Page 277 - Membranes for Industrial Wastewater Recovery and Re-Use

246 Mrmbranrs for lndustriril Wastrwritrr Recover!! rind Rr-use

Figtire 5. I I (a) Filterpressand (b) ovrrallschrmr at Chirk treatnientfacilitg

recovery across the bed of 98-9996. Finally the flow passes through a 5 pm
cartridge filter to remove any gross solids and filter grains that might pass
through the bed.

Reverse osmosis
The centre of the treatment plant is a single stream reverse osmosis plant
configured in a four-stage feed and bleed array, each with its own cross-flow
recirculation pump. The membranes are polyamide 8040 spiral-wound modules
developed with Osmonics. The plant contains a total membrane area of 18 5 6 m2
and is designed to produce up to 450 m3 d-l at a recovery of 90%. The
membranes operate at a mean transmembrane pressure of 2 5 bar producing an
average flux of 14 LMH at a temperature of 25-30°C. Membrane cleaning is
accomplished by 30 minute cycles of either hot water or caustic soda/proprietary
high-pH cleaning agents which are initiated every day and twice a week
respectively.

Carbon filter
The final stage of the treatment train is an activated carbon filter with a working
capacity of 12.5 m3. The bed is operated at a design empty bed contact time of 30
minutes.

5.5.3 Performance
The plant has been successfully operated since 1995 and has proved the ability
of the plant to recover all solid and liquid outputs thus generating near-zero
discharge. A mass balance across the process demonstrates the concept (Fig.
5.12) with water losses occurring only in the final product and from the driers in
the evaporation stage of production. The RO concentrate contains cellulose and
lignins which are returned for use in the resin binder. The filter press produces
480 tonnes y-' of dry solids which are burnt in the boiler or reused as feedstock
at the front end of the chipboard production line as a 4550% dry solids cake.
Some 659 tonnes of water enter the production process with 78% lost during the