Clarifier apparatus

A two stage clarifier apparatus for producing a clarified effluent from mixed liquor in a sewage treatment system wherein mixed liquor is partially clarified in a first quiescent zone in the first stage of the apparatus to produce a partially clarified effluent, the partially clarified effluent is transferred to an aeration zone in the second stage of the apparatus, a portion of the partially clarified effluent is transferred from the aeration zone to a second quiescent zone in the second stage of the apparatus, and fully clarified effluent is withdrawn from the second quiescent zone.

BACKGROUND AND SUMMARY OF THE INVENTION 
This invention relates to solids/liquids separators, and more particularly 
to a two stage clarifier apparatus for separating solids from mixed liquor 
in a sewage treatment system to produce a clarified effluent. 
The effluent from sewage treatment systems is commonly treated to remove 
solids and to produce a clarified effluent prior to disposal of the 
effluent, such as by releasing the effluent into the environment. Typical 
conventional clarifier apparatus devices include filtration devices, e.g. 
in a fixed bed filtration system such as that described in U.S. Pat. No. 
4,008,159 of Besik, and settling basins such as that described in U.S. 
Pat. No. 4,081,368 of Block et al. In addition, sewage treatment apparatus 
is disclosed in my prior U.S. Pat. Nos. 4,142,975 and 4,238,338 which 
includes a quiescent zone associated with the discharge end of the 
apparatus wherein solids are settled from liquids in the quiescent zone to 
produce a clarified effluent. 
Although each of the foregoing devices have met some degree of success in 
accomplishing their intended purposes, it has been determined that higher 
degrees of effluent clarification can be readily and economically obtained 
in a two stage clarifier apparatus having tank means defining a first 
quiescent zone, inlet means for supplying mixed liquor from the sewage 
treatment system to the first quiescent zone, second tank means defining a 
chamber, baffle means in the chamber for separating the chamber into an 
aeration zone and a second quiescent zone, first fluid communication means 
for withdrawing partially clarified effluent from an upper portion of the 
first quiescent zone and supplying the partially clarified effluent to the 
aeration zone in the treatment chamber of the second tank means, second 
fluid communication means providing fluid communication between a lower 
portion of the aeration zone and a lower portion of the second quiescent 
zone, and outlet means for withdrawing clarified effluent from an upper 
portion of the second quiescent zone. 
BRIEF DESCRIPTION OF THE DRAWINGS 
The inventive concepts may be more fully understood in association with the 
accompanying drawings, in which: 
FIG. 1 is a perspective view of one presently particularly preferred 
embodiment of the two stage clarifier apparatus of the invention, with 
portions removed, as used in association with one type of sewage treatment 
system; 
FIG. 2 is a top view in cross-section of the apparatus of FIG. 1, taken 
along the line 2--2 in FIG. 1; 
FIG. 3 is an end view in cross-section of a portion of the apparatus of 
FIG. 1, taken along the line 3--3 in FIG. 1; and 
FIG. 4 is an end view in cross-section of a portion of the apparatus of 
FIG. 1, taken along the line 4--4 in FIG. 1.

DESCRIPTION OF THE INVENTION 
Referring now to the drawings, the clarifier apparatus of the invention is 
shown to comprise a first stage, generally shown at 10, and a second 
stage, generally shown at 12. In the presently particularly preferred 
embodiment shown in the drawings, the two stage clarifier apparatus of the 
invention is illustrated as used in connection with a multiple stage, 
extended oxidation sewage treatment system, such as that described in U.S. 
Pat. No. 4,142,975. Thus, as shown in FIGS. 1--3, the fourth stage, for 
example, of the sewage treatment system is generally shown at 16. It is to 
be understood, however, that the two stage clarifier apparatus of the 
invention may be readily utilized in connection with other sewage 
treatment systems. 
