CA1043480A - Ozonation in waste water treatment - Google Patents

Abstract

OZONATION IN WASTE WATER TREATMENT

ABSTRACT OF THE DISCLOSURE
An ozonation waste water treatment is described in which ozone and oxygen are passed countercurrently to waste water in a first zone, contaminants are oxidized in a second zone, and solids are filtered from the treated liquid.

Description

10~;~4~0 The present invention xelates to ozonation of waste water to remove oxidizable 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 ozonation tr~at-ment of this invention. This application claims only the ozonation treatment.
In accordance with the present invention, there is provided a process for the ozonation of waste water con-taining bacterial and odor-imparting contaminants and other contaminants including suspended solids, dissolved organic material, nitrogenous material, phosphate material, turbidity-providing 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 through the height of the tank and -a second vertically-extending zone extending the height of the tank in fluid flow communication with the first zone at the lower end thereof only; establishing a liquid level in each of the zones and a flow path of liquid through the tank downwardly through the first zone and upwardly through the second zone; feeding the waste water to the first zone at the liquid level therein; feeding a gaseous mixture of ozone and oxygen into the first zone at the lower end thereof; allowing the gaseous mixture to rise in the first -zone countercurrently to the waste water flowing in the flow ~
path; absorbing ozone and oxygen from the gaseous mixture - ~-in the waste water in the first zone; passing the waste water having gases absorbed therein from the first zone to the second zone; oxidizing contaminants in the waste water

- 2 with the adsorbed oxygen and ozone in the second zone;
filterin~ from the treated liquid in the second zone adja-cent the downstream end of the flow path solids formed in the second zone; and withdrawing treated liquid having a decreased contaminants content from the downstream end of the flow path.
The invention is described further by way of illustration with reference to the accompanying drawings, in which:
Figure 1 is a schematic representation of a waste water treatment system embodying this 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 for use in the system of Figure l;
Figure 4 is a sectional scbematic representation of an ozonation unit which utilizes the process of this invention and 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 invention claimed in the aforementioned parent application includes a primary treatment 12, an adsorption-biooxidation treatment ~ :
14, a chemical treatment 16 and a fixed bed adsorption~
biooxidation treatment 18. Part of the chemical treatment 16 constitutes the subject of this invention. -Raw comminuted sewage is fed by line 20 to the ;~

- 3 primary treatment 12. As may be seen in more detail ~n 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 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 draw sludge out of the settling chamber 30 into and up the riser tube 42 under the influence of the gas rising in the tube 42.
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

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~043480 downwardly-extending portion and a horizo~tally-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 discharge members 48. The tangential dis-charge of the recycling MLSS causes rotation of the reacting liquor in the first chamber 2~ about the axis of the container 22.
The rotation of the material in the chamber 28 applies centri~ugal 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 ~naerobic 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.
In 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 equalize 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 ~e flash aerated from the reactor 54 by external flash aerator 56 and passed by line 58 to a clarifier 60. In the clarifier 60, the bio-logical reactions are extended, functioning thereby, ineffect, 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 ànd 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,s8Q,556.

1()43480 Reference 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 ozonation unit 70 constitute 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 biological sludge from the clarifier 60. This loss provides automatic and self-regulating control of the concentration of the microbial popu-lation in the adsorption-biooxidation treatment 14.
The first chamber 80, which acts as a reaction chamber for phosphates, contains coagulated suspended solids, i.e. chemical sludge, which are maintained in a rotating -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 of the chamber 80.
~he 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 f irst chamber 80 and the coagulation of the formed flocs occurs in the upper portion of the first 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 èxtends axially through the unit and ;~ -terminates immediately above the base of the second chamber 82. - - A gas flow tube 94 is positioned internally o~
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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,, . . ,, , ~
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lQ43480 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 ~aste w~ter flows upwardly from the first chamber 80 to the third chamber 84 for removal ~rom the unit 68 through 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 phosphate removal unit 68 in line 98 is fed by an external riser tube 100 inbo the ozonation unit 70 through pipe 102. The oæonation unit 70 incl~des an outer cylindrical container 104 and an inner cylindrical tube 106 perforated at its lower end by perfora-tions 108.
An 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~

~10434~
tions 108, it iscountercurrent~y 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 liquied, is less than the velocity of upward flow ~f the gas bubbles but greater than one-third of vel-ocity of a single rising in stationary liquid.
As the concentration of the ozone in the bubble volume decreases due to the diffusion of ozone into the liquid as the gas rises in the i-nner chamber 114, a concentration 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 con-centration gradient established in the radial direction ~the ~-~
bubble and increasing the concentration of ozone and oxygen at the bubble surface, and hence increasing the mass transfer rate of the diffusing absorbing gases in the packing 118. ;
The presence of the floating packing 118 in the ;~
first chamber 114 prevents axial mixing of the liquid -~-thereby creating conditions for continuous multistage ~
. ..-.. :..
absorption.
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 in the waste water settle out in the - ~ . .

