Apparatus for and method of recovering water used to backwash and rinse a filter

A system for recovering chemically-treated water used to backwash and rinse a manganese oxide zeolite filter. The backwash and rinse waters are placed in a recovery basin, preferably with a coagulating agent, wherein the waters are agitated and then allowed to settle and thereby to separate from the water impurities removed from the filter. The backwash and rinse water so purified is then returned to the filter inlet for a normal service filtering pass through the filter. A number of filters are preferably serviced by each recovery basin, and automatic control means for the system are also disclosed.

BACKGROUND OF THE INVENTION 
This invention relates generally to the water purification field. In 
particular, it is concerned with a system for recovering treated water 
used to backwash and rinse filters used to remove manganese and iron 
impurities from water. 
It is known to add treatment chemicals to water containing iron and 
manganese ions and to filter the treated water to remove such ions. U.S. 
Pat. No. 3,167,506 to Fackler et al describes one such method in which 
permanganate ions are employed in conjunction with a manganese oxide 
zeolite filter bed. Other treatment chemicals, such as chlorine and pH 
adjustment chemicals like sodium hydroxide, typically are also added to 
the water being treated. 
As the water passes through the manganese oxide zeolite bed, the iron and 
manganese ions dissolved therein are oxidized into an insoluble oxide 
and/or hydroxide either by the zeolite material operating as an oxidizing 
agent (in which event the filter must be periodically regenerated with a 
strong oxidizing agent, such as for example potassium permanganate), or by 
the catalytic effect of the manganese oxide zeolite bed. These oxidation 
mechanisms for precipitating iron and manganese ions are more fully 
described in the above-identified Fackler patent. 
After the filtering system has been in operation for a period of time, the 
filter bed becomes partially clogged by the precipitates. It is thus 
desirable to "back wash" the filter periodically by passing treated water 
in the direction opposite to normal filtering flow, i.e. from the filter 
outlet through the filter to the filter inlet, to remove the precipitates 
from the filter and restore the mechanical and catalytical efficiency of 
the bed. In processes heretofore employed, the treated backwash water 
containing suspended matter has been disposed of by merely depositing it 
in a sewer or natural body of water. 
During backwashing, the filter granules tend to become dislodged or 
unpacked so that the filter bed does not properly treat the first water 
passed through it after backwashing. It is conventional to "rinse" the 
filter with treated water immediately after backwashing. In rinsing, new 
water is passed through the filter in the direction of normal filtering 
flow to repack the filter granules. Heretofore, the rinse water also has 
been disposed of merely by depositing it in a sewer or the like. 
Inasmuch as the cost of treatment chemicals used to treat the backwash and 
rinse water frequently amounts to on the order of 3 to 12% of the cost of 
operating the filtering system, such disposal of backwash water results in 
significant waste and lack of economy in the overall operation of the 
system. A concomitant disadvantage of the prior method of disposing of the 
backwash and rinse water is that by placing the impurities containing 
backwash water into sewers or the like, the water treatment system emits 
wastes which contribute to pollution of other water sources, besides 
wasting the washwater itself. 
It is, therefore, desirable to provide a system for recovering the treated 
water used to backwash and rinse filter beds of this type. 
SUMMARY OF THE INVENTION 
In brief compass, the invention provides a recovery basin into which water 
used to backwash and rinse a manganese oxide filter is deposited. 
Preferably a coagulating agent such as a polyelectrolyte is added to the 
backwash and rinse water, the coagulating agent and water is agitated in 
the recovery basin, and then the precipitates or other impurities removed 
from the filter are allowed to settle to the bottom of the recovery basin. 
The treated water from which the impurities have settled is then returned 
to the filter inlet and passed through the filter in normal filtering 
operation so that the water used to backwash and rinse the filter exits 
from the filtering system as pure treated water. 
