Note: Descriptions are shown in the official language in which they were submitted.
o l~I C ~ r~o~
The invention described herein was made in
the performance of work under a N~SA contract and is
subjcct to tlle provisions of Section 305 of the
National ~eronautics and Space Act of 1958, Public
Law 85-568 (72 Stat. 435; 42 USC 2~57).
.~ .
~CKGROUN~ OF Tll~ INVENTION
1. Field of the Invention~
The present invention generally relates to
a waste water treatment process and, more particularly,
to a process and system for treating raw liquid waste
which contains organic matter which is dissolved and/
or suspended in the liquid.
' `
2. Description of the Prior ~rt:
.. ~
The ~robl~ms facing municipalities in treating
raw sewage, which is one ~orm of waste water, are well
: ~ ,
~;nown. The sewage consists of water contaminated by
; : ..
organic and inorganic matter which is dissolved in
the water as well as organic and inorgallic matter wilich
is not dissolved, namely suspended in t}~e water~ ~TIle
.
~ . --2--
'
. ` ~. ' `- `` - ~ ` : ` `. . . .
` :` . . , `: . `:.`
S~ i6
latter-type contaminant m~y be divided into two graups
of materials, those which are settleable in the water
and those which are not settleable and tend to float
on top of the water. The function of any sewage treat-
ment system is to separate substantially all thesuspended matter from the water as well as to greatly
reduce the organic matter dissolved therein, and there-
after dispose of the separated matter.
The separated contaminants which are mixed
0 with some water and therefore are in slurry form,
` often referred to as sludges, are biologically active
until stabilized by subsequent treatment~ The
stabilization is genexally achieved by bioLogical
digestion. Such digestion is sometimes used to
produce combustible gases such as methane, useful as a
source of enerqy. Howeverr the remaining solid material
presents diEficult and costly disposal problems.
Digested ~humic) solids have been processed to
fertili~ers and soil conditioners. lhis practice is
generally not economical and the quantity available
greatly exceeds the market demands. Municipalities are
findinc3 it increasinqly difficult to dispose o~ the
remaining sludge solids in waterways, oceans or land-
fills, due to their ecological impact. Legislation ~.
is being considered to reduce and eventually ~orbid such
`~ solid d~lmpinq. Thus , disposal of solids, produced by
prior art treatment systems, present a very severe pro-
` ~lem, in addition to the high disposal cost. Other
.:`'
.~
3~152
.,
~Sl56f~
disadvantages of prior art systems in which biological
digestion is employed include the large land area of
aeration basins required for their operation, ~nd the
releasillg of o~fensive odors. ~lso, prior art systems
are relatively inc~ficient and must be carefully
monitored and controlled to prevent any unbalancing
in the biological digestion. That is, the types and/or
amounts of contaminants per liter of water must be
controlled to be within specified limits in order not
to upset the biological digestion process.
.
~n attempt to reduce the amount of solids
~; re~uiring disposal is described in U.S. Yatent No.
3,640,820. Therein, a sewage treatment process is
described in which the sewage sludges are converted
into an active material which is used in the process. ~-
Several disadvantages of the system described in said
; patent are apparent. The proposed process is on~
employing biological digestion and therefore suffers from
all of the shortcomings, hereinbefore discussed. In
addition, it reguixes the use of a conditioning agent
in the active material production.
In the February 22, 1972 issue of Chemical
~ngineerin~, a process developed by DuPont and known
as P~CT for Powdered Activated Carbon Treatment is
;~ 25 disclosed. Therein, activated carbon, which is not
~ produced fro~ contaminants in liquid waste is required,
:` ~
~ ~
~ 3/1S2
~L~51~6~
ther~by increasing process costs. ~lso, t~le amount of
material, requiring final disposal, is not reduced and
therefoxe the disposal cost is high and the disposal
problems are not solved~
S O~J~C~l~S ~ND SUM~Y OF '~'~IE INV~NrrION
'.~ . . ' :
It is a primary object of the present
invention to provide a new sewage treatment s~stem
and process.
Anothex object of the invention is to provide
a sewage treatment process in which the contaminants
are used to form a material without the addition of a
conditioning agent, with the material being used in
~ the treatment process.
'. ~ ~ .