The first stage 10 of the clarifier apparatus comprises first tank means, 
defining a first quiescent zone 18, for containing mixed liquor from the 
sewage treatment system. In the illustrated embodiment, the first tank 
means comprises a tank having a generally circular sidewall 20, an end 
wall 22, and an end wall 24, which is shown in FIG. 1 to have a generally 
hemispherical configuration and to be integrally formed with the sidewall 
20. The circular sidewall 20 may be provided with structural reinforcing 
ribs 21, as desired. Baffle means, such as baffle 26 and first quiescent 
zone end wall 27, is provided in the first tank means for separating the 
inside of the first tank means into first quiescent zone 18 and the fourth 
stage 16, for example, of the sewage treatment system. In the embodiment 
of FIGS. 1, 2 and 3, baffle 26 extends longitudinally from end wall 22 to 
first quiescent zone end wall 27, and vertically downwardly from an upper 
portion of the sidewall to a lower, intermediate area in the first tank 
means. The first quiescent zone end wall 27 extends transversely across 
the first tank means in an area intermediate the tank end walls 22, 24 
from the tank sidewall 20 to the baffle 26, and vertically downwardly from 
an upper portion of the sidewall at the top of the tank to a lower portion 
of the tank sidewall at the bottom 5 of the tank. As more fully described 
in U.S. Pat. No. 4,142,975, an oxygen containing gas is supplied to the 
fourth stage 16 of the sewage treatment system, such as through supply 
conduit 28, and is dispersed into mixed liquor in the fourth stage of the 
treatment system, such as through dispersing nozzles 30, in a manner so as 
to cause a rapid movement and uniform mixing of mixed liquor in the fourth 
stage. Flow directing baffles 32 may be provided in the fourth stage to 
direct the movement of the mixed liquor in the fourth stage in a path 
generally represented by arrows 34 in FIG. 3. 
The first stage of the clarifier apparatus further comprises inlet means 
for supplying mixed liquor from the sewage treatment system to the first 
quiescent zone 18. In the embodiment illustrated in the drawings, the 
inlet means is provided by baffle 26 which terminates above the lower 
portion of sidewall 20, thereby providing fluid communication between the 
fourth stage 16 of the sewage treatment system and the quiescent zone 18. 
As mixed liquor or other liquids are added to the fourth stage 16 of the 
sewage treatment system, a portion of the mixed liquor in the fourth stage 
16 is forced under the baffle 26 and into the quiescent zone, as generally 
represented by arrow 35 in FIG. 3. 
Referring now to FIGS. 1, 2 and 4, the second stage 12 of the clarifier 
apparatus comprises a second tank means defining a chamber 36, for 
receiving partially clarified effluent from the first tank means and for 
effecting further clarification of the effluent. The second tank means may 
be formed, for example, by sidewall 38, having a generally circular 
cross-sectional configuration, by end wall 22, and by end wall 40, which 
is shown in FIG. 1 to have a generally hemispherical configuration and to 
be integrally formed with the sidewall 38. The second stage of the 
clarifier apparatus further comprises baffle means, such as baffle 42 in 
the chamber 36 extending longitudinally from end wall 22 to the end wall 
40, and from an upper portion of the sidewall 38 vertically downward to a 
lower intermediate area of the chamber 36, for separating the chamber 36 
into a first aeration zone 44 and a second quiescent zone 46. Fluid 
communication means 47 is provided in the second stage of the clarifier 
apparatus for providing fluid communication between the aeration zone and 
the second quiescent zone. In the embodiment illustrated in FIGS. 1, 2 and 
4, fluid communication means 47 comprises baffle 42 which terminates at 
its lower end somewhat above and spaced from the lower portion of tank 
side wall 38. Thus, as partially clarified effluent is supplied to 
aeration zone 44, as will be hereinafter further described, a portion of 
the liquids in the aeration zone pass under the baffle 42 in a path 
generally represented by arrow 48. 
The second stage of the clarifier apparatus further comprises gas supply 
means 50 for supplying an oxygen containing gas to the aeration zone at a 
location intermediate the baffle 42 and the tank sidewall 38 in an 
intermediate lower portion of the aeration zone. The gas supply means is 
located in relationship to the aeration zone so as to provide an adequate 
supply of oxygen to partially clarified effluent in the aeration zone to 
ensure aerobic metabolism of any microorganisms which may be located 
therein and to cause partially clarified effluent in the aeration zone to 
rapidly rise vertically upward in the aeration zone adjacent the baffle 42 
and then circumferentially outward and downward in a continuous 
semicircular pathway, generally indicated by arrows 52 in FIG. 4 to the 
bottom of the aeration zone and then vertically upward again, thereby 
causing a uniform, intimate and thorough mixing of the oxygen containing 
gas throughout the partially clarified effluent in the aeration zone and 
maintaining any solid, particulate matter and microorganisms in generally 
uniform suspension in the partially clarified effluent in the aeration 
zone. As best shown in FIGS. 2 and 4, the gas supply means 50 comprises a 
conduit 54 horizontally mounted in a lower intermediate portion of the 
aeration zone. The conduit 54 is provided with a plurality of diffusers 56 
spaced along the conduit 54 for diffusing an oxygen containing gas in the 
conduit into partially clarified effluent in the aeration zone. The gas 
supply means further comprises means for supplying an oxygen containing 
gas to the conduit under pressure, such as a pump (not shown), and an 
interconnecting conduit, such as conduit 58, for providing fluid 
communication between the pump and the conduit 54. 
