DOW Reverse Osmosis System Analysis (ROSA)

This is yet another well-designed, but free, reverse osmosis (RO) modeling program from Dow that allows you to directly evaluate the expected performance of their FilmTec membranes. The opening screen shot is shown below. You enter project information, notes, unit preferences, etc. You can download this program by clicking here or on the graphic below.

Dow ROSA main screen

Just like any other RO modeling program the most important data to be input is detailed water quality data as shown below. Water quality input is both similar but different between each program. For example, on the Avista program requires aluminum but neither GE Winflows nor Dow ROSA have this entry. I consider this to be a major oversight because aluminum fouling can be a serious problem and you would be surprised the source of the aluminum. It can come from a municipal water treatment that feeds too much aluminum sulfate (alum), probably the most common coagulant used in water treatment. Avista models the aluminum, GE and Dow do not. Another example is that GE wants bromide value while neither Avista nor Dow require. And Avista does not require boron but both GE and Dow do. So you’ll need to pay close attention to the water quality data requirements for each program. I have all of these parameters measured because I often do my RO modeling using two or three of the available RO programs. You can see the difference in water quality inputs between Avista, GE, and Dow by clicking here.

ROSA water quality

In the next screen shot I’ve filled in the water quality data which is Mississippi River water that has been lime softened. Keep note as you look at each graphic of where we are in the design process. In the graphic above, along the bottom, you can see that we are at step “2) Feedwater Data.” In the graphic below we are still on step 2 but now the data entry is complete.

ROSA water quality for Mississippi River

In the next screen shot below we can see a critical message in red. It states: “Antiscalants are required. Consult your antiscalant manufacturer for dosing and maximum allowable system recovery.” This screen, at the top, also shows that I’ve selected a permeate flow rate of 750 gpm, a feed flow of 1,000 gpm, and a system recovery rate of 75%.

ROSA warning about antiscalant

You enter your system design information on the screen below. That includes the number stages, passes, pressure vessels, membrane elements per vessel, and type of Dow membrane. Not the tab selected at the bottom of the screen: we are on 4) System Configuration. The first stage has 24 pressure vessels with 6 membrane elements per vessel. The second stage has 12 pressure vessels with 6 membrane elements per vessel to give us the classic 2:1 ratio from stage 1 to stage 2 and a 75% system recovery rate.

ROSA system configuration screen

Now we need to run the reports which you select by clicking on tab 5) Report at the bottom of the screen as shown below. We have no errors in terms of our design based on water flow, recovery rate, pressure vessels, membrane elements, etc. You can generate two reports on this page that you can print or save. I’ve generated the two reports and saved them as PDFs. You can get the first report by clicking here and the second report by clicking here.

ROSA report screen

The final report is a cost analysis which is the sixth and final tab at bottom of the ROSA screen. The cost report is shown below. I wanted you to see the results from all six tabs but I also need you to know that I never use the cost analysis tab.

ROSA cost analysis screen