Reverse osmosis makes mine-water drinkable

Reverse osmosis makes mine-water drinkable

Focus support for the fabrication of thin-film composite membranes. Among the coating materials are rubbery polymers like silicones for the separation...

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Focus support for the fabrication of thin-film composite membranes. Among the coating materials are rubbery polymers like silicones for the separation of organic vapors and organophilic pervaporation and glassy polymers like polyimides for separation of p e r m a n e n t gases. Typical coating thickness are between 0.2 and 2 mm. Module design is concentrated on a plate design leading to a configuration of stacked envelopes, dubbed the GS module. Modifications of this module type are used for liquid separations, e.g. pervaporation, reverse osmosis, ultra-and microfiltration, and gas and vapor separation. Advantages of the system are control of the flow velocity over the m e m b r a n e surface t h r o u g h staging the m e m b r a n e stack a n d an u n o b s t r u c t e d feed flow passage which allows the handling of particulate and viscous feed streams. Standard capillary m e m b r a n e can be produced with inner diameters from 5 0 0 p m to 1000 l~m. Asymmetric capillaries are usually produced with skin inside the bore. Modules are designed for the inside-out mode of

operation. Applications include dehydration of air, bubble-free introduction of gases into liquids, degassing of water and low flow applications for the VOC separation from air. In pervaporation, both hydrophobic and hydrophilic, pilot plant separations u n d e r realistic conditions include phenol from water, a r o m a compounds from juices, water from organic mixtures and carbon disulfide from water in a soil remediation project. Membrane separations in biotechnology are aimed at integrated product recovery (as in ABE fermentation) a n d / o r removal of biotoxic species from active bioreactors. GKSS contributes to the scientific interpretation of processes in the synthesis of materials and formation of membranes. It aims to provide the fundamental requirement and know-how for the development of technologies and their application in a variety of separation processes. The Institute of Chemistry of GKSS furnishes industry, scientific institutions and authorities with its experience and knowledge, particularly with regard to

resolving current and long-term separation problems. In addition, the institute promotes the education of technical, scientific and engineering personnel in m e m b r a n e technology by lectures at universities and supervising u n d e r g r a d u a t e and postgraduate students as well as post-docs. For further information, contact: Prof. Dr D. Paul, GKSS Research Center, Max-Planck-Strasse, 21502 Geesthacht, Germany. Tel: +49 4152 872461;fax: +49 4152 872444; e-mail: [email protected]

Would y o u like the opportunity to inform the global membrane c o m m u n i t y about your latest work on membranes? If so, and y o u work for an academic research institute, g o v e r n m e n t department, or any other non-profit making organisation, c o n t a c t the Editor who will consider publishing your latest developments in Membrane Technology.

Feature

Reverse osmosis makes mine-water drinkable B a s e d n e a r L e e d s , UK, S t A i d a n s W a t e r T r e a t m e n t W o r k s i s a 20 million litre a day plant that uses reverse osmosis membrane technology to treat water from an opencast mine for drinking purposes. The site was flooded during 1988 when the River Aire burst its banks, and since August 1996 Yorkshire Water has used the plant to provide an additional source of potable water, meeting the needs of up to 100 900 of its customers. Here, we look at the treatment works w h i c h w a s d e s i g n e d b y UK c o m p a n y ACWa S e r v i c e s Ltd, t h e main contractor on the project. The St Aidans opencast coal site at Swillington was flooded to a depth of 70 m in March 1988 through a b r e a c h in the n o r t h e r n b a n k of the River Aire. In order for mining operations to be reinstated, the river and the adjacent Aire and Calder

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Navigation Canal were diverted into a new combined watercourse to the south of the existing opencast site. The new watercourse was opened to navigation in April 1995, and four m o n t h s later R.J.B. Mining, the owners of the site, commenced

dewatering by p u m p i n g into the River Aire. The mine was offered to Yorkshire Water Services Ltd (YWS) during the drought of 1995/1996, and as part of its drought alleviation projects the c o m p a n y commissioned a feasibility study to assess various options for the removal and treatment of the water. The water in the lagoon contains high levels of m a n g a n e s e and iron, and there were also concerns that the river-water introduced pesticides from s u r r o u n d i n g farmland. The c o m p a n y had previously u n d e r t a k e n laboratory tests and a comprehensive review of the water quality, and it had determined that the water could be treated by a reverse osmosis (RO) plant to make it suitable for potable purposes.