Settling is preferred to other methods for separating the removed 
precipitates from the backwash and rinse water. The filter area needed to 
filter the impurities from backwash and rinse water would be prohibitively 
large and hence expensive in terms of space requirements. Centrifuging 
might also be employed, but the centrifuge would have to run at a very 
high speed so that the power requirements needed for such centrifuging 
would be prohibitively high and expensive. Ion exchange methods of 
separating impurities from water are inappropriate for removing 
precipitated solids from water. 
It is preferred to employ a polyelectrolyte because, otherwise, the time 
required for the precipitates removed from the filter to settle from the 
backwash and rinse water would be on the order of hours, days or weeks, 
while on the other hand, with the polyelectrolyte, settling requires less 
than one to two hours. 
Further in accordance with the invention, automatic control means are 
desirably provided for controlling the overall operation and sequence of 
events of the system to minimize the manpower needed to operate and 
supervise the system. 
Accordingly, it is an object of the invention to provide a method and 
apparatus for recovering treated water used to backwash a manganese oxide 
filter. 
Another object of the invention is to provide a method and apparatus for 
recovering water used to rinse a manganese oxide filter.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
A wash water recovery system according to the invention for use with a 
single filter is illustrated diagramatically in FIG. 1, wherein arrows are 
used to indicate the normal flow directions through the various water 
lines. 
Water to be treated, such as from a well, is fed into the system by inlet 
means including inlet pump 10 and inlet line 12. Treatment chemicals are 
added to the inlet water via means for feeding treatment chemicals 
including chlorine feed line 14, pH correction material feed line 16 and 
permanganate feed line 18. It is preferred that of the treatment 
chemicals, chlorine first be added to the untreated water. The preferred 
pH correction material to maintain the pH of the water at a level of at 
least 6.0 is sodium hydroxide, although it should be appreciated that 
other pH correction materials may also be used. The last treatment 
chemical added to the water is permanganate, preferably in an amount 
sufficient to produce a faintly pink color in the water at the entrance of 
the filter bed as more fully described in U.S. Pat. No. 3,167,506 to 
Fackler et al. 
For smaller installation, chlorine feed line 14 feeds a chlorine-containing 
solution into line 12, although for larger installations, it is frequently 
more economical to use gaseous chlorine. 
An inlet line meter 20 is located upstream of the feed lines 14, 16 and 18. 
The treatment chemical feed lines 14, 16 and 18 each includes a 
conventional chemical supply tank (not shown) and a controlled volume feed 
pump (not shown) which is electrically connected to the totalizing meter 
20 so that the chemical feeds may be automatically proportioned by 
conventional means to the actual inlet flow rate, which sometimes varies 
with time. An inlet valve 22 is located downstream of the meter 20 in the 
inlet line 12, from whence the inlet line 12 enters the top of a filter 
vessel 24, within which is a bed of manganese oxide or manganese oxide 
zeolite. The lower portion of the filter vessel is connected to an outlet 
line 25 in which an outlet valve 26 is placed. 
The backwashing means of the invention includes a backwash reservoir 30 
located near the outlet of line 25 which fills up with treated water 
during service operation of the system. The backwash reservoir 30 is 
regulated by a conventional float switch (not shown), and is constructed 
and arranged to provide a heat of about 50 psi. A backwash water recovery 
line 32 connects the inlet line 12 at a point downstream of the inlet 
valve 22 with a water recovery collection basin 34 and provides means for 
transferring backwash water to the recovery basin. 
A rinse water recovery line 36, which includes rinse water recovery valve 
38, interconnects lines 25 and 32. Backwash water recovery valve 40 is 
interposed in line 32 between the connection of line 32 and inlet line 12 
and the connection of line 32 and line 36. A recovery basin inlet valve 42 
is placed in line 32 downstream of its connection with line 36. 
