Carbonate Scale
The following cleaning procedure is designed specifically for a system that has had carbonate scale precipitated in the elements. In severe calcium carbonate scaling, the cleaning solution may have to be heated to above 35°C. Typical calcium carbonate cleaning is conducted at 20-25°C. The cleaning procedure is considered complete when the pH of the cleaning solution does not change during recycle and/or high flow pumping.
 
It may be possible to recover severely scaled elements by acid cleaning. Calcium carbonate scales dissolve easily in acids by releasing carbon dioxide. This can be observed as a foaming/bubbling reaction.

Cleaning Procedure
There seven steps in cleaning elements with carbonate scale.

1. Make up the cleaning solution listed from Table 6.5.
2. Introduction of the cleaning solution.
3. Recycle. Recycle the cleaning solution for 10 minutes or until there is no visible color change. If at anytime during the circulation process there is a color change, dispose of the solution and prepare a new solution as described in step 2. Maintain the pH for effective cleaning. Add additional cleaning chemical as needed to maintain pH.
4. Soak. For lightly scaled systems, a soak time of 1-2 hours is sufficient. Severely scaled systems can also be recovered with extended soak times. Severely scaled elements should be soaked individually outside of the pressure vessel in a vertical position. Check pH and adjust as required, or replace cleaning solution.
5. High-flow pumping.
6. Flush out.
7. Restart.

Table 6.5 Carbonate scale cleaning solutions

Introduction
In this paper we will consider in detail the factors impacting the decision to retrofit reverse osmosis (RO) ahead of an existing ion exchange (IX) system. The break-even point in total dissolved solids above which it is more economical to use one of these technologies over the others depends on a number of factors which will be addressed in this paper. The economic factors affecting the break-even point and project payback time include chemicals, resins, membranes, energy, operating labor, maintenance, and capitalrelated items (1-9).
 
In some instances technical considerations will outweigh economics in evaluating the possibility of retrofitting RO in front of an existing IX system. For example, retrofitting RO may insure compliance with environmental regulations which require a reduction in the volume of regenerant waste from IX. Or if the water source has a varying dissolved solids level, retrofitting RO will greatly minimize the impact on product water quality.
 
It should be noted that The Dow Chemical Company markets both reverse osmosis elements and ion exchange resins. It is our intention to provide an objective study utilizing conservative economic analysis without bias for one technology over another. It is also our intention to show the impact of the latest advances in membrane and resin technology on the total cost to produce water. This paper is a follow-up to the one written in 1987 (6) and is a companion paper to the one recently presented at WATERTECH ‘94 (9) on the economics of reverse osmosis and ion exchange in new systems.
 
In recent years the cost of chemicals and energy has not changed significantly. Higher active surface area elements (400 active square feet) and higher rejection of salt using FILMTEC® FT30 thin film composite membranes have lowered the total cost to produce water from a RO system. The cost of both IX resin and RO elements are lower than in previous economic models which reduces their periodic replacement costs.
 
 
Design Basis
The assumptions used in this economic evaluation are listed in Tables A, C and D. The water treatment systems were sized to produce three different quantities of mixedbed quality water. The flow rates were two hundred fifty thousand (250 Mgpd), five hundred thousand (500 Mgpd), and one million gallons per day (1000 Mgpd). Identical storage facilities for product water were assumed for each product water flow rate and for all cases studied. One train was used for the 250 Mgpd system size, two trains for the 500 Mgpd size, and four trains were used for the 1000 Mgpd size.
 
Four feed water qualities, varying only in the quantity of total dissolved solids (TDS) were utilized in the study. The TDS levels were 80, 160, 320, and 480 ppm (as CaCO₃). The quality of the feed water can vary significantly depending on the geographic location, and can affect any system design as well as the need for pretreatment systems, especially where reverse osmosis is contemplated. Surface water sources typically require more pretreatment while ground water sources typically need less. The feed waters used in this study have a high hardness ratio, high alkalinity, and no problems with organics, colloidal particles, or turbidity. Capital was included in the study for the additional pretreatment required by the RO system.
 
A raw water inlet temperature was assumed to be 55°F, a national average which may vary depending on the geographic location. Unlike previous studies, we did not heat the feed water for this analysis since there are many systems that do not utilize preheating to decrease the feed pressure required for reverse osmosis systems.
 