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Feature

Figure 1. S t A i d a n s W a t e r Treatment W o r k s is b a s e d on one o f the largest ultra-low p r e s s u r e reverse o s m o s i s (RO) s y s t e m s in the world. The RO units are h o u s e d in six s t a n d a r d shipping container w h i c h can be clearly s e e n here.

TWo pilot p l a n t t r i a l s w e r e t h e n c a r r i e d o u t o n - s i t e to c o n f i r m t h e d e c i s i o n a n d to c h e c k t h e p e r f o r m a n c e of v a r i o u s m e m b r a n e s . B a s e d on t h e f i n d i n g s of t h e s t u d y it w a s d e c i d e d to c o n s t r u c t a n e w i n t a k e a t t h e e a s t e r n e n d of t h e flooded a r e a to a b s t r a c t a p p r o x i m a t e l y 31 t c m d , a n d to c o n s t r u c t t h e treatment works near the existing site offices. T h e l a y o u t of t h e plant, and schematics that illustrate the treatment process a r e s h o w n in F i g u r e 1 a n d F i g u r e 2, r e s p e c t i v e l y .

Treatment process Pumps suspended from a pontoon located at the deepest p a r t of t h e l a g o o n deliver r a w w a t e r over a d i s t a n c e of 5 0 0 m to a n o n s h o r e collection t a n k . T h e w a t e r is t h e n d o s e d w i t h ferric s u l p h a t e , w h i c h is u s e d a s a coagulant. The raw-water tank h a s a c a p a c i t y of 5 0 0 m 3 a n d a c t s as a buffer between the raw-water pumps and the treatment plant. The intake system comprises four e l e c t r o - s u b m e r s i b l e pump-sets, -- three duty, one s t a n d b y - - e a c h r a t e d a t 323 m a / h a t 85 m h e a d . T h e p o w e r s u p p l y c a b l e s from t h e s h o r e to the pontoon are suspended b e n e a t h floating b u o y s a n d t h e pumps are started and stopped a u t o m a t i c a l l y b y s i g n a l s from a

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level t r a n s d u c e r in t h e r a w - w a t e r tank.

F r o m t h e t a n k t h e w a t e r is p u m p e d into 18 s k i d - m o u n t e d , s e l f - c l e a n i n g p r e s s u r e s a n d filters a r r a n g e d in six s t r e a m s of t h r e e . Common inlet and outlet p i p e w o r k is p r o v i d e d to t h e filters in e a c h s t r e a m so t h a t t h e t h r e e filters o p e r a t e in p a r a l l e l . E a c h filter is e p o x y - c o a t e d i n t e r n a l l y a n d e x t e r n a l l y a n d t h e filter m e d i a is c o m p o s e d of l a y e r s of gravel, g a r n e t , s a n d , m a n g a n e s e dioxide and anthracite. Each s t r e a m of filters is p r o v i d e d w i t h a dedicated back-wash pump, air blower, a n d a m o t o r s t a r t e r / p r o g r a m m a b l e logic c o n t r o l (PLC) p a n e l . Before e n t e r i n g t h e RO u n i t s , a p a r a l l e l a r r a n g e m e n t of 12 c a r t r i d g e filters r e m o v e fine p a r t i c l e s in t h e w a t e r , a n d it is t r e a t e d b y u l t r a - v i o l e t l i g h t to destroy naturally occurring bacteria. Six RO u n i t s or s t r e a m s , incorporating ultra-low pressure

Intake

1

Ferric Sulphate (Coagulant)

,I

Raw Water

Make-up

Raw Water Tank I_

Polyelectrolyte (Coagulant aid) _1 Settlement -I

Pressure Fiffers

1

1 1 1

Cartridge Filters

i Supernatant

Sludge Holding

I

Sludge to Skip

J

Storm

UV Unit

Sewer

to River

Reverse Osmosis Units J

t

Contact Tank Treated Water Tank

~

Treated Water Pumps

I

1

Sodium Hypochlorite (Super chlorination) Carbon Dioxide (Re-hardening) Lime (Re-hardening) Sodium Bisulphite (De-chlorination) Sodium Orthophosphate (Plumbosolvency control) Calcium Chloride (Re-hardening)

To Supply Figure 2. The various components that m a k e up the treatment process.

