Water clarification system adapted for removing particulate matter of greater than a predetermined size

Apparatus adapted for use in a water clarification system which removes particles of greater than a predetermined size from the clarified water includes a screen or a pair of concentric screens positioned in a clarified water storage area between an inlet and a clarified water outlet. One or more spray heads for direct a shower of high pressure filtered clarified water at the outlet side of the screen or screens to loosen or remove particles therefrom. In addition, a rotating brush can act on the inlet side of the screen. Particles removed by the cleaning elements are recirculated through the system. Water levels are maintained by overflow control or by monitoring the water level and utilizing the output from the monitor or monitors to selectively control valves in the inlet or outlets from the system.

This invention relates to water clarification systems and more particularly 
to apparatus for use in a water clarification system which removes 
particles of greater than predetermined size from the clarified water. 
BACKGROUND OF THE INVENTION 
There are many applications where it is desired to remove particulate 
matter from water either for ecological reasons or to permit the water to 
be utilized for a desired purpose. Most commonly, such systems are used in 
industrial applications, such as paper mills, to remove particulate matter 
introduced into the water during an industrial process before returning 
the water to the river, lake, or other body from which it was originally 
obtained. 
The second, and increasingly important, application of such systems is to 
purify water for domestic use. Such systems are normally utilized by towns 
or other municipalities. 
Water clarification systems are generally of two types, sedimentation 
systems or flotation systems. Flotation systems require much smaller 
equipment for the same particle removing capacity, and are therefore 
preferred. An example of a flotation water clarification system is shown 
in U.S. Pat. No. 4,022,696 issued May 10, 1977, to Dr. Milos Krofta, the 
applicant herein. 
This system has proved capable of reducing the suspended solids or 
particles in incoming water initially containing up to 1500 parts per 
million (ppm) to below 20 ppm. While this results in clarified water 
satisfactory for most industrial applications, it is still possible to 
have solid particles in the clarified water which are of a size in excess 
of 100 to 300 microns. Such particles are big enough to clog shower heads, 
nozzles, or other very small orifices through which water passes in 
domestic and some industrial applications. 
Therefore, in order to permit flotation water clarification systems of, for 
example, the type disclosed in the above mentioned Krofta patent to be 
utilized in domestic and other applications where the water may be 
required to pass through small orifices, it is necessary that an 
additional filtering step be performed. Ideally, such filtering would be 
done in the clarification system. However, particles trappped by the 
screen or other filtering element reduce clarified water flow and, if the 
filtering element is not continuously or at least regularly cleaned, would 
in a short time completely block the filtering element. Also, even if the 
filter is cleaned, there remains the problem of how to control the buildup 
of filtered particles. Heretofore, space limitations in the system and the 
complexity of equipment for effectively cleaning the filtering element(s) 
and flushing the filtered particles have necessitated that a separate 
installation be provided for the filtering step with separate tanks, 
pumps, piping, and other components. Having such a separate facility and 
separate equipment is costly, both in terms of the additional equipment 
required and the additional space for housing such equipment. 
It is therefore an object of this invention to provide a fine particle 
removal capability that can be incorporated in known water clarification 
apparatus. 
A more specific object of the invention is to provide a flotation water 
clarification system capable of continuously removing particles of above a 
predetermined size, such as for example 100 to 300 microns, from the 
clarified water without requiring a costly additional installation. 
Another object is to provide a fine particle removal capability that can 
filter either 100%, or some lower percentage, of the total clarified water 
flow. 
SUMMARY OF THE INVENTION 
In accordance with the above, this invention provides apparatus adapted for 
use in a water clarification system having an area for storage of 
clarified water and at least one clarified water outlet, which apparatus 
removes particles of greater than a predetermined size from the clarified 
water. The apparatus has a filtering element with openings generally less 
than the predetermined size positioned between the inlet to the clarified 
water storage area and a clarified water outlet. The filtering element is 
preferably a screen. There is also a cleaning means operative on the 
outlet side of the screen for loosening and removing particles from the 
screen. This cleaning means is preferably a row of shower nozzles which 
direct water, preferably filtered clarified water, under pressure along a 
line from substantially one edge of the screen to the other in one 
dimension, and means for moving the row of nozzles relative to the screen 
in the other direction, whereby fluid pressure may be applied across the 
entire outlet side of the screen. In a first embodiment, there is also a 
second cleaning means which is operative on the inlet side of the screen 
for cleaning particles therefrom. This second cleaning means is preferably 
a brush that rotates about its own axis and also is mounted to rotate 
around in the clarified water area to reach the entire screen. If the 
screen is positioned to intercept all, or substantially all, of the 
clarified water flow, the invention also includes means for controlling 
the buildup of fine particles at the inlet side of the screen. In the 
preferred form, this includes an outlet which removes a portion of the 
unscreened clarified water, typically 20%, and directs it back to the main 
raw water inlet via an air dissolver tube and a pump. 