Yet another object of the invention is to
provide a highly efficient sewa~e treatment process
in which biological processing is no~ required and in
which substantially all the objected-to contaminants
are removed in the process by means of a material which
is formed from the contaminants, with the amount of
material requiring final disposal being inert and
. . ~ . .
~ only a fraction of the total amount of contaminant . I;
'', .
~' .,
.
., ~
~ -5-
.;`
-- . . .
l~S~
~hese and other objects of the invention are
achieved by a treatment process in which at least the
non-dissolved matter, hereinafter also referred to as
solids of screened raw sewage are separated in a primary
settler from the water which contains the dissolved
organic and inorganic matter. As will be pointed out
hereinafter, the separation of the non-dissolved
settleable solids from the water is facilitated by the
addition of a slurry o~ an activated carbon and ash
material which has been used down-stream in the process.
The non-dissolved settleable soIids together with the
slurry of the activated carbon and ash material which
settle on the bottom o the primary settler are
removed as a wet slurry-and-primary-sludge mixture from
the primary settler and supplied to a filter. Therein,
the mixture is supplied to a pyrolysis reactor. The
latter is also supplied with the non-dissolved non-
; settleable contaminants (solids) from the top of the
primary settler.
In the reactor, the material supplied thereto
is converted into a material W}liC}I consists of activated
carbon and ash. The activated carbon and ash material
is iormed into a primary slurry by the addition of water
and is added to the water rom which the non-dissolved
matter has been separated in the primary settler.
The water and the activated carbon and a~h n~e
-6- :
,, .
~ ~'',,
,. .
.. . . . ~ ...... . ,. - - ~
- llD51S~i6
introduced illtO a secondary settler, wherein a very
high percenta~e of the organic matter, which is
dissolved in the water, is adsorbed onto ~he carbon
and ash~ The latter, after adsorbing the dissolved
organic matter is removed rom the secondary settler,
as a secondary slurry, and is directed to the primary
I settler into which the screened raw sewage is initially
introduced. The addition of the secondary slurrv,
i.e., tlle partially used carbon and ash material to the
screened ra~ sewage greatly reduces the separation time
of the non-dissolved settleable matter from the
sewage water. In addition, the pxesence of the carbon j~
in the slurry-and-primary-sludge mlxture which is
.; ~ !
supplie~ to the filter acts as a filtering aid. It
promotes faster dewatering of the mixture and therefore
drier material for the pyrolysis step. ,,
The novel features of the invention are set
;', :
~ forth with particularity in ~e appended claims. The
: -
invention will best be understood from the following
description when read in conjunction witll the
: ,
;l accompanying drawings.
BRIEF DESCRIPTION OF TflE D~A~IINGS
. :' r
~` Figuxe 1 is a general block diayram of the
l novel system and process of the present invention; and
:~
Figure 2 is a simplified cross sectional view
l of one possible embodiment of a pyrolysis reactor, shown r~
'.'' ,
in Figura 1.
`~; - 7
:- ' ~
lOS~5~
L)L::SCI~IPTIO~l OF THE PREFER~ED L.t~UODI~ NTS
~ttention is now directed to the dra~ing
wherein numeral 10 designates a primary settler of a
sewage treatment system in accordance with the present
invention. As is known, raw sewage or wastewater con-
sists of water contaminated by various organic and
inorganic m~terials, some of which are dissolved in
the water while others are non-dissolved and are
suspended ~lerein. The non-dissolved suspended materials
are either of the settleable or the non-settleable
types. The latter tends to float on top of the ,F
water. The ~unction of any raw sewage treatment process
is to remove the non-dissolved suspended materials,
and as much as possible of the dissolved organic
` 15 matter ~rom the water. r
:
~`~ In accordance with the present invention,
~j raw s~wage is first screened by appropriate means
., .
`~ (not shown) in a manner well known in the art to remove
~`~ all relatively large objects as well as most of the
sand in the raw sewage. The screened raw sewage,
hereinafter simply referred to as screened sewage, which
is fed to the system on line 11 is introduced into a
':: 1
contactor or 10cculator 12 wherein it is mixed
with an incoming secondary slurry. ~s will be
described hereinafter, the incoming secondary slurry is
~ ', , . '-
- 8-
:` `
~ )S156~
a slurry of activated carbon and ash material which
wa~ partially used down stream. ~fter appropriate
mixillg, the screened sewage Wit}l the secondary slurry
are fed to tlle prima~y settler 10.