 
The costs of the most dominant operating factors, energy and caustic, were set at $0.05/KWH and $0.16/lb (100%), respectively. The caustic price reflects a high purity grade specification. The cost of feed water to the RO/IX or straight IX system and the cost of waste disposal have been considered at $0.05/1000 gallons each. Labor and maintenance costs were also considered in the evaluation. Operating labor was considered minimal at one-eighth to one-quarter man per shift for the relatively continuous RO operations depending on system size. For straight IX, with more batch-type operations, the operating labor was doubled. Maintenance costs were set at 5% of equipment costs.
 
The initial direct fixed capital (DFC) costs were estimated by obtaining equipment cost estimates from two water treatment system manufacturers, based on defined system criteria provided by the authors. The estimates were then factored to represent a reasonable installed capital cost, which includes piping, instrumentation, and auxiliaries. It was assumed that the land and building were existing. The base estimates used in this study are listed in Table B for purchased, preassembled (not installed) equipment, and membranes. Capital for pretreatment is not included in these totals but was estimated separately. A 10- year straight-line depreciation based on total direct fixed capital, and taxes and insurance at 2% of DFC were assumed.
 

	Single Beds			Mixed Bed
	SAC Resin Volumme	SBA Resin Volumme	Exhaust Time hours	SAC Resin Volumme	SBA Resin Volumme	REg'n Freq.
Case	ft3	ft3	hours	ft3	ft3	days
1	80	49	15	25	25	30
2	160	85	15	25	25	30
3	321	161	15	25	25	30
4	481	240	15	25	25	30

 
Existing Three-Bed Ion Exchange System
A three-bed ion exchange system utilizing a strong-acid gel cation bed, a vacuum degasifier, a strong-base gel anion bed, and a mixed-resin polishing bed used in the design comparisons was assumed to be existing. All of the IX resins were assumed to have a gaussian particle size distribution. A flow diagram in Figure 1 depicts the ion exchange system utilized in this study.
 
Table C summarizes the bases and assumptions for the ion exchange computer projections and the subsequent cost analysis.
 

 
The degasifier was used to remove the carbon dioxide from the acidic cation effluent in order to reduce the quantity of anion resin and also the amount of caustic regenerant. Inclusion of the degasifier is logical due to the high level of alkalinity in the feed water.
 
In order to size the ion exchange demineralizer it is necessary to provide water for regeneration and rinse requirements as well as account for outages associated with regeneration cycles. Thus the average feed water flow was 209 gpm for each train which was designed to yield 250 Mgpd. The exhaustion times of the cation and anion beds ranged from 20 to 21 hours when the resins were new. It was assumed than an operating capacity decline of 50% would occur during the life of the anion resins due resin degradation and organic fouling. In order to estimate an average cost to produce water by IX, an exhaustion time of 15 hours was utilized. The regeneration cycle was approximately 4 hours. In all cases the mixed-resin polishers in the threebed ion exchange system were regenerated every 30 days rather than upon exhaustion.
 
The computer projections of the primary beds used co-current regeneration as this is the predominant regeneration scheme used in the United States. The proposed system utilized realistic regenerant levels and produced water low in sodium and silica with a resistivity of approximately 10 megohm-cm.
 
Sulfuric acid was used to regenerate the cation resins. The primary cation beds were regenerated with 6 pounds per cubic foot of resin which was applied at concentrations of 2%, 4% and 8% acid in a stepwise fashion. The anion beds were regenerated with 5 pounds of high purity caustic soda per cubic foot of resin applied at a temperature of 120°F to maintain a low level of silica leakage. The elevated temperature regeneration sequence included preheat, regeneration, and slow rinse on the anion bed. The mixed bed resins were regenerated with 8 pounds of regenerant per cubic foot of resin.
 
 
New Reverse Osmosis System/Existing Ion Exchange System
The new RO treatment system is shown schematically in Figure 2. Since a RO system is a continuous operation, the average inlet RO flow rate is 232 gpm per train with the outlet flow to the IX being 174 gpm or 250 Mgpd of permeate. The feed flow rate increases to 463 gpm for the 500 Mgpd and 926 gpm for the 1,000 Mgpd systems. A 5-micron cartridge filter is required ahead of the RO system as a polishing filter. This RO system was assumed to be a retrofit ahead of and used in conjunction with the existing three-bed IX system described above.
 

