EDI today must be pretreated with RO for numerous reasons. But what are the advantages and disadvantages of 1-pass and 2-pass RO as pretreatment?
Many EDI systems using Electropure™ EDI perform very well with 1-pass RO. It's easy to achieve 17+ Megohm with 1-pass RO. Most USP WFI and Purified Water systems easily meet requirements with 1-pass RO. And a 1-pass RO system is less expensive and less complex than a 2-pass RO system.
2-pass RO followed by EDI gives the following benefits, and is often used for power plants
- Lower conductivity = higher EDI quality
- Lower CO2 = higher silica removal
- No softening required
- ppb-level contaminants means infrequent EDI cleaning
- Higher rated flows for EDI
1-pass RO can be enhanced using GTM (e.g., Liqui-Cel®) for even better EDI performance. GTM can reduce the CO2 which enhances EDI performance, reduces scaling potential, and helps SiO2 removal by the EDI.
In summary, EDI systems have many options: