Page 288 - Membranes for Industrial Wastewater Recovery and Re-Use

Case studies 2 5 7

permeate (Table 5.20). Suspended solids and n-hexane extractable compounds
are similarly reduced from 1120 and 475 mg 1-1 to less than 1 mg 1-1
respectively. The final RO stage produces a permeate with a final conductivity of
125 pS cm-l.
Combined water and sewerage charges in the city of Yokosuka are 4607 mP3
($4.1 5 m-3). The plant operates for 260 days per years and so the installation
and operation of the reuse plant results in a direct saving (Table 5.11) of
420 338 000 ($139 315) per annum with an additional Y1400000 ($9590)
saved through reduced chemical demands on the boiler system. The total annual
costs of running the additional treatment technology is Y5 406 300 ($37 033)
resulting in a net annual saving of Y14 931 700 ($102 282). The cost of the
plant is covered by offsetting 43 000 000 ($20 550) per year as depreciation on
the plant over its projected lifetime yielding a true annual saving of Yl1 93 1 700
($81 732).

5.9 Pasfrost vegetable processing plant (Belgium)

5.9.7 Background
Pasfrost. located in Passchendaele, western Belgium, is a vegetable processing
company producing 65 000 tonnes of deep-frozen vegetables per year. The plant
processes a wide variety of vegetables depending on the season ranging from
squashes and leaf crops in the summer to root vegetables in the winter. Process
water is used at the site for a range of activities such as washing/rinsing.
blanching, steam peeling, caustic peeling and cooling.
Traditionally, water is supplied from groundwater sources that are
bacteriologically safc and rcquire no treatment prior to use. However, economic
development in the region has led to increasing pressures on the ground water
sources resulting in the need to abstract from wells over 300 m deep. The quality

Table 5.11 Cost sheet for wastewater treatment reuse plant (as of 1998)

Annual cost (Y) Annual saving (Y)
MBR energy (120 m3 d-l) 925 500 (6339)
MBR membrane (120 m' d-') 3 600000 (24 660)
RO energy (40 m3 d-') 280800(1923)
RO membrane (40 m3 d-' 1 600000 (4110)
Totalopex(Ymm-3) 205.8 (1.4)
Reduced water charges 9 469 200 (64 864)
Reduced sewage charges 9 469 200 (64 864)
Reduction in boiler chemical costs 1 400 000 (9590)
Total 5406 300 (37033) 20 338 000 (139 31 5)
Currency conversion ( x 0.00685) based on 12 August 1998 figures (http://www.oanda.com/convert/
fxhistory (accessed November 2002)).