U F ( Ultra filtration )Water Purifier
Ultrafiltration or UF is a pressure-driven membrane separation process that helps removes
particulate matter from aqueous solutions such as water. UF membranes typically have pore
sizes in the range of 0.01 to 0.10 μm and efficiently remove bacteria and most viruses,
colloids and silt. The smaller the nominal pore size, the higher the removal efficiency. Most
materials that are used in UF are polymeric and are naturally hydrophobic, such as
polysulfone (PS), polyethersulfone (PES), polypropylene (PP), or polyvinylidenefluoride
UF membrane is made from high-grade polymeric PVDF material to form a hollow fiber
membrane that is very durable and less prone to breakage. The hollow fiber has a dense
layer or skin on both the inside and outside surfaces, forming a double-walled structure that
contributes to its strength. In addition, its fouling resistance is improved by making the
membrane surface more hydrophilic than the underlying PVDF polymer. With uniform pore
size and outside-in flow, the UF membrane creates a barrier without sacrificing
How Ultrafiltration Works :
- UF modules utilize a double-walled hollow fiber H-PVDF membrane with a very small pore diameter for excellent removal of particulate matter and bacteria, and most viruses and colloids. Despite the small pore diameter, the membrane has a very high porosity, resulting in a stabilized flux similar to that of micro-filtration (MF).
Typically, UF is operated at a constant permeate flow. The transmembrane pressure (TMP) will naturally increase over time, and the module can be cleaned by back-washing and air-scouring to remove the fouling layer for longer service life.
Advantages of UF Technology :
- Low fouling : UF modules are made from H-PVDF material, which has excellent chemical resistance to strong levels of disinfectants such as peroxide or hypochlorite, allowing sufficient removal of bacterial growth.
- Very fine pore diameter : With a nominal pore diameter of 0.03 μm, UF technology effectively removes pathogens, most viruses and bacteria. In addition, the membrane’s high porosity allows high flux operation at a given transmembrane pressure.
- Durable double-walled fiber structure: The distinct structure provides excellent durability and resistance against breakage, even with periodic cleaning procedures to remove fouling.
- Outside-in flow configuration : Systems designed with UF use an outside-in flow configuration, which allows for low clogging and high solids loading, high flow area and easy cleaning.
- Dead-end or concentrate bleed capabilities : Although the primary flow design is dead-end filtration, modules can be easily adapted to a concentrate bleed mode.
Simple, modular design: UF modules can be configured in a simple modular design providing a compact footprint.
The Ultrafiltration membrane system has been specifically selected and designed to treat the secondary treated sewage. The UF is a skid mounted membrane system, which comprises mainly of the hollow fiber UF membrane modules, re-circulation and pneumatically actuated valves. All these are neatly interconnected into a compact and modular train, which comes complete with a slave control system.
The proposed UF System consists of one train to produce a net UF filtrate capacity of 3.0 to 3.5 m3/hr/module for Reuse as per your requirement. The UF system is incorporated to further reduce the Secondary Treated Domestic Waste Water turbidity to less than 0.3NTU and SDI less than 3.0 at all times. Each UF membrane module consists of thousands of hollow fibre membranes that are capable of removing virtually all suspended solids, colloids, bacteria and viruses bigger than 0.01- 0.015miron from the feed stream. A detail description of each train and membrane module is listed as followed:
The UF system consists of the following modes of operation :
- The UF membrane system operates on an out-to-in mode where the feed stream
flows on the outside of the membrane with the filtrate flowing through the inside. Due to
the double-skin construction of the membrane, the filtrate undergoes double filtration
during the operation. The reject stream flows off the outer skin of the membrane and is
concentrated along the length of the membrane.
To maintain a minimum cross – flow velocity, some of the reject stream is re-circulated to prevent the accumulation of solids on the surface of the membrane. The balance of the reject stream is bled-off to prevent the build-up of solids in the re-circulation loop. Such feed and bleed operation allows the UF to operate continuously before the need for backwash thereby improving recovery and availability of the system.
UF Backwash (BW)
- With the accumulation of solids during filtration, the resistance to flow will increase which can be overcome by subjecting the membrane to a reverse flow, with the product water Air-scouring is also introduced concurrently to improve the effectiveness of the Backwashing. This backwashing operation is carried out periodically which can be predetermined by either total flow or elapsed time. The overall system will be controlled such that only 1 train will undergo backwashing at any one time. The backwash stream is discharged to the waste sump.
Maintenance Cleaning (MC)
- To maintain optimum filtration efficiency, periodic chemical cleaning of the membranes is required. MC is an automated sequence meant for short-term regaining of permeability, which is a short duration cleaning with chlorine and citric acid as per pre-set schedule with minimum stoppage of the system. The frequency of maintenance cleaning is dependent on the raw water quality and its variation. The expected frequency of this short term cleaning is once in a week.
Recovery cleaning (RC)
- An extensive cleaning procedure requires longer stoppage on a process train for permanent regaining of the membrane permeability and performance. The membranes are subjected to a regime of soak and flush cycle which will remove the foulants or contaminants that cannot be removed by backwashing alone. Similar to MC, frequency of RC is dependent on the feed water quality and its variation; the expected frequency of this long term cleaning is once in 4 to 6 weeks.
The following equipments are required for the operation of the UF system:
- Backwash System : The backwash system comprises of two backwash pumps (one working and one standby) and the required backwash water is drawn from the filtrate tank.
- Compressed Air System : The backwash system comprises of two backwash pumps (one working and one standby) and the required backwash water is drawn from the filtrate tank.
- Clean-In-Place (CIP) System : The CIP system comprises a dedicated CIP tank and pump for both maintenance and recovery cleaning.
- Membrane Integrity Testing (MIT) : To monitor and detect the integrity of the UF
membranes, 2 different testing methods have been incorporated into the system.
Online Turbidity Test
The turbidity of the permeate water is continuously monitored via an on-line turbidity meter on each train. If there is any excursion observed above the baseline reading by a stipulated quantum, an alarm will be triggered but if the excursion occurred for an extended period, then the particular train will be isolated and shut down to prevent the carrying over of contaminants to the downstream process as well as highlighting the need for immediate attention of the operator. The affected train will have all its modules
tested for membrane integrity by using pressure decay testing (PDT).
The UF filtrate (or filtered water) will be stored in a UF filtrate/backwash tank. This tank will have two compartments, which the UF filtrate will flow to the first compartment that will be designed to hold backwash water required for at least three backwashes of the UF membranes. Water from the first compartment will overflow into the second compartment. The Treated water is been pumped to various source of usage for the UF Filtrate Tank.
ULTRAFILTRATION SYSTEM CLEANING
The following operational steps are required for continuous and successful operation of the UF system:
1. Service / Filtration
- 2. Backwash (BW)
- 3. Maintenance cleaning (MC)
- 4. Recovery chemical cleaning (RC)