Page 177 - Membranes for Industrial Wastewater Recovery and Re-Use

Industrial waters 149

Table 3.32 Process modification cost benefit examples (EPA, 1997; ETPB, 1997)

Company Action Cost benefit
Lancashire medical Elimination of two wash cycles from €1 700 reduction in effluent costs
textile company bleaching process
America1 Corporation Extension of length of dyeing time by 60% decrease in BOD and COD:
15 minutes to improve exhaustion 20% drop in FOG: 98% drop in
NH,-N. $35 000 decreasep.a.
Adams-Millis Co. Reuse of dyebath for nylon hosiery in 3 5% decrease in water use
rotary drum dyeing machines ($O.O4/kg product)
Bigelow Carpets Cycling of dyebath water between $60 000 p.a.. plus reduction in
pairs of dyeing machines to allow effluent BOD and colour
reuse over 20 cycles
A yarn finishing Reuse of rinsewater three times Reduction of 80% TSS, 55% COD
company following mercerising. with and 70% in Na2C03 in effluent
evaporation to recover caustic Na2C03 (and so HC1 for neutralisation).
$189 OOOp.a. (1 yearpayback)
North Carolina facility Bleach bath reuse 50% reduction in effluent COD
Lancashire medical Recycling of last rinse from beam-and- €2 700 p.a.
textile company winch bleaching operation
Wigan dyehouse Reuse of effluent from bleaching for €10 700 p.a. in effluent disposal
scouring wash and water consumption reduction

synthetic detergents, in both cases to reduce effluent BOD levels), and reuse of
other process waters, such as coolant (ETPB, 1997). None of these measures,
however, can substantially reduce wastewater discharge to the extent possible
through effluent recycling.

3.3.7 Reuse practice and opportunities

Reclamation and reuse
Given the capital intensive nature of ozonation, which represents arguably the
most reliable and established decolourisation process, it is perhaps unsurprising
that there exist examples of centralised wastewater treatment facilities based on
ozonation (Churchley, 1994; Mattioli et al., 2002). For one region, the Como
province of northern Italy, there exist two sewage treatment works
(Bulgarograsso STW and Fino Mornasco STW) designed to treat wastewater of
which around 50% originates from industrial activity and, of this, over 90%
from textile processing operations. Both plants, which have a combined capacity
of 100000 m3 per day, are based on conventional primary and secondary
treatment with ozonation tertiary treatment following pretreatment either by
sand filtration or coagulation/flocculation with lamella settling. Further
polishing of the effluent from these works using fixed-film granular activated
carbon, i.e. biologically activated carbon or BAC, produced water of a quality
found to be suitable for silk degumming and dyeing (Mattioli et al., 2002).
Although not extensive, the trial appears to demonstrate the feasibility of
recycling of dyewaste that has undergone ozonation tertiary treatment.