Page 261 - Membranes for Industrial Wastewater Recovery and Re-Use

2 30 il/lernbranes for lridustrial Wasteivater Recoiwg arid Re-use

Pre screen MF (duty/assist) MF tank RO (duty/asskt) RO tank

Product to
Demin plant

1
To inlet of sewage works
To final effluent chamber

a height of 2000 mm and an outside diameter of 150 mm. The plant has a total
membrane area of 1700 m2 and can produce up to 1500 m3 d-l (Table 5.20).
The membranes are operated at an average flux of 30.5 LMH and a
transmembrane pressure range between 0.4 and 3 bar yielding an overall
recovery of 90%. Membrane fouling is controlled through a sequence of
cleaning cycles. An automatic airfwater backwash is conducted every 12
minutes for 90 seconds. In addition each stream is chemically cleaned with a
hypochlorite and pH adjustment for 90 minutes every 14 days through an
automatic cleaning in place (CIP) system. Membrane integrity is monitored by
particle counters and turbidity with additional pressure decay tests conducted
periodically.

Reverse osmosis
The final stage of the treatment train is two parallel reverse osmosis units
arranged in a 4:2 array. The membranes are polyamide spiral-wound
modules supplied by Koch Membrane Systems (UK) and are rated at a molecule
weight cut off of 200 kDa. The plant contains a total membrane area of 1451
m2 and is designed to produce up to 1200 m3 d-' of high-purity water at a
recovery of approximately 80%. The membranes operate at a pressure range
between 6 and 16 bar producing an average flux of 34.5 LMH. Membrane
cleaning is triggered by a 15% reduction in the monitored variables and when
necessary initiates a 360-minute clean with high and low pH solutions to
remove both organic and inorganic fouling. Membrane integrity is monitored
by checking conductivity of the membrane banks and individual pressure
vessels.

5.1.3 Performance
The major challenge with using a sewage effluent as the feed to a high-purity
treatment plant is the natural variation in its quality which varies both
seasonally and throughout the day. Flag Fen produces an effluent water quality
with a mean BOD5 of 10 mg I-', COD of 51.3 mg 1-' and a total suspended solids
concentration of 17 mg 1-'. The quality is variable with a peak to mean ratio of