Reverse Osmosis System
	Array 1		Array 2
Case	PV	Total Elements	PV	Total Elements	Feed Pressure (psig)
1	5	30	2	12	241
2	5	30	2	12	242
3	5	30	2	12	245
4	5	30	2	12	248
Above equipment plus necessary pretreatment equipment.

 
The thin film composite (TF) reverse osmosis section consisted of a 5-2 array utilizing 42 high surface area, spiral wound, low pressure RO elements to produce 250 Mgpd (see Figure 2). The 500 Mgpd and 1000 Mgpd system sizes used twice and four times the number of RO elements and pressure vessels, respectively. Feed pressures of 241 to 248 psig were required for operation in the TDS range of 80 to 480 ppm as CaCO₃. The addition of a high quality antiscalant ahead of each RO system was used to control the formation of calcium carbonate and calcium sulfate scale in all four cases. Acid addition was used only in Case 4 in order to keep the Langelier Saturation Index (LSI) of the RO concentrate below + 1.5.
 
A system recovery of 75% was used in all cases. Higher recovery levels are theoretically possible at lower TDS levels, however, in order to optimize the total cost to produce water recoveries of 70 to 80% are typically utilized.
 
Table D summarizes design parameters and assumptions that were used for the computer projections of the new RO followed by the existing three-bed IX system. These projections of product quality and flow rate were run using current reverse osmosis and ion exchange computer design programs.
 

Discussion of Results
The results of this study are summarized in Figures 3 through 10 showing first the base cases and then the effect of caustic pricing and power pricing. We need to point out that the cost curves presented here only apply when using the set of assumptions as listed. The payback time period and break-even points are likely to change when significant changes in the assumptions occur. For example we assumed that the land and building already existed for the new RO system retrofit. If these needed to be purchased, then the payback period would be extended.
 
 
Three-Bed Ion Exchange System
The base case results for the three system sizes are shown in Figures 3 through 5. As would be expected, the total cost to produce water for straight ion exchange increases with increasing feed TDS. For the 250 Mgpd case the cost increases from $1.50 at 80 ppm as CaCO₃ to $3.35 per 1000 gallons of product water at 480 ppm as CaCO₃.
 
The effect of increasing system size is to lower the total cost to produce water. The total cost to produce water decreases from $1.50 to $3.35 per 1000 gallons for the 250 Mgpd to $0.90 to $2.50 per 1000 gallons for a system size of 1000 Mgpd.
 
The total cost to produce water is lower than projected for new ion exchange equipment due to our assumption that capital is fully depreciated with respect to the ion exchange vessels, pretreatment equipment, neutralization and storage facilities. (9) Therefore the cost of depreciation is minimal for the IX system in the calculation of the total cost to produce water. However, since the equipment and resins are not new, the operating capacity of the IX system has been reduced to account for resin degradation and organic fouling of the anion resins. This has resulted in increased chemical costs with respect to regeneration and increased waste disposal costs.
 
 
New Reverse Osmosis/Existing Ion Exchange System
Figures 3 through 5 show the RO/IX system water production costs increase only slightly compared to the existing IX system which shows a much greater increase in total cost to produce water with increasing feed water TDS. This is because the costs associated with the ion exchange system (caustic, sulfuric acid and resin replacement) are greatly reduced by retrofitting RO ahead of the existing IX system. Also, the capital costs associated with the new RO are relatively unaffected by increasing TDS.
 
The break-even point in TDS as CaCO₃ above which the total cost to produce water is more economical using RO ahead of existing IX versus straight IX is 150 ppm for the 250 Mgpd system size. This breakeven point moves up to 200 ppm at 500 Mgpd and to 250 ppm at 1000 Mgpd capacity. Above these breakeven points it is possible to calculate a payback period for retrofitting RO ahead of IX.
 
Figure 6 shows the impact of caustic pricing on the break-even point and total cost of water for a 250 Mgpd system. Increasing caustic pricing affects the IX system much more than the retrofit of RO ahead of IX when you look at the total cost to produce water. Also the break-even point moves from 120 ppm TDS at a caustic price of $0.24/lb to 180 ppm TDS at a caustic price of $0.12/lb which is significant considering the current trend of increasing caustic pricing.
 
The effect of power costs is shown in Figure 7 for a 250 Mgpd system. Here the increase in power costs affects the RO/IX system much more than the straight IX system. The break-even point moves from 150 ppm at $0.05/KWH to 220 ppm at $0.12/KWH.
 
