CA1184131A - Method and apparatus for separating suspended solids from liquids - Google Patents

Abstract

METHOD AND APPARATUS FOR SEPARATING
SUSPENDED SOLIDS FROM LIQUIDS
ABSTRACT
Liquid which has been partially clarified in the settling zone of a clarifier tank is channelled through a filtration compartment containing a buoyant particulate filtration media. The media particles are periodically agitated so that trapped solids are separated from the media and retained in the clarifier tank.

Description

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METHOD AND APPARATUS FOR SEPARATING
_SPENDEDlb9C~b7~~]~ UIUS
BACKGROUND
The present invention relates to the separation of solid particles from a liquid suspension. More specifically, it relates to the removal of suspended solids from liquid which has been partially clarified by gravitational separation in a clarifier tank.
The use of clarifier tanks for the gravitational separation of solids from liquids is well known. Such tanks have been used for separating precipitates formed in chemical processes and for a variety of other industrial purposes. One of the most well-known and widely practiced uses of gravitational clarification is the purification of water or liquid waste, such as water from municipal sewage.
Unfortunately, only a portion of the suspended solids contained in water or liquid waste can be effectively removed by gravitational clarification.
Water leaving a clarifier will normally contain a significant amount oE fine suspended solids. Further treatment to remove suspended solids from such liquid is thus required to obtain liquid of a high purity.
Typically, partially clarified liquid is piped to a location remote from the clarifier tank where it is processed in a tube settler, a sand filter or other conventional solids separation device.
Numerous filtration and other devices have been made to separate solids from a suspending liquid. For example, U. SO patent No. 3,343,630 to Rice et al. shows a filtration apparatus. Example 4 of that patent 3~
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describes the use of an upflow filter containing media comprised of materials having a densi~y somewhat less than that of waker.
More recent patents, UOS. No. 3,424,674 to Webber and U.S. NoO 4,115,266 to Ohshima show somewhat related upflow filtration systems containing buoyant media. Each of these prior systems has unique characteristics, but neither is particularly well suited for the purpose o~ separating suspended solids from partially clarified water or liquid waste which is the effluent of a clarifier tank.
Specifically, the above devices could not be integrally incorporated in a clarification system.
U.S. patent No. 4,062~775 to Pielkenrood and U.S~ patent No. 4,125,467 to Haddad et alO show devices containing multiple contactors which provide large areas of surface on which suspended solids can coalesce.
Haddad further shows ~he use of such material in a Dorr settling pond so that solid separation by yravitational settling and coalescence can take place in a single unit~
Although such devices might be useful for collecting solids and for other purposes r they could not sufficiently separate fine solids from clarified water or liquid waste. Even if a device shown in the Haddad or Pielkenrood patents could be used, a substantial amount of external processing equipment would be required to obtain high purity liquid from water or liquid waste which was partially clarified in a clarifier tank.

SUMMARY

The present invention is a method and appara-tus wherein water and liquid waste can be Ereed of suspended solids by a gravitational clarifica-tion-filtration operation which, using an uncomplicated mechanism in a single vessel, can bring waste water or other liquid waste to an extremely low solids content.
The filtra-tion apparatus comprises a compartment having an inlet and an outlet arranged in such a manner that the liquid to be filtered flows upwardly through the cornpartment. The compartment contains a normally immobile bed of particulate media of less density than the liquid to be filtered. The bed is contained in the compartment in such a manner that the liquid to be filtered rlows upwardly through the bed such that the solids in the liquid are collected in the pores of the particulate media.
Apparatus is provided for periodically cleaning collected solids from the bed. The apparatus consists of means for periodically increasing the volume of the bed without removing any media from the compartment or creating a counter current flow of fluid through the bed.
This is accomplished by constructing the cleaning means to expand the bed downwardly, away from the outlet, to such an extent that the solids collected in the particula-te media are released from the pores and separated from the media.

., ,~; , In some embodiments, the cleaning appara-tus comprises means to agita-te and/or expand the filter media which makes up the bed. Agita-tion or expansion of the bed causes trapped solids to separate from the filter media whereafter the solids descend by gra~ity to the bottom of the clarifier tank where they combine with the sludge layer. Agitiation and/or bed expansion can be accomplished by mechanical stirring or pumping of the filter media, by gas injection or by liquid backwashing.
Because the trapped solids are processed with the clarifier sludge, no separate solids handling facilities are required for processing filter sludge. It is thus possible to efficiently modify an existing clarifier tank to a construction and for operation --~-----------------~ ! - 3a -RJP/llg 12/16/8L 24385 A-l 1296C

accordiny to the present invention. ~nd, new installations for producing high purity liquid would require a minimal capital investment.
The present invention is particularly beneficial in sewage treatment systems. The clarifier filtration apparatus of the present invention makes it possible to accomplish both secondary and tertiary sewage treatment stages in a single tank which eliminates the need to pump effluent liquid from a clarifier to a separate filter. Gravitational separation, possibly assisted by flocculents, occurs in the clarifier tank, followed by a high efficiency, low headloss filtration of clarified waste water. Sludge from both the secondary stages is processed together;
and the flow of liquid through the clarifier tank does not need to be halted or diverted during filter bed cleaning.
It is an object of this invention to provide a compact apparatus for producing high purity liquid by the thorough separation of suspended solids from a stream of waste water or other liquid containing suspended solids.
A further object is to provide such an apparatus which is self contained in a single unit.
An additional object is to provide means for converting existiny clarifier tanks to perform a filtration of partially clarified liquids.
Another object is to provide a filter that includes a buoyant media so that the filter can be used in a clarifier tank without danger that filter media RJP/lly 12/16/81 24385 A-l 1296C

will somehow escape and combine with the sludge at the bottoin of the tank.
Yet another object is to provide an automated and substantially maintenance-free apparatus for removing solids from a clarified liquid.
Also an object is to provide a clarifier tank with a filtration apparatus that can be cleaned without interrupting the flow of liquid through the tank.
Various other objects and advantages of this invention will become apparent upon reading the following specification.

