FIELD OF THE INVENTION
The present invention generally relates to water pre-treatment system operable
under recirculation technique to reduce wastage of ultra filtered water in a
process of pretreatment of clarified raw water.
BACKGROUND OF THE INVENTION
The RO-DM water systems may comprise at least three main units
interconnected to each other for example, an ultra filtration unit (UF), a reverse
osmosis unit (RO), and a de-mineralization unit (DM). The system apart from the
main three units, further comprise sub-units namely:
Raw water dis-infection device;
Raw water pumping device;
Flocculation sub-unit;
Filtered water storage and supply device;
Cartridge filter device;
Degassing device; and
Membrane cleaning and protection device.

Additionally, interconnecting Piping's and Valves for control, isolation including
electrical, Controls and Instrumentation are provided for the system.
The clarified raw water from the reservoir is pumped and disinfected in a sump.
The disinfected water is pumped and filtered through Ultra Filtration (UF) unit to
reduce the total suspended solids (TSS) and organics to achieve required Silt
Density Index (SDI) and collected in a UF permeate tank. Necessary
pretreatment chemical dosing means are included in the flocculation sub-unit.
The pretreated (filtered) water from the UF permeate storage tank is pumped
through the cartridge filter device having a set of cartridge filters with chemical
conditioning and admitted in RO unit after verifying the SDI (Silt Density Index,
is a measurement of the fouling potential of suspended solids) values are within
the limits. During every startup of the RO unit, the SDI measurement is
mandatory before admitting the water into the RO unit. During the SDI
measurement process the pretreated water is continuously drained into the
waste water drain channel. Once the accepted feed quality for the membrane of
the RO unit is achieved, then the pretreated water is pressurized by HP (High
Pressure pump-1 and admitted to the RO stage-1 membranes to remove the
Total Dissolved Solids (TDS) in the feed. The permeate coming out from RO
stage-1 membrane is again pressurized to the required pressure by HP pump-2
and admitted to the RO stage-2 membranes for further reduction in TDS.

The low TDS permeate from RO stage-2 membranes are connected to the
degasser device to remove the entrapped carbon dioxide and is stored in a
degassed water tank. Then it is treated in the DM plant, consisting of Mixed Bed
(MB) ion exchanger and accessories to achieve the designed quality of the DM
water. The chemical process which occurs in the DM plant is ion exchange
through the DM resins.
The UF-RO-DM units are normally operated only for a few hours in a day based
on the demand of DM water for the process. If the pretreated water is stored for
few hours idle in the UF permeate water storage tank, a considerable quantum
of organic growth takes place which interalia seriously affects the SDI values of
UF permeate water. Hence during every restart of the UF-RO-DM plant, a huge
volume of pretreated water is presently wasted in order to achieve the desired
SDI value before admitting the water into the RO system.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose water pre-treatment system
operable under recirculation technique to reduce wastage of ultra filtered water
in a process of pretreatment of clarified raw water.
Another object of this invention is to propose water pre-treatment system
operable under recirculation technique to reduce wastage of ultra filtered water
in a process of pretreatment of clarified raw water which reduces the time
consumption for achieving silt density index (SDI) of the filtered water during
restart of RO unit.

Yet another object of this invention is to propose water pre-treatment system
operable under recirculation technique to reduce wastage of ultra filtered water
in a process of pretreatment of clarified raw water, which allows reduction in
use of consumables like cartridge filter elements, SDI paper and chemicals.
SUMMARY OF THE INVENTION
According to the invention, the UF permeate water is caused to recirculate back
to the feed of the UF unit during startup prior to admitting to the cartridge filter.
The system would considerably reduce the wastage of pretreated water as well
as Operation and Maintenance cost by way of reduction in the consumption of
cartridge filter elements and chemicals.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1 - shows a schematic of the water pretreatment system according to the
invention.
DETAILED DESCRIPTION OF THE INVENTION
Recirculation procedure:
According to the invention, and as shown in figure 1, the stagnant UF permeate/
RO feed water (11), having high organic growth in a UF permeate tank (4)
instead of letting into a drain (9) is bypassed back to a UF unit (3) feed. In order
to do so, a recirculation pipe line (10) with an isolation / bypass valve (8) is

introduced in between the RO feed pump (5) and an inlet of the Cartridge filter
(7). During each startup of a RO feed pump (5) an inlet valve (6) of the
cartridge filter is in closed position and the bypass valve (8) is kept in open
condition. The RO feed pump (5) is started to admit the contaminated UF
permeate / RO feed water (11) in the UF permeate tank (4) to the UF unit (3) as
an UF feed water (1) along a necessary dosing (2). The UF system (3) rejects
the organics and minimize the turbidity of the UF permeate / RO feed water (11).
The treated water is now admitted into the UF permeate tank (4). The UF
permeate turbidity is measured at an outlet of the RO feed pump (5). Once the
required turbidity is achieved, the SDI is to be measured online at the outlet of
RO feed pump (5). The bypass valve (8) in the recirculation line (10) is throttled
to obtain required back pressure for SDI measurement. Once the desired SDI is
achieved, the cartridge filter inlet valve (6) is opened and the bypass valve (8) is
closed. The accepted UF permeate is admitted through the Cartridge filter (7) to
a Reverse Osmosis (RO) unit as UF permeate / RO feed water (11) for further
treatment. During this recirculation process no water is wasted.
Formulate used:
1. The velocity in recirculation pipeline: V=(F/A)
2. Area of cross section of pipe: A =
3. The frictional loss in the recirculation line is calculated based on Hazen
and Williams formula.
4. System Design:

According to the invention, the newly introduced recirculation piping and valves
are sized to meet the velocity guideline pressure and temperature rating. The
relationship between turbidity and SDI are arrived based on the field feed study
and feed water quality.