The two stage clarifier apparatus of the invention further comprises fluid 
communication means 60 for withdrawing partially clarified effluent from 
an upper portion of the first quiescent zone 18 and supplying the 
partially clarified effluent to the aeration zone 44 of the second stage 
of the apparatus. In the embodiment illustrated in FIGS. 1, 2 and 3, fluid 
communication means 60 comprises a weir 62 extending longitudinally across 
an upper portion of the first quiescent zone 18 substantially from end 
wall 22 to first quiescent zone end wall 27 at about the upper liquid 
level 64 in the first quiescent zone. The weir 62 may be mounted in the 
first aeration zone by means of straps 66, or by other suitable means. A 
conduit 68 is provided extending through the end wall 22 and providing 
fluid communication between the weir 62 and aeration zone 44 in the second 
stage of the apparatus so that partially clarified effluent in the weir 62 
is allowed to freely flow into the aeration zone of the second stage of 
the clarifier apparatus. 
The two stage clarifier apparatus further comprises outlet means 70 for 
withdrawing clarified effluent from an upper portion of the second 
quiescent zone 46. In the embodiment illustrated in FIGS. 1, 2 and 4, 
outlet means 70 comprises a weir 72 extending longitudinally across an 
upper portion of the second quiescent zone 46 substantially from end wall 
22 to end wall 40 at about the upper liquid level 74 in the second 
quiescent zone. The weir 72 may be mounted in the second quiescent zone 46 
by means of straps 76, or by other suitable means. A conduit 78 is 
provided extending through end wall 40 and providing fluid communication 
between the weir 72 and the outside of the apparatus, thereby permitting 
suitable subsequent disposal of clarified effluent discharged from the 
weir 72. 
In a presently particularly preferred embodiment, the apparatus may 
additionally comprise transfer means 80 for transferring a portion of the 
liquids and/or retained solids in a lower portion of the aeration zone 
back to the sewage treatment system. In the illustrated embodiment, 
transfer means 80 comprises an airlift pump having an inlet 82 in a lower 
portion of the aeration zone 44, such as adjacent a lowermost area of 
sidewall 38 as shown in FIG. 4, an outlet 84 in the fourth stage 16 of the 
sewage treatment system, and interconnecting conduit means 85 for 
providing fluid communication between inlet 82 and outlet 84. A suitable 
gas, such as air, is introduced into an intermediate portion of the 
conduit means 85, such as from a pump (not shown) through gas supply tube 
87 and junction-T 87, to lift liquids and/or retained solids through 
airlift pump inlet 82 and carry the liquids and/or solids out of outlet 
84. In this manner, solid materials which might otherwise build up in the 
second stage of the clarifier apparatus may be continuously or 
intermittantly recycled and returned to the sewage treatment system for 
further biological treatment. 
In operation, mixed liquor which has been subjected to biological and/or 
chemical treatment in earlier stages, such as first, second and third 
stages (not shown), for example, of the sewage treatment system, is 
introduced into the fourth stage 16 of the treatment system through a 
conduit as indicated by arrow 91. In the fourth stage of the sewage 
treatment system, mixed liquor is maintained in continuous movement in the 
flow path indicated by arrows 34 due to the action of the oxygen 
containing gas dispersed into the mixed liquor through nozzles 30 and to 
the flow path guidance provided by baffles 26, 32 and by first tank means 
sidewall 20. A sufficient amount of oxygen containing gas is supplied to 
the fourth stage 16 of the sewage treatment system to maintain solids in 
substantially uniform suspension in the mixed liquor in the fourth stage 
16 and to provide substantially constant, uniform contact between the 
solids and oxygen from the gas. 
