Note: Descriptions are shown in the official language in which they were submitted.
~S743~11
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,. , ".
BACKGROUND OF T~E INVENTION
The inven~ion relates to apparatus and
, ' ~
process for the biological treatment of liquid wastes
employing fluidi~ed beds. In particular, i~ is directed to
a process for xemoving ammonia nitrogen from waste watex.
~, Untreated municipal wastes generally contain
.
from 2~ to 50 milligrams of ni~rogen per liter, mostly
in the form of ammoni5a and organic nitrogen. ~he serious
. j - - .
i detrimental environmental effects of these compounds had not
, been fully realized until the last decade. With the
large amounts o~ fixed nitrogen in the form of ammonia `
' and other compounds that are being introduced into the
- i i. I ;- ~. . -
biosphere by the large scale use of synthetic fertilizers, ~- -
' and with the demands man makes on his environment owing -
to population congestion, there definitely appears to be
; an imbalance developing in our ecological system that may
have long range consequences for future generations. The -~
presence of such nutrients in natural waters causes ~ ~
fertilization and vegetative growth in the form of algal ;
~ blooms. Such blooms often result in accelerated eutro~hicat-
! ion.
Conventional methods of municipal sewase i
treatment, chiefly activatcd sludge and trickling
;, .
i filtration are designed to remove solids and oxygen demand~
ing organic material from the waste water. During ~hese
.,: '
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57430
., i
treatment processes some of the organic nitrogen is
converted into the ammonia form. Chemical and physical
'methods such as chlorination and ion exchange have been
tried in small scale e-xperime-nts to remove these ammonia
compounds from the waste water, but costs have been too
prohibitive to attempt these methods of treatment in
large scale installations. Although ammonia stripping
is economically feasible, it suffers the disadvantages of
poor operation or shutdown in winter and the introduction
of ammonia into the atmosphere.
Biological methods of treatment have been
.; ji ' ~
most frequently used to remove ,ammonia in typical large
installations. Oxidation of ammonia nitrogen to nitrate
I~nitrogen can be accomplished in an activated sludge ~ -
` treatment plant by increasing aeration time in the plant
~from 3 - 6 hours to 10 or more hours. This requires the
use of large aeration basins and is often inefficient ~
because of difficulties in controlling the system. This ~ ;
oxidation of ammonia to nitrate, termed nitrification, can
also be accomplished by aerating the effluent from the
activated sludge treatment process in a separate aeration
basin. This facilitates control of the nitrification
I~
, process but requires additional aeration basins with an
additional aeration time of 3 to 6 hours.
. :
Certain experimental nitrification processes
have employed the use of up-flow columns or beds. Such
` ~ packed beds tend to become clogged as solids in the
waste water are filtered out and further as attached biota
undergo uncontrolled yrowth on the stone media. Such
-; . ,
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.,
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,
~OS~430
blockage causes insurmountable head losses. These losses ~.
must ~e relieved by frequent and impractical back washing
of the bed. Also, detention times in excess of one hour
are required.
An example of a prior art system.is described
Il in the publication by, St. Amant, P.P. and ilcCarty, P.L. :.
¦¦ "Treatment of High Nitrate Waters", JOURNAL OF AMERICAN
WATER WORKS ASSOCIATION, pp. 6~.9-66:9, 1.969. This ¦ .
publication is concerned with an up-flow denitrificaticn I :
system, which is basically a packed bed of one inch stone, `~
as compared to the present application which is concerned
.. with a ~uidized bed of small particles. Hence, the operating ..
s parameters and results are completely different. Another
` . ¦ example of a prior ar~ system is described in the publication .: ~ :
'~ ~ by, Weber, W.J. Jr. and Morris, J.C. "Kinetics of Adsorption
in Columns of Fluidized Media", JOURNAL OF ~MERICAN
i WATER WORKS ASSOCIATION, pp. 425,430, 443, 1965. This publi~
' 1 cation teaches the use of an expanded bed c~lumn for a
. l physical ad~orption process, i.e, the adsorption of
.:~ . organic carbon by porous adsorbent activated . `~ -
: ' carbon particles. The process of Weber et al does not ~:.
. . rely upon the use of biological action, as is the case in the
:. ; present application. . . ~ -
Still another example of prior art systems ;- ~.
~ is the Savage Patent No~ 3,709,364 issued in January
`. 1973. The process described in this patent is essentially
~ a'deep bed filter'r which employs a down-flow system.::
:~l ; With this type of system, as the spaces between the
.~. . particles.become plugged.with solid.wastes, great.head . .
