CA1043482A - Chemical treatment of waste water to remove phosphorus contaminants - Google Patents

Abstract

CHEMICAL TREATMENT OF WASTE WATER
TO REMOVE PHOSPHORUS CONTAMINANTS
ABSTRACT OF THE DISCLOSURE
Chemical treatment of waste water to remove phosphates is effected by coagulation in a rotating fluidized bed of chemical sludge.

Description

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The present invention relates to the chemical treatment of waste water to remove phosphate contaminants therefrom.
This application is a division of copending Canadian Application Serial No. 218,165 filed January 16, 1975. The parent application claims a multistage waste water treatment system which includes the chemical treatment process of this application. This application claims only the chemical treatment process.
In accordance with the present invention, there is provided a process for the chemical treatment of waste water containing at least phosphate materials in a single upright . -:
reaction tank which comprises: separating the reaction tank -; into a first vertically-extending zone extending upwardly .
from the bottom of the tank for part of the height thereof, . :.
a second vertically-extending zone extending upwardly from .` the bottom.of the tank to the height of the first zone and .~ in fluid 10w communication with the first zone at the upper end thereof only, and a third vertically-extending zone extending upwardly from the upper extremity of the first ' and second zones in fluid flow communication with the first ~ .
;............. and second zones; establishing a liquid level in the tank ~ .
' and a flow path of liquid through the tank downwardly through :- .
:~' the third and first zones respectively out of fluid flow . communication therewith and upwardly through the first and -...... -third zones respectively; establishing and maintaining a ...
$ rotating fluidized bed of chemical sludge in the .first zone; .
mixing the waste water with chemical coagulant; feeding the ;-~
mixture by gravity along the flow path from the upstream end thereof and tangentially into the lower end of the first :.
zone, pa~sing the mixture through the.rotating fluidized , - 2 - ~ : :
q ~, . . . .

bed of chemical sludge in the first zone; chemically coagula-ting the phosphate materials in the fluidized bed; passing treated liquid along the flo~ path through the third zone;
passing chemical sludge from the fluidized bed into the second zone to achieve separation of the treated liquid from chemical sludge in a separation zone; discharging : treated liquid having a decreased phosphate-materials content from the third zone at the downstream end of the flow path; and accumulating the passed chemical sludge in the second zone.
The invention is described further by way of illus- ,-tration with reference to the accompanying drawings, in which: : -, Figure 1 is a schematic representation of a waste water treatment system embodying the present invention;
Figure 2 is a sectional schematic representation of a primary treatment unit for use in the system of Figure :, ; l;
Figure 3 is a sectional schematic representation of a phosphate removal unit which utilizes the process of this invention and for use in the system of Figure l;
Figure 4 is a sectional schematic representation of an ozonation unit for use in the system of Figure l; and Figure 5 is a sectional schematic representation of a fixed bed adsorption-biooxidation unit for use in the system of Figure 1.
Referring to the drawings, a four-stage sewage ~.treatment system 10 provided in accordance with the inven-tion claimed in the aforementioned parent application - 30 includes a primary treatment 12, an adsorption-biooxidation ~,-treatment 14, a chemical treatment 16 and a fixed bed .

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adsorption-biooxidation treatment 18. Parc of the chemical treatment 16 constitutes the subject of this invention.

Raw comminuted sewage is fed by line 20 to the primary treatment 12. As may be seen in more detail in Figure

2, the primary treatment 12 occurs in a circularly cross-sectioned reactor 22. An inverted funnel-like member 26 is located within the container 22 and defines therewith a first chamber 28 between the funnel-like member 26 and the container ` 22, a sludge settling chamber 30 and a sludge separation chamber 32 inside the funnel-like member 26.
The funnel-like member 26 includes a skirt portion 34 concentric with and spaced inwardly from the inner wall of . the container 22, a truncated cone portion 36 and a throat : portion 38 also concentric with the container 22 and extending upwardly above the intended liquid level in the container 22.
The sludge settling chamber 30 also is defined by a tru`ncated conical wall 40 of the container 22 whereby the sludge settling chamber 30 has a decreasing diameter towards ~ ~