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Feature

Figure 3. A n o p e n container door reveals a n array o f m e m b r a n e modules. polyamide spiral wound membranes, each with a capacity to s u p p l y in e x c e s s of 3 0 0 0 m 3 p e r day, t o g e t h e r r e m o v e a n y remaining soluble components and produce a very high water quality. E a c h RO s t r e a m is c o n t r o l l e d b y its o w n PLC, a n d t h e p l a n t in e a c h s t r e a m is h o u s e d in a purpose- built stainless s t e e l - l i n e d s t a n d a r d 12 m s h i p p i n g c o n t a i n e r (Figure 3). A c o m m o n c l e a n i n g - i n - p l a c e (CIP) s y s t e m is p r o v i d e d for p e r i o d i c c l e a n i n g of t h e m e m b r a n e s . Reject w a t e r from t h e RO u n i t s is p u m p e d to a t a n k t h a t is l o c a t e d a d j a c e n t to t h e r a w - w a t e r t a n k , a n d w h e n it is full t h e r e j e c t overflows to t h e s t o r m sewer. T h e p e r m e a t e is d i r e c t e d t h r o u g h a c o m m o n p i p e l i n e to t h e t r e a t e d w a t e r t a n k . To e n s u r e t h a t t h e water remains disinfected, c h l o r i n e in t h e f o r m of s o d i u m h y p o c h l o r i t e is a d d e d a t t h e i n l e t point. B e c a u s e RO is s u c h a n effective a n d efficient s e p a r a t i o n p r o c e s s , all t h e h a r d n e s s a n d a l k a l i n i t y is r e m o v e d from t h e t r e a t e d water. However, d r i n k i n g

Membrane

T e c h n o l o g y No. 8 4

water regulations require that these elements are reintroduced. H y d r a t e d lime is a d d e d to t h e

w a t e r to a c h i e v e r e - a t k a l i s a t i o n , a n d p e r m a n e n t h a r d n e s s is introduced by adding calcium chloride. T h e p H is t h e n a d j u s t e d b y a d d i t i o n of CO 2. T h e p u r i f i e d w a t e r is c o n s t a n t l y m o n i t o r e d for pH, turbidity, conductivity and c h l o r i n e level b e f o r e b e i n g introduced into the Yorkshire W a t e r t r a n s m i s s i o n m a i n . In t h e event that the water leaving the site is o u t of p r e - s e t h i g h or low c h l o r i n e or p H levels, a u t o m a t e d valves a t t h e s t a r t of t h e m a i n d i v e r t t h e flow f r o m s u p p l y a n d b a c k i n t o t h e lake. W a t e r is a u t o m a t i c a l l y r e t u r n e d to s u p p l y once s a t i s f a c t o r y q u a l i t y levels have been achieved. The St Aidans Water T r e a t m e n t W o r k s is fully a u t o m a t e d . A PLC l o c a t e d in t h e motor control centre instrument s e c t i o n is u s e d to c o n t r o l t h e s t a r t e r s for t h e e q u i p m e n t in t h e raw-water, chemical treatment and treated water areas. Operational parameters can be altered using an operator m e s s a g e d i s p l a y . T h e PLC d o e s n o t c o n t r o l t h e RO u n i t s or t h e p r e s s u r e filters w h i c h h a v e t h e i r own PLC u n i t s . O n - s i t e SCADA equipment provides monitoring a n d m a n a g e m e n t facilities w i t h certain alarms on the system r e g i s t e r e d to p a g e r s c a r r i e d b y t h e operators.

Figure 4. The S t A i d a n s W a t e r T r e a t m e n t W o r k s is f u U y a u t o m a t e d a n d is controlled by a PLC a n d SCADA s y s t e m .

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Feature The t r e a t m e n t works is m o d u l a r a n d h a s b e e n designed to be removed once the w a t e r s u p p l y is e x h a u s t e d . At the time of writing Yorkshire Water is p l a n n i n g to d e c o m m i s s i o n the p l a n t in order for m i n i n g operations to r e s t a r t in August. Of the six RO p l a n t s , four have b e e n allocated to specific b o r e - h o l e s where there is a n i t r a t e problem.

