Page 205 - Membranes for Industrial Wastewater Recovery and Re-Use

174 Membranes for lndustrial Wastewater Recovery and Re-use

information a mass balance of the solutes is necessary. This is considerably more
complex than the water balance solution, which is obtained analytically using
Equation (2.22). because of the interrelationship between TMP, 0 and n, and the
complicating influence of concentration polarisation (Section 2.2.3). This means
that the impacts of the individual design parameters on operation (Table 4.1) are
largely interdependent, and that the array design solution is then only
obtainable iteratively.
To enable these array design calculations to be carried out, RO design software
packages are available for specific RO membrane products. Such software enables
the designer to simulate operation of any RO array under any set of operating
conditions. These packages (Table 4.2) are intended to allow the user to produce
an RO array design from base information, such as the required product flow
rate, overall process conversion and feedwater characteristics. The membrane
suppliers offer their own RO software to the (prospective) customer gratis.
Specific software from universities is also available, or else is under development,
at institutions such as RWTH Aachen and Saarland University in Germany,
University of Wales Swansea in the UK and the European Institute of Membranes
at the University of Montpellier in France. Some of these groups are developing
software for nanofiltration.
The starting point for all design packages is the feedwater composition. Whilst
data for the principal ions may be available, this is not always the case for some
scalant components, such as barium or silicate. These ions form extremely
insoluble precipitates, such that they may be close to saturation even at very low
concentrations. Most feedwaters, and industrial effluents in particular, are
subject to temporal fluctuations in composition, and this has to be accounted for

Table 4.1 RO design parameters
Parameter Impactd
Feedwater composition Osmotic pressure, scaling, membrane stability, permeate quality
Feedwater pH Scaling. membrane stability
Feedwater temperature Flux. membrane stability
Permeate flux Transmembrane pressure, concentration polarisation, fouling,
pressure loss
Cross-flow velocity Concentration polarisation. fouling. pressure loss
Membrane material Membrane stability, permeate quality, fouling

a Primary or most important in bold type.

Table 4.2 Relevant RO design software
Company Membrane name RO software

Dow Filmtec Rosa
Hydranautics Hydranautics Rodesign, Rodata
Koch Koch (Fluid Systems) Ropro, Costpro
Osmonics Osmonics, Desal WinFlows
Toray. Ropur. Trisep Toray. Ropur. Trisep WinCarol, 2p flows