Katlyn Graham: Hello, I’m Katlyn Graham, here with VJ Nathan, the technical director here at QUA. Welcome, VJ.
VJ Nathan: Thank you very much, Katlyn. Thanks for this opportunity.
Katlyn: Thanks for joining us. Today, we’re discussing one of your premier products at QUA. Why don’t we start off with just explaining what QUA does, first of all?
VJ: QUA is a manufacturer for advanced membrane products used in water, and waste water treatment systems.
Katlyn: One of your products is called FEDI. Am I pronouncing that correctly?
VJ: Yes.
Katlyn: I’m told that involves electrodeionization. What is electrodeionization?
VJ: Electrodeionization is a combination of electrodialysis and ion exchange process. Basically, it will remove dissolved ionic impurities from water. What it does is ion selective resin media, which is mixed resin and ion selective membrane, which is cationic‑anionic membrane, move the ionic impurities present in water uni‑directionally under an electrical potential.
In this process, the anionic and cationic membrane are placed alternatively with a small flow‑through chamber between them. Water to be treated is passed through alternate chamber called the dilute chamber. The dilute chambers are filled with mixed resin.
The remaining chambers are called the concentrate or reject chamber through which waste water is taken out. At the end of the alternating dilute and concentrate chambers are placed two electrode plates, one on each side. The cathode or the negative plates faces the anionic membrane and the anodic or the positive plate faces the cationic membrane.
Then, you pass predetermined DC current through these electrodes, the electrical potential applied transports the dissolved ions through the ion selective membrane making the feed water pure.
Please note that water cannot pass through the membrane, and only the ions can pass through it to the respective concentrate chambers adjacent to them.
A small water flow, about five to seven percent of the feed flow is maintained through the concentrate chamber continuously, which rinses out the removed ionic impurities. The concentrate flow can be recycled, if necessary, to improve the recovery.
Bulk of the DC current applied also splits the water molecule at the resin beat surface into hydrogen and hydroxyl ion, which continuously regenerate the exhausted resin. There is also a third flow, in addition to the dilute and the concentrate flow, through the EDI unit, which is called the electrode flow.
This is a very small stream of water to keep the electrodes cool, and these are provided at the electrode ends. EDI or FEDI is a polishing technology to produce high quality treated water and normally follows an RO unit. The EDI or FEDI is a chemical‑free process and have been replacing chemical intensive mixed bed ion exchanger at many sites.
Katlyn: It sounds like FEDI removes impurities in the water and leaves the water more pure?
VJ: That is correct.
Katlyn: Without using harsh chemicals.
VJ: Without using harsh chemicals.
Katlyn: That’s a huge innovation I would think. Who would use FEDI, and who would benefit from this process?
VJ: The industry, which will benefit with EDI process are basically those requiring very high purity water for their boiler feed or for process application in the 10 to 18 megaohm range resistivity.
We are looking at customers like power stations, oil refinery, petrochemicals, LNG projects, electronics, food and beverage, and pharmaceuticals.
As already told, EDI is an effective replacement for mixed bed polisher. With EDI process, the treatment is of continuous type requiring no downtime for regeneration as well as there is no chemical waste to be treated.
Katlyn: That’s definitely a plus. Now, I had asked you initially what is electrodeionization. Now, this product uses fractional electrodeionization. What is the difference between those two?
VJ: The electrodeionization and fractional electrodeionization, both are electrodeionization. The main difference is, in a fractional electrodeionization, the separation of the ionic impurities takes place in two stages instead of a single state separation in a regular EDI process.
Fractional electrodeionization is a patented process, which carries out the electrodeionization in two stages. FEDI, stage one, is operated at a lower voltage and the stage two at a higher voltage. This is different from the other EDIs in the market, which operates at a single uniform voltage.
Also, the FEDI has two distinct separate concentrate chamber. Stage one operating at lower voltage is called hardeners or strongly ionized impurities removal zone and stage two operating at a higher voltage is called silica or weakly ionized impurities removal zone.
The voltage applied has direct relationship to the pH in the concentrate chamber. Theoretically, hydrogen ion is more mobile compared to hydroxyl ion at a lower voltage. Thus, by applying lower voltage in stage one, more hydrogen ions are transported to the concentrate chamber making the concentrate chamber acidic with a pH of 4.5 to 5.
Now, as known, at a lower pH, hardness scaling is eliminated, FEDI can tolerate higher hardness in the feed water. Thus, FEDI can successfully operate on a single pass RO product, which has a higher hardness and a double pass RO product is not always required.
The second stage of the FEDI operates at a much higher voltage, which is also called the silica removal zone. Due to reduced transport of hydroxyl ion in the stage one, there are now excess hydroxyl ions available in the second stage, which makes it alkaline.
This considerably improves the silica rejection and thus produces a much superior treated water in the stage two. The concentrate or the reject flow in this stage two is at a much higher pH of about 9 to 9.5.
Having separate concentrate chambers for stage one and stage two, the waste or reject do not mix within the stack and are separately led out for final blending. Both the stage one and the stage two process is done inside a single stack.
Katlyn: So it definitely leads to a highly purified water.
VJ: Yeah, highly purified water in a position to tolerate higher hardness in the feed water.
Katlyn: Anything else you want to add about FEDI or QUA, your product study?
VJ: Probably, I would have to talk about the plants we have already supplied.
Katlyn: Oh, definitely. What kind of companies have already purchased FEDI?
VJ: FEDI has been in the market for the last four years or so, and already there are a number of reference plants, in large installation in power stations, in refineries, in LNG project, and some of the FEDI systems supplied are some of the largest capacity systems in the world.
Some of the FEDI units supplied for the LNG projects or the refinery projects are in the capacity ranges of 3,000 GPM and upwards.
Katlyn: Can you give us an idea of how…that’s a lot it sounds like
VJ: It’s a very large systems.
Katlyn: Very large systems, and they’ve been reporting good success, they’ve liked the FEDI?
VJ: Yeah, all the FEDI plants, which are already commissioned, they are all working very satisfactorily. The customers are quite happy, and pleased with the performance.
Katlyn: It sounds like you’re putting out a great product and creating highly purified water, which we certainly need. Thank you so much, VJ, for explaining all this.
VJ: Thank you.