Page 142 - Membranes for Industrial Wastewater Recovery and Re-Use

116 Membranes for Industrid Wastewater Recovery and Re-use

the use of ultrafiltration is the tubular ultrafiltration plant at Borregaard sulphite
pulp mill in Norway, which has been used to process spent sulphite liquor since
1981 (Table 3.18). The UF concentrate contains high molar mass fractions of
lignosulphonates and small amounts of sugar and salts. The concentrate is used
for vanillin production.
To meet the emission levels stated by legislation or to improve the efficiency of
the external biological treatment some specific effluents, e.g. bleaching effluents
with high COD loads, have been separately pre-treated prior to biotreatment. For
these reasons several ultrafiltration plants were installed in the early 1980s to
treat the first alkaline stage effluent, El, from the bleaching process (Haagensen,
1982; Okamoto et aI., 1985; Jonsson, 1987). For example, in the Taio Paper Co.
mill the COD reduction obtained was 79%, equating to 5.5 t d-l. This was
enough to meet the emission level and the efficiency of the biological effluent
treatment plant was significantly increased. The concentrate was incinerated
with the black liquor. The average permeate flux of the polysulphone UF
membranes used for the 3.5 million litres per day (MLD) plant was about 100
1 m-2 h-l (LMH), giving a total membrane area requirement of 1480 m2.
Even though the processes using tubular membranes perform well, they do so
at a substantial cost. The packing density of the tubular membranes is relatively
low (Table 2.5) such that membrane plants based on this modular configuration
have a relatively large footprint. In addition, fluxes attainable from tubular
membranes are limited by the high fouling propensity of the liquids arising.
The cross-rotational (CR) filter (Section 2.1 -4, Fig. 2.12), originally developed
by ABB Flootek, Sweden (now Metso Paperchem, Finland), entered the market in
the late 1980s. It was shortly adapted for mill-scale ultrafiltration applications,
such as treatment of bleaching effluents and board machine white water as well

Table 3.18 UItra6ltration of spent sulphite liquor at Borregaard Industries, Norway (PCI
Membrane Systems, 1988)
Parameter Details/value

Membrane BXl , PCI Membrane Systems
Total membrane area, m2 1120
Process design 2 lines with 6 stages in series with diafiltration
Feed flow, m3 h-' 50
Concentrate flow, m3 h-' 16
Solids content, % Feed 12
Concentrate 22
Pressure, bar 10-1 5
Cross-flow velocity High
Temperature, "C 60-65
PH 4.2-4.5
Washing Alkaline detergent daily for 2 hours
Relative costs Membranes 65%
Energy 2 6%
Mechanical spare parts 6%
Chemicals 3%