."' , ~
~4~
'''' ~ '' ' ' ' . ' ~' . ' ' ~.' '
j ~L[)57~L3~ .
. :
.: .
; losses result. Savage recognized this problem and
provided means for intermittent back- washing to agitate
this filter media and remove suspended solids collected on
it. Thus, the Savage system was predicated on different
; principles and employed different parameters as compared
to the present application.
,Other related patents and publications in this
art include the following~
:~ .
~ United States Patents
,,.: - .
No. 2,676,919 M. Pirnie April, 1954
` l No. Re 24, 219 M. Pirnie September, 1956
No. 2,834,466 L. Hament May, 1958
No. 2,992,986 W.T. Ingram July, 1961
No. 3,075,828 Tsuneo Kato et al. January, 1963
:, l; , ~ .
- No. 3,173,862 J.S. Clements et al.March, 1965
No. 3,219,577 T.J. Powers November, 1965
No. 3,424,674 P.J. Webber January, 1966
~.
No. 3,23~,434 W. Albersmeyer Pebruary, 1966
No. 3,371,033 E.D. Simmons et al February, 1968
No. 3,401,113 R.D.Pruessner et al September, 1968
No. 3,543,937 J.M. Choun December, 1970
No. 3,547,816 Horiguchi et al. December, 1970
, , : .
~ ~ Publications
~ ~ :- . .
- Weber, W.J., Jr., Hopkins, C.B. and Bloom, R.Jr.,
Physiochemical Treatment of Waste Water", Journal
Water Pollution Control Federation, Vol. 42, pp.83-89,
(1969).
'; ~
.~ . . ~.
:' ' :
~5~
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1057430
Tamblyn, T.A. and Sword, Bryan R., "The Anaerobic Filter
for the Denitrification of Agricultural Subsurface
Drainage" Paper presented at 24th Annual Purdue
Industrial Waste Conference, Lafayette, Indiana
on May 7, 1969~ -
Beer, Carl, "Evaluation of Anaerobic Denitrification
and Processes", Proc. Paper 7211, Seidel, D.F. and
Crites, R.W., Ed., (April, 1970).
Castaldi, F. and Jeris, J.S., "Still Wanted: Economical
Controlled Denitrification", Water and Wastes En~ineering
Vol. 41, 36-38, (June 1971).
.: .
Beer, C., Jeris, J.S. and Mueller, J.A. "Biological
Denitrification of Effluents in a Fludiized Granular
Bed, Phase I" prepared for New York State Department of ~ `
Environment Conservation, published Manhattan College;
(March 1972).
.
- Weber, W.J., Jr., and Morris, J.C. "Kinetics of Adsorption ~
` in Columns of Fluidized Media" Journal of American ~- -
Water Works Association, pp. 425,430, Vol. 443 (1965).
St. Amant, P.P. and McCartyj P.L., "Treatment of High
~' Nitrate Waters", Journal of American Water Works
Association pp. 659-662 (1969). ' ;
.. ~ "
McCarty, Perry L. and Haug, Roger T., "Nitrification
l with submerged Filters" Journal Water Pollution Con-
`~, trol Federation , Vol. 44, No. 11 (~lovember 197~).
;~ j McCarty, Perry L. and Young, James C., "The Anaerobic
; Filter for Waste Treatment", Journa Water Pollution
Control Federation, VolO 41, R 160 (1969).
. ' " ~ . .
Weber, W.J., Jr., Friedman, L.D. and Bloom, R.Jr., ~;
"Biologically - Extended Physicochemical Treatment", ~ -
Paper presented at 6th International Water Pollution
'~ ~ Control Conference at the University of Michigan on
June 22, 1972.
' . ~
This article discloses an adsorption process
and therefore a porous substrate is necessary, i.e. sand
and the l~ke material cannot be employed. There is no
build-up of .51udge disclosed and stoichiometric amounts
of oxygen are not employed.
:~` ':
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. , . :
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~5~3~) ~
Accordingly, while the art has recognized
the desirability of employing biological organisms to
remove ammonia from waste water, it has not succeeded in
,:
providing an inexpensive and highly efficient process
for rapidly treating large quantities of waste water.
~ Accordingly, there exists a critical need for a process
-~ free of the defects and deficiencies of the prior art to
purify waste water.
SUMMARY OF THE INVENTION
.
; Ii is, therefore, a primary object of the
invention to provide a relatively inexpensive process
, employing biological organisms for oxidizing the ammonia
nitrogen content of waste waters to oxidized forms of
nitrogen.