As mixed liquor is introduced into the fourth stage 16 of the sewage 
treatment system, a portion of the mixed liquor in the fourth stage flows 
out of the normal flow path 34, under the baffle 26 and into the first 
quiescent zone 18 of the first stage of the two stage clarifier apparatus. 
A substantial portion of the biological sludge, or other solid particulate 
matter, in the mixed liquor settles to the bottom of the quiescent zone 18 
and reenters the flow path 34 in the fourth stage of the sewage treatment 
system for further biological treatment. The supernatant in the upper 
portion of the quiescent zone 18 thereby becomes a partially clarified 
effluent. As best shown in FIGS. 1, 2 and 3, baffle 26 may be provided 
with a baffle extension 93 at its lower edge which is downwardly, inwardly 
sloped with respect to quiescent zone 18 to provide a settling plate 
surface 94 for assisting in the settling of solids from mixed liquor in 
the quiescent zone. The baffle 26 and the baffle extension 93 may be 
supported in the first tank means by support members 98 or by other 
suitable means. 
As mixed liquor is introduced into the fourth stage 16 of the sewage 
treatment system, a corresponding amount of partially clarified effluent 
is withdrawn from the first quiescent zone 18 through weir 62 and is 
transferred into the first aeration zone 44 of the second stage of the 
clarifier apparatus. 
Liquids and any solids in the first aeration zone 44 are maintained in 
continuous movement in the flow path indicated by arrows 52 due to the 
action of oxygen containing gas dispersed into the liquid through nozzles 
56 and to the flow path guidance provided by baffle 42 and by second tank 
means sidewall 38. A sufficient amount of oxygen containing gas is 
supplied to the first aeration zone of the clarifier apparatus to maintain 
any solids in substantially uniform suspension in the liquid in the 
aeration zone and to provide substantially constant, uniform contact 
between the solids and oxygen from the gas. Since there is no raw organic 
matter in the aerobic environment of the first aeration zone, any 
biological solids in the liquid of the aeration zone become cannabalistic, 
undergo autodigestion or are subject to consumption by higher organisms in 
the food chain, as more fully disclosed in U.S. Pat. No. 4,142,975. Thus, 
any biological solids in the partially clarified effluent in the first 
aeration zone undergo further biological treatment at this stage of the 
clarifier apparatus. 
As partially clarified effluent is introduced into the first aeration zone 
44, a portion of the partially clarified effluent in the first aeration 
zone flows out of the normal flow path 52, under baffle 42 and into the 
second quiescent zone 46 of the second stage of the clarifier apparatus. 
Any remaining biological sludge, or other solid particulate matter, in the 
partially clarified effluent settles to the bottom of the second quiescent 
zone 46 and reenters the flow path 52 in the first aeration zone to 
undergo further biological treatment. The supernatant in the upper portion 
of the second quiescent zone thereby becomes a fully clarified effluent. 
As best shown in FIGS. 1, 2 and 4, baffle 42 may be provided with a baffle 
extension 95 at its lower edge which is sloped downwardly and inwardly 
with respect to the second quiescent zone 46 to provide a settling plate 
surface 96 for assisting in the settling of solids from partially 
clarified effluent in the second quiescent zone. The baffle 42 and the 
baffle extension 95 may be supported in the second tank means by support 
members 99 or by other suitable means. 
As partially clarified effluent is introduced into first aeration zone 44, 
a corresponding amount of fully clarified effluent is withdrawn from the 
second quiescent zone 46 through weir 72 and is transferred out of the 
clarifier apparatus through conduit 78, as indicated by arrow 97, for 
suitable disposal. 
In the event that an undesirably large amount of solids should accumulate 
in the first aeration zone 44, a portion of the partially clarified 
effluent and accumulated solids may be intermittantly or continually 
removed from the second stage of the clarifier apparatus through airlift 
inlet 82 and recycled back to the fourth stage 16 of the sewage treatment 
system through outlet 84. 
While the inventive concepts have been described in association with a 
presently particularly preferred and illustrative embodiment of the two 
stage clarifier apparatus, it is contemplated that various modifications 
may be apparent from the disclosure. For example, although the invention 
has been described as used in association with a four stage extended 
oxidation sewage treatment system, it is apparent that the inventive 
concepts may be readily modified for use in association with other types 
of systems. Such modifications are intended to be within the scope of the 
appended claims, except insofar as precluded by the prior art.