For further information, contact: A C W a Services Ltd, A C W a House, Keighley Road, Skipton, North Yorkshire, BD23 2UE, UK; Tel: +44 1756 794794;fax: +44 1756 790898.

Table I. A s u m m a r y o f t h e t r e a t m e n t w o r k ' s rating.

*To comply with site owners r e q u i r e m e n t s . TCMD = t h o u s a n d cubic m e t r e s / d a y .

SU Soviet Union

AT A u s t r i a BE Belgium CH Switzerland DE West G e r m a n y EP E u r o p e a n P a t e n t s FI F i n l a n d GB Britain IL Israel IT Italy KP North Korea LU L u x e m b o u r g NO Norway RU R u s s i a SE Sweden

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(Patent T r e a t y Cooperation publication)

The British Library P a t e n t Express 25 S o u t h a m p t o n Buildings London WC2A lAW, UK Fax: 0171 323 7230

s p i r a l l y - w o u n d m e m b r a n e s , one b e h i n d the other in the direction of flow. A h e a t e r is positioned b e t w e e n the two m e m b r a n e s . Retentate leaving the u p s t r e a m m e m b r a n e is h e a t e d before it flows as the feed solution into the d o w n s t r e a m m e m b r a n e . The claimed a d v a n t a g e of the p e r v a p o r a t i o n device is in the u s e of spiral m e m b r a n e s which r e d u c e the capital cost c o m p a r e d to other designs, a n d in the improved energy efficiency within the all-enveloping p r e s s u r e vessel.

(The British Library will also s u p p l y a list of UK libraries included in the P a t e n t Information Network.)

Patent number: WO 9633798 Date: 3 1 s t October 1996 Inventor: R.S. Danziger Applicant: Krebs a n d Co. AG

Patents This is a list of recently p u b l i s h e d p a t e n t s covering designs a n d inventions of relevance to s y n t h e t i c m e m b r a n e technology. Where the s a m e device h a s b e e n p a t e n t e d in several countries, we n o r m a l l y give the British p a t e n t number. If there is no UK p a t e n t , we give the n u m b e r of a n E n g l i s h - l a n g u a g e p a t e n t , if one exists. The p a t e n t s list is compiled from i n t e r n a t i o n a l s o u r c e s by BHR G r o u p ' s i n f o r m a t i o n service. The facility c a n also be u s e d to carry o u t retrospective p a t e n t s e a r c h e s - - to test the validity, novelty or i n f r i n g e m e n t of existing p a t e n t s or new ideas. BHR Group, Cranfield, Bedford MK43 OAJ, UK, will provide free e s t i m a t e s on request. Countries c a n be identified by the code in front of the n u m b e r as follows:

TCMD 20 5 25 6

Designed t r e a t e d w a t e r o u t p u t RO p l a n t reject s t r e a m Raw-water i n p u t *Additional a b s t r a c t i o n

BHR Group does not operate a d o c u m e n t delivery service for p a t e n t s , b u t full copies of the original p a t e n t d o c u m e n t s can be obtained from the following addresses:

US P a t e n t Office Scientific Library 15th a n d E a s t Streets, NW Washington, DC 20231, USA The J a p a n e s e P a t e n t Office 4-3 K a k s u m i g a s e k i 3-chome Chiyoda-ku, Tokyo 100, J a p a n

AU A u s t r a l i a BR Brazil DD E a s t G e r m a n y DK D e n m a r k ES S p a i n FR F r a n c e HU H u n g a r y IR Eire JP Japan LI Liechtenstein NL N e t h e r l a n d s RO R o m a n i a A p r e s s u r e - r e s i s t a n t cylindrical US United S t a t e s vessel contains two WO World P a t e n t

Energy saving

pervaporation clevlee

Performance optimization Tangential flow of a fluid a c r o s s a m e m b r a n e surface, a l t h o u g h u s e d to minimize s u r f a c e effects, still allows some c o m p o n e n t s of the fluid to r e m a i n a t t a c h e d to the s u r f a c e a n d form a concentration polarization g r a d i e n t which affects the p e r m e a t i o n of c o m p o n e n t s of the fluid. The p r e s e n t p r o c e s s optimizes the m e m b r a n e p e r f o r m a n c e by t a k i n g into a c c o u n t the variety of flux a n d c o m p o n e n t p a s s a g e behaviour, so obtaining m a x i m u m recovery of a

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