As employed in this application the term ~ ;~
~, "waste water" or "liquid waste" includes organic or ; ~
inorganic liquids or mixtures thereof containing biologi- -
~` , cally decomposable contaminants and containing the equiva- ;
. :-
lent of at least about 10 milligrams per liter of nitrogen
, in a reduced form; particularly the ammonia form. Most
municipal waste waters and industrial waste waters of
equivalent strength fall within the above definition
of waste water.
It is another object of the invention to
' reduce the ammonia nitrogen content of waste water -~
'~ employing a fluidized bed of biological organisms and
~ simultaneously controlling the tendency of the bed
i ~ i
particles to become excessively enlarged by excess
biological growth.
It is an additional object to treat waste
. ' ' '
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-7~
,.~.,., ., . .. , : ,
~0574~30
, water containing significant amounts of suspended solids
without effectively reducing the efficiency of the process.
A further object of the invention is to provide
an efficient waste treatment process adapted to
operate at lower detention times compared to traditional
, ~ processes.
The aforementioned and other objects are
met in a process for removing ammonia nitrogen from
~ ' waste water by generating a fluidized bed from waste
; ; water and biota,adapted to oxidize ammonia nitrogen by ~'
` use of aerobic biota attached to a solid particulate
~, carrier adapted to be fluidized; then metering sufficient
.. . . .
~ ~ amounts of oxygen into the bed to allow the biota to
','~, oxidize the ammonia nitrogen content of the waste water
', ~ passing therethrough and thereafter removing excess
bacterial growth formed on said carrier during the pro~
, cess.
~ The term "fluidized bed" as employed herein ~ -
`i refers to the flow of a suitable liquid upwardly through
~' 1. ' , .
a bed of suitable sized particles at a velocity sufficiently ~,
' ' high to buoy the particles, to OvercQme the influence ' ,~
,~ of gravity, and to impart to ~hem an appearance of
' , movement within the bed; said bed being expanded to a
'", greater depth than when no flow is passing therethrough. '~'
The particles travel to different parts of the bed and
are imparted with movement within the bed. On the con- ;
l , trary, in an expanded bed as employed in the prior art
,~ systems such as the systems mentioned hereinbefore in '~'
.,~
~', connection with the two Weber et al publications and the
', Huether Patent No. 3,658,697, the particles are primarily
`'1 substantiallY suspended in a ~iven volume by the water
passing therethrough.
~f~ As waste water containing nitrogen in the
:, ,
~ 8
1057430
form of ammonia is passed through the fluidized bed,
bacterial growth on the particle~s is accelerated and
the bed particle size increases. If unchecked, the bed
particles become enlarged and may agglomerate, thus
reducing the biological surface area per unit folume of
the reactor and the efficiency of the column. Further,
the particles tend to be reduced in specific gravity as they
enlarge and/or agglomerate and tend to be carried away
from the bed. It is a feature of the present process
that the excess cellular material or bacterial growth
formed on the particles during the process is mechanically
removed thereby overcoming the tendency of the particles I ~ ¦
to be carried away in the process effluent. Accordingly, ¦
the term "excess cellular material" as employed herein
refers to the excess of such material attached to the
particulate carrier beyond that needed for the normal
operation of the system.
Employing a fluidized bed for biological treat-
ment al~o p~rmits waste water containing substantial
amounts of suspended matter to be treated. Such suspended
matter readily passes through the fluidized bed. Other
types of beds, such as packed beds, are subject to plug-
ging and excess pressure losses caused by excess growth
and by retention of suspended particulate matter contained i ;
in waste water.
Another substantial advantage of the present
fluidized bed process is the unexpected high flow rates
and removal efficiencies achieved by the fluidized system.
The process is readily adapted to meet the water and waste
water purification needs of municipalities and industry.
~'', , I '
l -9
ll ~L05~30 1 ~
In view of the foregoing r this invention contem-
I , plates a new and improved biological process for removing `
; 1 amm,onia nitrogen from waste water which includes
i the steps of forming a fluidized bed of microorganisms
- 1l attached to a solid particulate carrier, continuously
passing waste water to be treated through the fluidized
, I bed, adding oxygen to the fluidized bed, and retaining
! the waste water in ~he fluidized bed for a sufficient
. j . .. . ............................... .
period of time, while maintaining the fluidized bed at
a sufficient temperature, and while maintaining the
fluidized bed under aerobic conditions to biologically
.. ~ ~, I .
convert substantially all of the ammonia nitrogen to be
`I removed from the waste water to oxidized forms of nitrogen,
`~including nitrite and/or nitrate nitrogen, water, and
j1 cellular material. The process further comprises the
~,steps of continuously withdrawing the oxidized forms of
nitrogen and water from the fluidized bed, and removing
excess cellular material from the particulate carrier. In ;
il another form of the inVentiQn, apparatus is provided to
; ~ effect the foregoing process.