The payback period in years for retrofitting RO ahead of an existing IX system is shown in Figures 8 through 10 for system sizes of 250 Mgpd, 500 Mgpd and 1000 Mgpd. The base case is shown as the middle line and reflects the capital estimate average obtained from two system suppliers. The top and bottom lines show the impact on payback if the equipment cost increases or decreases by about 25%. If you assume that a 5 year payback is acceptable then you can justify retrofitting RO ahead of IX if your feed water TDS is in the range of 280 to 340 ppm for a system capacity of 250 Mgpd. As the system capacity increases the TDS range for justifying a RO retrofit increases to 320 to 390 ppm for 500 Mgpd capacity and to 360 to 430 ppm at 1000 Mgpd capacity. This interpretation assumes that the IX capital is fully depreciated and that the IX operating capacity declines by 50% over the resin lifetime.
 
 

Conclusions
1. The break-even point above which the total cost to produce water is more economical using a new RO ahead of an existing IX system rather than an existing IX system is about 150 ppm as CaCO₃.

2. Increasing system size increases the break-even point from 150 ppm for a 250 Mgpd system to 250 ppm for a 1000 Mgpd system.

3. A retrofit of RO ahead of an existing IX system may be economically feasible above 320 ppm assuming an acceptable payback is 5 years.

4. The payback period at a given TDS level becomes longer as system size increases from 250 Mgpd to 1000 Mgpd.

5. Increasing caustic pricing favors the economics of retrofitting RO ahead of IX.

6. Increasing power pricing favors staying with existing IX rather than retrofitting RO ahead of IX.

 
 
References
1. Lefevre, L., "Water Demineralization Using Reverse Osmosis and Ion Exchange,"Technical Data Sheet Volume 8, Number 2, Dow Chemical USA, 1978.

2. Coulter, B. and Jones, G.D., "The Application of Reverse Osmosis to Mexican Waters," paper presented at the First Mexican Conference, Mexico City, Mexico, February 20- 22, 1980.

3. Printz, J. and Wainwright, R., "Comparing Ion Exchange and Reverse Osmosis in the Electric Utility Industry," paper presented at the American Power Conference, Chicago, IL, April 26- 28, 1982.

4. Little, D. and Lefevre, L., "The Economics of Reverse Osmosis and Ion Exchange," paper presented at the Water Supply Improvement Association, 10th Annual Conference, Honolulu, HI, July 27, 1982.

5. Pittner, G., Levander, R., and Bossler, J., "Unique Double-Pass Reverse Osmosis System Eliminates Ion Exchange for Many Deionization Applications,"ULTRAPURE WATER, September/October 1986.

6. Whipple, S., Ebach, E. and Beardsley, S., "The Economics of Reverse Osmosis and Ion Exchange," paper presented at the Ultrapure Water Conference and Exposition, Philadelphia, PA, April 13-15, 1987.
7.Smith, B. and Whipple, S., “RO Pretreatment Eases Strain on Demin System,” POWER, March 1994.

8. Hamann, H., Buyok, W., and Whipple, S., “Reverse Osmosis Pretreatment of Boiler Water for Cost Savings and Waste Reductions,” paper presented at the International Water Conference, Pittsburgh, PA, October 31-November 2, 1994.

9. Beardsley, S., Coker, S., and Whipple, S., “The Economics of Reverse Osmosis and Ion Exchange,” paper presented at WATERTECH ‘94, November 9- 11, 1994.
 
 
Acknowledgments
The authors greatly appreciate the cooperation of Christine T. Wilson of Glegg Water Conditioning, Inc., and Robert D. Governal of Illinois Water Treatment Company in providing capital equipment estimates.

The AD line of reverse osmosis membranes from GE is being discontinued. At this time, these membranes do not have any direct replacements, although we still carry other GE membranes which may be suitable for your application.  To aid comparison and help you select a possible replacement, the table below includes the technical specifications of the GE membranes we offer:

GE Osmonics™

We still have very limited quantities available for purchase.  If you need assistance finding a suitable replacement product, please contact us.  You can also click here to browse the other reverse osmosis membranes that Sterlitech carries.

Sterlitech is proud to announce that new nanofiltration, ultrafiltration, and microfiltration membranes from Nanostone Water are now available for purchase on our website. These new membranes expand our selection to cover a wider selection of potential applications and are sold in variety of test sizes and sheets.  Contact us to learn more about our new membranes from Nanostone or check out tables below.

