Water Journal : Water Journal September 2015
water september 2015 50 Feature article pressures based on the selected membrane type, configured parameters and vessel array. Users have the option to let AqMB calculate the array based on the specified design flux and lead element flux, or configure the number of vessels for each stage with all other membrane design parameters. Hybrid designs are also possible by configuring each stage separately. If there is a potential problem with the design, the unit operation is highlighted red on-screen. AqMB allows designers to compare membrane performance from different membranes and manufacturers using real-world design scenarios where there may be multiple: • Recycles • Clarifiers • Sand filters • Ponds • Other pre- and post-treatment processes • Degassing • Chemical dosing. The whole-of-process consideration provided by AqMB therefore reduces the time to select the most suitable membrane for further refinement using vendor projection software during detailed design. nanofIltratIon MeMbranes To illustrate the capability of the software for membrane selection, a saline water high in calcium and magnesium sulfate was modelled in AqMB for five different NF membranes, as shown in Figure 3. Figure 4 shows the stream properties determined by the user and Figure 5 shows the outputs from running the scenario for five different NF membranes. The objective was to select a membrane that displayed a high rejection of magnesium sulfate and a low rejection for sodium and calcium compounds. During the modelling it became evident that some of the tighter membranes displayed a high rejection of sodium and calcium bicarbonate, causing major precipitation in the concentrate stream at 90 per cent design recovery. Changes in the rejection of bicarbonate and carbonate species had a marked impact on the pH of the concentrate stream, due to the change in alkalinity, which then affected the solubility of carbonate species. The entire exercise was completed within two hours. It provides an example where permeate and concentrate stream properties and ionic concentrations affected NF membrane performance, and interpreting this information leads to confident selection of a suitable membrane type for detailed design. reverse osMosIs MeMbranes The technical selection of RO membrane types for seawater desalination applications usually comes down to a few parameters: permeate TDS, feed pressure, fouling resistance and boron rejection. The pre-treatment design can affect some of these parameters due to the impact of pH on speciation chemistry and species solubility. Accurately modelling the pH and oxygen concentration can help to optimise any chemical dosing required, and also reduce the need for an anti-scalant. Under a given set of feed conditions, six different RO membrane types were compared with the AqMB software downstream of a typical seawater process design. Figure 5. Quantitative results returned from running the Aqmb plant/feed scenario for five NF membrane types. Figure 6. A typical seawater process design configured in Aqmb was used to compare rO membranes.
Water Journal August 2015
Water Journal November 2015