... ,1 1 . :.
j BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a flow sheet illustrative of the
process of the invention with the various processing
:.
components shown more or less diagrammatically, and
Fig. 2 is a flow sheet illustrative of the process of
1 a second embodiment of the invention.
.. . .
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~057430
I D~SCRIPTION OF Tll~ PREFERR~D EMBODIMENTS
,j _ I
While applicable to the treatment of any fluid
containing ammonia-nitrogen to which bacteria can become
acclimated, the present process is most readily adapted
for nitrification at secondary waste water treatment faci-
1 lities. Designed for complete nitrification of wastewater, the process may also be installed at overloaded
conventional trickling filtration plants or activated
sludge processing facilities where BOD is being removed
; but where nitrification becomes necessary particularly
; where land availability is limited. It has far-reaching
. !
capabilities to augment overloaded treatment systems.
~ Ij For most practical applications, the waste water
¦ I to be treated will contain at least the equivalent of about ;
~' ' 10 milligrams per liter of ammonia nitrogen. Of course,
j , the process is able to treat waste water containing less
than this amount. I
There must be sufficient oxygen in the feed
waste water in order to provide the stoichiometric amount
for oxidation of the ammonia to be removed. Pure oxygen or ani
, oxygen cor.taining gas, such as air, may be injected into
. ~j . . .
the feed preferably prior to entry of the feed into the
fluidized bed. If desired, the oxygen may be injected into ~ ;~
-~ the fluidized bed or both into the feed and bed To ~ ~ ~
increase the efficiency of the oxygen transfer, the ; ~ ~1
effluent gases from the fluidized bed can be recycled
into the waste water, or the waste water may be recycled
to enhance greater oxygen adsorption.
By way of an example of the process, waste
~, water is passed through the up-flow fluidized bed accor-
~ .
_ ~ ] _
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: , , : . . : -
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:- . ... . . . ?. -
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0574;~ZO
, ~
; ding to the invention in the presence of appropriate
;:, li ; .
microorganisms which convert am~Zonia nitrogen to oxidized
forms of nitrogen, including nitrite and/or nitrate nitro-
gen and cellular material. A general equation for the
biological phenomenon may be expressed as follows:
C2 + NH3 ~ 2 + Microorganisms-~ N02 and/or NO
H20 ~ Microorganisms
Sufficient oxygen must be present to satisfy this
stoichiometric minimum in light of the amounts of ammonia `
present in the waste water. Generally, from about 3.0 to
about 5.0 milligrams of dissolved oxygen are needed for
each milligram of ammonia oxidized. Lesser amounts can be ~ 1
employed; however, the process generally becomes less
efficient. If greater amounts are employed, then an
excess of oxygen is provided which is unnecessary to the ~;
implementation of the process. In certain instances it
will not be possible to accurately determine the ammonia
nitrogen in the waste water. Therefore, as a practical
measure it is preferable to saturate the waste water as
far as practicable with dissolved oxygen. The solubility
of pure oxygen is about 40 milligrams per liter at room
temperature at atmospheric conditions. I -
In order to provide dissolved oxygen in
amounts approaching the solubility of pure oxygen it has
been found that a fermentor turbine can be efficiently
employed. The fermentor turbine has a hollow annular
shaft with blades or turbines at the base of the shaft.
Waste wateris passed through a tank into which the fermentor
turbine is disposed. Oxygen is passed through the central
orifice of the turbine and is broken up into a plurality
12
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5~436)
of tiny bubblcs by ~he spinning blades at the base of the
turbine shaft. Other gas transfer devices known in the -
art may also be used.
A fluidized bed system is preferably generated
by passing ~aste water through an upright column containing
microorganisms attached to a particulate carrier or sub-
¦ strate. In general, the carriers will be seeded withbacteria from aerobic processes adapted to feed on waste
water. Nitrosomonas and nitrobacter, which are
naturally found in municipal waste water are particularly
I preferred for this purpose.
¦ Suitable carrier material~ for the biota or
microorganisms include natural or artificial materials
such as coal, volcanic cinders, glass or plastic beads, ~1
sand, alumina, garnet and activated carbon particles. The ~
:!
¦ size of the particles chosen is a function of both specific
1I gravity and surface area. For the most part, the carrier
particles are between about 0.2 and about 3 millimeters
1 in diameter. Employing the preferred flow rates of the l ~
¦~ present invention, enhanced results are obtained by bed ,3 :
¦! particles having a diameter of from about 0.4 to about 1.5
millimeters. The above discussion assumes the presence !
of spherical particles, but the particles in most cases
would not be spherical. Most preferably, the particles are
of a uniform size. While the aforesaid bed carriar materials
are illustrative of the preferred substrates, nonetheless
other materials, nontoxic to the bacteria, whether natural
or synthetic, can be employed.
