What is chemical enhanced backwash in Ultrafiltration plants?
Ultrafiltration membranes don't need a supporting frame because they are self-supporting. One inline filter with isolation valves is present in these systems. The filter shields the UF membranes from foreign objects that can clog or harm them. Before and after the filter, on the piping carrying filtrate, and on the backwash to drain line of the UF system, sample valves are offered.
Thus, to clean the complete UF system, three cleaning connections are offered, the feed, filtrate, and backwash. If a pressured feed source is used to feed the UF system, the source must be controlled to a maximum of 10 psig.
Here, in this article we will discuss about the chemical enhanced backwash in ultrafiltration plants, and the procedure of chemical enhanced backwashing.
Operation of Ultrafiltration plants
The four operational modes of Ultra Filtration devices are filtration, backwashing, chemically enhanced backwashing (CEB), and standby.
The instruments and a PLC monitor all modes. When there are critical circumstances, such as the low suction pressure, the PLC will shut down the system. On the control interface, there are indicators for every alert and shutdown state.
Later, for chemical tank low levels and pump suction pressure switches, dry contact inputs are available. A 4-20 mA input signal is used by the system to monitor the level of the filtrate storage tank. When the Filtrate Storage Tank is full, the device is switched to "Standby" mode.
Chemical Enhanced Backwash (CEB) Mode in Ultrafiltration plants
In CEB mode, the backwash flow rate is cut in half and chemicals are added to help the membrane's internal surface, be cleaned of pollutants more thoroughly. When used appropriately, the CEB will successfully stop membrane fouling over time, and save extended periods of downtime, needed to start a more thorough cleaning of the fibres.
The control mechanism enables the use of chemicals to select up to 3 CEB cycles:
Acid, caustic, and chlorine are common chemical choices for CEBs. To guarantee an even distribution for best cleaning effectiveness, the CEB flow feeds in directions, first in one direction, and then the other.
The chemical is then allowed to soak for a user-specified amount of time, before being washed away and the device being put back in use.
How does the chemical enhanced backwashing (CEB) work in ultrafiltration plants?
Chemical enhanced backwashing, also known as maintenance cleaning, is effective in preserving membrane performance, in addition to the practise of adding chemicals to backwash water. Maintenance cleaning involves submerging the membrane filament in a chemical solution, for several minutes each day.
Also, following physical cleaning without the use of chemicals, such as backwashing and air scrubbing, TMC is typically carried out. The quality of the raw water determines how often maintenance cleaning and soaking are required; Typically maintenance cleaning is performed once a day with 20 minutes of soaking each time.
Step-by-step CEB procedure for UF plants
(1) Open the lower discharge valve and the concentrated water valve (V4 and V-3).
(2) To inject backwash water containing chemicals into the membrane module, open the backwash valve (V-6) and turn on the NaClO dosing pump and backwash pump.
(3) The filtration flow rate is set to be 1.0–1.5 times the backwash water flow rate. Do not exceed the specified maximum backwash flow rate.
(4) Close the discharge valve as soon as NaClO is found in the discharge water (V-3).
(5) Stop the NaClO dosing pump, close the backwash valve (V-6), and stop the backwash pump after making sure that water exits the upper side of the membrane module.
(6) Open the air scrubbing valve (V-2) for a while after soaking the membrane filament, in the chemical solution typically for 20 minutes.
(7) To remove the chemical from the membrane module, close the air scrubbing valve (V-2) and open the discharge valve (V-3).
(8) Shut the backwash valve (V-6) and start the backwash pump after closing the discharge valve (V-3), typically for the 30s.
(9) Open the air wash valve after stopping the backwash pump and closing the backwash valve (V-6), typically for 30s.
(10) Keep going back to above steps until the overflow water's water quality is acceptable.
11) Ensure that the backwash pump is off and that the air wash valve (V-2) and backwash valve (V-6) are both closed.
Design configuration of the ultrafiltration plants
Thousands of capillary membrane fibres make up the module. These modified (polyether sulphonic) PES fibres have seven capillaries with a diameter of 0.9 and 1.5 mm. The greater mechanical fibre strength produced by the membrane design leads to:
- Complete defence against germs and viruses, increasing protection for subsequent treatment steps.
- Because, there is less fibre breakage, maintenance is decreased, and production is boosted.
- Better feed water distribution along the fibre and reduced pressure drop.
- Increased inner diameter (optional 0.9 mm and 1.5 mm) fibres offer a high tolerance against high suspended particles loading, minimising fouling, and fibre strength enabling high backwash pressures and velocities.
- These membranes function as in-out filters. Water enters each fibre by its capillaries, and filtered water exits the tubes through their sidewalls.
The filtrate then moves radially outward towards the annulus where the distribution pipe and the shell meet. As a result, the radial velocity is essentially constant throughout the module diameter, resulting in:
- Minimal fouling as a result of an extremely effective backwash impulse across the entire module cross section.
- Enhanced module integrity because the feed and filtrate sides are not separated by o-rings.
- A longer lifespan because the fibres are not under as much mechanical stress.
Conclusion
In cycles that feed from each end of the fibre, flow is supplied and backwashed. Just backwashing the modules could be the main technique for cleaning the membrane in many applications. For more challenging applications like ultrafiltration, periodic chemically enhanced backwash is carried out to maintain peak performance.
Are you still confused about the role of CEB in ultrafiltration plants?
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