Page 208 - Membranes for Industrial Wastewater Recovery and Re-Use

System design aids 177

Feedwater quality
The quality of the feedwater(s), comprises composition, pH and temperature, i
typical window (from Rodesign by Hydranautics) being shown in Fig. 4.1. Mos
design packages allow entry of concentrations as either mg/l (i.e. ppm) or meq/l
with some also incorporating “ppm as CaC03”. Only the most common ions arc
included, however. Hence, any other ions that need to be added to the feedwate:
specification must have their permselectivity properties entered. If no sucl
rejection data is available, and they can only realistically to be obtained througk
experimental measurement, then there is nothing to be gained by adding them tc
the specification. All major suppliers’ packages will prompt if correction of thc
analysis with sodium or chloride is required to attain electroneutrality. P
number of different feedwater streams can be specified for most of the desigr
packages.

Flows and conversion
Flow rates and/or the overall conversion is also a required input (Fig. 4.2, fron
RoPro by Koch-Fluid Systems). Flow rates can be entered in both imperial an(
metric units, and it is usual to specify one of the flow rates (feed or product
and the recovery. Some packages allow for bypassing of the membrane array b!
part of the feedwater. Most of them have a simple percentage fouling allowancc
that the user can enter to correct for a lower, more conservative estimate o
permeate flux when calculating the design.

Figure 4.7 Feedwater quality dialogue box (Rodesign, Hydranautics)