It has keen found that substantial amounts of ammonia
~3 can be aerobically nitrified in a fraction of bed, sometimes
-: in the first few feet adjacent the influent feed. Accordingly,
it may be sufficient to provide aerobic conditions for only a
fraction of the bed height. 5imilar results are obtained for
aerobic removal of B~D. Further, it is within the scope of the
invention to carry out the process in this manner.
'
-13-
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1057430
, '" I . .
; For enhanced ammonia removal, the bed particles
preferably have a thin layer of bacteria seeded thereon.
Preferably, the bed particles are first cultured with
seed bacteria such as those present in sewage. Seeding is
' provided externally, or yreferably, internally within the
; " .
fluidized bed column. For this purpose the carrier parti-
cles are introduced into the column and thereafter waste
water which is to be trea~ed is fed through the column. It
has been found that seeding is enhanced by recycling all
- .
;
or a portion of the flow, controlling the pN and con-
< I centrations of NH3 and alkalinity. Seed bacteria
or bacteria naturally present in the sewage rapidly
grow around the bed particles and become acclimated to
the system~ The specific gravity of the seeded particles
s I is preferably no less than 1.1 and preferably at least
about 1.2 in order to insure that such particles are not
carried out of the system during operation of the fluidized
, ;I bed. I ;
-` " By way of an example of the operation, waste
water, appropriately oxygenated if necessary, enters a
l vertical cylindrical column through a distribution manifold ,
in the column base. A suitable distribution manifold
i has a series of spaced apart inlet ports which regulate
the flow of waste water through the column. Obviously,
a wide assortment of conventional distribution manifold
'I , :
systems could be utilized also.
The pressure of the waste water influent at
the point of fluidization varies depending on many factors,
including the quantity of bed particles, their specific
gravity and the degree of pressurization set in the column~
.i, , ; .
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, , . I
-14-
~05743(~ 1
For the vertical column fluidized bed systems, the oxygen-
ated feed is pumped into the column at a rate sufficient
'I
to support the seeded particles in the state of fluidiza-
tion as hereinbefore described.
Where waste water contains highly concentrated
wastes, microorganisms or occluded solids, it may be
desirable to inject the oxygen at greater than atmospheric
pressure. At increased pressures larger amounts of oxy-
, gen are dissolved in the waste water to satisfy the increasedstoichiometric requirements. For example, amounts as great
, ,l as about 150 milligrams of oxygen per liter of waste water
, and more can be supplied to the feed at super atmospheric
pressure. ~ ;~
In general the flow rate into the col~mn is
~J ¦~ sufficient to provide a fluidized bed according to the
invention. Depending upon the size and specific gravity of ~-
the bed particles, among other factors, the flow rate
,' is usually at least about 6 gallons per minute per square
foot of bed. By adjusting the specific gravity of the
,' bed particles, by employing denser bed particles and
!
ii~ the like, the process can be carried out at very high
.1 ' ,1
flow rates, possibly even the order of hundreds of gallons
per minute per square foot of bed. Commercially, it
is desirable to operate at flow rates approaching 100
gallons per minute per square foot of bed. Fluidized
beds operating according to the fundamental principles of
the present invention have been successfully operated at
flow rates of about 25 gallons per minuke per square foot
of bed and operations at higher rates are well within
present technology as set ~orth herein.
: . .
It has been found that enhanced results are
.~ :
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~L0579L3~ ;
obtained, and accordingly, it is preferred to provide a
flow rate into the column from about 6 to about 40
gallons per minute per square foot of natural or artificial
bed.
Further enhanced results are obtained when the flow
rate is from about 8 to about 25 gallons per minute per
square foot of bed. Depending upon the specific flow rate
selected, the actual dwell time within the column for a
volume of waste water can be as little as from about 2
to about 5 minutes. In general, the dwell time within the
column is usually under about 30 minutes and most fre-
quently less than about 15 minutes per up to about 12 feet
of bed height, but the actual dwell time is a function of
the size of the reactor. The flow rate iæ preferably
adjusted to compensate for the size and specific gravity
of the seed particles.
For a given bed, as the flow rate is incre~sed
;~ in order to increase the volume of waste water being
`~3 ; treated, the specific bed of microorganism attached
~ particles will increase in height. In order to compensate
.
for the tendency of the bed to increase in height at higher
: . ~
flow rates, it is desirable to employ additional bed
particles or to employ bed particles of higher specific
` gravity.
