Nanofiltration membrane

News and Views technological developments have reduced the risk of m e m b r a n e failures a n d increased its attractiveness. At small remote sites, s u c h as those at Le Balzll in n o r t h e r n France, a n d S t o n e h a u g h on the English/Scottish border, water is d r a w n from local g r o u n d sources a n d treated to potable s t a n d a r d s b y ultrafiltration A report in World Water and Environmental Engineer, December 1992, outlines the b a c k g r o u n d to these installations, their commissioning a n d installation, their operation so far, and the future of s u c h s y s t e m s The installation at S t o n e h a u g h uses a unit supplied b y the French c o m p a n y Aquasource, which was installed in F e b r u a r y 1991 The system u s e s three filter cartridges 100 m m in diameter a n d 1.5 m long. The enclosed cellulose polymer m e m b r a n e s are in the form of hollow fibres, a b o u t 1 m m in diameter Raw water p a s s e s along the axis of the fibre, p e r m e a t i n g t h r o u g h the walls a n d into the b o d y of the cartridge to be led off to supply In this instance the u n i t s are vertically m o u n t e d and operate in parallel Current demand, at 25 m 3, is u s i n g only 50% of the design capacity The plant at Le Baizfl was installed in J u n e 1992, a n d consists of two 300 m m diameter vertical m o u n t e d cartridges operating in parallel It is designed to remove tl,}rbidity a n d disinfect a daffy t h r o u g h p u t of 100 m Further Information f r o m Aquasource, 9 A v e n u e Alexandre Matstrasse, F-92500 Ruell-Malmaison, France. Tel +33 1 4 7 1 0 0820 F a x +33 1 4710 0821

Nanofiltration membrane

Table 2 Daytona Beach lonlc rejections

470 hrs

Table 1 Daytona Beach raw w a t e r analysis Raw water concentration

TOXFP I (ppb as Cl) Colour (cpu) NPDOC 2 (ppm)

1120 31 9

TDS (ppm) Na (ppm) Total H a r d n e s s (ppm as CaCO3) Calcium H a r d n e s s (ppm a s CaCO3) CI (ppm) Alkalinity (ppm a s CaCO3) Fe (ppb) pH

368 20 289 264 29 295 372 63

I TOXFP = Total organic halide formation potential 2 NPDOC = Non-purgable dissolved organic c a r b o n

2

R e j e c t i o n v e r s u s o p e r a t i n g t i m e {%)

Solute

A significant a m o u n t of work h a s been carried out on nanofllters a n d their u s e in softening a n d organic precursor removal applications, including the work

Solute

being done by Dr J a m e s Taylor at the University of Central Florida, USA. The US-based company, TrlSep Corp, h a s finalized the development of the m e m b r a n e u s e d for pilot testing in Dr Taylor's work, a n d h a s introduced the TS80 series of nanoflltration spiral w o u n d cartridges in 4 and 8 inch diameters Pilot plant studies of the m e m b r a n e were carried out using a groundwater source at Daytona Beach, Florida, a n d a surface water source at Melbourne, Florida The tests were carried out by a n independent testing organization All c r i t i c a l process variables were logged on a daily basis along with periodic monitoring of inorganic as well as various organic halide formation potentials For the test at Daytona Beach, carried out over 8000 hours, the raw water pretreatment consisted of acid dosing a n d cartridge filtration Results showed that the TS80 elements gave very good inorganic ion rejections and trihalomethane formation potential (THMFP) rejections The m e m b r a n e also exhibited very high water flux rates, a n d proved to be resistant to fouling - - see Tables 1 a n d 2 The test at Melbourne was carried out over 3800 hours, with a pretreatment of a n activated carbon filter, acid and a scale inhibitor dosing The results of both tests showed that the m e m b r a n e is a superior m e m b r a n e for m e m b r a n e softening applications requiring high inorganic and THMFP rejections at low operating p r e s s u r e s Further Informatlon f r o m TrL~ep Corp, 93 S. La Patera, Goleta, CA 93117, USA Tel +1 805 964 8003. Fax +1 805 964 1235

4 7 5 4 hrs

8152 Ins

TOXFP l THMFP 2 Colour NPDOC 3

99 98 99+ 97

97 99 97 99

98 98 98 99

TDS Na Total H a r d n e s s Calcium H a r d n e s s

97 87 97 99

97 84 99 99

96 83 98 98

C1 Alkalinity Fe

94 -99

93

94 93 97

96

96

Notes The above listed rejections are actuals based on average feed-brine concentrations a n d have not been normalized. The raw d a t a for thls test is available on request from TriSep i TOXFP = Total organic halide formation potential 2 THMFP = Trthalomethane formation potential 3 NPDOC Non-purgable dissolved organic carbon ----

M e m b r a n e T e c h n o l o g y No. 3 0