1~4~4~g) the second chamber 116 and - lQa -. . ... .

~043480 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 oxidation of the waste water in the ozona-tion unit 70 results in an effluent of decreased colour, odor and turbidity, containing chemically oxidized organic and inorganic compounds and is disinfected.
lf ~urther treabment is required, the effluent from the chemical ;- -treabment may pass by line 124 to the fixed bed adsorption-bicoxidation treatment 18. The adsorption-biooxidation treatment 18 is .... :. .
conducted in a cylindrical vessel 126, shown in detail in Figure 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 .

~)43480 carbon increases to the point where microorganisms can survive and biooxidation can occur.
The concentration of residual organic material in 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 required 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 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 an~ line 140.
Valved backwash water and air feed lines 142 and 144 respectively may be provided along with a backwash overflow line 146.
Ozone for the ozonation unit 70 is provided by line i48 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, in which movement of liquids is achieved by utilizing gravity 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~aporation, reverse osmosis, ion-exchange and disinfection.
Solid wastès 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 dispo$al is, however, quite small.
The ozonation treatment to remove bacterial and odor-imparting contaminants is illustrated by the following Example of the overall multistage waste water treatment system defined in the aforementioned parent application.

-. ..... - .. .

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Example ~ 34 An approximately 4000 gallon perday sewage treat-ment pilot platn operation was set up utilizing the equipment illustrated in Figure l and was operated con-tinuously for a period of 38 days. 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 Ran~e Avera~e Feed flow rate GPD 1872 to 4896 3168 Hydraulic detention time (Hrs. -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 P04 reactor 4.8 to 12.8 7/~l4 Ozonation 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. (baeed on Q) -primary clarifier 0.19 to 0.50 0.32 -A-B clarifier 0.17 to 0.34 0.23 -P04 reactor-clarifier 0.11 to 0.31 0.20 The water quality at various locations in the pilot plant was detemined, namely, the effluent from the primary clarifier, the effluent from the adsorp-tion-biooxidations process, the effluenb from the Pp4 reactor-clarifier, the effluent from the ozona-tion unit and the effluentfrom the multimedia fil- - -tration. These water quàlity results are reproduced -in the following Table II:
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1~)43480 From the results reproduced in the above T~ble 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
TreatmentContaminant BOD5 TOC SOC TKN NH3 NO PO4 S~S. Turb. Coli. `
% % % ~ % mq~l % % ~ %
.
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 i -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 a wide range of liquid 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 ~
blocks, and the like. ~ - -The present invention, therefore, provides an operation treatment for removal of certain contaminants from waste water.
Modifications are possible within the scope of this invention.

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Claims (2)

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

1. A process for the ozonation of waste water con-taining bacterial and odor-imparting contaminants and other contaminants including suspended solids, dissolved organic material, nitrogenous material, phosphate material, turbidity-providing 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 through the height of the tank and a second vertically-extending zone extending the height of the tank in fluid flow communication with said first zone at the lower end thereof only, establishing a liquid level in each of said zones and a flow path of liquid through said tank downwardly through said first zone and upwardly through said second zone, feeding said waste water to said first zone at the liquid level therein, feeding a gaseous mixture of ozone and oxygen into said first zone at the lower end thereof, allowing said gaseous mixture to rise in said first zone countercurrently to said waste water flowing in said flow path, absorbing ozone and oxygen from said gaseous mixture in said waste water in said first zone, passing said waste water having gases absorbed therein from said first zone to said second zone, oxidizing contaminants in said waste water with said adsorbed oxygen and ozone in said second zone, filtering from the treated liquid in said second zone adjacent the downstream end of said flow path solids formed in said second zone, and withdrawing treated liquid having a decreased contaminants content from the downstream end of said flow path.

2. The process of claim 1, including settling solids in said second zone and periodically removing said settled solids.