Page 210 - Membranes for Industrial Wastewater Recovery and Re-Use

Systern design aids 179

[ TWO Stage Concentrator I

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,Two Parr with lnterparf Pump
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Figure 4.3 Process design dialogue box (ROPRO, Koch-Fluid Systems)

and the nominal permeate flow per membrane, as specified by a RO CAD
package's specific dialogue window or simply the membrane specification sheet.
The element specification can be quite detailed: The Osmonics Winflows package
(Fig. 4.4) allows stipulation of element age to account for deteriorating hydraulic
performance with age.

Pretreatment and post-treatment
Pretreatment selection is usually limited to the selection of acids (sulphuric or
hydrochloric) or bases (caustic soda) to adjust the scaling index value (Fig. 4.5),
according to the principles outlined in Section 2.4.3. It is normal practice to
ignore pretreatment for the first trial run of the CAD and then add the
appropriate amount of acid or base according to the scaling index value
automatically calculated by the software. Similarly, post-treatment, which can
take the form of pH adjustment and/or degassing to remove the dissolved C02
down to some selected value, is usually carried out following the first run.
When all necessary input values have been entered, the software is ready to
perform a first calculation. The software calculates and presents data for the
composition of the different sub-streams plus all hydraulic data (flow and
pressure) for all parts of the array (Fig. 4.6). The designer is then able to analyse
the results and adjust the operating conditions so as to optimise the system and/
or attain the target permeate water quality. This may demand several runs, and
the solution ultimately obtained through iteration. The software packages
produce a dialogue box indicating warnings (amounting to errors or