As the waste water is pumped into the column an
area immediately above the distribution manifold may be
;l free of seeded particles although bed particles with
sufficient growth may remain. This phenomenon has also
been observed during initial seeding periods of the bed but
disappeared as seeding of the carrier particles progressed.
' This interface height, then ~the height from the distri-
bution manifold to the bottom of the seeded fluidized bed
in a vertical column) is a function of the flow rate of the
column, the temperature, the specific gravity of the
bed particles and the length of time of the seeding
` ' ' - /~' :
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1057430
period as ~ell as the nature of the distribution manifold. I
Practically, this phenomenon has a minimal effect, if any,
on the column's efficiency. Generally as flow rate
increases interface height increases and conversely as
flow rate decreases interface height decreases.
In general~ the pH of the fluidized system
will not require external manipulation. If need be, it
may be adjusted to fall within the range of from about
5.5 to 9.5. Best results are obtained at a pH from
about 6.0 to 9Ø The internal temperature of the
fluidized column should be sufficient to permit bacterial
activity. For this purpose the bed temperature is from
about 5 to about 45 C. The bed temperature will vary
with that of the influent waste water and, accordingly,
ambient operating temperatures on the order of from about
8 to about 30 C. will be the nominal bed temperatures and
are entirely satisfactory.
As the ammonia oxidation reaction proceeds
in the fluidized bed, bacteria tend to grow on the surface
!
;~ oE the carrier particles. After a time, if unchec~ed, bed
particles tend to form thick layers and expand to the extent
that they form agglomerates, and/or gelatinous masses. I 1
Should this be permitted to occur, then the surface area
-'
`~ per unit reactor volume available for biological reaction is great
. ~ .
ly reduced and the efficiency of the process is correspondingly
reduced. Further, particles tend to be carried out of the
fluidized bed as their specific gravity decreases. They
aldo tend to entrap or become attached to gas bubbles, such as
-17-
,: . . .... . .~:, , ~ ,
1057~3(~
oxygen bubble~ from the injected source. The gas
bubbles reduce the specific gravity of the particles
and tend to carry them away from the bed toward the top
of the column where they can collect as an undesirable
floc and/or leave the system.
In order to overcome these problems excess
bacterial growth is preferably mechanically removed from
the particles although chemical and biological means or
combinations thereof may be employed to supplement mechani-
cal removal. Sufficient growth in the form of a ~hin layer
of bacteria must remain on the particles in order to
.i , .
` preserve the efficiency of the process. Removing all growth
~, which has been suggested in the prior art for up-flow
` expanded bed process used for treating waste water to re-
move carbon by adsorption, des~roys the efficiency of the
. ,,
present process. In one embodiment, growth is regulated
by removing predetermined quantities of bed particles from
the column by a valve-controlled outlet port and mechani-
cally ~gitating and abrading the particles. Thls operation
may be performed in a separate abrasion vessel employing
a mixer which resemh-les the rotating knife in a Waring Blender.
The abraded particles are ~hen returned to the bottom of the
fluidized bed. Alternately, the particles in ~he abrasion
vessel are subjected to the action of compressed air or
water sprays to remove excess microorganisms. Other suitable
agitation mechanisms and apparatus wiil be apparent to
those skilled in the art. After treatment, the abraded
particles are metered into the fluidized bed at its base
by a suitable inlet port. The withdrawal of measured
amounts of bed particles, their cleaning and recyling into
:
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Il ~057gL30
. . .
the process can be accomplished without a significant
,1 interference with the continuity of the process.
., ,
By way of example, in a second embodiment,
bed particles are allowed to be carried out in the effluent
i from the column into a set-tling tank ~rom which they are
pumped into the bottom of the column. Separation of the ~j
excess cellular material growth fr,om ~h,_ par~ti,_ulate~carrier
;¦ is effected by the pump. Fig. 1 illustrates this process.
Waste water and air or oxygen is introduced into a flui~
dized bsd column 10 through an inlet port 11 for treatment
therein. The treated waste water containing bed particles is ~ :~
¦ exhaus~ed as at 12 from the fluidized bed column 10 into a
settling tank 14. Separation of the treated waste water or
.!' ,¦ effluent 16 and bed particles 18 occurs in the settling tank.
The separated bed particles are-then pumped back into the
j fluidized bed column as indicated at 20. Separation of the
growth from the carrier particles occurs by abrasion in a
pump 22. When the mixture of the abraded carrier and the
~` !
growth or excess cellular material is pumped back into the
column 10, the carrier particles will remain in the column
while the excess cellular material will be carrii~d on
through the system to the effluent 16.