DRAWINGS

In the drawings:
Fig. 1 is a plan view of a circular clarifier and filtraton apparatus according to the present invention;
Fi.g. 2 is a partial, oblique, sectional view of the apparatus shown in Fig. l;
Fig. 3 is a partial, sec~ional view of a first alternate embodiment of the invention as it would appear if taken along line 3-3 of Fig. l;
Fig. 4 is a partial, sectional view showing a second alternate embodiment;
Fig. 5 i~ a partial, sectional view showing a third alterna-te embodiment;
Fig. 6 is a partial, sectional view showing a four~h alternate embodiment;
Fig. 7 is a partial, sectional view showing a fifth alternate embodiment;

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Fig. 8 is a plan view of a circular clarifier and filtration apparatus including an annular filtration compartment dlvided by radially extending walls into a plurality of chamber 5, Fig. 9 is a partial sectional view showing a sixth alternate embodiment;
Fig. 10 is a partial sectional view showing a seventh alternate embodiment;
Fig. 11 is a partial sectional view showing an eighth alternate embodiment; and Fig. 12 is a vertical, schematic view of a test clarifier and filtration apparatus according to the present invention.

DESCRIPTION
In most industrial and municipal waste processing and water purification installationst clarifiee tanks are used for the gravitational separation of suspended solids from liquids. Such tanks are constructed in a variety of shapes and sizes, most being generally rectangular tanks with vertical walls or circular cylindrical tanks of the type shown in Figs. 1,

2 and 12 of the drawings.
The various drawing figures show a typical clarifier tank 20 of the type used for secondary clarification of sewage. The illustrated tank 20 has a single, cylindrical sidewall 24 which deEines a settling zone 22. A bottom 26 completes the enclosure.
Rectangular tanlcs, having pairs of opposed side and endwalls, and tanks in other shapes, can also be used for clarification.

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The clarifier tank is provided with an inlet for waste water or other liquid waste and an outlet through which clarified liquid is discharged. In the illustrated embodimen-ts, the outlet is an effluent weir 34. The liquid level in the tank 20 is maintained substantially at a constant height by the height of the weir.
The weir 34 extends along the top of the sidewall 24 along all or part of its length. The top of the weir 34 is horizontal along its entire length and is positioned to comprise the lowest portion of the tank boundary so that clarified liquid leaving the tank flows over the weir 34. V-notch weirs of standard construction are suitable for most applications.
For the purpose of this discussion, "clarified"
or "partially clarified" liquid should be understood to mean any liquid which has passed through the settling zone 22 wherein some portion of any suspended solids is removed by gravitational separation.
A liquid collection trough or channel 38 is located outwardly of the weir to collect clarified liquid effluent. Typically, the channel 38 wiLl extend the ull length of the weir along the sidewall 24.
The effluent of a clarifier tank may sometimes be used directly for industrial or other purposes. But frequently, it is necessary to further treat the effluent liquid to remove fine particles which do not readily sepaxate by gravity in the clarifier. For example, to effectively reduce the turbidity of clarified waste water, the clarifier eEfluent might be ~ -7-

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piped from the channel 38 to a filtration unit for the removal of suspended fine solids.
According to various embodiments of the present invention, filtration apparatus is located directly on or within a clarifier tank. Such filtration devices take advantage of their proximity to liquid in the clarifier tank by including one or more chambers which contain a buoyant filter media disposed at or near the surface of liquid in the tank.
According to a first embodiment of the present invention, shown in Figs. 1 and ~, a high efficiency, low headloss filtration apparatus is formed inside the tank 20 by a vertical baffle 42 which is located inwardly of the weir 34 and which generally conforms to the shape of the weir. Specifically, the baffle 42 is a cylinder of smaller diameter than that of the concentrically cylindrical weir 34. The baffle extends to a greater height than the weir so that a compartment 44 is defined. The compartment is bounded on one side by the baffle 42 and on the other side by sidewall means including the weir 34 and sidewall 24.
Both the top and bottom of the compartment are open so that a downwardly facing annular inlet opening 46 connects the settling zone 22 with the compartment 44. The open top of the compartment is an annular compartment outlet opening 48 through which liquid flows to the weir.
A horizontal foraminous member such as a screen 52 extends between the baffle and sidewall means and is located in such a position to divide the compartment 44 ~ 8-RJP/llg 12/16/81 24385 A-l 1296C

into upper and lower regions. Positioned within the lower region of the compartment is a bed of particulate media 54 which has a density less than that of the liquid to be filtered. ~ecause the bed o~ the media is trapped beneath the screen 52 and maintained against the bottom surface of the screen due to buoyancy of the media, all partially clarified liquid from the settling zone 22 flows upwardly through the bed enroute to the weir 34. As partially clarified liquid moves through the bed, solids are separated and collect in the bed.
After an extended period of operation, the bed of media 54 will become clogged with collected solids so that flow through the bed will be reduced. In an extreme circumstance, the bed might become so clogged that flow would cease entirely and liquid would break an unobstructed passageway through the media. It is therefore necessary to provide a means for periodically cleaning the filter media to maintain a good flow of liquid through the hed.

The most advantageous methods Eor cleaning the media employ an apparatus for agitating the media particles 54 so that collected solids are shaken loose and can descend by gravity to the bottom 26 of the tank 20. As illustrated in Figs. 1 and 2, this apparatus may comprise means ~or mechanically circulating media particles 54 through a liquid ~o dislodge solids collected in the bed.
The illustrated sleaning apparatus includes a collector head 58 which connects to a conduit 60 extending to a pump 62~ A discharge conduit 64 extends ~3 _9_ 3~
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from the pump and terminates in outlet opening 66 which is located at a position below the inlet opening 46 of a compartment 44O This entire cleaning apparatus may be supported on a moveable scraper arm 68 which extends along the bot~om 26 of the ~ank 20 and connects to a rotary shaft at the center of the tank.
As the scraper arm 68 travels along the bottom 26~ it carries the collector head 58 through the compartment 44 along the lenyth of the weir. As it moves along, the pump 62 pulls a stream of liquid and some media particles through the opening of the collector head 58; and subsequently releases the stream through the outlet opening 66. As the media particles pass through the conduits and the pump, trapped solids are dislodged. Thus, when ~he stream is released at the outlet 66, the dislodged solids flocculate and se~tle to the bottom 22 of the tank. The buoyant media particles move upwardly and back into the compartment 44.
As the media particles travel upwardly through the liquid located beneath the compar~ment 44, they are washed by the passing liquid so that additional collected solids are shed from the media par~icles and fall to the floor 22 of the tank.
Fig. 3 shows another filter embodiment using a circulation mechanism for cleaning buoyant media.
~ he apparatus of Fig. 3 is related to the apparatus shown in Figs. 1 and 2. Accordingly/ so~e components shown in Fig. 3 are identifi2d by reference numbers used to identify analogous components shown in Fiys. 1 and 2. In Fig. ~, the cleaning means are RJP/llg 12/16/81 24385 A-l 1.296C