the base of the container 22. . .
A hollow riser tube 42 is positioned axially of . the-container 22 and extends through the sludge separation :
~ chamber 32 into the sludge settling chamber 30 to a location ;
,~ spaced immediately upwardly of the base of the container 22, the -j riser tube 42 flaring outwardly towards the lower end thereof.
~ A gas feed tube 44 is situated within the riser - .
; ., ... . -¦ tube 42 to feed air, oxygen or other gas into the riser tube 42 adjacent the lower end of the riser tube 42 to dr~aw sludge out of the settling chamber 30 into and up the riser tube 42 ~ -under the in~luence of the gas rising in the tube 42. -:
_ 4 _ ~:
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~)43482 The riser tube 42 adjacent its upper extremity but within the reactor 22 communicates with cross-arm members 46 extending radially of the container 22 which in turn com-municate with tubular discharge members 48 which include a downwardly-extending portion and a horizontally-extending portion.
The sewage is fed to the container 22 through pipe 24 and is mixed with recycling mixed liquor suspended solids fed from the dischargè members 48. The tangential dis-charge of the recycling MLSS causes rotation of the reacting liquor in the first chamber 28 about the axis of the oontainer 22.
The rotation of the material in the chamber 28 'applies centrifugal forces to the suspended solids, causing the solids having a specific gravity greater than the liquid medium to concentrate adjacent the inner wall of the container 22.
while the solids having a specific gravity less than the -- liquid tend to move towards the axis of the reactor 22.
Gravitational forces acting on the heavy solids causes them to settle towards the sludge settling chamber 40.
Anaerobic decomposition of the settled solids in the chamber 40 occurs, decreasing their volume and mass. The rotation of the solids in the chamber 28 provides the mixing required to speed up the anaerobic reactions.
The lighter suspended solids move upward with the waste water through the sludge separation chamber 32, wherein further gravitational separation of suspended solids occurs.
The microorganisms in the liquid consist~of facultative and anaerobic bacteria responsible for hydrolysis and fermentation of complex organic compounds to simple organic acids. The microorganisms tend to be retained and are recycled with the recirculating sludge in riser tube 42 and hence assist in hydrolyZing and decomposing the suspended solids.

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Tn this way, suspended solids present in the sewage feed in line 24 and separated in the chambers 28, 30 and 32 are continuously hydrolyzed and fermented, thereby continuous-ly decreasing their volume and mass. Thus, withdrawal of solids from the reactor 22 rarely is required, such withdrawal being made typically by pipe 50. The reac-tor 22 also tends to decrease the concentration of soluble organic matter and to e~ualize wide variations in soluble organic matter concentration in the feed sewage.
The processed waste water is removed from the upper portion of the chamber 32 through a pipe 52 for passage to the adsorption-biooxidation treatment 14.
The adsorption-biooxidation treatment consists of contact with activated carbon and a mixed microbial popula-tion in a reactor 54. This contact serves to remove organic matter, organic nitrogen, ammonia and nitrite and nitrate nitrogen from the processed waste water.
The waste water, if required, may be flash aerated from the reactor 54 by external flash aerator 56 ana passed by line 58 to a clarifier 60. In the clarifier 60, the bio- -logical reactions are extended, functioning thereby, in effect, as a second stage reactor. The suspended solids are separated from the liquid phase in the clarifier 60 by settling.
. ... .
The settled sludge mainly is withdrawn from the clarifier 60 `-by a flash aerator for recycle, after saturation with oxygen, to the reactor 54 by line 62. The clarified effluent is removed from the clarifier 60 by external riser 64 for dis-charge from the adsorption-biooxidation treatment 14 by line 66 to the chemical treatment 16. Excess sludge may be with-drawn from the adsorption-biooxidation treatment 14 by pipes 65 and 67 respectively associated with the reactor 54 and the clarifier 60.

The adsorption-biooxidation treatment 14 is described in more detail and forms the subject of U.S. Patent No.3,980,556.

Refe.rence may be had to the latter patent for additional process and constructional details of the reactor 54 and the clarifier 60.
The processed waste water in line 66 is passed to the chemical treatment 16, which consists of a phosphate re-moval unit 68 and an ozonation unit 70. The operations which are effected in the phosphate removal unit 68 con-stitute the present invention and are defined in the claims.
Prior to feed of the processed waste water to the phosphate removal unit 68, a chemical coagulant, typically alum, is added to the processed waste water by line 72. If, desired, additional chemicals such as hypochlorite may be ..
added, as may an anionic polymer by line 74.
As may be seen more particularly from Figure 3, the phosphate removal unit 68 consists of a cylindrical con-tainer 76 in which a conical body member 78 is positioned, defining a first chamber 80 between the conical body member 78 and the interior wall of the container 76, a second chamber '' 82 within the conical body member 78 and a third chamber 84 ,-located above the conical body member 78.
The processed waste water in line 66 with added chemicals is fed tangentially into the first chamber 80 through outlet pipe 86 of a hydrostatic head box 88 located in the upper portion of container 72. The processed waste water in line 66 also may include occasional loss of bio-logical sludge from the clarifier 60. This loss provides automatic and self-regulating control of the concentration ~ --of the microbial population in the adsorption-biooxidation treatment 14. ~' The ~irst chamber 80, which acts as a reaction chamber for phosphates, contains coagulated suspended solids, , "

