Portable Exchange D.I., Part II

Important topics that were excluded last month but that should be discussed are in the following article.

PEDI Plant Required Accessories

Exchange Bottles.

  • Types of exchange bottles and tanks come in various sizes that normally are referred to in cubic feet.
  • Handle small bottles by using a two- or four-wheel cart. (Define small bottles as those having a maximum inlet/outlet connection of 1 inch for reference purposes). These bottles range in size from 0.25 cubic foot capacity to an average 3.5 cubic foot capacity. Two bottle types exist—the most common made of fiberglass and others made of steel.
  • In addition, there are skidded bottles that are handled with the use of powered or manual floor jacks and/or tow motor forklifts. These bottles range in size from 10 cubic foot capacity through 40 cubic foot capacity and larger. The average inlet/outlet connection sizes are greater than 1 inch with most being 2 inches or 3 inches. These tanks are available in both steel and fiberglass though generally they are steel constructed because it is more versatile than fiberglass. As a result, there is a larger diversity of shapes, sizes, connections and other construction considerations.

Bottle Fittings and Connections.
There are numerous connection styles. All of them have two parts—the end that connects to the bottle and the end that connects to the hose. Most use a union nut or camlok connection. Important considerations include the selection of fittings, which allow only inlet to inlet and outlet to outlet connections. This feature prevents a tank from mistakenly being reverse connected. (A reverse hook up could put resin into your customer’s service line.) Keep in mind that your fitting selection should be easy to use, minimize leaks, allow venting of the bottles and be durable. Realize that the longer an exchange vessel stays in the field the better. For example, routing a customer for 30 days and exchanging every 20 days will create higher labor and transportation costs. Lower profits may result, causing additional bottles (at no additional cost to the customer) to be on site.

Monitoring Equipment.
Indication is necessary to alert the user when an exchange is needed. The most common is quality lights. These can be single or multiple lights with various ranges of 20K ohm, 50K ohm, 200,000K ohm, 1-meg ohm, etc., or a monitor having adjustable end point settings. Other available monitors provide automatic bank changing, while some will report existing status through phone lines.

Pretreatment Needs

Necessary pre-treatments may include

  • Multimedia Filtration—Traps debris/particles from feed water.
  • Carbon Filtration—Removes chlorine/organics from the water supply.
  • Softeners—Provide some hardness protection against overruns.
  • Resin Organic Traps—Improve treated water quality and reduce resin fouling.
  • Reverse Osmosis—Use on high TDS feed waters to increase DI run length and treated water quality.

Post Treatment

  • Cartridge Filtration—Use as a resin trap or to further polish the water.
  • Ultra Filtration—Use cartridge or membrane style for more critical applications.
  • UV Sterilizers—For virus and bacteria protection.

Market Considerations

Know Your Market Waters.
The two types of water supplies are ground and surface. Each has its own special needs. Groundwater may be high in TDS or have Fe and/or Mn problems. Surface water may have organic or silt issues to solve. Municipalities often use a combination of surface and well supplies. Numerous manufacturing plants have their own private supply.

Know Your Market.
Review your potential market. The Yellow Pages provide numerous leads. Also, speak with your local chamber of commerce, review the Dodge reports or work
with local engineers.

Know the Customer’s Applications.
Knowing the individual customer requirements and operating parameters including quality, quantity, hours of operation, etc., is important. Know and understand how your customer uses the treated water. Some considerations include the following.



  • Is the application once through using municipal feed water?
  • Is it a 24-hour operation?
  • Will service people have to be on call 24 hours?
  • Is this a rinse recycle application? If so, what type of contaminants will the resins be subjected to?

Know the Customer Applications.


  • Does this need consideration for resins and/or pretreatment out of my normal supply?
  • What issues of flow rate and pressure drops exist?
  • Will extra bottles be left for customer installation when existing bottles exhaust?
  • How is the customer affected if poor quality water occurs, and how quickly must I respond?

Plant Logistics

A general idea of your market’s needs helps define the plant’s type and accessories. Planning should include

  1. Daily Regeneration’s—How many cubic feet of resin will be needed?
  2. Account Types—Will accounts be low volume, low flow, high volume, high flow or a combination? What quality of water is needed—high quality or low quality?
  3. Tracking—Employ a method of tracking your resins and bottles.