A coagulant feed line 44 feeds into the water recovery line 32 at a point 
upstream from the recovery basin 34. The water recovery line 32 feeds 
recovered backwash and/or rinse water into the recovery basin 34, and an 
agitator, such as a rotatable set of paddles 46 driven by motor 47 is 
provided in the recovery basin to mix the coagulating agent and recovery 
water. At the bottom of the recovery basin is a sludge removal line 48 in 
which is positioned sludge removal valve 50 and sludge removal pump 52. 
The sludge removal line feeds to a sewer or other waste depository. 
Recovered water return line 54 connects the water recovery line 32 at a 
point downstream of the valve 42 and the inlet line 12 at a point 
downstream of the meter 20. A recovered water return valve 56 and pump 58 
are positioned in the line 54. 
A second chlorine feed line 61 and pH correction material feed line 63 feed 
into the outlet line 25 at a point downstream of the outlet valve 26 for 
correcting the pH of the effluent to approximate neutrality. 
In normal service operation, the inlet valve 22 and outlet valve 26 are 
open and the valves 38, 40, and 42 are closed so that untreated water 
(under the influence of the pump 10) passes through the inlet line 12, is 
treated with chemicals through feed lines 14, 16 and 18, passes into the 
top of the filter vessel 24, through the filter and then out the outlet 
line 25 as treated water. The backwash reservoir 30 is also filled during 
normal service operation. By virtue of the zeolite filter bed properties 
which tend to oxidize and filter out impurities (as more fully described 
in U.S. Pat. No. 3,167,506), the iron and manganese impurities in the 
water precipitate out and, over a period of time, tend to clog the filter 
so that the pressure drop across the filter increases. When the pressure 
drop across the filter becomes significant, it is necessary to backwash 
the filter periodically to remove the precipitates therefrom. 
Backwashing is accomplished by closing inlet valve 22 and opening backwash 
water recovery valve 40 and valve 42. When the inlet valve 22 is closed, 
thereby cutting off the supply of water under the influence of the pump 
10, the pressure of the treated water in the backwash reservoir 30 forces 
treated water back through outlet line 25 in reverse or backwashing flow 
to the bottom of the filter up through the filter to backwash the filter. 
The reservoir 30 is typically quite large, i.e., on the order of 1,000,000 
gallons, so as to provide the serviced community with a day's supply of 
water as well as to provide a source of treated water for backwashing. 
The backwash water leaving the top of the filter in reverse flow through 
inlet line 12 carries with it iron and/or manganese precipitates, which 
have been cleansed from the filter, and flows through water recovery line 
32 to the water recovery basin 34. The coagulant agent feeding means adds 
a coagulating agent to the recovered water, through line 44, which agent 
is preferably an organic polyelectrolyte that functions to enhance 
agglomeration of the precipitants to decrease the time necessary for the 
precipitants to settle out of the recovered water in the recovery basin. A 
number of coagulating agents to perform this task are known to those 
skilled in the art. A preferred example of a coagulating agent is the 
potable, watergrade coagulant sold by Dow Chemical Company under the 
trademark "Separan NP 10," although it will be readily apparent to those 
skilled in the art that other coagulants such as that sold by Dow Chemical 
Company under the trademark "Purifloc N17," and other synthetic high 
molecular weight organic polymers may also be employed. 
The recovered backwash water and coagulating agent are fed into the 
collection basin 34 where the mixture is agitated, such as for example by 
rotating agitating means or paddles 46, for a period of time sufficient to 
coagulate or agglomerate the impurities removed from the filter. 
The backwashing of the filter bed tends to loosen or unpack the granules of 
the filter bed so that the first water passing through the bed in the 
filtering direction, i.e., from inlet line 12 to outlet line 25 is not 
filtered properly. To avoid passing impure water out of the filter bed 
immediately after backwashing, it is preferred to "rinse" the bed, that is 
to compact the filtering granules, by passing rinse water through the 
filter in the direction of filtering flow. To this end, the invention 
provides means for rinsing the filter. Rinsing is accomplished by opening 
the inlet valve 22 and rinse valves 38, and closing outlet valve 26, and 
closing valve 40 so that water coming through inlet line 12 passes through 
the filter vessel 24 in the direction of filtering flow to outlet line 25. 
