Design of the Filtration Stage
17 | 37
Form-No: TM-WW002 // Revision: A // Date: Oct. 10, 17
Pressure Measurements
The TMP is measured according to the equation given in
chapter 3.2. Therefore pressure sen-
sors must be installed at the feed and on the permeate headers in each UF rack. In case of
smaller UF racks without headers then the pressure sensors must be located near to the mem-
brane module to reduce the influence of pressure loss caused by piping.
The pressure during back flush shall be monitored to ensure that back flush is carried out cor-
rectly and within the allowed pressure limit of the UF modules. The back flush TMP should be
similar for each back flush. Investigation has to be done if that is not the case.
The feed pressure must be measured before and after the pre-treatment filters in order to de-
termine the differential pressure in order to decide for cleaning or replacement of the pre-filters
elements. Additionally, it also allows for manual monitoring to ensure that the pre-strainer is op-
erating correctly. Correct operation of the pre-straineris important to protect the membrane for
the entrance of harmful particulate matter.
The air blower pressure (P2) shall be monitored closely as well to ensure that there is sufficient
pressure to push the air into the modules and the pressure into the modules must not exceed
0.6 bar.
Flow measurement
A permeate flowmeter shall be installed at least to the permeate line in order to monitor the cor-
rect flow during back flush and filtration. If the UF plant consists of multiple UF racks then the
backflush flow transmitter can be located with the commonly used back flush pumps and hence
is shared with other UF racks.
Turbidity measurement
A turbidity measurement can be added in order to monitor the permeate turbidity and to detect
a potential fiber breakage or system failure. However the turbidity sensor could be omitted as
periodic sampling and turbidity analyses on a hand-held analyzer is usually sufficient to monitor
the performance of the UF system.
pH measurement
During the soak period of the EBF the operator shall take samples and check if the recom-
mended pH is achieved for effective cleaning effect. Additionally, the pH range must be at-
tained according to MICRODYN AQUADYN
®
UA860 data sheet.
5.1.5 Piping
A series of pipes and fittings are necessary for connections to the auxiliary equipment and
modules. A plumbing system according to good engineering practice is imperative to ensure
the entire UF system works at its optimum. The necessary piping shall be designed effectively
without dead legs and as compact as possible and with minimum quantity of fittings such as el-
bows to minimize pressure losses across the UF rack.
The feed and permeate piping shall be designed with a flow velocity max. 1 m/s (V
p
< 1 m/s)
while the backwash piping designed with a flow velocity not more than 2 m/s (V
b
< 2 m/s), tak-
ing into account that air provided by Air Scouring (AS) is present. Air pockets in the piping up-
stream, inside the UF rack and downstream the UF rack shall be avoided. In the event it cannot
be avoided to have or accumulate air pockets in the piping then those shall be vented on a fre-
quent basis by installing vent valves at the top of the piping.
Design of the Filtration Stage
18 | 37
Form-No: TM-WW002 // Revision: A // Date: Oct. 10, 17
5.1.6 Air Quality Requiremment
During UF system operation, compressed air is required for pneumatic valve, air-scouring and
integrity testing (if applicable). Compressed air supply shall meet the following specifications:
Pneumatic valve operations: ISO 8573-1, class 2/3/2 (oil/water/particles) @ 6 barg min. pres-
sure.
Air-scouring: ISO 8573-1, class 1/3/1 (oil/water/particles) @ 1.0 to 2.0 barg pressure.
Integrity test: ISO 8573-1, class 1/3/1 (oil/water/particles) @ 1.0 (+/- 0.1) barg pressure.
The air source rate range is indicated on the datasheet in Appendix
–
MICRODYN AQUADYN
®
UA 860 Data Sheet.
Cleaning Strategy
5.2
Depending on the water source, specific application and water quality, organic and biological
fouling and inorganic scaling may occur, requiring different cleaning regimes.
Organic and biological fouling is normally caused by growth of micro-organisms and organics
adsorbed on the membrane surface that can typically be cleaned by executing a EBF or CIP
with sodium hypochlorite (NaOCl) and sometimes with addition of caustic soda (NaOH), but
prevent exceeding pH 10, see also for pH limits on the MICRODYN AQUADYN
®
UA860 mem-
brane datasheet.
Inorganic scaling is caused by the precipitation of metal salts on the membrane surface that
can be removed by EBF or CIP with acid, for instance citric acid and/or hydrochloric at pH 2.
There are two different modes that can be adopted, EBF and CIP. Additionally, dependent on
the feed water quality and applications, different chemicals can be adopted for an optimum
cleaning efficiency.
The cleaning frequency depends on the site conditions.
Chemically Enhanced backflush (EBF)
Back flush water flows to the membrane module via the back flush pump, at the same time
chemicals are injected via a dosing pump into the pipeline and well-mixed by a static mixer be-
fore it is sent to the membrane module. Once the chemicals are in the UF modules the back-
flush pump is stopped and the soak timer is started.
The purpose is to clean the lumen side of the fibers, as the chemical mixed water will flow from
the inside of the fiber outwards to the reject outlet.
After the soak timer has elapsed the backflush pump rinse out the chemicals.
Cleaning-In-Place (CIP)
A cleaning solution is prepared with clean water in the CIP tank and with a pH meter can be
checked if sufficient of the desired chemical has been added to the clean water in the CIP tank.
Before commencing to circulate the CIP solution, we strongly recommend to replace the pre-
screen from the normal more open screen size to a much tighter screen size of 1 to 5 µm or to
add an additional safety screen with 1 to 5 µm. The reason is to capture the material which
comes out of the UF modules and to prevent re-entry of those back into the UF modules.
Before switching on the UF feed pump to draw in the CIP solution, make that all valves are
open to enable circulation across the CIP tank and that all other valves are closed.
Once the pH of the CIP solution is confirmed at the desired pH value, the pre-screen size (bag
filter) is replaced and all valves are in the correct position, the UF feed pump can be started at a
low speed. Then the CIP solution is drawn from the CIP tank into the UF system and enter the
UF modules via the air supply connection (normally used for air supply for the air-scouring) at