For a second preferred embodiment, the filtering element is a pair of 
spaced, concentric circular screens positioned in the area for storage at 
a point spaced from the side walls and the bottom of the storage area. The 
cleaning means in this embodiment includes means positioned in the space 
between the screens for applying water under pressure to the outlet side 
of both screens. 
More specifically, this invention relates to a water clarification system 
which includes a cylindrical flotation tank, a carriage rotating above the 
tank, first means rotating with the carriage for inputting water to be 
clarified into the tank, such water having dissolved air and flocculating 
chemicals therein which combine to cause particles in the water to float 
to the surface of the tank, second means rotating at least in part with 
the carriage for collecting particles on the surface of the tank and for 
outputting the collected particles, and third means rotating with the 
carriage for removing clarified water from a point near the bottom of the 
tank. The system also has a clarified water outlet, a circular screen 
having openings of less than a predetermined size positioned between the 
third means and the clarified water outlet to remove particles of greater 
than said predetermined size from the clarified water and means rotating 
with the carriage for cleaning the screen. The means for cleaning the 
screen may include a brush in contact with the inlet side of the screen, 
means for rotating the brush, and means for mounting the brush for 
rotation with the carriage about the inlet side of the screen. The means 
for cleaning may also include a row of shower nozzles positioned to direct 
clarified water from substantially the top to substantially the bottom of 
the outlet side of the screen, and means for mounting the row of nozzles 
for rotation with the carriage over the outlet side of the screen. For one 
embodiment of the invention, a pair of spaced circular concentric screens 
are provided near the center of the clarified water storage area with a 
head having a row of nozzles facing each screen being positioned in the 
area between the screens and rotating with the carriage to effect cleaning 
of both screens. 
In one embodiment of the invention where 100% of the clarified water is 
filtered, desired water levels are maintained by monitoring the water 
level in at least one area and controlling either the rate at which water 
is applied to selected areas or preferably the rate at which water is 
removed from such areas to maintain desired water levels. In a second 
embodiment of the invention, desired water levels are maintained by 
permitting excess clarified water to spill over into a removal area. 
The buildup of removed particles in the clarified water storage area, which 
could alter flow rate, is controlled in one embodiment of the invention by 
flushing and draining a sufficient quantity of the unfiltered clarified 
water, for example 20%, to prevent a buildup of such particles. In another 
embodiment of the invention, a flow path of clarified water is maintained 
which carries such particles to an overflow removal outlet. 
The foregoing and other objects, features and advantages of the invention 
will be apparent from the following more particular description of 
preferred embodiments of the invention as illustrated in the accompanying 
drawings.

DETAILED DESCRIPTION 
The water clarification system 10 shown in FIGS. 1 and 2 is basically the 
system of the beforementioned Krofta U.S. Pat. No. 4,022,696 with certain 
modifications to be discussed herein to incorporate the teachings and 
apparatus of this invention. To the extent the system of this invention is 
the same as that described in the beforementioned patent, the description 
of the system herein shall be in only sufficient detail to enable an 
understanding of the current invention. Reference may be had to the patent 
for a more complete description of the water clarification system. 
The system consists of a cylindrical flotation tank 12 having a carriage 14 
mounted for rotation over the tank. As may be best seen in FIG. 1, 
carriage 14 is in the form of a frame having a pair of side bars 16A and 
16B which are joined at their far end by an arc-shaped bar 18 and are 
joined at a point beyond the center of the system by a cross bar 20, 
behind which is a C-shaped end bar 22. Frame 14 is supported by rollers 24 
which ride on the top of outer wall 26 of tank 12 and a roller 28 which 
rides on the upper surface of an inner wall 30 of the system. Roller 28 
completes a revolution around the upper surface of wall 30 as rollers 24 
complete a revolution about the upper surface of wall 24. 
Internal of cylindrical tank 12 is a clarified water storage area 34, the 
outside perimeter of which is defined by a wall 36 attached to carriage 14 
and the inside surface of which is defined by the wall 30. Area 34 is 
divided into subareas 34A and 34B by a screen 38 positioned in area 34. As 
may be best seen in FIG. 1, screen 38 is circular in shape and, for ease 
of installation and removal, is formed in three sections which are joined 
at joints 40. While the screen has been shown as divided into three 
sections in FIG. 1, it is apparent that the screen can be divided into any 
number of desired sections, or could be a single piece, depending on 
application. 
