MECO - A worldwide leader in water purification

Design Features

MECO Electrodeionization units eliminate the need for acid and caustic regenerants associated with traditional ion exchange. The units are modular in design such that a multiple of stacks can be configured to provide a variety of outputs. MECO EDI units are also available in the MASTERpak™ series, a system that incorporates Pretreatment, RO, and EDI all on a single packaged skid used to produce USP Purified water. All MECO clients benefit from MECO's exclusive MASTERsupport™ service capabilities.

Electrodeionization

• No brine recirculation
• Modular design
• Compact design
• Stainless steel concentrate & electrolyte lines

EDI Basics

The electrodeionization process uses a combination of ion selective membranes and ion exchange resins sandwiched between two electrodes (anode (+) and cathode (-)) under a DC voltage potential to remove ions from RO-pretreated water.

Ion selective membranes operate using the same principle and materials as ion exchange resins, and they are used to transport specific ions away from their counterions. Anion selective membranes are permeable to anions but not to cations; cation selective membranes are permeable to cations but not to anions. The membranes are not water permeable.

By spacing alternating layers of anion and cation selective membranes within a plate and frame module, a "stack" of parallel purifying and concentrating compartments are created. The ion selective membranes are fixed to an inert polymer frame, which is filled with mixed ion exchange resins to form the purifying chambers. The screens between the purifying chambers form the concentrating chambers.

This basic repeating element of the EDI, called a "cell-pair," is illustrated in the figure below. The "stack" of cell-pairs is positioned between the two electrodes, which supply the DC potential to the module. Under the influence of the applied DC voltage potential, ions are transported across the membranes from the purifying chambers into the concentrating chambers. Thus, as water moves through the purifying chambers, it becomes free of ions. This stream is the pure water product stream.

The RO feed to the EDI module is split into three separate streams.

1. Product stream
2. Concentrate stream (typically 10%, may be recycled to RO feed)
3. Electrolyte stream (1%, anolyte + catholyte to drain)

The third (electrolyte) stream flows past the anode and cathode sequentially. The anolyte-bathing stream first flows past the anode (+) through a compartment formed by a gasketed monofilament screen, which is located between the anode and an adjacent anion selective membrane. In this compartment, the pH drops and Cl2 (dissolved) and O2 (gas) are generated. This stream then flows into the cathode compartment, formed between the cathode (-) and its adjacent cation selective membrane. In this compartment H2 (gas) is generated. Thus, the electrolyte waste stream expels the unwanted chlorine, oxygen, and hydrogen gas from the electrodes.

MECO MASTERedge™ Optimized Design

EDI modules are rated for specific flowrates. Each module in a system can handle a maximum and a minimum amount of flow. If the product flowrate of the RO falls within the specified limits of the EDI modules, there should be no need for feed flow control to the EDI module. The only flow control required is the reject flow.

Adjustment of the reject flow should be set based on the product quality of the RO and should require very little adjustment. The reject flow is typically set at 10% of the feed flowrate. It is important to note here that the quality of the RO design will play an important factor in the way the EDI operates. A poorly designed RO that has constant product quality fluctuations will cause upsets in the EDI system and will make the EDI difficult to control.

Maximizing EDI Module Potential

As you can imagine, there are some ions that are easily removed by the EDI process and others that are more difficult to remove. Since the EDI module works by removing charged ions from the feed water, you can see how a highly charged ion would be easily removed. Weakly charged ions are more difficult for the EDI module to take out of the feed stream. Again, this is where the design of the RO unit plays a major factor in the EDI system's performance.

Ions with a strong ionic charge, such as Na+, Cl-, Ca+2, H+, and OH-, are easily removed in the first portion of the resin bed, which is referred to as the "working" bed. Ions with weak ionic charges, such as CO2, SiO2 (Silica), and H3BO3 (Boron), are difficult for the EDI to remove and require more residence time in the second portion of the module called the polishing bed. To ensure that all of the ions are removed, the resin bed should be maximized for removal of whichever ions are more prevalent in the feed water. For example, if it is expected that CO2 levels are going to be high in the RO permeate, the EDI should be maximized so that the working bed is small and the polishing bed is large. This means proper RO design to remove as much of the "easy ions" is critical. Conversely, if CO2 and Silica are expected to be low, then the working bed can be expanded to remove a higher load of "easy" ions.