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i.e. chemical sludge, which are maintained in a rota~ing fluidized bed. The rotation of the sludge in the first chamber 80 is maintained by the tangential inlet flow throughout outlet pipes 86 at the lower ends thereof and further by action of external riser tube 64 communicating with the first chamber 80 through opening 90.
The upflow velocity of the liquid in the first chamber 80 is responsible for fluidization of the coagulated particles in at least the upper portion o~ the chamber 80.
The upflow velocity is proportional to the flow rate of the waste water through outlet pipes 86 and to the cross-sectional area of the first chamber 80.
The chemical reactions between the added chemicals and the impurities occur in the lower portion of the first chamber 80 and the coagulation of the formed flocs occurs in the upper portion of the ~irst chamber 80. The coagulated flocs tend to form a layer of chemical sludge in the upper portion of the first chamber 80 which adsorbs impurities and hence tends to increase the overall removal efficiency of the unit.
The coagulated sludge overflows from the first chamber into the second chamber 82, which acts as a settling chamber for the coagulated sludge. The conical shape of the second chamber 82 causes thickening of the sludge therein. A
riser tube 92 extends axially through the unit and ~-terminates immediately above the base of the second chamber 82.
A gas flow tube 94 is positioned internally of the riser tube 92 for feed of air, or other gas, into the riser tube 92 adjacent the lower end thereof, the consequent upward flow of gas in the riser tube 92 causing material to be drawn from the second chamber 82 into and upwardly in the ,, ' ~, ; :''.

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riser tube 92 for discharge of the chemical sludge from the unit 68 through pipe 96,either continuously or intermittently, as desired.
The chemically-treated and clarified waste water flows upwardly from the first chamber 80 to the third chamber 84 for removal from the unit 68 throu~h pipe 98, Gases formed in the phosphate removal unit 68 may be vented therefrom by vent 99. Sludge accumulations in the first chamber 80 may be removed through pipe 101 as required.
The chemically-treated effluent from the phDsphate removal unit 68 in line 98 is fed by an external riser tube 100 into the ozonation unit 70 throu~h pipe 102. The oæonation unit 70 includes an outer cylindrical container 104 and an inner cylindrical tube 106 perforated at its lower end by perfora-tions 108.
; ~n ozone feed tube 110 is located axially of the inner cylindrical tube 106 and terminates at its lower end in a diffuser ring 112 located above the perforations 108.
The inner cylindrical tube 106 and the outer cylindrical container 104 define inner and outer chambers 114 and 116 respectively within the ozonation unit 70. An upper portion of the inner chamber 114 is packed with polyethylene -pall rings 118 or similar floating packing material. Simi-larly, an upper portion of the outer chamber 116 is packed with polyethylene pall rings 120 or similar floating packing material.
The liquid to be treated is fed by line 102 to .:~ ;the top of the inner chamber 114. As the waste water moves ::~
downwardly through the inner chamber 114 towards the perfora- -~
tions 108, it i8 countercurrently contacted with ozone and :
oxygen fed to the inner chamber 114 through the diffuser 112.

