Page 302 - Membranes for Industrial Wastewater Recovery and Re-Use

Case studies 2 7 1

generated from an indirect financial driver such as changes to legislation
(textile, food) or a need to secure sufficient water supplies. For instance, in
the case of the textile plant, legislation imposed a treatment requirement on the
plant. Once money had to be spent to comply with the legislation, the benefits of
ensuring the water could be recycled became important as otherwise the capital
expenditure could not be recovered. The regulation requirements can go as far
as zero liquid discharge, in which case reuse is a necessity rather than an
option. In such cases, the driver is to reduce overall treatment costs (Doswell).
However, in a number of the schemes the driver has been directly one of
reducing operating costs of which water supply can be a major component
(Eraring, Livingston).
The selection of membranes in the reclamation process train has occurred in a
number of ways. In some industries either membrane technology is already used
(Germany, Livingston) or the plant involves similar levels of technology
(Eraring). At other schemes the use of membranes has been a radically new
development (South Wigston). The familiarity with the technology appears to be
in part linked to the need for indirect financial drivers to exist before reuse is
considered. This is probably because a high degree of confidence is required in
the technology designed for reclaiming thc water, since it cannot be allowed to
adversely affect core production quality.
As expected it is difficult to draw commonalities from a broad range of
industries. However, a number of points can be concluded. The key facet of the
reclamation system in all cases has been its ability to withstand variations in
the wastewater quality, whilst producing a water quality suitable for reuse.
EMuent quality from membranes is usually very good, such that the main
concern is achieving sufficient throughput without incurring excessive cost.
This is reflected in the level of pretreatment required from the different schemes.
In cases where simple closed loops are being generated the pretreatment
requirement is minimal (as in the automotive industry). However, in situations
such as the reuse of secondary effluent and other wastes with high fouling
propensities, more involved pretreatment is required. In some cases this involves
two membrane stages and in other cases more traditional pretreatment (such as
coagulation followed by depth filtration).
Overall, the case studies have shown the suitability of membrane technologies
in particular for industrial effluent recovery and reuse. The ability to produce
reclaimed water of sufficient quality is dear. However, the throughputs are quite
different between the schemes. For instance, comparing the specific fluxes of the
four RO schemes described reveals a range between 0.56 and 3.63 LMH bar-'
reflecting the differences in the RO feed water matrices. This demonstrates that
each scheme is in part unique, potentially involving problems that have not been
encountered in other industries. Moreover a common problem with potential
industrial reuse schemes is a paucity of data describing the water quality and
hence the design limits, Table 5.20 clearly illustrates this point where in some
cases little or no water quality data are known in actual operating schemes.
Although easily remedied, data paucity remains a major barrier to uptake of not
only membranes for reuse but any treatment technology.