Nanostone™ Nanofiltration Membranes

Nanostone™ Ultrafiltration Membranes

Nanostone™ Microfiltration Membranes

Our specialty site, the Glass Fiber Store, is now closed.  When it went live in 2011, it was the place to find best selection of glass fiber filters from Sterlitech and Advantec.

The products in the Glass Fiber Store have been integrated into our main site. If you’re looking for something that used to be there, try the following links:

• Glass Fiber Filters
• Extraction Thimbles
• Cellulose Filter Papers

First announced this past spring, the Botanical Extraction section of our website is now up and running! This section houses everything you need to make a complete, basic vacuum filtration system for herbal/botanical extracts including vacuum filter holders, membrane filters, trap bottles or flasks, and vacuum pumps.  You can also find optional accessories, such as manifolds, that can be used to modify the filtration process to best suit the project requirements and throughput volume.

If you have a need to perform any of the following applications:

• Cold-filtration to remove lipids or waxes, often called winterizing
• Clarification or plant debris removal
• Bacterial removal (using 0.2 or 0.45 micron PES filters)
• Batch processing with manifolds
• Ethanol washing

Then head to our Specialty Applications Section to find the best equipment to work with your botanical extraction process.

Sterlitech was awarded as one of the Puget Sounds 100 fastest growing private companies in 2015!

Inc. Magazine ranked Sterlitech Corporation on its 34th annual Inc. 5000, an exclusive ranking of the nation's fastest-growing private companies.

The list represents the most comprehensive look at the most important segment of the economy—America’s independent entrepreneurs. Companies such as Yelp, Pandora, Timberland, Dell, Domino’s Pizza, LinkedIn, Zillow, and many other well-known names gained early exposure as members of the Inc. 5000.

The TriSep UE10 flat sheet membrane is being discontinued by the manufacturer and replaced by TriSep UF10 membrane.

¹ GFD: Gallons per Square Feet Membrane Active Area per Day

Discontinued products will include the following Sterlitech Part numbers:

• YMUE101905
• YMUE10475

Limited quantities of UE10 are available at the moment, please contact Sterlitech for more information or if you need assistance finding a suitable replacement product. You can browse other UF membranes that Sterlitech offers at the moment here.

Sterlitech is launching new flat sheet membranes from TriSep: UF5 and UF10 ultrafiltration membranes. UF5 and UF10 are particularly suited for food and dairy process applications, and applications involving protein concentration.

¹ GFD: Gallons per Square Feet Membrane Active Area per Day

These new additions are available in large sheets, as well as in precut coupons for use in the Sepa CF filtration cell, CF042 filtration cell, and most stirred cells. Custom membrane sizes are also available upon request. For more information about UF5 and UF10 or if you need assistance to find products suited for a specific application, please contact Sterlitech. To browse our complete selection of UF membranes or to place an order with us, click here.

Sterlitech is launching new flat sheet membranes from Dow: BW30XFR. This is a Brackish Water Reverse Osmosis Membrane particularly suited for water treatment and desalination.

¹ GFD: Gallons per Square Feet Membrane Active Area per Day
² 99.65% NaCl rejection at 2,000 ppm NaCl feed, 225 psig feed pressure, 77°F (25°C).

These new additions are available in large sheets, as well as in precut coupons for use in the Sepa CF filtration cell, CF042 filtration cell, and most stirred cells. Custom membrane sizes are also available upon request. For more information about BW30XFR or if you need assistance to find products suited for a specific application, please contact Sterlitech. To browse our complete selection of RO membranes or to place an order with us, click here.

The Toray UTC-73U flat sheet membrane is being discontinued by the manufacturer and replaced by the Toray UTC-73UAC membrane.

¹ GFD: Gallons per Square Feet Membrane Active Area per Day
Discontinued products will include the following Sterlitech Part numbers: 

• YM73USP18
• YM73USP195
• YM73USP4205
• YM73USP475

Limited quantities of Toray 73U are still available. For more information or for assistance with finding a suitable replacement, please contact Sterlitech. Additional RO membranes can be found here.

Sterlitech is launching new flat sheet membranes from TriSep: SBUF and SBNF membranes. SBUF and SBNF are particularly suited for treating surface waters and for the removal of organics and color.