supported on a carriage 72 which extends above ~he clarifier tank 20. When used with a circular tank of the type illustrated, the carriage 72 is supported on the outer wall of ~he trough 38 by casters 74. The inner end of the carriage is supported by a ro~ating central shaft 76. The carriage 72 rotates as the shaft 76 turns so the collector head 58 is carried throuyh the compartment 44.
The outlet opening 66 is located at a distance behind the advancing collector head 58 so that there is no interference between particles returning to the bed and those being collected in the collector head 58.
This spaced relationship of the collector head to outlet opening 66 works well in a circular tank since the cleaning mechanism always revolves in a given direction and never approaches an endwall which would limit its travel.
In a rectangular tank, a carriage preferably would be supported at each end by casters riding on two opposite tank sidewalls and the carriage would move back and forth across the surface of the tank. With such an arrangement it would be advantageous to have the collector head 58, outlet opening 66 and other components of the cleaning mechanism subs~antially aligned in a vertical plane. A cleaning mechanism so arranged could most closely approach the endwalls of the rectangular tankO
Other emdodiments of the invention are i.llustrated in Figs~ 4 and 5O In both these embodiments, the baffle means comprises two separate ~11 -L.~
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baffles 80, 82 spaced apart from one another. Both of the baffles 80, 82 extend to a greater height than the weir 34 ancl are located inwardly from the weir so that a filter compartment 84 is defined beween the ba~fles at a location inwardly of the weir. Preferably, the baffles 80, 82 will conform to the weir so tha~ in a circular tank, the weir 34 and baffles 89, 82 will comprise three concentric cylindrical walls.
A submerged div,ider 86 extends inwardly from the sidewall 24, below the baffle 80 and upwardly into the compartment 84 so that the top of the divider 86 is located at a level below the top of the weir 34. The compartment thus has a downwardly facing inlet opening 88 which is defined between the divider 86 and the baffle 82 which is furthest from the sidewallO The inlet opening 88 connects the settling zone 22 with the compartment 84.
A downwardly facing outlet opening 90 is defined between the divider 86 and the baffle 80 which is nearest the sidewall 24. This outlet opening 90 connects the compartment 84 with a re~ion 92 which exists between the baffle 80 on one side and the sidewall 24 and weir 34 on the other side.
In the embodiments of Figs~ 4 and 5, buoyant filtration media 94 is contained between the baffles 80 82~ Because the media is less dense than liquid which flows through the bed to the weir 34, it is retained between the baffles 80, 82 so long as liquid in the tank 20 is maintained at a predetermined minimum level.
Because the baffLes 80~ 82 are higher than the weir 34, 3:~
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neither liquid nor media can be carried over the baffles into the region 92. En route to the weir 34, liquid flows through the inlet opening 88 over the divider 86, passing through the bed of media 94, then through ~he outlet opening 90 and into the region 92 before discharge over the weir 34.
In both the embodiments of Figs. 4 and 5, one or more pu~ps are provided for periodically removing a portion of the media 94 from the compartment 84 and for releasing the removed portion oE media at a position below the compartment so that the removed portion rises through liquid located beneath the bed. In both the illustrated embodiments, these pump mechanisms are mounted on an overhead carriage 72.
The particular embodiment of Fig. 4 shows a cleaning apparatus having collector 98 which extends into the inlet opening 88. The collector 98 comprises the open end of a conduit 100 which connects to the first of two pumps 102. A conduit 104 extends Erom the second of the pumps 102 and terminates in an outlet opening 106 which is located beneath the compartment 84 in such a positiQn that material discharged from the outlet opening 106 enters the compartment 84 through the outlet opening 90.
The appara~us of Fig. 4 is thus cons-tructed to remove media through the inlet opening 86~ and replace the media through the outlet opening 90 so that the media travels through the compartment 84 countercurrently to liquid moving through the compartment from the inlet opening 88 to the outlet ' ~ -13-RJP/llg 12/16/81 24385 A-l 1296C

opening 90. Thus! the fraction of media which contains the greatest amount of trapped solids is removed while the cleaned media is replaced at the downstream end of liquid flow through the compartment 84.
As previously described, suspended solid material collected in the media is dislodged as the media travels through the circulation system including the conduits 100, 104 and pumps 102. Liquid discharged through the outlet opening 106 thus includes media which is substantially clean and solid particulate material which was separated from the media. The solid waste material, which was increased in particle siæe due to collection in the media, descends by yravity to a floor portion 110 of the divider 86. The solid waste material may be collected from the floor 110 by any o the methods co~nonly used to collect sludge rom the bottom of a clarifier tank~ Scrapers, drain outlets, or siphon mechanisms can be employed.
To provide added agitation for cleaning the particulate media 94, a washer apparatus 114 can be included between the pumps 102. Such a washer apparatus could include a blender or agitator to more thoroughly agitate ~he particles and thereby separa~e absorbed solids. Also, the washer 114 could include apparatus for washing the media with a stream of liquid in such a manner that solids separated from the media are carried off with a flow of effluent washing liquid. If such a washer is used, there is no way or solids to reenter the clarifier tank through the outlet opening 105 so that no substancial collection apparatus wowld be required to clear solids from the floor portion 110.

