Page 145 - Membranes for Industrial Wastewater Recovery and Re-Use

Industrial waters 11 9

Figure 3.21 Water treatment system in a recycled linerboard mill, McKinley Paper Ltd, New Mexico
(courtesy of L. Webb, Envirocell (Webb, 1999))

press and 100 mg 1-1 in the RO permeate. Thus the RO removes 98-99% of the
COD in the original wood room effluent. In this case the RO process was found to
be significantly cheaper than any other treatment methods. This was because
the plant is mechanical, including only a few process stages thus reducing the
capital investment cost compared to other systems such as evaporators or
biological systems. Operating costs are substantially lower than those of the
traditional treatment technologies as outputs can be recycled or reused thereby
reducing the volumes and generating financial benefits from reduced effluent
disposal and freshwater demand. In addition, there is no generation of by-
products, such as waste activated sludge. Thus the costs for the RO membrane
process are only around $1.5 per m3 ultimate disposal: the biological and
evaoprative processes would have respectively cost, in this case, €5 and €1 5 per
m3, based on ultimate disposal.
One of the first nanofiltration (NF) plants to be employed in the pulp and paper
industry was reported by Lien and Simonis (1995). This 10 MLD plant located in
the Pacific rim for cleaning paper mill and total effluent, produced from
newsprint, printing paper and de-inked pulping operations, employs spiral
wound NF modules (Osmonics). As with any dense membrane process, extensive
pretreatment is required (Fig. 3.22) to reduce the fouling propensity of the water.
The cleaning cycle time is over two weeks.
In the 1990s another high-shear membrane module, the VSEP filter (vibrating
shear enhanced processing filter: Section 2.1.4, Fig. 2.12) entered the market.
Existing mill-scale applications of the VSEP filter in the pulp and paper industry
include weak black liquor, box plant effluent, and MDF wastewater treatment