UltraFLEX UF & RO Membrane Systems

Water from the source will be delivered directly to the filtration skid or to a raw water supply tank and then pumped to the UltraFLEX UltraFiltration Skid.

The operator can select the raw water flow rate to the filter skid on a PID controller located on the Filter Control Panel. A flow meter will be located on the feed line to the filter skid to measure and record the flow.

Feed Water pumps will be controlled by Variable Frequency Drives The VFD will provide a “soft start” for the pump to reduce the hydraulic shock to the membranes associated with stopping and starting the flow.

The feed water must pass through a 150-micron stainless steel strainer. This strainer will prevent debris and large particulate matter from entering the filter. This prevents plugging, pre-mature fouling or destruction of the membranes. The strainer will feature automatic backwashing for maintenance-free operation.

The level of the raw water supply tank will be controlled with a float valve. The Filter Control Panel will control the well pump. In addition, a low level pump cut off float will be hard-wired to the pump and to the filter alarm system.

The Feed Water will be continuously monitored for turbidity.

At certain times of the year the quality of the water may degrade due to storm events or runoff to a point that coagulant addition may be required. The specific requirements for that will need to be verified during piloting or by analysis of the feed water.

The purpose of the coagulant aid is to flocculate particles so that they collect on the membrane surface. The coagulated particles are easier to remove during backwash, which reduces the rate of membrane fouling.

Jar testing can indicate the dosage and effectiveness of coagulant addition. Actual field operation or piloting will be required to accurately determine the dosage and chemical requirements, if any.

The chemical feed pump would be flow-paced to the feed water flow to the filter skid(s). If the flow rate to the filter skid is adjusted the pump speed will be adjusted accordingly to maintain the selected dosage.

Each UltraFLEX skid consists of standard X-FlowTM low-pressure membrane vessels containing the hollow fiber element and the distribution and collection piping. The skid is completely pre-assembled with all piping brought to individual flanged connections for feed water, filtered water, backwash supply and backwash to drain. A separate drain can be provided for the chemically enhanced backwash waste, which will alternately have a high or low pH.

Each X-FlowTM filtration element on the UltraFLEX UltraFiltration skid contains approximately ten thousand “hollow fiber” membranes. The inside diameter of each of these hollow tubes is approximately 0.8 mm. For extremely turbid waters, a 1.5 mm fiber can be used. The walls of the hollow fibers are porous and will allow the passage of water, but will limit the passage of particles greater than 0.01 micron.

The hollow-fiber elements are encased inside a pressure vessel. The pressure vessel is flooded with feed water that flows freely through the pressure vessel, through the hollow-fiber elements and through the inside of the tubes. The pressure of the feed water across the hollow fiber membranes provides the force to push the water from the inside of the tube, through the wall and to the outside of the tube. All particles above the Molecular Weight Cut Off (MWCO) of 250 remain behind.

The flow of water through the hollow fibers during filtration is from the inside to the outside. The feed water flows through the inside of the hollow fibers and is forced through the walls of the hollow fibers to the outside.

The operator will determine the interval between Hydraulic Cleanings (backwash) by entering the value on the Graphic Interface System.

The system is capable of operating between 20 – 60 minutes between hydraulic cleanings. The interval is based on the quality of the quality of the incoming or settled raw water and the basics of the skid design.

Filtered and chlorine-dosed water from the UltraFlex system is delivered to the system clearwell. This tank provides chlorine contact time. Part of the flow is diverted to the backwash supply tank to provide particle-free water to the membranes during backwash.

The level of the backwash supply tank will be controlled with a float valve. In addition, a low level pump cut off float will be hard-wired to the pumps and to the alarm system.

The backwash supply for the UltraFLEX unit can be from an existing Clearwell with either a new or existing backwash supply pump, from the pressurized distribution system or from a separate backwash supply tank.

Over time, the particles that don’t pass through the walls of the hollow fiber begin to build up. The particles reduce the ability of clean water to pass through the walls causing the Trans Membrane Pressure (TMP) to increase. After a certain time (approximately 30 minutes) the hollow fiber membranes will require backwashing.

The Hydraulic Cleaning or backwash cycle consists of three main steps – Ra wWater flush, filtered Water Backwash and a follow up raw water Flush.

During the first hydraulic cleaning step, raw water enters the module from one end and flows though the fibers to the opposite end where it is sent to the backwash outlet header. This step is designed to take away any particles that are on the surface of the membrane and can be flushed away.