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The embodiment of Fig. 5 completely avoids the problem of solids settling on the floor portion 110. In this embodiment, particles of media and liquid are removed from the compartment 84 through a collector 118 which is the open end of a conduit 120 that extends into the outlet openlng 90. Media and liquid are pumped through the conduit 120 by means of a pump 122. The mixture of media and liquid is returned to the settling zone 22 through a conduit 124 which terminates with an outlet opening 126.
The media and liquid traveling through the compartment 84 move concurrently so that liquid entering the compartment 84 first contacts the cleanest media.
Media containing the greatest amount of trapped solids is removed by the cleaning apparatus through the outlet opening 90.
A particularly advantageous feature of the embodiment shown in Fig. 5 is that the divider 86 inGludes a downwardly facing ramp surface 130 which ex~ends generally upwardly and away from the sidewall 24. The media circulation mechanism is constructed with its outlet opening 126 located below this ramp surface 130 so that media particles discharged from the outlet opening 126 rise until they contact the ramp surface 130. Thereafter, the particles move along the ramp surface and eventually back into the compartment 84 through the inlet opening 88. The divider 86 can be hinged to the sidewall ~4 so that the tilt of the ramp surface is adjustable.

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As mentioned above, the arrangement of Fig. 5 substantially eliminates any need for collecting solids on the floor portion 110 of the divider 86. It is a further advantage that contact between particles of media 94 and the ramp surface 130 enhances the separation of solids from particles of media 94 due to frictional contact between the ramp surface 130 and the particles. Because the ramp surface 130 extends over the settling zone 22, solids separated from the media particles fall to the bottom of the separating zone 22 by gravity and are collected with sludge which accumulates at the bottom of that zone.
Figs. 6 and 7 show still other embodiments of the present invention. In many respects, the embodiments of Figs. 6 and 7 are similar to those shown in Figs. 2 and 3. Accordingly, analogous features are similarly numbered.
The embodiment shown in Fig. 6 incorporates a gas injection means for cleaning particles of media 54 by introducing a stream of gas bubbles into the filter bed. This is accomplished by providing a distribution conduit 134 which is connected to a source of pressurized gas, such as air~ Feeder lines 136 extend from the conduit 134. Each of the lines 136 terminates with a gas injection orifice 138 which is located at a position belcw the bed of media 54. As illus~rated in Fig. 6, the orifices 138 are posi~ioned between the sidewall 24 and the baffle 42 so that all gas will pass upwardly through the bed~

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sursts of air are periodically injected -through the orifices 138 to agitate media 54 which forms the bed. This agitation causes the separation of solids trapped in the bed. After separation, solids fall to the bottom 26 of the clarifier tank where they combine with sludge at the bottom of the tank and are collected by ordinary means.
Fig. 6 further illustrates the use of means to prevent media 54 from being carried into the settling zone 22 should there be a reduction in the level of liquid in the compartment 44. This media retention means comprises a second foraminous panel such as a screen 142 which extends between the sidewall 24 and the baffle 42. Should the level of liquid in the settling zone 22 drop below the bottom of the baffle 42, none of the particulate material will escape into the settling zone, but will be retained above the screen 142.
Fig. 7 illustrates another arrangement for preserving media inside the compartment 44. This embodiment comprises a normally submerged trough defined by a wall 148. The outermost end 150 of the wall 148 is located above the bottom of the baffle 42 so that liquid will be maintained in the trough at ~he level of ~he end 150 even iE the settliny zone 22 is drained of liquid.
Thusr particles of particulate media 54 can not descend below the level of the baffle 42, because the trough always remains filled with liquid.
Solids separa~ed from the bed in media 54 will collect in the trough of Fig. 7 when the bed of media is agitatedr so means must be provided for removing ~ -17-3~
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separated solids from the floor of the trough. The illustrated suction collector 152 and pumps 154 can be used for that purpose. Other devices, such as drain outlets or siphon collectors, could also be used. The solids collection mechanism, including pump 154, is suspended fro-ln an overhead carriage (not shown)O Means for agitating particulate media 54 could be of the type shown in Figs. 3 or 6 or some similar device~
Fig. 8, which is a plan view of the apparatus shown in Fig. 6, illustrates a filtration compartment divided into a plurality of small chambers. In this particular embodiment, the sidewall 24 and weir 34 forrn a cylinder concentric with the baffle 42. A plurality of substantially vertical divider walls 158 extend radially through the compartment 44 to divide the compartment into a plurality of chambers. By dividing the compartment in this manner, it is possible to assure that the distribution of media is sub~tantially uniform throughout the entire compartment. Periodic cleaning can be accomplished by operating a cleaning apparatus in one chamber a~ a time while uninterrupted filtration proceeds in oth r chambers.
A separate, vertically moveable weir segment can be provided for each chamber. The weir segment of any given chamber could be raised to stop the flow o~
liquid from that chamber into the trough 38 during cleaning of that chamber This would eliminate any possibility of an inadvertent discharging of separated solids into the trough 38 during cleaning of the chamber.

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Still other means for agitating the media particles are shown in Figs. 9 11. In Fig. 9, particles of media 54 are retained beneath the screen 52. For cleaning, khe particles are agitated by a mechanical agitator rake apparatus 170 which is mounted to an overhead carriage~ As the carriage moves along sidewall 24 9 the agitator rake 170 is drawn through the bed of media 54 thereby agitating the media particles and dislodging collected solids. The fingers of the rake may be fixed or may be rotatably mounted. If rotatable, the fingers can include directionally oriented veins which facilitate rotation and thereby multiply the agitation which results as the rake 170 is drawn through the bed. ~lso, a stream of air may be delivered to the rake 170 and injected into the bed from outlets on the rake to further agikate the media.
Fig. 10 shows a very simple apparatus which is especially well suited for use in rectangular settling tanks. In this embodiment, the baffle 42 is mounted to the sidewall 24 by means of an expandible device such as a telescoping shaft 174. No screen extends between the sidewall 24 and baffle 42, but a vertical screen 176 extends upwardly from the weir 34.
To agitate particles using the apparatus of Fig. 10, the bafle 42 i5 moved away Erom the sidewall 24 by extending the telescoping shaft 174 so that the bed widens and becomes more shallow. During lakeral expansion of the bed, particulate media is less closely packed than when the bed is ak rest~ Due to the dispersion and movement of media particles through ~19-3~
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liquid in the compartment 44, collected solids are separated and fall to the floor of the settling zone.
Like the embodiment of Fig. 10, the apparatus of Fiy. 11 includes a vertical screen 176 which extends upwardly from the weir 34. In this embodiment the baffle 42 is mounted in a fixed position, and a skimm2r mechanism 180 is included to move across the surface of the bed and thereby agitate the media.
The illustrated skimmer 180 is suspended Erom an overhead carriage and includes a collector head 182 wi~h a downwardly opening orifice connected by a conduit 184 to a pump 186. The pump pulls a stream of clarified liquid and particles of media 54 from the top of the bed. The stream moves through the conduit 184 into the conduit 188 and is discharged through an outlet opening 190. The outlet opening 190 is located beneath the bed of media 54 so the discharged media rises ~o the bottom oE the bed and solids separated from that media, due to agitation while being pumped through the conduits 184, 188, fall downwardly to the bottom of the settling zone.

