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146 Membranes for Industrial Wastewater Recovery and Re-use

Table 3.29 NSPSs for liquid effluents from cotton woven fabric finishing: 30 day average
(1 day maximum) in kg/MTof product (EPA, 1997)
Process BOD COD TSS Sulphide Phenol Chromium pH
Simple 1.7 (3.3) 26.9 (41.7) 3.9 (8.8) 0.1 (0.2) 0.05 (0.1) 0.05 (0.1) (6-9)
Complex 1.9 (3.7) 44.2 (68.7) 6.4(14.4) 0.1 (0.2) 0.05 (0.1) 0.05 (0.1) (6-9)
Desizing 2.8 (5.5) 38.3 (59.5) 6.9 (15.6) 0.1 (0.2) 0.05 (0.1) 0.05 (0.1) (6-9)

Table 3.30 Pollutant load in kg m-3, median values, from woven fabric finishing (UNEP,
1992)
-
Sub-category BOD COD TSS Oiland Phenol Cr Sulphide
grease
Simple processing 22.6 92.4 8.0 9.1 8.2 4.3 7.6
Complexprocessing 32.7 110.6 9.6 3.8 7.7 2.6 12.5
Complexprocessing 45.1 122.6 14.8 4.1 13.1 20.9 Na
plus desizing
a N, sufficient data not available to report.

There exist examples of regulatory bodies imposing discharge consents
relating to textile processing activities. One of these concerns the Wigston
sewagetreatment works in the Severn Trent region of the UK, to which a number
of dyehouses were discharging coloured effluents. This resulted in the sewage
treatment works, which was of conventional design, discharging coloured
effluent into the River Sence. The Environment Agency imposed colour consent
limits on the works, which Severn Trent Water, the sewerage operator, passed
on to the five dyehouses discharging to the sewage treatment works. This
dramatically influenced the economics of effluent recycling, as is explained in the
case study in Section 5.7.

3.3.5 Conventional treatment
Conventional technologies for textile wastewater treatment mainly comprise
biological treatment, precipitation, coagulation/flocculation, flotation,
oxidation and adsorption (Table 3.31), and have recently been reviewed
(Vandevivereetal., 1998; SlokarandLeMarechal, 1998; Rott andMinke, 1999;
Delee et al., 2002). Since the bulk of the COD for many textile wastewaters is
biodegradable most textile effluents are discharged to sewer, sometimes
following rudimentary aerobic biological treatment. For high COD loads, such as
those arising from desizing of starch or wool washing and scouring, anaerobic
pretreatment can be employed (Sacks and Buckley, 1999; Shaw et al., 2002;
Delee et al., ZOOZ), although this appears not to have reached commercial scale.
Coagulation, often followed by sand filtration, is also extensively used.
The problems imposed by dyewaste, however, are particularly vexing.
Biodegradability studies have indicated the feasibility of reducing the BOD and