Back-washable Spiral Ultrafiltration Technology for Domestic & Industrial Water Purification

Introduction

Ultrafiltration (UF) refers to the separation of species through membranes on size exclusion principle. It differs from micro filtration with reference to the size of the species being separated. Ultrafiltration membranes are thin polymeric film having pores of the sizes 2 nm to 100nm, operate at relatively low pressure (< 5 bar) and separate the micro species based on size exclusion principle. 

BARC has developed and deployed various types of membranes and membrane devices for wide range of water related applications and already transferred the know-how of online domestic water purifier based on ultrafiltration polysulfone membrane to a number of private companies who have successfully commercialised the product in market under different brand names. These domestic water purifiers are of low capacity, zero operating cost gadgets meant to satisfy the need of safe water for small families. 

BARC presents the technology for producing ‘Back-washable Spiral Ultrafiltration Membrane Element’ for water purification (for removal of bacterial & colloidal species) for large capacities, communities and industrial water treatment. At present single unit devices with capacity range from about 0.5 LPM to 4 LPM per unit have been demonstrated, which can be deployed in multiple units for any desired capacity. 

Backwashable spiral ultrafiltration (UF) membrane element consists of Polysulphone membrane wound in spiral configuration for compactness. The unit can produce purified water with respect to microorganisms, suspended solids and colloids. The special feature is the backwashability of the UF element to restore its stabilized pure water flux. It removes bacteria and turbidity and produces crystal clear water. These units can be used for domestic as well as industrial purposes. 

Salient features of Back-washable spiral UF Units 

• Crystal clear water free from turbidity, bio-contaminants, colloidal species. 

•  Compact and delivers stable output quality.

• Ensures continuous operation with less footprint area.

• Very low operating pressure of about 2-3 Bar, back washable pressure up to 2 Bar.

• Cross flow mode of operation preferred for higher turbidity feed of >10 NTU.

• Eco-friendly as no chemicals are used (other than for need based cleaning).

• Adaptable for high turbidity industrial water (with changes in operating parameters).

Process

Process of production of back washable spiral ultrafiltration module involves:  

• Preparation of a membrane casting solution consisting of basic polymer, selected additive and solvent for preparation of ultrafiltration membrane of about 100 µm thickness over a porous non-woven fabric substrate by phase inversion technique either manually or using automatic membrane casting machines, and the post treatment of these membranes for rolling them in spiral configuration.

• Fabrication / assembly of above cast ultrafiltration membranes in a spiral configuration of 2.5” diameter and length of 12”.

• A procedure to use the spiral module in back-washable mode for purification of drinking water systems.

Raw Materials

• Non-woven porous substrate *

• Polysulfone polymer *

• Other chemicals like solvents and additives used for making ultrafiltration membranes
  
  *raw materials are imported but available readily through local agents in the country. 
  

Infrastructure

• Membrane casting machine 

• Membrane Test set-up and other instruments/hardwares

• Spiral module rolling machine 

• A room with controlled humidity (RH<40%) of size 6m x 6m 

• Routine laboratory equipment/hardware, like analytical balance, conductivity meter etc 

Manpower

Minimum one chemist, one skilled and two semiskilled labourers are sufficient for regular membrane preparation and spiral membrane element rolling in sequence. Actual manpower would depend on production capacity..