Operation All the illustrated embodiments of the invention operate in a similar manner. The basic me~hod of operation is best understood with reference to Fig.
12 which schematically illustrates a test clarifier oE
the type specifically shown in Fig. 6.
A stream of li~uid water or liquid waste containing suspended solids is carried into a clarifier tank 20 via an inlet line 202. The line 202 opens into the tank's center well which is defined by a cylindrical , ~ -20-.~

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wall 204. Because the wall 204 is higher than the weir 34, liquid deposited in the well via -the inlet pipe 202 flows from the well through the settling zone 22 en route to the weir 34 which is the outlet over which liquid escapes from the tank 20.
The rate at which liquid is introduced through the line 202 and the size of the settling zone 22 are selected so that the liquid is retained in the settling zone for a period of time sufficient that suspended solids in the liquid are gravitationally separated and descend to the bottom 26 of the tank 20. Solids on the tank floor are moved to the center of the tank by the scraper arm 68 to be removed through the drain line 206. Liquid, partially clarified in the settl.ing zone 22, leaves the tank 20 by passing over the weir 34O On its way to the weir 34 a stream of the partially clarified liquid passes through the bed of particulate filtration media 54. As the liquid passes through the bed, solids remaining in the par~ially clarified liquid are collected so that the effluent liquid is substantially free of solids.
In the particular embodiment illustrated in Fig. 12, cleaning of the media 54 is accomplished by periodira].ly injecting air through the oriices 138.
The media 54 is agitated to such an extent that solids collected in the bed are separated from the media and descend by gravity through the inlet opening 46 to the tank bottom 26.
A number of tests have been conducted to determine t.he suitability of the present invention for ~ ~ -21~

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the purification of a partially clarified liquid. These are discussed in the following examples.

A five foot plexiglass cylinder, having a 5 3/~
inch inside diameter, was supported vertically. The top and bottom ends of the cylinder were closed except that a 5/16 inch tube extended through the top closure to carry effluent liquid out of the cylinder and a similar tube was provided through the bottom closure to supply influent liquidO
A circular wire screen was positioned six inches below the top of the cylinder to limit the upward movement of buoyant media inside the cylinder. A
suEficient amount of media, polyethylene beads of 3 mm.
diameter, was introduced so that a 12 inch layer of media formed beneath the screen when the cylinder was filled with liquid. A variable speed pump was used to maintain a flow of influent liquid into the cylinder via the tube extending through the bottom closure.
To test the suitability of this filtration apparatus, water from the effluent channel of the Albany, Oregon sewage treatment plant was pumped through the influent tubing into the base of the plexiglass cylinder. The liquid flowed upwardly ~hrough the cylinder, the bed of filter media beads and the screen~
It then left the cylinder through the tube which extended through the top closure.
Flow rate was established at -Eour hundred milliliters per minute to simulate a typical overElow rate for the final clarifier at the Albany sewage ~ 2~-3~' RJP/llg 12/16/81 24385 A 1 1296C

treatment plant. Four hundred milliliters per minute was selected as a conservative figure to account for the increased flow rate which ~ould result during a period of heavy rain fall.
After operating for eight hours, influent and effluent samples were obtained. The pump was then disconnected and the top closure removed from the cylinder. The beads were agi~ated with a rod so that the solids lodged in the filter media would be released. After obtaining a complete mixture by agitation and stirring~ a sample of the mixture was collected. Analysis of the samples showed that up to 10.0 mg. oE suspended solids were removed from ea~h liter of water passing through the apparatus.
During operation of the apparatus, it was noticed that turbulence from the inflowing liquid would stir the bottom inch of the beads in the bed but that the top eleven inches remained stationary~ After three hours of operation, a visible amount of suspended solids had been trapped in the lower inch of stationary beadsO
There was also a noticeable color difference between the influent liquid below the beads and the six inches of effluent above the screen.
A~ter eight hours~ tr~pped particles were visible in the lower four inches of the sta~ionary beads. When the flow was stopped and a valve was opened briefly to create backflow, the resulting turbulence caused the beads to release trapped solids which immedlately began to settle to the bottom Q~ the cylinder.

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The test of Example L was repeated at a higher liquid flow rate of two liters per minute. This was done to approximate the cond:itions which would result if a band of filter media were located at the outer edge of a clarifier to form a filter of the type shown in the drawings.
An analysis of samples obtained during this test showed the removal of up to 6.6 mg~ of suspended solids per liter of water~

A second series of test runs were conducted using a box-like test filter of 16 inches by 16 inches in cross section. The filter contained a twenty-four inch bed of polyethylene beads approximately three millimeters in diameter and 0.952 in specific gravity.
The beads were retained in position by a screen covering the top of the filter. A bottom screen was installed about thirty inches below the top screen to provide suXficient room for bed expansion during cleaning.
The test apparatus was operated as an upflow filterO The Eirst four of six runs were conducted using secondary clarifier effluent rom the package activated sludge sewage treatment plant of the city of Philomath, Oregon as influent for the filterO
The influents used in runs 5 and 6 ~ere formulated by adding a small amount of mixed liquor to the secondary clarifier effluentO The result was a composite fluid which contained a somewhat higher solids concentration than the secondary clarifier effluent.