Q: What are the feed water requirements for an EDI?

A: All EDI units require a properly designed RO to meet EDI feed water requirements. A properly designed RO is key to extending the life of the EDI modules and maintaining consistent high quality product water. The feed water requirements for an EDI are as follows:

Conductivity = 4 to 30 Microsiemens
Hardness - 1.0 ppm
Organics - 0.5 ppm TOC
Silica - 0.5
Total CO2 - 5 ppm or less
PH - 5.0 to 9.5
Temperature - 5C to 35C

If the pretreatment meets or exceeds these requirements, you can expect to get the highest quality water possible out of the EDI module. If the water quality is less than that stated above, the product water quality will be less than 17-18 Mega Ohm but may still meet USP requirements.

Q: What materials of construction are available for piping?

A: PVC piping as well as sanitary piping can be provided on EDI units.

Q: What voltage do EDI units use?

A: EDI units use a Voltage Control Module to convert AC current to DC current. The input voltage to the Voltage Control Module can be either 208/240 or 440/480. The DC voltage that the EDI module uses ranges from 0 to 400V depending on the feed water quality. Good feed water quality will require less voltage to get the desired product quality.

Q: How often do I have to regenerate the modules?

A: EDI modules use the voltage to continuously regenerate the resin. Periodic regenerations are not necessary and regeneration chemicals are not required.

Q: How long do EDI modules last?

A: EDI modules have an approximate lifespan of 5 years. If proper care is given to the modules, the life expectancy can be greatly increased. Repeated cleanings, poor RO design and repeated hot water sanitization will all decrease the life of an EDI module.

Q: How much will it cost to run an EDI module?

A: That is a tough question because there are numerous EDI modules on the market with different electrical consumptions. Some modules use amperage, as opposed to voltage, as the medium of ion removal. This can significantly increase the operating cost of the module. MECO's typical EDI module, operating under normal conditions, will use about 300V while drawing 2 amps per 10 GPM. This translates to about $1.00 per 8 hours per 10 GPM. This is based on an estimated $0.12/kW-hr energy cost.

Q: What is the recovery of an EDI unit?

A: EDI units typically run at a 90% recovery rate. In certain applications it is possible to increase the overall recovery of the EDI to 99% by bringing the concentrate back to the feed of the RO unit.

The MECO Electro-Deionization MASTERedge Package™

Versatile System

The base MASTERedge™ system will meet all of your Multi-Mega Ohm water quality needs, but MECO has gone the extra step to design a system that can be expanded to meet even the most demanding requirements. While a simple system will make the EDI easier to operate, MECO can incorporate any number of special controls, instruments, or valves that may be required.

Cost Effective Design

A MECO EDI system does not need a brine recirculation system or a 2 pass RO to produce Multi-Mega Ohm water. This drastically reduces both capital and maintenance costs.

Compact Design

MECO uses some of the smallest and lightest EDI modules on the market. This allows for a smaller installed footprint, easier installation and maintenance. Our EDI modules are light enough to be removed by hand if ever necessary.

Low Voltage

This system uses EDI modules that use some of the lowest voltages in the industry. The maximum applied voltage is 400V. This is 200V less than comparable designs. Standout Features Include:

• Sanitary and non-sanitary designs available
• Hot water sanitization available
• Stainless Steel concentrate and electrolyte lines
• Spare modules can be shipped and received in 24 hours or less

Anytime. Anywhere.

• 24 hours, 7 days a week access to effectively manage your water system.

Real Time Access to:

• Purchase spare parts online
• Track status of outstanding orders
• Review shipping information
• Review invoice/payment history
• Review online maintenance records
• Request technical information
• Online electronic manuals
• Remote system monitoring capabilities

   MECO understands the importance of providing our customers with the parts and services required to maintain systems operating at optimum capacity. Our online service center - MECO MASTERsupport™ is a good example of that. It enables you to monitor your system remotely, place orders, access service records and view your system's manuals when it's convenient for you. Anytime. Anywhere.

With a simple point and click, our entire parts inventory is available to you. Through the online service center, you also get real-time access to invoices, orders, shipping status, system manuals and service trip reports. Everything you need to know to effectively manage and maintain your treatment plant is right at your fingertips.

It's another example of MECO's commitment to providing the highest quality spare parts and cost effective support throughout the life-cycle of the product.

» Launch MASTERsupport™ Online