Internal of clarified water storage area 34 is a cylindrical sludge storage 
area 42 which is defined in one dimension by wall 30 and in the internal 
dimension by inlet pipe 44. Water to be clarified is applied to the system 
through inlet pipe 44 and distribution pipe 46 which pipe rotates with 
carriage 14. A plurality of pipes (not shown) extend down from pipe 46 
into tank 12 and direct jets of water at various heights into tank 12. The 
water applied to the system through pipe 44 has air and a flocculating 
chemical such as alum dissolved therein. This results in particulate 
matter in the inlet water forming and accumulating around air bubbles in 
the water and rising to the surface of tank 12, such flotation occuring in 
a well known manner. A scoop 50 mounted for rotation with carriage 14 
collects sludge from the surface of tank 12 and passes the collected 
sludge through pipe 52 and area 42 to sludge outlet pipe 54. Any sludge 
accumulating at the bottom of tank 12 is removed through ducts 55 and 56. 
A plurality of pipes 60 extends from the wall 36 into the tank 12 at a 
position a few inches from the bottom of the tank. In FIG. 1, three pipes 
60 are shown. With particulate matter floated to the top of tank 12, the 
water at the bottom of the tank in the area of pipes 60 is clarified. This 
clarified water passes under the action of gravity through a plurality of 
openings (not shown) formed in each pipe and through pipes 60 into 
clarified water storage area 34. The wall 36 and the pipe 60 are mounted 
to the cariage 14 and rotate in unison with it. As noted in applicant's 
U.S. Pat. No. 4,022,696, a rubber seal mounted at the lower edge of the 
wall 36 provides a movable barrier between the tank 12 and the clarified 
water storage area 34. 
While the water entering area 34, and in particular area 34A thereof, has 
had most of the particulate matter removed therefrom and is adequately 
clarified for most applications, particles still exist in such water of a 
size in excess of 100 to 300 microns. As previously indicated, particles 
of such size are large enough to clog shower heads and other small 
orifices. 
Therefore, in accordance with the teachings of this invention, the screen 
38 is positioned in area 34 between the inlets thereto from pipes 60 and 
clarified water outlet 64. The size of the openings in screen 38 will vary 
with application, but would typically be in the 100 to 200 micron range. 
Water passing through screen 38 to area 34B and out through outlet 64 thus 
has all particles of a size in excess of the screen size removed. Since it 
is important that all water passing from area 34A to area 34B pass through 
screen 38 rather than over the top of the screen, the height of screen 38 
must be higher than the maximum anticipated water level in area 34. As may 
be best seen in FIG. 2, the water level 65 in tank 12 is higher than the 
water level 67 in storage area 34A which is in turn higher than the water 
level 69 in storage area 34B. Thus, by maintaining the screen 38 at least 
as high as the highest water level in the system, level 65, the objective 
of assuring 100% filtration is maintained. However, this requires that all 
water levels remain as shown in FIG. 2. In the system of the 
beforementioned Krofta patent, desired water levels can be maintained 
through use of an overflow control valve. However, in the system of FIG. 
2, such an overflow control is not usable. Therefore, a level control 
monitor 71 having an output line 73 is shown in storage area 34B. The 
output signal on line 73 may be utilized to control a valve 75 in 
unclarified water input line 44 or to control a valve 77 in the output 
pipe 98 from storage area 34B. In either event, the desired water levels 
may be maintained, assuring that 100% of the clarified water being 
outputted from the system is filtered. 
A major problem with having a screen such as screen 38 in a water 
clarification system is that the screen quickly becomes clogged by the 
filtered particulate matter and would thus eventually block flow of 
clarified water if a means were not provided for continuously cleaning the 
screen. Depending on configuration, such blockage would normally occur 
within 5 minutes to a half hour of use without cleaning. Heretofore, an 
effective method of continuously cleaning the screen in a water 
clarification system has not existed and it has therefore not been 
possible to provide a screen in such systems. However, in accordance with 
the teachings of a first embodiment of this invention, means are provided 
which (a) clean the outer or inlet side of the screen, (b) apply water 
pressure to the inner or outlet side of the screen to loosen and remove 
particles trapped by the screen, forcing such particles into chamber 34A, 
and (c) flush the particles filtered by and removed from the screen. 