The results of these tests are sum~arized in Table I:

Ln O ~ o~ Ln ~ ~ r~ r o i U~ U~
o ~ ~r ~ o o o L-) o r-o o ~ ~ ~ ~ ~ ~
H

~ ~P Lr~ ~ I el~ ~ O ~ ~
~ oo a~

n . ~
O ()O ,~d' ~1 1-- I L-)L~
O O I O O O O O

H~I L~ O
H ~ 1 ' ~ ~1 I t~ 0 C

o o o~
~1 H t~

Lt I t o o o1~o ~ o o ~t ~ t l~ ~ ~St ~ r` ~ , Lt ~t ~ ~ ~ ~ ~~ L~t Lrt , n ¦ ,~, O Lr t ~ tr) d' ~ ~ L~ 9 ~ Lt t- _ O ~) Lt Lt S-l Lt Lt ) ~
~ ~ 3 ~ 3 ~ ~ ,~ u 1 'O ~ ~r ~ V
~ g~ ~t ~ g~ Ct ~ Lt .~ '~
'~
r ~ ~ *

3~L
RJP/llg 12/L6/81 24385 A-l 1296C

Several methods were used to clean filters during the test runs. Both downward water je-tting and air scouring were found to be effective~
Water jetting was accomplished using a jet of water issued from a 1/8 inch tube at a pressure from 20 to 55 pounds per square inch. A single jet would agitate an area of media about four inches in diameterO
A suitable cleaning system could thus be constructed by arranging a fixed nozzle array of twelve 1/8 inch nozzles per square foot of media bed to accomplish cleaning in about 15 seconds. Alternatively, a single jet could be used to sweep across the media bed.
Air scouring was performed by supplying air beneath the bottom screen of the test apparatus through a diffuser. The air orifices were 1/l6 inch in diameter and were spaced at intervals of three inches. About four orifices were required per square foot of media.
The amount of air required for effective cleaning varied with the depth of the media. To effectively clean a bed of media two feet deep, about three cubic feet per minute per square foot of media bed surface was necessary for a filter operating at an upflow rate of six gallons per minute per square foot. The amount of air required for effective cleaning increased as the depth of the media bed or ~he filter upflow rate was increased.
During either water jetting or air scouring cleaning, most of the solids detached from the media would settLe to the tank bottom. But, a small fraction o~ separated solids would be carried over to the ~ -26-RJP/llg 12/16/81 24385 ~-1 1296C

effluent side if liquid continued to flow upwardly through the disturbed bed. It appeared that ten to twelve percent of the collected solids would escape with the filter effluentl if liquid flow through the filter was maintained during a cleaning operation, Thus, if high filter effluent quality is critical, flow of liquid through the filter should be stopped during the cleaning cycle. For a filter contained within a clarifier tank as illustrated in the drawinys, the flow of clarifier influent could be halted during filter cleaning. But, such a flow stoppage would~ however, be disruptive to plant operation.
Continuous operation could be maintained by using a filter compartment divided into multiple chambers. A
single chamber could be isolated and cleaned while flow continues through all other chambers. This procedure avoids the necessity of periodically stopping the entire flow of clarifier influent and effluent.
EXA~IPLE 4 Tests were conducted in a nine foot circular clarifier with a ten foot sidewall diameter, using apparatus substantially as diagrammed in Fig. 12. The filtration compartment 44 extended around the perimeter of the clarifier and was divided into two chambers by ver~ical divider walls. The chambers each enclosed a total horizontal area of 3.2 square feet~
A firs~ of the chambers contained a two foot bed of polyethylene beads which were about th~ee millimeters in diameter. The beads were contained between the two horizon~al screens S2, 142 made of No.

RJP/]lg 12/16/81 24385 A-l 1296C

10 screening. The top screen was about 12 inches below the top of the effluent weir 34 and the bottom screen 142 was located three feet below the top screen 52. A
steel baffle 42 was positioned concentric to the existing clarifier weir.
The second chamber was not filled wi~h filter media. Rather, its portion of the weir was blocked off;
and regulated flow from the second chamber was obtained using a siphon. The flow rate through the siphon was matched to flow rate through the filter media in the first chamber to substantially equalize the clarifier hydraulics.
In this series of tests, eight runs were conducted using influent liquids obtained from the Philomath, Oregon sewage treatment plant. The first six runs were made using mixed liquor having a suspended solids conkent which ranged from 1280 to 2140 mg. per liter and averaged about 1710 mg. per liter. The average sludge volume index of the mixed li~uor supplied to the test clarifier was 411 and fell within a range of 182 to 608. Runs seven and eight were conducted using an influent of clarifier effluent from the Philomath sewage treatment plant. The results of these test runs appear in Table II.

-2~-.~

3~L' ~ ~ 1 o ~ D
.

o^l c~
3 o o o o ~$
I
~P ,~

O ~ O d~
.,, ~ . ~ ~ ,, ~ ~ o ~ ~ o o o o o o ~ .~
o o o ~
H~1 ~ ~1 ~ . . , . . , r~

o o ~1 ~ ~ . ~ o o ~r cc, c;~
~ H 5~ ~~1 ~ ~C~ ~ ~1 ~1 a ~ 1 8 8 o o o o ~ W S~

o o ~ o o o ~ ~ ~ 8 o~
8 ~ ~ o ~ o 5~ H
~ 8 ~ 8 ~

~,9 ' ,~h

4~

RJP/llg 12J16/31 24385 A~l 1296C

During the first six runs, mixed liquor was fed to the center well of the clarifier at a rate of about twenty-one gallons per minute. The rate of sludge withdrawal through the drain line 206 was about thirteen gallons per minute. Because of poor settleability of the mixed liquor used during the test, no clear sludge interface could be located. Samples used to determine the filter influent solids content were taken at a level just below the bottom screen 142.
After each run, the filter was cleaned by air scouring, using air injected through the orifices 138.
Although most of the separated solids descended to the bottom of the tank 20, some wash out solids stayed in suspension on top of the media and then were carried over the weir 34 when filtration was resumedO Some mud balls were formed in the compartment 44 during the test. Some of these were larger than the screen openings and thus could not descend to the floor of the tank 20 during cleaning. By adopting an apparatus that omits the bottom screen 142, any difficulty resulting from mud ball formation is eliminated.
While I have shown and described the preferred embodiments of my invention, it will be apparent to those skilled in the art that changes and modifica~ions may be made withou~ departing from my invention in its broader aspects. I therefore intend the appended claims to cover all such changes and modifications as follow in the true spirit and scope of my invention.