In the present invention, substantially
all of the non-dissolved suspended solid material is
removed from the sewage water in settler 10. The
non-settleable material which is generally skimmed
of~ the top of the water is supplie~ to a pyrolysis
j 10 reactor 15 directly via line 16. The settleable
I material, ~enerally referred to as primary sludge,
` whicl~ is quite ~et, i.e., has a hiqh water content,.
is supplied to a dewatering stage 17, such as a ~ilter. I
The function of the filter 17 is to dewater the ~
primary sludge. The dewatered solids, generally in !':
the form of relatively dry cakes of solids, are
1, , ~
, supplied to the reactor v:ia line 18. Thus, the
reactor 15 ls supplied with all the non-dissolved ~ ;
suspended matter, both organic and inorganic, pxesent
in the incoming screened sewage. The sewage ~Jater
from which all the suspended matter was removed in
; settler 10, is supplied via line 21 to a contactor
.: :
22 and therefrom to a secondary settler 20. The water
from filter 17, which is relatively free of any suspended
matter is preferably combined with the effluent of
settler 10 in line 21 or in contactor 22, as represented
by daslled line 23.
: ;, ' ' '~:' ' '.~'
'
: ` ' '
:. .
. . .
~~~ 73/152
~OS~S66
~s is appreciated, the settling time of
settleable contaminants in screened sewage is quite
lon~. It has been discovered that the settling time
; for all non-dissolved settleable matter can be reduced
to less -than an hour by mixiny the screened sewage
in the contactor 12 with a material consisting of
activated carbon and ash and thereafter introducing
- the mixture into settler 10 wherein settlin~ ta};es
place. The settling rate of the non-dissolved
settleable matter seems to depend on the ash content
as well as the carbon particle size o the activated '
carbon and ash material. Tests with an activated
carbon and ash material with 50~ ash and particle
size in the range of 200 mesh, produced total settling
(in settler 10) of all settleable matter in 35
-` minutes, as compared with com~ercial carbon containing
little or no ash which showed very poor settling
characteristics. ~ith such material, fine matter
xemained in suspension for as long as 24 hours.
.; .
The activat~d carbon tends to adsorb to some
extent, various substances, such as DDT, phosphates,
nitro~enous substance, some metal salts, and organic !
complexes of mercury which are not easily separable
from water by other means. It has been discovered that
thc additioll of the carbon and ash material reduces
turbidity, removes odors and reduces foaming.
' ',
1 0 -
.~. . ' ~ .
``` ~05~66
~ s will be pointed out h~reinafter, in the
novel process of the pres~nt invention, an activated
carbon and ash material is produced in reactor 15 from
all t~le contamillants extracted from the sewaye water.
This material after being partially used to extract
- most of the organic matter which is dissolved in the
water is mixed with screened sewage in contactor 12
and thereafter, the mixture is supplied to the primary
settler 10 to facilitate the separation of the non-
dissolved settleable matter from the water. In
accordance with the present invention, the material
which is supplied to the filter 17 is not only primary
sludcJe (non-dissolved settleable matter) but rather
a mixture of a carbon and ash slurry and primary sludge.
Alternately stated, it is a slurry of a mixture of
carbon and ash particles and primary sludge. ~he '~
presence of the carbon in this mixture is very helpful
in the filtering operation~ The carbon acts as a
iltering aid. It tends to promote faster filtering
and higher dewatering of the mixture. Thus, drier
material is supplied from the filter 17 to the reactor
15.
~ . ;.
From the foregoing, it is thus seen that the
reac~or 15 is supplied with the relatively dry solids
from tlle filter 17 and ~ith the non~settleable sewage
con taminants from the primary settler 10. In the
reactor, all the supplied material is pyrolyze~ under
~, r
,~
- -- ....... __ ~... .
1[1~1566
controlled temperature and pressure conditions and
is converted into an activated material which consists
of activated carbon and ash. This is achieved without
the addition of any conditionin~ agents. ~s part of
the pyrolysis operation, various ~ases, including
combustible gases, such as methane and carbon monoxide,
are released. Such gases are used to provide at least
par. of the energy needed for the system's operation.