By way of example, in a third and more preferred ~-
emkodiment, the particles are treated in situ in order
to remove excess bacterial growth from their outer sur-
faces. It has been found that excess bacterial growth
is readily removed from floc, agglomerates ard/or bed
particles at the top (or downstream side) of the bed, by a
sharp rotating blade or flexible agitator. These mechanisms
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79~30
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shear the bacteria from the carrier particle and thereby
remove excess growth. The stirrer provides continuous
control of the height of the fluidized bed. Other
mechanical mixers, ultrasonic devices, bafle plates and
other abrasion-type surfaces, or even water or compressed
air jets directed upwardly and sidewardly against the
column walls to create agitation vortices and
the like, as well as other suitable conventional agitating
means, can be employed within the column.
Where the bacteria are abraded batchwise to
control growth, it has been found that sufficient growth
is removed, when the height of the fluidized bed after
treatment is reduced on the order of from about 10 to 25
percent of its original expanded length at the same flow
rate. At highly elevated or substantially reduced flow
rates, the height may be somewhat above or below the afore-
said range. For removal of excess growth in situ using the
.. .
i' air cleaning method, for example, the flow rate to the
. ~ , .
column may be reduced to about 1/3 normal flow (reduction
,
is dependent on operating flow rate). The bed will settle
to a new lower height. Air is injected into the bed to
cause abrasion. During and immediately after this abrasion,
the removed growth is carried out of the reactor and exhaus-
ted from the system. Thereafter, the flow rate may be
increased to its normal velocity.
Depending upon the nature of the waste water
and the concentration of contaminants, it may prove useful to
employ more than one column connectedin series. It has been
found practical in many cases to employ the effluent from
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105743~
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th~ first column as the influent feed for a second column.
Accordingly, a plural column system may provide enhanced
results for treatment of industrial, municipal and other
waste waters. In a two col~mn system, ammonia nitrogen is
further oxidized by directing ~he effluent from the first co-
lumn into the second column as the sole influent, or in
combination with fresh sewage. During start-up of the column
it has, in certain cases, been found useful to recycle
at least a portion of the effluent treated to the column
.; , .
in order to promote initial growth of bacteria on the bed
carrier particles in situ.
. ! .
By way of example, Fig. 2 shows a somewhat
preferred embodiment of the process according to the
invention. Waste water is introduced through an inlet pipe
23, valve 24 and inlet port 25 into the Iower portion of
cylindrical column 26 through a manifold 28 in the base of
the column. Microorganism or biota-seeded bed particles
are fluidized by the passage of waste watar thrsugh the
column and form a fluidized bed 30. The interface height sf
the fluidized bed is indicated at 32j forming a chamber 33 7 '
thereabsve in the column. Treated waste water or effluent
is exhausted from the column after passage through the
fluidized bed and chamber 33, as at 34. Then the effluent
may be passed thrsugh an effluent purifier 35 such as a
settling tank or for treatment with flocculants or the like, ~;;
if necessary. Selected portions of the effluent,as xequired, ;~
are recycled through pipe line 36, containing a pump 37, to
the influent waste water inlet port 25. This serves the i~
following purposes: (13 to promote growth of the biota or ~
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microorganisms on the particles during seeding operations;
(2) to maintain uniform flow where input flow decreases;
(3) to dilute the concentration of ammonia into the bed,
if necessary to provide uniform concentration of waste
water; (4) to provide more oxygen to the waste water; (5) to
permit additional removal of ammonia remaining in the efflu-
ent. Oxygen is metered through an inlet pipe 38 and valve 40
into a mixing chamber 41 and then into the waste water inlet
port 25 in sufficient amounts to satisfy the biological
reaction for the oxidation of the ammonia. The metering
of sufficient amounts of oxvgen may be conducted automatically
by providing a conventional oxygenating system, such as the
UNOX process of Union Carbide, Inc. In some installations,
in addition to the oxygen supplied through inlet pipe 3B,
or as an alternative thereto, oxygen ls metered through
. .~ ;
inlet pipe 42, valve 44 and inlet port 46, direc~ly into the
`~ fluidized bed 30. In order-to faoilitate the dissolution
~ of relatively large quantities of oxygen into the waste
; water, the system may be pressurized to several atmospheres
of pressure or more. Additionally, effluent gas, if any,
may be recycled. Provision can be made for metering in
- oxygen in response to the output o~ an oxygen ana yzer
(not shown) placed within the bed, in the effluent line or
adjacent the feed, if desired.