~ -30-, ~,`
h,

Claims (25)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A filtration apparatus comprising:
a compartment having an inlet and an outlet arranged so that liquid flows upwardly through the compartment;
a normally immobile bed of particulate media of less density than the liquid from which solids are to be filtered, the bed being contained in the compartment in such a manner that liquid flows upwardly through the bed so that solids in the liquid are collected in pores of the bed; and cleaning means for periodically increasing the volume of the bed, without removing any media from the compartment or creating a countercurrent flow of fluid through the bed, the cleaning means being constructed to expand the bed downwardly, away from the outlet, to such an extent that solids collected in the bed are released from the pores and separated from the media.

2. A filtration apparatus for installation on a clarifier tank which tank defines a settling zone and includes an inlet means for delivering liquid with suspended solids into the settling zone, wherein the liquid is partially clarified, the filtration apparatus comprising:
containment means for defining a compartment having an inlet and an outlet, the containment means being constructed to mount on a clarifier tank in such a position that liquid flows upwardly through the compartment after the liquid is partially clarified in the tank;

a normally immobile bed of particulate media of less density than the liquid, the bed being contained in the compartment in such a manner that liquid in the compartment flows upwardly through the bed so that solids in the partially clarified liquid are collected in pores of the bed; and cleaning means for periodically increasing the volume of the bed by agitating the media without removing any media from the compartment or creating a countercurrent flow of fluid through the bed, the cleaning means being constructed to expand the bed downwardly, away from the outlet, to such an extent that solids collected in the bed are released from the pores and separated from the media.

3. An apparatus for removing solids from liquid water or liquid waste comprising:
a clarifier tank defining a settling zone wherein liquid is partially clarified by gravitational separation of suspended solids from the liquid;
inlet means for delivering liquid with suspended solids into the settling zone, filtration means including a compartment having an inlet and an outlet arranged so that liquid flows upwardly through the compartment, and a normally immobile bed of particulate media of less density than the liquid, the bed being contained in the compartment in such a manner that liquid flows upwardly through the bed so that solids in the partially clarified liquid collect in pores of the bed, the bed being positioned so that partially clarified liquid leaving the settling zone flows through the bed;

cleaning means for periodically increasing the volume of the bed by agitating the particulate media without removing any media from the compartment or creating a countercurrent flow of fluid through the bed, the cleaning means being constructed to expand the bed downwardly, away from the outlet, to such an extent that solids collected in the bed are released from the pores and separated from the media.

4. An apparatus for waste water purification comprising:
a clarifier tank defining a settling zone wherein waste water is partially clarified by gravitational separation of suspended solids from the waste water;
inlet means for delivering waste water with suspended solids into the settling zone;
filtration means including a compartment having an inlet and an outlet arranged so that liquid flows upwardly through the compartment, and a normally immobile bed of plastic beads of less density than the liquid and of a diameter no greater than 10 mm., the bed being contained in the compartment so that partially clarified liquid leaving the settling zone flows upwardly through the bed so that solids in the partially clarified liquid collect in pores of the bed; and cleaning means for periodically increasing the volume of the bed, without removing any media from the compartment or creating a countercurrent flow of fluid through the bed, the cleaning means being constructed to expand the bed downwardly, away from the outlet, to such an extent that solids collected in the bed are released from the pores and separated from the media.

5. An apparatus for removing solids from liquid water or liquid waste comprising:
a clarifier tank including a bottom and sidewall means which define a settling zone wherein liquid is partially clarified by gravitational separation of suspended solids from the liquid;
inlet means for delivering a stream of liquid with suspended solids into the settling zone;
outlet means comprising a horizontal weir which extends along the top of at least a portion of the sidewall means and which is the uppermost extension of that portion of the sidewall means;
filtration means including a generally vertical baffle means extending along and spaced from the weir to define a compartment with inlet and outlet opening located so that liquid partially clarified in the settling zone flows upwardly through the compartment;
located within the compartment, a normally immobile bed of particulate media of less density than the liquid, the bed being positioned so that the partially clarified liquid flows upwardly through the bed and solids in the partially clarified liquid collect in pores of the bed; and cleaning means for periodically increasing the volume of the bed by agitating the particulate media without removing any media from the compartment or creating a countercurrent flow of fluid through the bed, the cleaning means being constructed to expand the bed downwardly, away from the outlet, to such an extent that solids collected in the bed are released from the pores and separated from the media.

6. An apparatus according to claim 5 wherein the cleaning means comprises means for introducing gas bubbles into the bed.

7. An apparatus according to claim 5 wherein the cleaning means comprises means for mechanically circulating the particulate media through a liquid to dislodge the solids collected in the bed,

8. An apparatus according to claim 5:
constructed to contain a volume of partially clarified liquid beneath the bed; and wherein the cleaning means comprises a pump for periodically removing a portion of the media from the bed and for releasing the removed portion at a position beneath the bed so that the removed portion rises through the partially clarified liquid located beneath the bed.

9. An apparatus according to claim 5 wherein:
the baffle means comprises a baffle which is located inwardly of and conforms to the weir and which extends to a greater height than the weir so that the compartment is defined between the baffle and the sidewall means and has a downwardly facing inlet opening connected to the settling zone and an upwardly facing outlet opening through which liquid flows to the weir; and the filtration means further comprises a foraminous means extending between the baffle and the sidewall means in a position to prevent the media from being carried upwardly through the outlet opening.

10. An apparatus according to claim 9 further comprising media retention means to prevent the media from being carried into the settling zone when there is a reduction in the level of liquid in the compartment.

11. An apparatus according to claim 10 wherein the media retention means comprises a foraminous means extending between the baffle and the sidewall means in a position to prevent media from being carried downwardly through the inlet opening.

12. An apparatus according to claim,10 wherein the media retention means comprises means for maintaining the level of liquid in the compartment above the bottom of the baffle.

13. An apparatus according to claim 12 wherein the media retention means comprises trough means constructed to contain the filtration means and to contain liquid at a predetermined level which is above the bottom of the baffle.

14. An apparatus according to claim 5 wherein:
the baffle means comprises two baffles spaced from one another, both of the baffles extending to a greater height than the weir and being located inwardly of and conforming to the weir so that the compartment is defined between the two baffles at a location inwardly of the weir; and the filtration means further comprises a submerged divider means which extends inwardly from the sidewall means, below the baffle nearest to the sidewall and upwardly into the compartment to a level below the weir so that the compartment has a. a downwardly facing inlet opening which is defined between the divider means and the baffle farthest from the sidewall and which is connected to the settling zone, and b. a downwardly facing outlet opening which is defined between the divider means and the baffle nearest to the sidewall and which is connected to a region between the weir and the baffle nearest to the weir.

