WaterSolutions Steps to Design an RO / NF Membrane System

Accurate system design is critical to getting the most from your water treatment system. Dozens of factors can impact the productivitiy of a system. ROSA (Reverse Osmosis System Analysis) design software program from Dow is designed to offer the most precise design recommendations to optimize system performance.

An entire RO / NF water treatment system consists of a pretreatment section, the membrane element system, and a post-treatment section. The membrane element system includes an inlet for feed water and outlets for permeate and concentrate.

RO / NF system performance is typically characterized by two parameters, permeate (or product) flow and salt rejection. These should always be referenced to a given feed water analysis, feed pressure, temperature, and recovery. The goal of the designer of an RO / NF system for a certain required permeate flow is to minimize feed pressure and membrane costs while optimizing permeate quality and recovery.

The steps to design such a membrane system are described here. Dow also offers the ROSA computer program to carry out designs.

How to Design a RO / NF Membrane System:

Step 1: Consider Feed Source, Feed Quality, Feed / Product Flow, and Required Product Quality
Step 2: Select the Flow Configuration and Number of Passes
Step 3: Select Membrane and Element Type
Step 4: Select Average Membrane Flux (Design Flux)
Step 5: Calculate the Number of Elements Needed
Step 6: Calculate the Number of Pressure Vessels Needed
Step 7: Select the Number of Stages
Step 8: Select the Staging Ratio (Array Ratio)
Step 9: Balance the Permeate Flow Rate
Step 10: Example