The waste water absorbs ozone and oxygen from the rising gas bubbles.
The downward velocity of the waste water through the inner chamber 114, which determines the contact time of the gas bubbles in the inner chamber 114 and hence the proportion of oxygen and ozone absorbed by the liquid, is less than the velocity of upward flow of the gas bubbles but greater than one-third of the velocity of a single bubble rising in stationary liquid.
As the concentxation of the ozone in the bubble volume decreases due to the diffusion of ozone into the ..
liquid as the gas rises in the inner chamber 114, a concen-tration gradient develops in the gas bubbles and the rate of , mass transfer decreases~
When the gas bubbles encounter the packing 118, they break down and reform. There results mixing of the gas in the volume of the bubble, disrupting the concentration gradient established in the radial direction of the bubble : and increasing the concentration of ozone and oxygen at the bubble surface, and hence increasing the mass transfer ra~e of the diffusing absorbing gases in the packing 118.
The presence of the ~oating packing 118 in the first chamber 114 prevents axial mixing of the liquid, thereby creating conditions for a continuous multistage abs~-ption. -The ozone saturated waste water exits from - -the first chamber 114 through perforations 108 into the lower portion of the second chamber 116. Suspended solids present ~e in the waste water settle out in the second chamber 116 and may be periodically removed from the ozonation unit 70 by line 122.
Oxidation of the contaminants present in the waste water occurs as the water rises in the chamber 116 first through the lower portion and then through the packing 120.
A fine precipitate is formed in the oxidation and is trapped in the packing bed 120. The volume of precipitate is very small and hence long continuous operation of the ozonation unit 70 is achieved before backwash of the packing bed 120 is required.
Oxidized waste water is removed from the ozonation unit 70 through pipe 124 located at the top of the second chamber 116. The o~idation of the waste water in the ozona-tion unit 70 results in an effluent of decreased colour, odo-and turbidity, containing chemically oxidized organic and inorganic compounds and is disinfected.
lf further treabment is required, the effluent from the ch ~ cal treatment may pass by line 124 to the fixed bed adsorption-biooxidation treatment 18. The adsorption-biooxidation treatment 18 is conducted in a cylindrical vessel 126, shown in detail in Fiqure 5, and having a multiple number of beds of different materials therein for percolation of the waste water feed in line 124 therethrough.
The waste water in line 124 is fed into the vessel 126 through a distributor 128 on the upper surface of ~
a bed 130 of granular activated carbon. Suspended solids -~ -are removed from the waste water by the granular activated --carbon bed 130 by filtration and the dissolved organic matter is removed by adsorption on the activated carbon. The concen-tration of organic matter on the surfaces of the activated carbon increases to the point where microorganisms can survive and biooxidation can occur.
The concentration of residual organic material in ' ' .:

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; the waste water in line 124 is very low and hence the dissolved oxygen present in the waste water is sufficient for the bio-oxidation and additional aeration is not required.
Backwashing of the fixed carbon bed 130 is requir~d only very infrequently and hence the microbial population in the media is acclimatised to the type of food present in the waste water. Therefore,the adsorptive capacity of the activated carbon is continuously restored by the microorganisms and ~¦ thus consistent removal of organic carbon from the waste water ! lo on the fixed carbon bed 130 is achieved.
Successive beds of anthracite 132, sand 134 and gravel 136 are provided for consecutive filtration of residual suspended solids from the waste water, the processed water being recovered from the vessel 126 through collector 1~8 and line 140.
' Valved backwash water and air feed lines 142 and l; . . . .144 respectively may be provided along with a backwash overflow line 146.
Ozone for the ozonation unit 70 is provided by -;
s 20 line 148 from any convenient source thereof. The air required for the flash aerators in the primary treatment vessel 22, -^ the adsorption-biooxidation reactor 54 and clarifier 60 and `~ the riser tubes 56, 64, 82 and 100 may be provided by a common : ~-air line 150 with suitable valving, as required.
The hydraulically-integrated waste water treatment .~ .
system 10 therefore provides a four-stage treatment of waste water to remove substantially completely contaminants from ;~
the waste water, including suspended solids, organic material, nitrogenous material, phosphates, coliform, turbidity and odor, -~

. . . .

, - 12 - ~ ~

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1043gl82 in which movement of liquids is achieved by utilizing gxavity or air riser tubes.
! The filtered effluent in line 140 may be treated further, if desired or required, to provide water of potable quality. Such procedures may include one or a combination of e~poration, reverse osmosis, ion-exchange and disinfection.
Solid wastes removed from the system in lines 50, 65, 67, 96, 101 and 122 may be disposed of in any desired manner. The quantity of wastes requiring disposal is, however, quite small.
The chemical treatment to remove phosphate effected in the phosphate removal unit 68 is illustrated by the following Example of the overall multi-stage waste water treatment system defined in the aforementioned parent application.

