Page 296 - Membranes for Industrial Wastewater Recovery and Re-Use

Case studies 2 6 5

Table 5.15 Cost sheet for post paint rinse water reuse plant (as of 2002)
Annual cost, € ($) Annual saving, € ($)
Energy 16 500 (16456)
Membrane cleaning 5500 (5485)
Recovered paint 100 000 (99 739)
Water and effluent 327000(326 146)
Labour 30 000 (29 921)
Total 22 000 (21 942) 457000 (455 807)
Currency conversion (x 0.99739) based on 12 August 2002 figures (http://www.oanda.com/convert/
fxhistory (accessed November 2002)).

would have a payback period in the region of 13 months due to the reduced
water prices.

5.1 1 NEC Semiconductors: microelectronics wastewater
reclamation (UK)

5.11.1 Background
NEC Semiconductors (UK) Ltd, Livingston, was formed in 1982 as part ofthe NEC
Corporation and was originally assigned for assembly and testing before
expanding into manufacture. The fabrication facility produces several millions
chips per month and has the largest operational clean room floor area in Europe
(dated 1999). NEC incorporates reclamation and reuse within its business
strategy achieving IS0 14001 accreditation in December 1991. Included in the
strategy is both reduced chemical consumption and waste recycling. For
instance, reduction in machine bath volume and photo-resist dispensing
volumes generated significant savings in hydrofluoric acid (€40 000 ($62 040)).
Materials such as cardboard, paper, plastics, acids and reject silicon wafers are
also recycled. For instance, the waste silicon is used in aluminium production
acting as a strengthening agent for the final product.
The initial driver for water recycling was to ensure sufficient water
resources at facilities where external water was limited. The experience gained
at these sites has led to reclaim plants operating at sites were water is plentiful
and inexpensive. In such cases the driver for reuse is to reduce operating and
capital costs of water supply with the added benefits of environmental
preservation and associated publicity. Reclamation at some sites has even
extended to ZLD (zero liquid discharge).
The majority of the DI water required at the production facility is used in the
wet bench machines in the clean room where the silicon wafers pass through at
various stages during production. The wet benches consist of a concentrated
acid bath, for etching, followed by a series of rinse baths. The wafers are initially
lowered into the acid bath for a preset time to achieve the required etch depth.