During the second hydraulic cleaning step, filtered water is added to the hydraulic flow. The filtered water flow is reversed through the pressure vessel and the membranes. A fresh supply of filtered water will be delivered to the outside of the tubes, passing through the walls of the hollow fibers and washing away the accumulated particles on the inside of the hollow fiber assisted by the raw water.

During the third hydraulic cleaning step, the filtered water is turned off but raw water continues to flow through the module. This step washes away any particles that have been lifted up from the membrane fiber by the filtered water backwash step.

Consistent, periodic backwashing will extend the life of the hollow fibers and prevent pre-mature fouling.

It has also been fund beneficial to perform an enhanced backwash using 10 – 25 ppm of chlorine on a periodic basis will greatly increase the amount of time between chemically-enhanced backwashes. The operator can select the frequency and dosage requirements.

Despite periodic back flushing, organic matter from some surface water sources will cling to the walls of the hollow fibers and begin to grow and become difficult to remove through regular backwashing alone. If these organisms are not removed, they will “foul” the membranes. Most systems address this problem on a monthly basis. The UltraFLEX UF & RO Membrane System provides for chemical cleaning on a daily basis.

Because of the excellent chemical resistance of the X-FlowTM SXL-225 membrane, chemicals can be added more frequently. Because the microorganisms have not been given time to grow and work their way into the membrane, they are easier to remove. In the UltraFLEX UF & RO Membrane Systems, backwashing is enhanced with the use of chemicals. This Chemically Enhanced Backwash alternates between two cycles, CEB1 (low pH) and CEB2 (high pH).

During CEB1 caustic soda and/or chlorine is added through the backwash water and the pH is raised to approximately 12. During CEB2 hydrochloric or sulfuric acid is added through the backwash water and the pH is lowered to approximately 2.

During either of the chemically-enhanced backwash cycles, the pressure vessels and membranes are saturated with the caustic or acidic solution and soaked for 10 minutes. Alternately, CEB1 (chlorine and/or caustic) will dissolve mineral deposits and scale and CEB2 (acid) will hydrolyze organics, microorganisms and parasites. For hard water sources that have a tendency to form scale, CEB2 will immediately be followed by CEB1.

After the membranes have been given time to soak during chemically enhanced backwash, they are backwashed and rinsed to remove the chemically treated waters. A pH meter on the backwash effluent line monitors the pH to ensure that the filters are not placed back into service before all of the chemicals are rinsed out and the pH returns to normal.

Because the microorganisms are killed daily (instead of monthly or less frequently as in other systems) they do not have time to grow until they become problematic. Membrane fouling is prevented. In addition, incorporating the chemical cleaning with the regular backwash cycles eliminates lengthy downtime required for monthly cleaning. The membranes remain in operation constantly.

Because of the periodic, chemically enhanced backwashing, the filtration skid will be out of service for short periods of time. During this time, the clearwell or finished water storage tank provides filtered water to the system.

The backwash supply flow-rate setpoint for both regular and chemically enhanced backwash will be selectable by the operator and controlled by a VFD on the backwash pump.

Individual hollow fibers can be damaged because of misuse, hydraulic shock, high pressure or debris. Despite safety features incorporated into the design of the UltraFlex system, the integrity of the hollow fiber membranes must be monitored. The integrity of the system is automatically tested following a CEB or once per week, whichever comes first. The purpose of the Membrane Integrity Test (MIT) is to verify that all of the membranes are intact.

Membrane Integrity Tests will automatically occur immediately after a Chemically Enhanced Backwash after the rinse step. Membrane Integrity Tests will be performed at least once per week in the absence of a CEB. At the end of a MIT, a 168 hour timer is started and in another 168 hours, an MIT will be performed again.

After the feed-water side is drained, The MIT is performed with low-pressure air. Air is used because it will not pass through the membrane walls. After the skid is pressurized to 15 psi, the air supply valve is closed and the system is monitored for a pressure drop.

A clear PVC pipe is installed on the effluent of the membrane module. This pipe will provide visual indication of air bubbles during the Membrane Integrity Test. The presence of air bubbles indicates a membrane fiber failure. Individual fibers can easily be repaired in a matter of minutes.

Additionally, the results will be automatically calculated and logged in the SCADA system.

The system integrity will be based on the quality of the filtered effluent turbidity, which will consistently be below 0.01 NTU.