The rinse water passes from outlet line 25 through rinse water line 36 and 
out water recovery line 32 for transfer to the collection basin 34. 
The recovered backwash and preferably rinse water and coagulating agent 
added thereto are agitated by the paddles 46 for a period of time in the 
recovery basin. After agitation has proceeded for a time sufficient to 
coagulate the precipitants and other impurities removed from the filter 
vessel 24, agitation is stopped and the impurities are allowed to settle 
to the bottom of the recovery basin 34. 
Agitation in the basins 34 may take place while the filter 24 is being 
backwashed and rinsed. Once rinsing has occured, the filter is desirably 
returned to service operation to minimize its "down time" and settling in 
the basin 34 takes place while the filter 24 is in service operation. 
After settling, the treated water from which impurities have been removed 
is transferred from the recovery basin to the inlet line 12 through water 
recovery line 32 to recovered water return line 54 where it is pumped by 
pump 58 back to the inlet line 12 for a service filtering pass through the 
filter vessel 24 and then to the treated water outlet 25. During the 
recovered water return step, the water return valve 56, inlet valve 22 and 
outlet valve 26 are open and water recovery valves 40 and 42 and rinse 
valve 38 are closed so that the returned water is filtered through 
filtering vessel 24 along with the main inlet stream. 
It should be apparent from the foregoing that the backwash and rinse 
recovery system of the invention recovers the treated water used for 
backwashing and rinsing which has heretofore been discharged to a sewer or 
the like. This results in significant economy because almost all water 
subjected to the treatment chemicals from feed lines 14, 16 and 18 is 
processed by the treatment system and is available for use, in contrast to 
the waste inherent in merely disposing of the backwash and rinse water. 
The recovery system also has advantages from an ecology point of view 
because polluted backwash and rinse water is not placed in a sewer. 
The time required to backwash and rinse a filter vessel, i.e., the time 
that the system is not in service outputting treated water, is relatively 
short in comparison with the period of time that any given filtering 
vessel is treating water before it requires backwashing and rinsing. It is 
therefore preferred that any given water recovery system be employed to 
service more than one filter vessel 24. To amplify, the backwash water 
from a plurality of filters 24 should be transferred to a smaller number 
of recovery basins 34. 
This is illustrated diagrammatically in FIG. 2, wherein six filter vessels 
24a, 24b, 24c, 24d, 24e, and 24f are serviced by two recovery basins 34a 
and 34b. Each of the filter vessels 24a-f has inlet and outlet equipment 
and backwash water and rinse water recovery lines and valving similar to 
those shown in FIG. 1. For the sake of simplicity, only the piping and 
valving associated with filter vessel 24a is shown, although it should be 
understood that each of the remaining five filter vessels has a similar 
complement of such equipment. The numerals used to designate the various 
lines and valves associated with filter vessel 24a in FIG. 2 are identical 
to the numerals used to designate the corresponding parts in FIG. 1, but 
with suffixes. 
The backwash water and rinse water recovered from filter vessels 24a-c is 
fed to recovery basin 34a via water recovery lines 32a. Coagulating agent 
feed line 44a feeds into water recovery line 32a. Similarly, the backwash 
water and/or rinse water recovered from filter vessels 24d-f passes to 
recovery basin 34 b via water recovery lines 32b and is injected with a 
coagulating agent from coagulating agent feed line 44b. 