    • Keep separate resins used on recycle re-use and tap water applications.
    • Keep separate resins used on high purity from low purity applications.
    • Know the age of your resin and plan for replacement.

  4. Supplies—Remember to have bottles in-house for reconditioning, in transit, and in use/stand-by at the customer locations. In-house chemicals will be consumed on a regular basis. Fittings will break, new hoses will be needed, etc., so plan for extra. Plan for a minimum of 3 percent to 5 percent resin loss annually.

Selling the Service

The best pricing method will depend on the existing program, competitors’ programs and customer requirements. Some variations include



  • Selling by the gallon. Base charges on meter readings of gallons used. Include bottle rental and regeneration in price per gallon of water provided with a minimum monthly demand.
  • Leasing tanks and charge for regeneration as required.
  • Applying a monthly rental charge with additional charges for regeneration.
  • Charging on each exchange and regeneration and delivery costs.
  • Selling tanks initially and charging for regeneration and resin upkeep.

Other Sales Opportunities.

A PEDI plant can provide degrees of water quality to match customers’ needs. Also consider the following.



  • Back-up support for fixed self-regenerating equipment.
  • Pilot plant services, which may define customer needs when quality has not previously been defined.
  • The customer may have other water treatment needs, opening additional sales opportunities.

Troubleshooting and Maintenance

Once the bottles are installed at a customer’s location there is no real way of knowing the care taken during the service run. For example, does the customer exchange the bottles when the indicating light says it is time, or are the bottles allowed to continue service flow in an overrun situation? Be sure to watch for

Resin Fouling.
The most common foulants include



  • Hardness fouling of anion resin caused by system overrun and exhaustion of the preceding cation;
  • Organics caused by feedwater carry through and/or low usage resulting in time for growth; and
  • Oil and grease (Found in specific recycle systems).

Poor Quality Water.
Watch for these common causes



  • Resin fouling—Determine foulant and treat resin accordingly.
  • Low Regenerate Dose—Causes include low caustic temperature, low available treatment chemical and/or low regenerate dosage.
  • Low Utilities—Poor water supply and pressure causes poor resin regeneration.
  • Improper Mix—Mixed-bed units require an equilibrium amount of each. Though dependent on resin type, this generally means 60 percent anion with 40 percent cation mixed thoroughly.
  • Rate of Flow—Too low may cause channeling; too high reduces resin/water contact time.
  • Bottle/Tank Distribution—Poor distributor design may cause channeling.
  • Regenerate Types—The wrong chemicals may foul resins.
  • Resin Age—It may be time to replace resin if it has lost its capacity.
  • Maintenance—Scheduled maintenance is essential to keeping a plant in top form. Clean and sanitize your plant on a regular basis, making sure to include all plumbing lines including hoses and fittings. Check working components such as pumps, valves and solenoids and repair and replace as necessary. Also, maintain the resin float. Plan its retirement by moving older resins in high quality applications down to lower quality applications.

    Plant operation can be rewarding financially by providing a steady capital flow and personally by solving a customer’s problem or filling a need. It requires attention to the details of customer needs, local water supplies and maintaining a regenerating plant.

    SIDEBAR: Resin Types

    There are two basic types of resin—cation and anion—with many variations of each. All DI units use a strong acid cation resin. The anion resin is the more critical of which there are three primary choices. These are weak base, strong base type 2 and strong base type 1. The type that best suits your market depends on your market waters and needs.

    • Weak base anion (WBA) is used for low quality two-bed DI water applications and long service runs. This is used for water qualities of 20K ohm and below.
    • Strong base type 2 (SBA 2) is used for 50K ohm to 500K ohm two-bed waters and as pretreatment to mixed beds. This may be the resin of choice for mixed-bed bottles (qualities greater than 1 meg-ohm) when feed water supplies are high in organics.
    • Strong base type 1 (SBA1) is used for 50K ohm to 500K ohm two-bed waters, highest silica reduction and mixed bed DIs when water qualities must be 1 meg-ohm or higher.


    About the Author

    Nevin Rudie is senior application engineer at Ecodyne Water Treatment, Inc. in Naperville, Ill. He has been in water treatment since 1976, having been involved in the design and operation of PEDI plants for 16 years. He can be reached by phone at 630-637-2116; e-mail ecoeng@earthlink.net.

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