Ultrafiltration

Ultrafiltration membranes

There are two ultrafiltration module configurations:

Pressurized system or pressure-vessel configuration: TMP (transmembranous pressure) is developed by a feed pump that increases the feed water pressure while the permeate stays at atmospheric pressure. Generally, pressure-vessels are standardized which allows the design of membrane systems to proceed independently of the characteristics of specific membrane elements.
	Immersed system: membranes are suspended in basins containing feed water and open to the atmosphere, so pressure on the influent side is limited to the pressure provided by the water column. TMP is developed by a pump that develops suction on the permeate side. They are configured with multiple basins with their own permeate pump so that one basin can be isolated and washed or repaired.

Advantages

Drawbacks

Pressurized

-Dead-end or cross flow

-High trans-membrane flow at 20°C

-Restricted turbidity in the feed water (20 NTU, according to Zenon study)

Immersed

-Dead-end only

-MBR can be used

-Aspiration modules i.e. filtrate is “sucked”

-Limited TPM, so low flow

-Wash frequently

-Need for an intermittent turbulence along the membrane using air

Source: Water Treatment Handbook, Degrémont Suez, 7th edition

Membrane cleaning

The membrane can be cleaned in three different ways:

	Frequency	Chemicals
Backwash	Approx. every hour	fresh water + oxidizing + sometimes air scrubbing
Chemical Enhanced Backwash (CEB)	Approx. every 3 days	No. 1: fresh water + oxidizing + base No. 2: fresh water + oxidizing + acid
Cleaning In Place (CIP)	from time to time	Idem as CEB but membrane has to be cleaned with higher alkaline and acid doses.