The overall sequence of operation of the system shown in FIG. 2 is as 
follows. The service or filtering cycles of filter vessels 24a and 24d are 
interrupted and those filter vessels are backwashed and preferably rinsed 
with the backwash and rinse water directed respectively to recovery basins 
34a and 34b, where the water is mixed with a coagulating agent. Once 
backwashing and rinsing have been accomplished, the filter units are 
returned to service operation, and the mixing means or paddles 46a and 46b 
are deenergized so that the precipitates in the recovery water may settle 
to the bottom of the recovery basins. Settling normally requires on the 
order of 30 to 80 minutes. At the end of settling, the treated water, from 
which precipitates have been removed, that remains at the top of the 
recovery basins is passed back to the inlet lines for the respective 
filters 24a and 24d after the sludge is removed from the bottom of the 
collection basins by opening sludge valves 50a and 50b and energizing 
sludge pump 52. When the recovery basins 34a and 34b are emptied and the 
recovered water has been passed through the filters and the sludge has 
been removed, the cycle is then repeated to backwash and rinse filter 
vessels 24b and 24e, at the end of which cycle the process is again 
repeated to backwash and rinse filter vessels 24c and 24f. 
In operatively connecting each recovery basin to a greater number of filter 
vessels, the recovery basins are utilized more economically than if one 
recovery basin is used to service one filter vessel only. 
It is preferred that the system be operated and controlled automatically so 
as to minimize manpower required to operate and to supervise it. Automatic 
control means for controlling the system is illustrated diagrammatically 
in FIG. 3 wherein the various valves, pumps and other equipment are shown 
electrically connected to a program timer 60, such as the program timer 
manufactured by Automatic Timing & Controls of King of Prussia, 
Pennsylvania, and sold under the trade designation ATC Model 2300 Cam 
Timer. In FIG. 3, the program timer 60 is shown electrically connected to 
valves, pumps and the like of only one filter vessel 24a of the system. 
This is solely for illustrative purposes, and it should be understood that 
the program timer 60, in operation, also controls the operation of filter 
vessels 24b-24 f. The sequence of operation of each filter system is 
identical and those skilled in the art will be able to understand the 
invention from the following description of the operation of one system. 
The valves 22a, 26a, 38a, 40a, 42a, 50a, and 56a may be any one of a number 
of electrically or pneumatically actuated valves now available, such as 
those manufactured by Centerline, Inc. of Tulsa, Okla., under the trade 
designation 29000 Pneumatically Operated Butterfly Valve. In preferred 
form, each of these valves is pneumatically operated by an electrically 
activated valve connected to the timer 60, such as the solenoid valves 
made by Automatic Switch Co. of Florham Park, N.J., under the trademark 
ANSCO. 
The contacts of the program timer 60 for filter 24a are set so that unless 
the program timer is activated, the filter is in service for filtering 
operation, in which inlet valve 22a and outlet valve 26a are open, rinse 
valve 38a, recovery valves 40a and 42a and return valve 56a are closed, 
and the inlet pump 10 and chemical feed pumps for lines 14a, 16a, and 18a 
are energized. 
When it is desired to backwash and preferably rinse the filter vessel 24a, 
the program timer is activated whereupon the following sequence of events 
occurs. Initially, the inlet valve 22a is closed, and recovery valves 40a 
and 42a are opened to place the system in the backwashing condition. At 
the same time, the coagulating agent feed pump for line 44a is activated 
to add the coagulating agent to the recovery basin 34a, and the paddle 
drive motor 47a is energized to rotate the mixing paddles 46a, whereby the 
filter is backwashed and the backwash water passes into and progressively 
fills the recovery basin 34a. Backwashing normally requires approximately 
10 minutes, and it is preferred to use the level of recovered water in the 
recovery basin as the control to determine the end of the backwashing 
stage of the cycle. To that end, a pressure sensitive switch 64a (see FIG. 
2) is positioned in the recovery basin at a level selected to designate 
the end of the backwashing stage of the recovery cycle. When the water 
level in the recovery basin has reached a predetermined point, the 
pressure sensitive switch 64a actuates the program timer 60 to switch the 
system to the rinsing stage of the cycle. 