More particularly, referring to FIG. 3 in conjunction with FIGS. 1 and 2, 
it is seen that a pair of soft brushes 70 are provided which are 
vertically mounted adjacent to and in contact with the inlet side of 
screen 38 at positions spaced approximately 180.degree. from each other. 
Each brush 70 is attached to a shaft 72 running through its center which 
shaft is attached through suitable gearing, if necessary, to be rotated at 
relatively low speed by a motor 74. Brushes 70 would typically rotate at a 
rate of 10-100 rpm. Each shaft 72 passes through a bracket 78 which is 
attached to frame 14. Brushes 70 thus rotate with the frame. The spacing 
between the brushes and roller 28 are such that, as the frame rotates, the 
brushes are caused to move across the entire outer or inlet surface of 
screen 38. 
Also passing through each bracket 78 is an inlet pipe 80 containing 
clarified water and preferably clarified water from which large 
particulate matter has been removed (i.e. filtered water from outlet 98). 
The water in pipe 80 is applied through head 82 to a plurality of nozzles 
84, each of which directs a shower 85 of high pressure water against the 
inner or outlet side of screen 38. The vertical spacing between the 
nozzles 84 and the dispersion of the water shower therefrom is such that 
head 82 causes water to be showered along a continuous line of screen 38 
from the top thereof to the bottom. 
The water from each pipe 80 is also diverted through pipe 86 to shower head 
88 which directs a shower of high pressure clarified water 90 against the 
corresponding brush 70 to wash and flush particles removed from the screen 
by the brush. 
The water from showers or jets 85 loosens and removes particles trapped by 
screen 38, permitting the particles to be easily removed from the screen 
by brush 70, and prevents particles from being pushed through the screen 
by the brush into area 34B. The water from water jets 85 which passes 
through screen 38 in conjunction with the water in shower 90, flushes 
removed particles from the screen and brush and carries the removed 
particles to outlets 94 and 96. The clarified water which passes through 
screen 38 and thus has the particulate matter of less than 100 to 300 
microns removed, exits from the system through outlet pipe 98. 
In order to prevent a buildup of removed particles in area 34A, and thus to 
maintain uniform flow rate, roughtly 20% of the clarified water in area 
34A is removed through the bottom of this area and through pipes 94 and 
96. The water in these pipes is passed through an air dissolving tube 
(ADT) 99 and a pump (not shown) which recycles such water to inlet pipe 
44. A portion of the clarified water outputted through pipe 98, for 
example 25% of such water, may be fed back into the system through pipes 
80 to be used for cleaning the screen and flushing particulate matter. 
Since each pipe 80 is attached to a corresponding bracket 78 which is in 
turn attached to frame 14, each head 82 and nozzle 88 rotate about screen 
38 in conjunction with the corresponding brush 70. 
FIGS. 4, 4A shows a second preferred embodiment of the invention differs in 
several respects from the embodiment shown in FIGS. 1-3. First, this 
embodiment of the invention is far less expensive to produce and operate. 
Second, with this embodiment of the invention, only a percentage of the 
clarified water is filtered, for example, 50 to 60 percent of the 
clarified water, rather than 100% of the water being filtered as in the 
embodiment of FIGS. 1-3. This embodiment of the invention would thus be 
suitable for applications where some of the water is being used for 
example for domestic applications where the water may be required to pass 
through small orifices while the remainder of the water is being used for 
industrial or other purposes where the presence of a small quantity of 
particulate matter of a size in excess of 100 to 300 microns is 
acceptable. Third, cleaning of the screen, in this case two screen, is 
accomplished by use of water pressure applied to the outlet side of the 
screens only, and brushes or other cleaning apparatus on the inlet side of 
the screen are not employed. Fourth, desired water levels are maintained 
by the simpler overflow control rather than requiring the more expensive 
monitor and valves. 
Considering the second embodiment in greater detail, the clarified water 
storage area 34 is subdivided into three areas 34X, 34Y and 34Z. Areas 34X 
and 34Z are separated by a wall 100 which is formed in two telescoping 
sections 102 and 104. Section 102 is fixed to the bottom of storage area 
34 while section 104 may be raised or lowered for reasons to be discussed 
in more detail later with respect to section 102, to alter the height of 
wall 100. 
Area 34X is separated from area 34Y by a pair of spaced concentric circular 
screens which are mounted in area 34Y and are supported by a frame 
structure 108 having a solid bottom 110. Each screen 38A and 38B is of the 
same type as screen 38 of the first embodiment and performs the same 
filtering function. Clarified filtered water passing through area 34Y is 
removed from the system through an outlet pipe 112. Unfiltered clarified 
water which flows into area 34X is removed from the system through outlet 
pipe 114. 
