< Back to Top

No. Even with a two pass RO unit, you will not consistently produce USP grade water. While it may be possible to produce USP grade water immediately after startup, as the membranes age the water quality will likely not meet the USP requirements. The use of Deionization bottles or Continuous Electrodeionization will be required after the RO to meet USP requirements.

< Back to Top

It is difficult to predict the permeate quality of an RO. RO product quality relies heavily on the quality of the feedwater and the types of membranes used. The most effective tool in helping to determine the permeate quality is an accurate water analysis. MECO can evaluate the water analysis and run RO projections to help determine the permeate quality of any RO design.

< Back to Top

Hot water sanitization and chemical sanitization are both used to sanitize RO units. Hot water sanitization has a much higher initial cost as it requires more instrumentation, a heat exchanger, controls, and special membranes. The high heat (180ºF) can also reduce the life of the membrane if frequent sanitizatons are required.

Chemical sanitization has a much lower initial cost. Chemically sanitized units do not require stainless steel feed lines, special membranes, heat exchangers, controls, and added instrumentation. A CIP skid is required, but if a customer already has one for an existing piece of equipment, it can easily be adapted for use on the RO as well. The drawback is that sanitization chemicals have to be purchased, handled, and disposed of every time the unit is sanitized.

< Back to Top

RO units need a good bit of attention. The RO unit should be monitored on a daily basis and records should be kept on pressures, flowrates, and water quality. This helps to determine when the RO unit is experiencing problems with scaling, biofouling, membrane degradation, etc. Since problems with RO units are usually not associated with catastrophic failures, having the ability to trend data makes diagnosing a problem much easier.

Even with proper care, RO membranes will have to be replaced. The average life of RO membranes is about three years. Replacement will require a full shutdown of the RO unit. Depending on the number of membranes in the system, this can be an expensive maintenance cost that should not be overlooked.

Membrane cleaning is a task that will have to be performed on a regular basis. Cleaning of the membranes is required for removal of scale and biofouling. Depending on the size of the RO unit, it should be noted that cleaning may be a very time consuming task and the RO unit must be shutdown.

< Back to Top

The first consideration you should make is what type of materials of construction do you need. PVC is an inexpensive material to make an RO out of. The capital cost of the unit will be greatly reduced at the expense of a more sanitary design. If a sanitary design is a major concern, then a stainless steel O.D. tube permeate is required at a greater cost.

Membrane selection is another important area of concern. Different membranes have different rejection rates. Typically, the highest rejection rates are associated with the highest operational pressures. The higher the operational pressure, the more pump horsepower is required to boost the pressure. A larger horsepower pump will incur a higher electrical utilities cost for daily operation.

Membrane flux is the amount of water that can be passed through a square foot of membrane. The unit of measure for flux is referred to as GFD (gallons per square foot per day). The higher the flux rate, the higher potential for scaling problems. It is best to consider a conservative flux rate when designing an RO system. Running the membranes close to their maximum flux will increase the potential for scaling and will shorten the life of the membranes.

< Back to Top

All EDI units require a properly designed RO to meet EDI feedwater requirements. A properly designed RO is key to extending the life of the EDI modules and maintaining consistent high quality product water. The feedwater 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.

< Back to Top

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

< Back to Top

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 feedwater quality. Good feedwater quality will require less voltage to get the desired product quality.

< Back to Top

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

< Back to Top

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.

< Back to Top

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.

< Back to Top

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.