In the rinsing stage, the inlet valve 22a is opened, the outlet valve 26a 
is closed, rinse valve 38a is opened, recovery valve 40a is closed, and 
valve 42a remains open. Throughout the rinsing stage, the inlet pump and 
chemical feed pumps, coagulating agent pump and paddle drive remain 
energized. The program timer maintains the system in rinsing condition for 
a predetermined period of time, such as for example approximately 5 
minutes. The rinse water passes to recovery basin 34a where it is mixed 
with the coagulating agent from line 44a. 
At the end of the rinsing stage, the program timer automatically resets the 
system valving back to service condition, that is the inlet valve 22a and 
outlet valve 26a are opened and the valves 38a, 40a, 42a, and 56a are 
closed so that the filter vessel 24a is again processing and outputting 
treated filtered water. When the filter system is thus returned to service 
condition, the recovery basin 34a is placed in its sludge settling stage 
in which the paddle drive 47a and the coagulating agent feed pump in line 
44a are deenergized. The sludge settling stage of the recovery cycle last 
for a predetermined period of time, such as for example on the order of 30 
to 80 minutes. During settling, the precipitates removed from the filter 
during backwashing and rinsing, after coagulation with the coagulating 
agent, are allowed to settle out of the recovery water to deposit a layer 
of sludge at the bottom of the recovery basin. The duration of the 
settling stage should be such as to allow substantially all of the 
precipitates to settle, and the coagulating agent introduced to the 
recovery water via coagulating agent feed line 44a functions to shorten 
settling time. The precise length of time required for settling is of 
course dependent on the type and quantity of impurities present in the 
water being processed and also upon the characteristics of the coagulating 
agent employed. 
At the end of the settling stage, the recovery basin is cleansed of the 
settled sludge by opening desludging valve 50a and energizing desludging 
pump 52 so that the sludge is removed from the bottom of the tank and 
disposed of. The desludging state preferably is controlled by the 
reduction of water level in the recovery basin by virtue of removal of the 
sludge, and for this purpose a second pressure sensitive switch 66a (see 
also FIG. 2) is positioned in the recovery basin 34a below the location of 
pressure sensitive switch 64a at a predetermined distance selected so that 
a lowering of water level equal to the distance between the switches 64a 
and 66a indicates that substantially all of the sludge is removed from the 
recovery basin. Sludge removal continues until the water level has dropped 
to a point where pressure sensitive switch 66a is closed to activate the 
program timer 60 to place the system in return stage of the recovery 
cycle. 
During the return stage, the program timer 60 opens return valve 56a and 
energizes return pump 58 so that the clarified water is returned from the 
recovery basin 34a to the inlet line 12a back through recovery line 32a 
and through return line 54a. 
The recovered backwash and rinse water returns to the filtering system, 
passes to the filter inlet through the filter and exits from the system as 
pure treated water. The water return system continues to run until the 
water level in the collection basin has reached a low level pressure 
sensitive switch 68a (see also FIG. 2) located near the bottom of the 
recovery basin 34a, which pressure sensitive switch triggers the program 
timer 60 to in turn deenergize return pump 58 and close return valve 56a. 
At this point, the recovery cycle has been completed for the filter vessel 
24a. 
It should be apparent that the recovery cycle for filter unit 24a and 
recovery basin 34a takes place at the same time as the recovery cycle for 
filter vessel 24d and recovery basin 34b. After the recovery cycle for 
those two filter vessels has taken place, the program timer then switches 
over so that filter vessels 24b and 24e are backwashed, rinsed, and the 
backwash and rinse water recovered and returned to the inlet of the filter 
units in association with recovery basins 34a and 34b, respectively. After 
the cycle has been completed with respect to these two filter vessels, 
then the recovery basins are connected to filter vessels 24c and 24f and 
the cycle is repeated to backwash and rinse these two filter vessels. 
It should be apparent that the foregoing detailed description of the 
preferred embodiment may suggest to those skilled in the art a number of 
modifications and equivalents thereof which fall within the spirit and 
scope of the invention as defined by the appended claims.