WE CLAIM :
1. An improved water pre-treatment system operable under recirculation
technique to reduce wastage of ultra filtered water in a pretreatment
process of clarified raw water, the system comprises:
an ultra filtration (UF) unit operably connected to a Reverse osmosis (RO)
unit which inter alia connected to a de-mineralization (DM) unit to implement
a chemical process of ion exchange through de-mineralization resins, wherein
the UF unit is enabled to reduce total suspended solids (TSS) and organics
from the received clarified raw water duly disinfected, to pretreat the TSS
reduced water through chemical dosing in a flocculation device, to chemically
condition the filtered water via a cartridge filter device with inlet and outlet
valves and to transfer the conditioned water after measuring and ensuring a
desired slit density index (SDI) of the water to said RO - unit,
wherein the RO-unit is configured to receive the conditional water via a RO feed
pump having membranes from the UF - unit, pressurize in various stages the
treated water to remove the TDS including the entrapped carbon dioxides in the
water by means of a plurality number of high pressure pumps and degassers,
and transfer the water to said DM unit,
the improvement is characterized in that the system is provided with a
recirculation pipeline (10) including a bypass valve (8) disposed in between the

RO feed pump (5) and Cartridge filter (7), the system is enabled during each
startup to the RO feed pump (5) to place the cartridge filter inlet valve (6) in
closed position and the recirculation / bypass valve (10) kept in open condition to
start the RO feed pump (5) and re-circulate a contaminated UF permeate water
in an UF permeate tank (4) to the UF unit (3) as an UF feed Water (1), the UF
unit (3) rejecting the organics and minimize the turbidity of UF permeate water
(11), to store the treated water in the UF permeate tank (4) to measure once the
required turbidity is achieved the SDI online at the outlet of the RO feed
pump (5), to throttle the bypass valve (8) in the recirculation line (10) to obtain
required back pressure for SDI measurement, and to reiterate the activities till a
desired SDI before Cartridge filter (6) inlet is achieved.


feed pump (5) to place the cartridge filter inlet valve (6) in closed position and
the recirculation / bypass valve (10) kept in open condition to start the RO feed
pump (5) and re-circulate a contaminated UF permeate water in an UF permeate
tank (4) to the UF unit (3) as an UF feed Water (1), the UF unit (3) rejecting the
organics and minimize the turbidity of UF permeate water (11), to store the
treated water in the UF permeate tank (4) to measure once the required
turbidity is achieved the SDI online at the outlet of the RO feed pump (5), to
throttle the bypass valve (8) in the recirculation line (10) to obtain required back
pressure for SDI measurement, and to reiterate the activities till a desired SDI
before Cartridge filter (6) inlet is achieved.

ABSTRACT

ABSTRACT
TITLE: 'WATER PRE-TREATMENT SYSTEM OPERABLE UNDER
RECIRCULATION TECHNIQUE TO REDUCE WASTAGE OF ULTRA
FILTERED IN A PROCESS OF PRETREATMENT OF CLARIFIED RAW
WATER'
The invention relates to an improved water pre-treatment system operable
under recirculation technique to reduce wastage of ultra filtered water in a
pretreatment process of clarified raw water, the system comprises an ultra
filtration (UF) unit operably connected to a Reverse osmosis (RO) unit which
interlia connected to a de-mineralization (DM) unit to implement a chemical
process of ion exchange through de-mineralization resins, wherein the UF unit is
enabled to reduce total suspended solids (TSS) and organics from the received
clarified raw water duly disinfected, to pretreat the TSS reduced water through
chemical dosing in a flocculation device, to chemically condition the filtered water
via a cartridge filter device with inlet and outlet valves and to transfer the
conditioned water after measuring and ensuring a desired slit density index (SDI)
of the water to said RO - unit, wherein the RO-unit is configured to receive the
conditional water via a RO feed pump having membranes from the UF - unit,
pressurize in various stages the treated water to remove the TDS including the
entrapped carbon dioxides in the water by means of a plurality number of high
pressure pumps and degassers, and transfer the water to said DM unit. The
improvement is characterized in that the system is provided with a recirculation
pipeline (10) including a bypass valve (8) disposed in between the RO feed pump
(5) and Cartridge filter (7), the system is enabled during each startup to the RO
feed pump (5) to place the cartridge filter inlet valve (6) in closed position and
the recirculation / bypass valve (10) kept in open condition to start the RO feed
pump (5) and re-circulate a contaminated UF permeate water in an UF permeate
tank (4) to the UF unit (3) as an UF feed Water (1), the UF unit (3) rejecting the
organics and minimize the turbidity of UF permeate water (11), to store the
treated water in the UF permeate tank (4) to measure once the required
turbidity is achieved the SDI online at the outlet of the RO feed pump (5), to
throttle the bypass valve (8) in the recirculation line (10) to obtain required back
pressure for SDI measurement, and to reiterate the activities till a desired SDI
before Cartridge filter (6) inlet is achieved.