15. The apparatus of claim 14 further comprising media circulation means for removing media from the bed through one of the openings and for returning the media to the bed through the other of the openings.

16. The apparatus of claim 15 wherein the media circulation means is constructed to remove media through the inlet opening and replace media through the outlet opening so that media travels through the compartment countercurrently to liquid moving therethrough.

17. The apparatus of claim 15 wherein:
the divider means includes a downwardly facing ramp surface which extends generally upwardly and away from the sidewall means; and the media circulation means is constructed to remove Media particles through the outlet opening and replace the particles by depositing the particles beneath the ramp surface so that as the buoyant particles rise, such particles move upwardly along the ramp surface, through the inlet opening and into the compartment.

18. The apparatus of claim 5 wherein:
the sidewall means and baffle means comprise substantially concentric cylinders; and the apparatus further comprises a plurality of substantially vertical divider walls extending radially through the compartment to divide the compartment into a plurality of chambers.

19. A filtration apparatus comprising:
a compartment having an inlet and an outlet arranged so that liquid flows upwardly through the compartment;
a normally immobile bed of particulate media of less density than the liquid to be filtered, the bed being contained in the compartment in such a manner that liquid flows upwardly through the bed so that solids suspended in the liquid are collected in the bed; and cleaning means including gas injection means for periodically injecting gas into the media, for periodically increasing the volume of the bed, without removing any media from the compartment or creating a countercurrent flow of fluid through the bed, the cleaning means being constructed to expand the bed downwardly, away from the outlet, in such a manner that solids collected in the bed are released from the pores and separated from the media due to gas injection.

20. A method for removing solids from a stream of liquid water or liquid waste comprising:
channelling a stream of liquid containing suspended solids into a settling zone defined by a clarifier tank;

retaining the liquid in the settling zone for a sufficient period of time that the liquid is partially clarified by gravitational separation;
channelling a stream of the resulting partially clarified liquid through a compartment which has an inlet and an outlet arranged so that liquid flows upwardly through the compartment and which contains a normally immobile bed of particulate filtration media of less density than the liquid so that solids in the partially clarified liquid are collected in the bed; and periodically agitating the media to such an extent that solids collected in pores of the bed are separated from the media.

21. A method for removing suspended solids from a stream of liquid comprising:
channelling a stream of liquid containing suspended solids through a compartment which has an inlet and an outlet arranged so that liquid flows upwardly through the compartment and which contains a normally immobile bed of particulate filtration media of less density than the liquid so that suspended solids are collected in pores of the bed; and periodically injecting gas into the media in such a manner that the volume of the bed is increased, the bed expand the bed downwardly, away from the outlet, the bed is expanded downwardly, away from the outlet, and solids collected in the bed are released from the pores and separated from the media, without removing any media from the compartment or creating a countercurrent flow of fluid through the bed.

22. A filtration apparatus comprising:
a compartment having an inlet and an outlet arranged s0 that liquid flows upwardly through the compartment;
a normally immobile bed of particulate media of less density than the liquid from which solids are to be filtered, the bed being contained in the compartment in such a manner that liquid flows upwardly through the bed so that solids in the liquid are collected in pores of the bed; and cleaning means for periodically increasing the volume of the bed, without removing any media from the compartment or creating a countercurrent flow of fluid through the bed, the cleaning means being constructed to include air injection means located in the compartment to periodically inject air bubbles into the bed to agitate the media particles and thereby expand the bed downwardly, away from the outlet, to such an extent that solids collected in the bed are released from the pores and separated from the media.

23. A filtration apparatus comprising:
a compartment having an inlet and an outlet arranged so that liquid flows upwardly through the compartment;
a normally immobile bed of particulate media of less density than the liquid from which solids are to be filtered, the bed being contained in the compartment in such a manner that liquid flows upwardly through the bed so that solids in the liquid are collected in pores of the bed; and cleaning means for periodically increasing the volume of the bed, without removing any media from the compartment or creating a countercurrent flow of fluid through the bed, the cleaning means being constructed to include means for periodically removing a portion of the media from the bed and releasing the removed portion at a position beneath the bed so that the removed portion rises through liquid located below the bed as the released portion moves upwardly and thereby expands the bed downwardly, away from the outlet, to such an extent that solids collected in the bed are released from the pores and separated from the media.

24. A filtration apparatus comprising:
a filter vessel which is open at the top and which is constructed to provide a compartment having an inlet and an outlet arranged so that liquid flows upwardly through the compartment;
a normally immobile bed of particulate media of less density than the liquid from which solids are to be filtered, the bed being contained in the compartment in such a manner that liquid flows upwardly through the bed so that solids in the liquid are collected in pores of the bed;
a bridge moveably mounted above the vessel to support cleaning and/or other apparatus which extends downwardly into the bed and moves therethrough as the bridge travels horizontally; and cleaning means for periodically increasing the volume of the bed, without removing any media from the compartment or creating a countercurrent flow of fluid through the bed, the cleaning means being constructed to expand the bed downwardly, away from the outlet, to such an extent that solids collected in the bed are released from the pores and separated from the media.

25. A filtration apparatus for filtration of liquid supplied from a pond having a liquid surface which is normally maintained at a substantially constant elevation, comprising:
a compartment including a downflow chamber and an upflow chamber through which chambers water flows vertically, the downflow chamber having an inlet which communicates directly with the pond at a location below the pond water surface, the upflow chamber having an inlet and an outlet arranged so that liquid flows upwardly through at least a portion of the compartment, the outlet being at an elevation below the pond water surface elevation, and the compartments communicating only at elevations below the downflow compartment inlet and the upflow compartment outlet;
a normally immobile bed of particulate media of less density than the liquid from which solids are to be filtered, the bed being contained in the compartment in such a manner that liquid flows upwardly through at least a portion of the bed so that solids in the liquid are collected in pores of the bed; and cleaning means for periodically increasing the volume of the bed, without removing any media from the compartment or creating a countercurrent flow of fluid through the bed, the cleaning means being constructed to expand the bed downwardly, away from the outlet, to such an extent that solids collected in the bed are released from the pores and separated from the media.