~uring treatment, bacterial growth on the ~ ;
particles is monitored as a function of bed expansion by
a conventional optical device or other type of solids sensor
480 ~hen bed expansion reaches a predetermined height
~whereby the sensor device is activated, the bed particles
are regenerated by abrasion or the like to remove excess
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growth. A mechanical stirrer assembly 5n is preferably
provided at the top of the column to remove excess growth
of the cellular material. The stirrer is in the form of
sharp rotating blades or is formed from a flexible length
of synthetic polymeric material, polyethylene tubing, as
desired.
In some installations it is desirable to employ
an upwardly-outwardly directed conical portion at the upper
end of the Fluidized bed column to reduce the upward flow
velocity to prevent the bed particles from being carried
off in the eFfluent, among other desirable features. Further,
. this feature serves at least as an assisting means for
, controlling the growth on the bed particles.
In some installations, the present process can be
employed to provide the nitrified feed, or otherwise uti-
lized in cooperation with a carbon-denitrif1cation process. ~;
Further, the present process can be utilized to provide
~5
feed for the denitrification process set forth in Canadian
patent No. 986,239, issued March 23, 1976.
Further, in some installations, it is possible
to employ a plurality of stages in a single fluidized bed
column. The first or lowermost stage of the column is
~ maintained in such condition as to remove BOD aerobically,
:~ the second stage in the column is maintained in such
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~574~ ~
condition as to remove BOD aerobically; the third stage i5
maintained in such condition as to effect nitrification
of the waste products; and the fourth stage is maintained
in ~uch condition as to effect denitrification of the
waste products. Further, various recycle means may be
employed to recycle at least a portion of the products
through one or more of the stages. All or some of the
forgoing stages may be employed in a single fluidized bed
column. It should be recognized that it may be possible to
carry out more than one of the above processes simultan-
eously in a single stage of a multiple system. It will
;`:. !
also be appreciated that the foregoing sequence of stages
may be varied, if desired.
; EXAMPLE OF INVENTION
To demonstrate the process a number of tests
were made as indicated hereinafter using a 12 foot high,
; by 3 inch diameter Plexiglas~ olumn. Sand of a silica ~ ~
composition of about 0.4 to 0.8 mm size was used upon which ~ - "
to grow the nitrifving organisms. The synthetic waste ``
water was fed into the bottom of the column and taken
out at the top. The synthetic waste consis~ed of tap water
, to which ammonia and bicarbonate were added as major
ingredients, and phosphorus to a lesser degree. During the
, test period the height of the fluidized bed was about
5O5 feet, the influent flow was 1800 milliliters/min. and
the temperature averaged 21C.
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~ 105743~
NITRIFIC~TION TE5T DATA
DISSOLVED 2 pH NITRATE-N NITRITE-N
TEST INF. EEE'. INF. EFF. _NF. EFF. INF. EFF
1 8.4 0.3 7.1 6.6 1.6 4.2 1.7 4.4
2 ~.1 0.4 7.6 6.3 1.6 4.1 0.~ 4.3
; 3 8.2 0.6 8.0 7.0 0.7 3.3 0.8 3.9
4 8.6 0.7 7.6 7.0 0.7 2.6 0.8 3.2
8.6 0.5 7.4 6.6 1.8 3.6 0.7 4.3
6 9.8 0.8 8.1 7.1 1.8 5.8 0.6 ~.4
7 8.5 0.5 7.6 6 9 0.6 5.5 0.1 0.1
AVERAGE ~.7 0.5 7.6 6.8 1.3 4.2 0.7 3.8
, ~:
l At the flow rate of 9.7 gallons per minute per square
'! ~ foot, the detention time in the 5.5 foot fluidized bed
was less than 5 minutes. It can readily be seen that
oxygen was limiting the process as only 0.5 mg/l was left
~-, in the effluent and if pure 2 had been used re ammonia '
.~.~ . . . ..
'`J~ could have been nitrified. Also, only half or less of
~ the column was seeded during this test period and much
. ~ ~ , . .
. ' greater nitrification would be expected for a fully seeded --
`~ column. In effect, 6 mg/l of NO2-N ~ NO3-N were pro- ~ `
~` duced in this short time period which is truly signi- ~
-' ficant in light of the long detention periods normally ~ ;
required with prior art processes.
The presently preferred embodiments of the inven~
tion have been described for purposes of explanation. It
; should be understood that modifications ma~ be made therein
as will appear evident to those skilled in the art to which
~t
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~ ~57430
the invention pertains. It is therefore, intended to
: , encompass all such changes as fall within the true spirit
of the invention.
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