CapDI vs Traditional Technologies- AGWT

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CapDI

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vs Traditional Technologies

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LET'S EXPLAIN At Voltea, we are firm believers in the benefits of Membrane Capacitive Deionization, our CapDI. The technology is relatively new to the industry and there are often many questions as to how CapDI differs to Reverse Osmosis (RO) and other traditional deionization technologies, such as ED(R). We hope that this document will help answer those questions. Let's begin with comparing CapDI and RO: CapDI behaves like a flow-through capacitor where the feedwater travels through stacks of capacitor plates. Ions are adsorbed by carbon electrodes covered with cation and anion ion exchange membranes. The membranes are employed to keep positive and negative ions from migrating to their respective opposite poles during the regeneration sequence. These membranes are impermeable to water, allowing only ions to pass. Alternately, RO water desalination technology employs semi-permeable spiral wound membranes, operating under high pressure, to remove ions, molecules, and larger particles from water. HOW DO THE MEMBRANES IN CAPDI DIFFER TO THOSE IN RO? COMPARING CAPDI TO REVERSE OSMOSIS (RO) RO is very good at removing >95% of salts as the membrane rejects them. To achieve this, the water must be fed at high pressure to force the water through the semi-permeable membranes. The downside to this is twofold; the membrane, behaving as a barrier, can easily become fouled with particulate matter. Also, the energy cost associated with a high pressure pump can be steep. With CapDI, the membranes are not physical barriers and are much more resistant to fouling. Another impact of the difference in membranes is the efficiency of operation with regards to changing salt concentrations and water temperature. As RO removes the water and leaves the salt at low salt content, the system must work hard to move a lot of water. Since CapDI removes the salt and leaves the water, at these lower feed concentrations it can be significantly more efficient and hence have a lower OPEX. Additionally, there are numerous applications where high salt removal is not required. In these cases, RO permeate is typically blended with raw feed water (sometimes the RO’s brine stream) or re-mineralized with select media. Here, blend consistency can be challenging and often with less than optimum results. With CapDI, the potential across the capacitor can be simply and easily adjusted (tuned) to proportionally control the amount of salt removed from the feed water. This can also reduce OPEX. Unless configured in a batch operation scheme, RO produces a continuous permeate and concentrate waste stream. Consequently, the exposure time to precipitates is high, increasing the fouling potential. CapDI produces a batch of purified water, then regenerates producing a batch of concentrate. If a more continuous output stream is required, two modules (or systems) can be operated out of phase so that one is regenerating when the other is purifying. By producing in batches, the CapDI carbon electrodes are not continuously exposed to concentrate water, which reduces the precipitate fouling risk. HOW DOES THE FLOW PATTERN DIFFER? HOW DOES THIS AFFECT PERFORMANCE?

WHAT IS THE ONLINE OPERATION TIME?

RO is more often than not configured for continuous operation. However, in situations where frequent start/stops can occur, such as batch operations, membrane life can be shortened and potential failure increases. Being an electrochemical process (no moving parts), CapDI affords the benefit of not having any issues associated with frequent start/stop cycles occurring.

MEMBRANE TECHNOLOGY CapDI RO

Batch Process

Continuous Process

Pure/Concentrate OUT

Permeate OUT

Brine OUT

∆ e -

∆ P

Water IN

+

RO Membrane

Membrane

-

Ions + Ions

H  O 2

H  O 2

Membrane

-

Salt

Spiral Wound Membranes

Stacked Cells

Water IN

COST EFFECTIVENESS CapDI, when comparing to RO, is highly cost effective on an OPEX basis at low to mid-level brackish TDS. Chart 1 below displays the cost benefit of CapDI versus RO at TDS levels below 2,500 ppm.

Chart 1

CapDI

Cost Benefit

RO

0

2,500

TDS (ppm)

Chart 2 below illustrates the energy cost benefit of CapDI versus RO, with CapDI maintaining a consistent energy cost across all water temperatures. While RO no longer works at higher temperatures, CapDI specializes in deionization at low and elevated temperatures, all while maintaining energy efficiency.

Chart 2

RO

CapDI

0

Feed Water Temperature (°C) 45

60

GETTING MORE SPECIFIC Membranes               Electrodes              Electrochemical Process COMPARING CAPDI TO ELECTRODIALYSIS/REVERSAL (ED AND EDR)

With so much in common, what makes CapDI different from ED and EDR? Let’s start with the set-up differences. CapDI has an electrode pair for each membrane pair, in contrast to ED(R) where there is one electrode pair for several membrane pairs (ref. 1). This difference in arrangement drives several other differences. The first being how the electrical force is applied across the membranes. In CapDI, the distance between the electrodes is smaller, so a lower voltage can be applied. In ED(R), a higher voltage is required to compensate for the larger distance between the electrodes. At higher voltages, more water splitting occurs, potentially damaging the membranes closest to them and increasing fouling risk. This may also cause a higher electricity operating cost, as well as the need for degasification. Another strong difference is that ED(R) allows for continuous or semi-continuous pure and concentrate streams. This means that some end users benefit from the continuous nature of the process. There is a downside, however, in that there are areas of the set-up that are continually exposed to high concentrations of combined anions and cations, and as such, are at high fouling risk. To mitigate this, HCl (acid) and anti-scalants are often employed (ref. 2). CapDI does not have a continuous concentrate stream, so the fouling risk is significantly reduced and hence less (if any) chemicals are necessary.

EDR

CapDI

ref. 1

What is the difference between ED and EDR? EDR is ED with the addition that after a set time, the polarity switches to reduce some of the fouling that may have occurred at the membrane and spacer surface within the concentrate channels and at the electrodes.

Chemical

Acid Pure

Pure

Acid

ref. 2

MEMBRANE TECHNOLOGY CapDI EDR

Batch Process

Continuous Process

Brine Brine Pure

Pure/Concentrate OUT

Pure

∆ e -

Water IN

+

H  O 2

H  O 2

Brine

Brine

Membrane

-

-

Ions Ions +

+

H  O 2

Membrane

-

Ions Ions - + Ions -

Electrode (Pair)

Membrane (Pairs)

Stacked Cells

Water IN

TRIPLE COMPARISON

This triple comparison table shows what we believe to be some of the most important differentiating factors of CapDI, RO, and EDR.

CapDI

RO

EDR

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Tunable

Built-in Automatic CIP Remote Monitoring/Control Modular (Size) Removes TDS at High Temps

Chemical-Free

Chlorine Tolerance

Fouling Potential Energy Consumption

Low Risk

High Risk

Medium Risk

Medium

Low

High

Consumables

Low

High

High

Maintenance Requirements

Low

High

High

Flow Path

Long

Short

Long Electrostatic (Ion-Exchange)

Electrostatic (Ion-Exchange)

Mechanical (Filtration)

Membrane Type

Questions?? CONTACT US!

info@voltea.com www.voltea.com EUROPEAN OFFICE Wasbeekerlaan 24 Sassenheim 2171 AE The Netherlands +31 (0) 252 200100 U.S. OFFICE 1920 Hutton Court #200 Farmers Branch, TX 75234 +1 (469) 620 0133

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Advanced Global Water Technologies (Phils.) Inc. +63 995 984 7397 www.agwtphilinc.com

All Voltea trademarks and logos are owned by Voltea B.V. All other brand or product names are trademarks or registered marks of their respective owners. Because we are continuously improving our products and services, Voltea reserves the right to change specifications without prior notice. Voltea is an equal opportunity employer. CapDI vs Traditional Technologies/Highlighted Features © 2017. All rights reserved.

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