Ultrafiltration

Introduction

UF- ultrafiltration is a type of Physical Filtration in which Pressure removes Suspended Particles from water based on the pore size of the membrane. Its pores size varies from 10-100 nm and sometimes pore size can be measured by molecular weight cut-off (MWCO), expressed in Dalton, It gives an idea of which size molecules will pass through a membrane. Filtrations having smaller cut-off than UF are Nano-filtration and Reverse osmosis and Filtration having Large Pore size then UF is Microfiltration. Most of Uf plants are Run Automatic with the help of PLC. The lifespan of the UF membrane is 2 to 5 Years depending on inlet Water Quality. Because of high porosity, we have to apply less pressure compare to Nanofiltration and R.O.

USES

It removes suspended solids and turbidity of water. It partially removes Bacteria, Virus, Paint pigment. TDS (Total dissolve solid) is passed through the membrane.


Type of UF

Ultrafiltration layers are offered in different designs by manufacture, with every setup having a particular utility and going with advantage and disadvantage. Different designs include:

  • Pipe-shaped membranes:- capillary, hollow fiber or tubular;

  • Plate-shaped membranes:- flat plate, spiral.

But most common type is a Hollow fiberUF membrane. Hollow fiber Membrane can be classified in two way.

  1. Dead end membrane- We can get only permeate water.

  2. Cross Flow membrane- we can get both permeate and reject water.

  3. In cross-flow, there can be on two type of flow direction. Inside to outside or Outside to inside( Means water flow through Outside the hollow fiber.) We can obtain Flux ranging from 0.2 to 8 m3/h for effective Surface Area 7 to 72 m2.


Common Cycle of UF (out to in)

  1. Filtration: simple forward filtration.

  2. Back Wash: we can reverse the direction of flow for cleaning Purpose, we use Permeate water for BackWash.

  3. Forward Flush:  Simple Forward flow in which both rejection and permeate flow can be Dump to ETP.

  4. Air Scouring: With the help of air we Shake the Membrane to remove solids.

  5.  Backwash: this is the last step of the cycle.

 


Membrane fouling

A major challenge faced in UF membrane is fouling.

Over the time filtrate will accumulate and block pores, Permeate flux eventually decrease due to high resistance, This will lead to a high-pressure drop and reduce the effectiveness of membrane recovery.

Also, we face breakage of Fiber is obscured in Hollow Fiber System.

Method to reduce fouling

  • Select an appropriate Pre-treatment of raw water that reduces the fouling propensity of UF feed water.

  • Optimize the pH of the feed solution to minimize the adsorption and desorption.

  • Select a membrane with optimum pore size.

  • The proper operating condition should be maintained to reduce fouling.

Different method use for Treat fouling

  1. Backwash

  2. Chemical cleaning

  3. Air cleaning

Method

Time

Backwash

After 30-60 min

Chemical cleaning

2-5 week

Air cleaning

After backwash

 

 

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