A spray head 113 which is connected to be fed by pipe 80 passing through 
bracket 78 is positioned in area 34Z substantially midway between screens 
38A and 38B. As for the first embodiment, a portion of the filtered 
clarified water from outlet 112 is pumped or otherwise fed to pipe 80. The 
spray head 113 has a first row of nozzles 114 which direct a high-pressure 
shower of filtered clarified water at screen 38A and a second row of 
nozzles 116 on the side of the head opposite nozzles 114 which direct a 
high-pressure shower 118 of filtered clarified water at screen 38B. The 
high-pressure water directed at the outlet side of both screens is 
effective to loosen and remove particulate matter trapped by the screens 
and to maintain the screens sufficiently clean to permit continued flow of 
clarified water therethrough. As with the previous embodiment of the 
invention, since pipe 80 is mounted to the bracket 78 which is in turn 
mounted to the rotating frame, head 113 rotates at a relatively low speed 
around area 34Z to clean the entire area of screens 38. Depending on the 
size of the system, the speed of frame rotation, and other factors, a 
single head 113 may be employed or two or more such heads may be utilized. 
In operation, clarified water collected by pipes 60 in tank 12 is passed 
through one or more openings 120 in the bottom of wall 36 into area 34X. 
As before, wall 36 is rotating with carriage 14 and a seal 122 is provided 
between the bottom of this wall and the bottom of the tank to prevent 
seepage of water. The water flowing into area 34X fills this area with 
clarified water and also follows a flow path under bottom wall 110 of area 
34Y and over wall 104 into area 34Z. The water flowing through this path 
carries with it particulate matter accumulating on the bottom of area 34X 
and causes some percentage of these particles to flow into area 34Z and 
out through outlet 114. Area 34Y being mounted above the bottom of are 34X 
provides a flow path for the water and particles under area 34Y to area 
34Z. 
Thus, unlike the first embodiment of the invention previously described, 
for the embodiment of the invention shown in FIG. 4, only a portion of the 
clarified water flowing into the clarified water storage area 34 is 
filtered and passed to filtered water outlet 112. The remaining clarified 
water which is unfiltered and which in fact has some extra particles which 
have been removed from the filtered water flows over wall 100 and through 
area 34Z to outlet pipe 114. The percentage of clarified water which is 
filtered is determined by the height of wall 100. If this wall is raised 
to substantially the level of the water in tank 12, substantially 100% of 
the water is filtered, and water flowing out through area 34Z and pipe 114 
is basically overflow to control fluid level, eliminating the need for 
sensor 71 and valves 75 and/or 77. If the wall is lowered, a percentage of 
the clarified water applied through inlet 120 flows over the wall into 
area 34Z. In typical applications, 40% to 50% of the clarified water 
inputted through opening or openings 120 would overflow and pass through 
outlet 114 as unfiltered clarified water. 
Apparatus is thus provided for use in an existing water clarification 
system which permits particulate matter above a predetermined size to be 
removed from the clarified water in the system. More particularly, a 
filtering screen is provided in the system between the clarified water 
inlet and outlets and means are provided which rotate with an existing 
frame (although the frame might have to be slightly modified) to permit 
continuous cleaning of the screen and to continuously flush particulate 
matter collected by the screen. Desired water levels are maintained 
throughout the system. 
While for the preferred embodiments described above, a screen has been 
shown as the filtering element, a porous material or other filtering 
element capable of removing particulate matter above a predetermined size 
might be utilized. Similarly, while the screen has been stationary and the 
brushes and heads used for cleaning the screen and flushing have been 
rotated for the preferred embodiment, it is within the contemplation of 
the invention for there to be continuous relative motion between the 
filtering element and the cleaning elements, and this may be achieved by 
rotating either one or both of the elements. The exact configuration will 
vary with application. The nature and location of the screen or screens 
will also vary with the application, as will the specific configuration 
used for cleaning and flushing. Thus, while two brushes 70 and heads 82 or 
heads 113 have been shown for preferred embodiments, depending on the 
speed of rotation of the elements and the size of the system, only one set 
of cleaning elements may be required in some applications and three or 
more sets of cleaning elements may be required in other applications. 
Further, while brushes have been shown for the first preferred embodiment 
of the invention, a squeegee or other suitable element may be utilized for 
this purpose. A vacuum or other cleaning element may also be utilized in 
appropriate applications. 
Thus, while the invention has been described above with respect to 
preferred embodiments thereof, the foregoing and other changes of form and 
detail may be made therein by one skilled in the art without departing 
from the spirit and scope of the invention.