Page 295 - Membranes for Industrial Wastewater Recovery and Re-Use

264 ivembranes for lndiistrial Wnstrwatrr Rrcowrg iind Re-nsc

Fresh Dl water
I

Polluted Permeate
nnse wat to nnsing bath
Acid

Concentrate back
to E-coat bath
Figiirr 5.2 3 Procrssflowdiagram ofpostpaint water recycling systrrn

plant results in a membrane replacement life of over 3 years. Membrane integrity
is checked during both manufacture and operation. During manufacture
membrane quality is monitored using air permeability tests. During operation,
permeate quality is monitored by a combination of visual inspection and on-line
turbidity meters. Any individual permeate tubes seen to be passing retentate are
removed from the collector and diverted back to the treatment tank and so there
is no need to make interventions for incidental damage.

5.10.3 Performance
The plant operates within the required specifications for recycling water and
recovering paint. The main operational concern with the system is the stability
of the paint solids which would otherwise coat the membrane, a problem which
is controlled by pH adjustment. Bacteria contamination is also a problem due to
the close contact of the rinse water with air. Growth is controlled through the
use of paint-compatible biocide, but ultimately the membranes may need
mechanically cleaning by hand.
The high water demand of the process and the ability to recover valuable paint
make the recycling scheme very favourable economically. The plant reduces the
requirement for water and effluent treatment by 60 000 m3 y-' resulting in a
€327000 ($326 146) saving. Some 18 600 kg y-l of paint are also recovered
representing 22% of the total annual saving accrued from the plant. The
remaining saving are in labour costs associated with having to clean the rinse
water tank less regularly. The major cost of running the plant is energy to run
the pumps and cooling circuit which equates to a total annual energy demand of
324000 kWh. The remaining costs are due to membrane cleaning and
replacement resulting in a total opex of €0.36 m-3 ($0.355 rnp3). The plant cost
a capital outlay of €270000 ($269 000) with a further €24000 ($23 600)
required for first year financing. The annual net cash flow is €435 000
($433 900) resulting in a pay back period of less than 8 months. Although the
economic success of the plant is country-specific a similar scheme in the IJK