Tne ash component represents the pyrolyzed
inorganic matter, the major components of which are
believed to be calcium, magnesium, iron, phosphates,
; sulphates and oxides. The carbon component represents
the pyrolyzed organic matter. ~ careful inspection of
the material reveals that it does not consist of a
mixture of separate carbon particles and ash
particles but rather of particles which are a combination i
of carbon and ash. It has been noted that`the activated
carbon and ash material pxoduced from typical domestic
screened raw sewage has about a 50% ash content which
is very useful in the separation of the settleable
solids from the water in the primary settler lO.
'
; It should be stressed that the material
produced in the rcactor 15 is activated rather than r
inactivated carbon and ash. Activated carbon and various
25 tec`~niques of producin~ it are described in a book
; entitled "~ctivated Carbon" by John ~. }~ssler,
; publishecl in 1963 by Ch~mical Publishin~ Companyj Inc.,
of Ne~r York.
": - '.':,
~ 12-
.: :
3L~S~i66
Tll~ fresh activated carbon and ash from the
reactor 15 is combined with clean water to form a
primary carbon-ash slurry which is supplied to the
con-tactor 22 via line 2~. The latter may incorporate
a pum~ 25 to pump the primary slurry to the contactor
22. The pump which may be a centrifugal pump may also
be used to control the average size of the particles
of the carbon and ash material. The fresh activated
carbon and ash is mixed in contactor 22 with the
water, from which all non-dissolved matter was removed
and which now contains only the dissolved matter, both
organic and inorganic. This mixture is then supplied
to the secondary settler 20. Therein the activated
; carbon and ash adsorbs a very hign percentage of the
dissolved organic matter and settles on the bottom
of settler 20. F
' ' '
The adsorption eficiency was found to be
quite high due to the fact that the adsorbing carbon
; is the fresh carbon from the reactor 15. ~lso, since ;~
the water in settler 20 is free from any non-dissolved
contaminants such as greases, which were removed in
the primary settler 10, none of the carbon-ash particles
becomes coated with any matter which may inhibit the
adsorbability of organic matter thereon. The
activated carbon and ash material is capable of
aclsorbing the organic matter dissolved in the water
even at relatively low organic matter concentration.
It has been discovered that very good results are achieved
. ' ' ~
- -13-
.~ .
''
.. . . . . .
lOS~SG6
when tl~e primary slurry contains an amount (by weight)
of carbon about equal to the amount of total organic
matter in the original screened s~ewage which enters
the prim~ry settler 10. After an appropriate contact
S time, e.g., 20 minutes, ~he activated carbon and ash,
which adsorbed the organic matter is removed as a
secondary carbon-asll slurry from settler 20 and i5
supplied via line 26 to the contactor 12, to which the
screened sewage is supplied.
The reasons or adding the secondary carbon-
ash slurry to the raw sewage have bèen previously
discussed. Even though the carbon and ash material in
the secondary slurry was already partially used in the
secondary settler 20, its usefulness is not at an end. -`
It facilitates the separation of the non-dissolved
suspended matter of the sewage in addition to adsorbing
or otherwise removiny some materials which are difficult
to othe~rise separate from the water. The partially
used activated carbon and ash in the primary settler
10 is also believed to adsorb some of the inorganic
: . .
and organic matter dissolved in the water. ~lowever,
its primary function is to ~acilitate the separation
of non-dissolved matter from the sewage water.
.
;~ From the foregoing, it is thus seen that in
~ 25 accorc~ance with the present invention, an activated
: ,~
.
carbon and ash material is formed from the contaminants ,`
of the screened sewage without the addition of any
., ,~ .
` -14-
:. , ,, , . .. .. _
~051'~6
conditioning agents. This activated carbon and
ash matcrial is first used to adsorb most of the
organic matter dissolved in the sewaye water from which
non-dissolved matter was previously removed. Then,
5 the p~rtially used carhon and ash material is mixed
with the incoming raw sewage. The presence of the
material facilitates the separation of non-dissolved
settleable matter from the sewage water by greatly
reducing the settling time. The mixture of the wet
non-dissolved settleable matter, representing primary
sludge, together with the used carbon and ash material
are then supplied as a slurry-and-sludge mixture to
the filter, whose function is to reduce the mixtur2
water content. The carbon present in the mixture acts :
as a filtering aid which increases filtering rates and
reduces the water content of the solid materials which
~ are supplied to the reactor 15 for pyrolysis.
