Page 191 - Membranes for Industrial Wastewater Recovery and Re-Use

160 Membranes for Industrial Wastewater Recovery and Re-use

Several systems have been used to recycle this water, with various degrees of
water product purity. Filtration, pH adjustment and chlorination does not
address the high TDS and demands a constant bleed: the treated water
quality does not meet potable guidelines and consequently this system has
only been used in the event of severe water shortages. Carbon dioxide
addition, dealkalisation by ion exchange and UV sterilisation represents an
improvement over filtration-based methods and has been implemented in
some German facilities. Filtration followed by pH correction and reverse osmosis
has been used only in very few installations because of the high capital and
operating cost, and can only be justified where both the water and effluent costs
are high.
In the majority of cases the water from the final rinse can be used virtually
untreated in applications such as crate washers and as pasteuriser make-up after
cooling. In addition the water can be collected and used for floor washing.
Because the cost of treatment in these cases is negligible, most of the reclaim
applications adopt these procedures.
A recent example of water recycling and reuse is at the Coca Cola Amatil plant
in New South Wales (Environment Australia, 2001). Two simple recycling
initiatives have been undertaken at this plant, the first involving reuse of the
backwash water and the second the reuse of container rinse water. Interestingly,
the first of these, which recovers around 200 m3 day-' of backwash water
from the sand and carbon filters, appears to be blended with the mains water and
reused in the manufacturing process. The blend is maintained at less than 1:5
recovered:mains water. The payback time for the recycling system, which
comprises pipework and a backwash water recovery tank, is estimated to be
around two years. The recovered container rinse water, on the other hand, is
used in the evaporative cooling towers following filtration. About 16 m3 day-l
is recovered for this duty.

Caustic recovery
In the majority of food and beverage applications a large amount of caustic soda
is used for bottle washing and CIP (clean in place) applications. The disposal of
the spent caustic solution is problematic and expensive. In most cases the
effectiveness of the caustic solution is assessed by assaying for carbonate
contamination or dirt content: when these levels reach a certain limit the
solution is disposed of. The caustic content may still be quite high, however, and
nanofiltration membranes have been developed (Koch and PCI Memtech) to
clean and concentrate the spent caustic solution. The process plant for this duty
is quite expensive, and the economics are such that the plant is only justified if
the caustic volume used and cost of its disposal are both very high.

Bottle or can pasteurisers
An improperly balanced pasteuriser can use a large amounts of water which is
often discharged direct to drain. In most cases this water can be recycled back to
the pasteuriser directly after cooling and filtration. Checks must be made on
product contamination in the case of bottle pasteurisers.