of the pond, as described above for the aeration ponds. . However, the sedimentation basin and the clarification pond are not aerated, so that no opening is required.

The clarification pond is disinfected in any suitable way to provide sufficient control of E. coli.
For example, clarification tank chlorination is one possible approach. Preferably,
To reduce the chlorine level in the process effluent, the sedimentation basin effluent is irradiated by an artificial ultraviolet source 60, effectively disinfecting the clarification tank effluent 8.

[0024] The septic pond effluent is released into a water environment such as a stream, river, swamp, pond, bay, sea, or other nature. The present invention is particularly well suited for use in cold climates,
And useful. In cold climates, for at least part of the year, 2-10 mg / L,
Sites characterized by an average ambient temperature low enough that the ammonia emission concentration of preferably 5-10 mg / L is not substantially harmful to the aquatic flora and fauna species polluting said aqueous environment are included.

The process of the present invention effectively reduces the effluent concentration to within acceptable limits. Biochemical oxygen demand can be reduced to less than about 10 mg / L, preferably less than about 5 mg / L, and more preferably to about 3 mg / L. Solid suspensions can be reduced to less than about 12 mg / L, preferably less than about 10 mg / L, more preferably less than about 6 mg / L. Ammonia can be reduced to less than about 2 mg / L, preferably less than about 1 mg / L, more preferably less than about 1 mg / L. The pH ranges from about 6.5 to about 9, preferably from about 7 to about 8.5, more preferably from about 7 to about 8 without adding a neutralizing agent such as carbon dioxide or a strong acid to the wastewater to be treated. Can be controlled within the range. Chlorine can be controlled below about 0.02 mg / L, preferably below about 0.01 mg / L.

As shown in the following examples, the result of the present invention is a wastewater treatment process effluent with unexpectedly improved properties.

Example I A four-pond wastewater treatment facility for a 0.15 MGD wastewater flow rate was constructed. The floating module cover was installed on the sedimentation and purification ponds, but not on the aeration or equalization ponds. No sedimentation attached growth biomedium was used. Dechlorination of the equalization pond was performed. The drain flow rate was about 0.08 MGD and the process effluent was as described in Table I. In Table I, "SS" means "solid suspension".

Example II The same conditions as described in Example 1 were used, except that the attached growth biomedium was settled in the aeration pond as described above. The wastewater flow rate was about 0.04 MGD, and the process effluent was as described in Table I.

Example III The same conditions as in Example II, but the floating module cover was also installed in the aeration pond. The wastewater flow rate was about 0.04 MGD and the process effluent was as described in Table I. Table I The above examples are provided for illustrative purposes only and do not limit the scope of the invention as claimed in any way.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of the four-pond wastewater treatment process of the present invention.

FIG. 2 is a perspective view showing some prior art floating casings connected together by fasteners and fixed cables.

FIG. 3 is a detailed view of the prior art system of FIG. 2 for securing a floating casing together.

FIG. 4 is a perspective view showing another casing fixing system.

FIG. 5 is a diagram showing a conventional biomedium.

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Claims (13)

[Claims] 1. A method for treating wastewater, comprising: providing a wastewater process stream to an aeration pond; exposing the process stream to a biomedium submerged in the aeration pond; Providing a shade to at least a portion of the aeration pond to a degree that substantially inhibits it. 2. The process of claim 1, wherein said awning is provided by non-living material. 3. The method according to claim 2, wherein the non-living material is shaped sufficiently regularly to allow substantially all regular coverage of the pond liquid level. A method consisting of multiple floating modules. 4. The method of claim 3, wherein each of said modules comprises:
A casing having a floating core housed within the membrane material, said membrane material forming an edge and a fastening system joining together adjacent casings along said edge so as to resist wind forces. How you can. 5. The method of claim 1, wherein providing the awning is effective to reduce solid suspension from the method to less than about 10 mg / L. 6. The process of claim 1, wherein said biomedium supports nutrient-enriched microorganisms. 7. The step of claim 6, wherein the biomedium is supported by a structure submerged in the pond so as to substantially immobilize the biomedium. 8. The method according to claim 7, wherein the submerged structure is placed in the aeration pond so as to minimize hydraulic power or flow acting on the microorganism. 9. The method of claim 1, wherein the biomedium has a plurality of fibers on which microorganisms are supported, wherein the fibers are made of a single composition. 10. The method according to claim 9, wherein the composition is polyvinylidene chloride. 11. The method according to claim 10, wherein the bio-medium is RING.
A method that is a LACETM brand adherent growth biomedium. 12. The method according to claim 1, further comprising: supplying the effluent of the aeration pond to a sedimentation basin; supplying the effluent of the sedimentation basin to a purification pond; Providing a shade to at least a portion of each of the sedimentation basin and the clarification pond to substantially prevent algae growth in any of the liquor, the sedimentation basin and the clarification basin. 13. A wastewater treatment apparatus, comprising: an aeration pond; abiotic flotation means for providing awning in the aeration pond; and a biomedium submerged in the aeration pond. .