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Example An approximately 4000 gallon per day sewage treat-ment pilot plant operation was set up utilizing the equipment illustrated in Figure 1 and was operated continuously for a period of 38 da~s. The contaminants of the sewage in the feed line 20 varied widely over the test period. The operation was unattended except for the taking of samples for analysis.
The hydraulic characteristics of the pilot plant operation over the test period are reproduced in the following Table I:
TABLE I
Characteristic Range A~erage -Feed flow rate GPD 1872 to 4896 3168 ;

Hydraulic detention time (~rs.-based on Q) Primary clarifier 2. 9 to 7.7 4.5 -A-B process - reactor 4.3 to 11.0 6.7 , ! - clarifier 1.7 to 4.6 2.7 Chemical treatment -PO4 reactor 4.8 to 12.8 7.4 Ozon~tion 2.4 .to 6.3 3.7 Recycle percent (based on Q) ~ -for A-B process 370 to 490 420 Surface overflow rates GPM/
sq.ft. (based on Q) - primary clarifier 0.19 to 0.50 0.32 - A-B clarifier 0.17 to 0.34 0.23 -~
- PO4 reactor-clarifier 0.11 to 0.31 0.20 . The water quality at various locations in the pilot plant was determined, namely, the effluent from the ;
primary clarifier, the effluent from the adsorption-biooxidation process, the effluent from the PO4 reactor-clarifier, the -effluent from the ozonation unit and the effluent from the multi~
media filtration. These water quality results are reproduced in the following Table II:

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~0434~2 From the results reproduced in the above Table II,it is possible to calculate the contribution of the individual steps to the overall removal efficiency of the system. The results of this calculation are reproduced in the following Table III:
TABLE III
Treatment Contaminant BOD5 TOC SOC TKN NH3 NO PO4 S.S. Turb. Coli.
_ % % ~ % % mg~l % % % %
.
10 PrimarY 12 24 113 0 ~0.8 5 50 35 Adsorption-biooxidation 80 67 72 90 ~ 8 +3.0 20 42 62 Chemical 6 5 85 0 -0.4 70 3 1 ~99.99 Media Filtration 1 3 71 0 - -4 4 Total 99 99 9899 98 - 91 99 99 ~99.99 The above tabulated results demonstrate the effectiveness of the system of Figure 1 in removing substantially completely organic' nitrogenous, phosphorus, suspended solid and coliform contaminants -~ `
from waste water. -~
The sewage treatment system 10 may be designed to handle -i 20 a wide range of liguid feed rates while remaining unattended, `-typically from 5000 to 100,000 gallons per day, and hence provide an effective waste water renovation system for use in apartment ~lock-~, ana the like.
The present invention, therefore, provides a chemical treatment for waste water for the removal of phosphates.
Modifications are possible within the scope of this invention. ` - -,.

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Claims (5)

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

1. A process for the chemical treatment of waste water containing at least phosphate materials in a single upright reaction tank, which comprises:
separating said reaction tank into a first vertically-extending zone extending upwardly from the bottom of the tank for part of the height thereof, a second vertically-extending zone extending upwardly from the bottom of the tank to the height of the first zone and in fluid flow communication with the first zone at the upper end thereof only, and a third vertically-extending zone extending up-wardly from the upper extremity of said first and second zones in fluid flow communication with said first and second zones, establishing a liquid level in said tank and a flow path of liquid through said tank downwardly through said third and first zones respectively out of fluid flow communication therewith and upwardly through said first and third zones respectively, establishing and maintaining a rotating fluidized bed of chemical sludge in said first zone, mixing said waste water with chemical coagulant, feeding said mixture by gravity along said flow path from the upstream end thereof and tangentially into the lower end of said first zone, passing said mixture through said rotating fluidized bed of chemical sludge in said first zone, chemically coagulating said phosphate materials in said fluidized bed, passing treated liquid along said flow path through said third zone, passing chemical sludge from said fluidized bed into said second zone to achieve separation of said treated liquid from chemical sludge in a separation zone, discharging treated liquid having a decreased phosphate-materials content from said third zone at the downstream end of said flow path, and accumulating said passed chemical sludge in said second zone.

2. The process of claim 1, wherein said waste water also contains additional contaminants including suspended solids, dissolved organic materials, nitrogenous materials and turbidity-providing materials and including adsorbing said at least part of additional contaminants in a layer of chemical sludge in said fluidized bed.

3. The process of claim 1 wherein said first zone has a decreasing cross-sectional size in an upward direction in at least the upper portion thereof and said second zone has a decreasing cross-sectional dimension in a downward direc-tion.

4. The process of claim 1, 2 or 3, including with-drawing a portion of said waste water from said first zone to exterior of the reaction tank and recycling said withdrawn portion exteriorally of the reaction tank to the upstream end of said flow path.

5. The process of claim 1, 2 or 3, wherein said accumulated sludge is withdrawn by entrainment in a gas stream rising in a flow path passing through said third zone to a location external of said tank.