Reverse osmosis is a water treatment process that is still the principal method of removing impurities from water. But some applications such as pharmaceuticals require an even higher level of purity. In most situations, electrodeionization systems can provide higher ultrapure chemical free water production.
Reverse osmosis (RO) and electrodeionization (EDI) are complimentary but distinctly different technologies. Here are some differences between reverse osmosis (RO) and electrodeionization (EDI) systems and their applications.
RO vs. EDI
Reverse osmosis is a pressure driven process. RO systems use high pressure feed to and a semipermeable membrane to remove impurities in water. As water goes through the membrane, ions and particles remain on the feed side. You can achieve high rejection using RO membranes.
Electrodeionization is an electrical current drive process. EDI feeds lower pressure water through ion exchange mixed bed resin. A DC electrical potential across the module regenerates resin and simultaneously removes the charged contaminants. EDI conserves any energy the module does not use.
The Challenge of Removing Total Dissolved Solids (TDS)
As a chemical free water purification system, reverse osmosis membranes typically reject 90-98% of TDS (Total Dissolved Solids). This is an excellent technology to remove bulk of the TDS, but it is very inefficient at removing low levels of dissolved solids.
Ion exchange resin is the primary removal method of dissolved solids in EDI and will typically remove 99.9%+ of the feed TDS within its capability. Each EDI module has a limited amount of resin, so there is a limit of feed TDS the EDI can handle. Therefore EDI is not capable of removing large amounts of TDS, but very efficient of removing low levels of TDS.
The process of first using RO as primary TDS removal and polishing the RO permeate with EDI is the perfect combination for high purity water production.
The Practicality of Electrodeionization
When it comes to choosing chemical free water purification methods, most plants opt for RO-EDI. A reverse osmosis system is very good at removing hardness, TDS and other contaminants usually to 5-10 microsiemens. EDI is very good at treating 5-10 microsiemens and producing <0.058 to 0.1 microsiemens/cm (10-17+ MegOhm-cm).
The engineer must be very experienced with both RO and EDI systems to properly size the correct RO membranes and EDI module stacks, design for correct feed pressure, instrumentations and program proper controls to provide reliable operation based on a specific feed water at a specific location.
Space and Maintenance Requirements
EDI systems require a considerably smaller space than chemically regenerated mixed beds. EDI modules are more flexible and capable of a larger output with the same footprint. RO and EDI systems can be supplied on a common skid to save floor space or fit in a limited space.
It is possible to remove some EDI modules without affecting the output. The only difference is that you’ll have to increase the electrical energy going into the system. As a result, it is easier to have flexible maintenance schedules that do not result in equipment downtime.
Choose a Chemical Free Water Purification That Works
The simple setup of the RO-EDI electrodeionization solutions means that it requires less supervision by the operator. That makes it a suitable candidate for automating water treatment. Therefore, RO-EDI is the chemical free water purification technology that will transform operations for modern industrial plants. For more information on electrodeionization systems and how this chemical free water purification works, contact Agape Water Solutions today.