: :
From the foregoing, several significant
. . .
; advantages of the present invention should become
ap~arent. First, the present invention eliminates
the biological digestion stage which is typical of most
prior art systems. Its elimination reduces system
size, c~mplexity and cost. Secondly, all the
material which is needed for the treatment process,
i.e., thc activated carbon and ash material is produced
.
fxom the scwage contaminants Wi~O~It tlle nced for any
additional conditioning agents. Tests of the
present invention with typical screened sewage indicate
~, .
, .:,
.` . ,
-15-
. .
: .. ...... . .. ... .. ...
: , . ~ - .. . . .. . .... .
951~
tllat in the pyrolysis step, suficient combustible
matter and gases are formed which can provide nearly
all the power necessary to sustain the system's opera-
tion. Thus, energy from external sources may not
be required. ~lso, these tests indicate that the
amount of material which has to be disposed of is
only about 1/10 the total contaminant materials in the
sewage, thereby gr~atly reducing ~le material
disposal problem. !
The basic system in accordance with the
present invention is effectively a 2-stage system since
it includes only the primary and secondary settlers
in the water flow ~ath. Laboratory tests indicate
that with the present system and process between 87
and 93% of all organic matter can be removed ~rom the
.Y
water after passing through the secondary settler. In
the prior art, 2-stage systems, with one of the stages
being a biological digestio~ stage, only about 80-85% of
the organic matter is removed. Thus, the present system
is clearly more efficient.
~ ~ .
It is believed that the organic matter
xemaining in the water, in settler 20 a~ter it was
treated by the fresh activated carbon and ash material r
consists o~ matter of high molecular weight which i5 .
generally not adsorbable by carbon. By hydrolyzing
the raw sewage in the primary settler or ahead of it,
r
,~ .
.~, .
-16-
, .
:,' , .............. ~
... .. .~
~05156~;
~l~ molecul~r weiyht of such m~tter may be lowered so
that even a higher percentage of the organic matter
will become adsorbed by the carbon. Thus~ hydrolysis
may increase the system's efficiency.
S In practice, most of the activated carbon
and ash material which is introduced into the ~-
secondary settler 20 settles therein and is removed
tllerefrom as the secondary carbon-ash slurrv.
~owever, the carbon and ash material includes some
very small particles which tend to remain suspended
in the water in the secondary settler. They can be
removed by passing the water effluent from the secondary
settler 20 through an appropriate filter, designated ~ -
by numeral 30. The carbon parti~les t~apped by filter
30 may then be removed from the filter in the form o r~.
a fine carbon slurry and thereafter be combined with
- the secondary carbon-ash slurry for subsequent use in
the primary settler 10. ~lternately, the fine carbon
. ~
slurry from filter 30 may ~e supplied directly to the
filter 17 as indicated by dashed line 32, for use
therein together with the other matter which is
supplied thereto from the primary settler 10
It should be appreciated that for
the system to be self-sustaining, at least as far as
the E~roduction of the activated carbon and ash material,
the treated Se~Jage should contain a sufficient amount
. .~ r
'
-17-
~ _ ............................................... . ..
of organlc contaminants. Processed typical domestic raw
sewage contains a sufficient amount of contaminants.
~'he average composition of domestic raw sewage has been
described in the literaturc and is well known by those
familiar with the art. The present invention is
capable of processing sewage with higher than conven-
tional contaminant content. The hi~her contaminant ~!
content merely results in tlle production of more
activated carbon and ash material which is no way
detrimental to the system's operation. The additionalcarbon and ash material may be used as a source of
energy. This is not the case in prior art systems in
which biological digestion is employed. Therein, the
types of contaminants, such as toxic chemicals and/or
tlleir amounts cannot exceed certain limits. Otherwise,
- the biological digestion process is greatly upset ,
- ~hich often causes the entire treatment process to be
shut down. It is this high sensitivity of prior art
.i, .~ ~ .
systems, which employ biological digestion to over-
contaminated sewage, ox to liquid wastes which contain
- certain contaminants, e.g., chromium, acids, and
alkalies, whicn often forces municipalities to iI~ibit
various industries from injecting their wastewater into
the wast~water networks of the municipalities.
.. ~
~lthough ~le invention has been described in
connectioll with treatillg screene~ raw sewage, it should
be apparent that it is applicable to trea~ any type of
waste water, which is contaminated by organic and inorganic
., ~
- ~
:
materials. Screene~ raw sewage is only one type of
waste ~ater. Furthermore, the invention can be used
to treat any liquid contaminated by oryanic and inor-
ganic materials in any industrial or agricultural
- S process. As used herein, the term raw liquid waste -
inten~s to refer to any contaminated liquid, including
water but not limited thereto. For example, the
present invention may be used to treat raw liquid
waste produced in an industrial or agricultural
process in order to enable the liquid to be reused.
~lso, it may be used to reduce the contaminant content
of the liquid waste to permit the liquid to be
j injected in the general wastewater network of a
neighboring municipality or into the natural
surroundings.
., ~ .
. ; ,~.
In one embodiment, which was actually reduced
~ to practice, very satisfactory activated carbon and ash
`l material was produced in reactor 15 which operated at
~; a temperature between 1200 and 1800 degrees Fahrenheit
t660 to 98Z degrees Centigrade) under an atmosphere
composed of a mixture of gases. l'he mixture of ~ases,
at a pressure slighly higher than atmospheric press~re,
was composed of the gases derived from the pyrolysis
operation consisting mainly of carbon dioxide, carbon
; 25 monoxide, hydrogen and water vapor in the form of
;~i s~lperheated steam. The pyrolysis reactor 15 consisted
~-` of three principal reaction zones comprised of: Zone 1,
watcr cvaporation or drying, Zone 2, carbonization or
:`! r
: , :
.
. .
.....
l~D515~
decomposition, Zone 3, activation or selective oxida-
tion, as shown in simplified form in Fiyure 2. The
pattern supplied to the reactor unit lines 16 and 18
was introduced into Zone 1 thrcuyh a valve 40. The
matter was advanced from zone to zone ~y ral~es supported
on a rotatable shaft (not shown). ~leat was provided by
a combustion chamber 42. The mixture of gases which
was formed served to dry the matter in Zone 1 as well as
activate the carbon in Zone 3. As is appreciated,
some of the gases, such as methane and carbon monoxide
which are combustible, can be used as a source of
ener~y. Although, the superheated steam was used to j~;
produce a satisfactory activated carbon and ash, if ~-
desired, steam produced from clean water may be used -~
for the carbon activation.
r~
- Retention time in Zone 3, activation, deter- j
mined the degree of activation and varied from 15
minutes to one hour. ~etentlon time is a function
oi the r~actor furnace design and can vary from as
little as five seconds to as much as five ~lours.
Lon~er times ~or activation tend to produce ~reater
activation of the carbon but reduce tlle proportion of
carbon and increase the proportion of ash. Lower
retention times for activation tend to decrease the !
de~ree of activation and increase the proportion of
carbon and decrease the proportion of ash. The
activation retention times of lS minutes to one hour
.; ~ .
`~ . ' , '~ ''.
.. l , .
-20-
~,'`. ' . ' , .
~05~LS66
~as founcl to pro~uc~ ~he proper dec3ree of activation
o~ tl)c product and t~le proper combination oE carhon
and ash for satisfactory operation of the process.
'''
It should be appreciated that modifications
S may be made in the system and process`hereinbefore
; described without departiny from the spirit of the
invention. For example, if the raw liquid waste is o
a type in which the non-dissolved settleable matter ~,
settles speedily without the addition of any carbon
and ash material, the secondary carbon-ash slurry from
settler 20 may be supplied directly to the ~ilter
as represented by dashed line 44 rather than to contactor
12 and therefrom to the primary settler lO. Also, if
the raw liquid waste is highly contaminated so that a
larye amount of activated carbon and ash material is
produced, some of the material may be supplied directly
- to contactor lO rather than through secondary settler
20, while the rest of the material may be used for -
adsorbing the dissolved organic matter in the liquid
in settler 20. ~lso, although various parts of the
system were described as contactors, settlers, ekc.,
any devices performing e~uivalent functions may be l`
substituted therefor. ~ll such modifications and
equivalents are deemed to fall within the scope of the
invention as claimed in the appended claims.
~. ,
. ~ .
. r
` . ' ., `:
-21-
' . ' '
... '.