¹ GFD: Gallons per Square Feet Membrane Active Area per Day
These new additions are available in large sheets, as well as in precut coupons for use in the Sepa CF filtration cell, CF042 filtration cell, and most stirred cells. Custom membrane sizes are also available upon request. For more information about SBUF and SBNF or if you need assistance to find products suited for a specific application, please contact Sterlitech. To browse our complete selection of flat sheet membranes or to place an order with us, click here.

Sterlitech is excited to announce the availability of small spiral wound membrane elements. At about 1.8” diameter and 12” in length, 1812 spiral wound elements are perfect for scaling up from flat sheets or as a more complete test before pilot scaling. 1812 elements are also ideal for small-scale production, feasibility studies, and product or process development. Operable up to 600 psi, Sterlitech offers SS316 Housing, which is a universal design compatible with the 1812 elements commercially available here.

Sterlitech currently offers commercially available 1812 spiral wound membrane elements from GE, Nanostone, Sydner, and TriSep in a wide range of MWCO, membrane material and surface properties. To browse our complete selection of 1812 spiral wound elements or to place an order with us, click here.

For more information or if you need assistance to find products suited for a specific application, please contact Sterlitech.

The U.S. Department of Labor’s Occupational Safety and Health Administration (OSHA) announced a final rule to improve protections for workers exposed to respirable silica dust. The rule will curb lung cancer, silicosis, chronic obstructive pulmonary disease and kidney disease in America’s workers by limiting their exposure to respirable crystalline silica. The rule changes the Permissible Exposure Limits (PEL) from the current levels of 100µg/m³ of air in general industry (250µg/m³ in construction) to 50µg/m³, averaged over an eight-hour shift. In addition, OSHA affirms in the rule the use of X-Ray Diffraction on silver membrane filters as one of two validated methods for detecting and quantifying airborne crystalline silica in the affected workplace environments.

Sterlitech silver membrane filters are an ideal tool to help keep at-risk workplace environments safe and in accord with the Department of Labor’s final ruling. Affected industries include foundries, abrasive blasting operations, paint manufacturing, glass and concrete product manufacturing, brick making, china and pottery manufacturing, manufacturing of plumbing fixtures, and many construction activities including highway repair, masonry, concrete work, rock drilling, and tuck-pointing. New uses of silica include countertop manufacturing, finishing, and installation (Kramer et al. 2012; OSHA 2015) and hydraulic fracturing in the oil and gas industry (OSHA 2012).

Citations: US LABOR DEPARTMENT ANNOUNCES FINAL RULE TO IMPROVE U.S. WORKERS’ PROTECTION FROM THE DANGERS OF ‘RESPIRABLE’ SILICA DUST

Sterlitech is launching new flat sheet membranes from Microdyn Nadir: NP010 and NP030. Both NF membranes have a Polyethersulfone (PES) active layer and Polyethylene/Polypropylene (PE/PP) support layer. NP010 and NP030 are chemically resistant and can be used at high temperatures, which makes them suitable for applications such as acid/caustic preparation, and for the metal and chemical industry.

¹ LMH stands for Liter per Meter Square Membrane Active Area per Hour

These new additions are available in large sheets, as well as in precut coupons for use in the Sepa CF, CF042, and CF016 filtration cells, and most stirred cells. Custom membrane sizes are also available upon request. For more information about NP010 and NP030 or if you need assistance to find products suited for a specific application, please contact Sterlitech. To browse our complete selection of NF membranes or to place an order with us, click here.

Forward Osmosis has been known and exploited as a separation process for a variety of applications including water and wastewater treatment, food processing, and power generation since the early 1960’s. Can this process also be applied for air de-humidification? Recent publications and patents have demonstrated that combining capillary condensation with osmosis separation through a semi-permeable membrane, introduced as Osmotic Membrane Dehumidification process, can be an efficient de-humidification method.

In the Osmotic Membrane Dehumidification process, a humid air stream is brought into contact with a semi-permeable membrane, which separates the air stream from an osmotic solution, i.e. draw solution (draw solution is generally a salt solution). Water vapors in the air stream condense by capillary condensation in the pores of the membrane and the condensed water is transferred into the draw solution by osmosis.

Unlike the conventional de-humidification processes, in this process there is no need to cool the humid air stream to the dew point of water and to subsequently reheat it to the comfortable temperatures. Therefore, energy savings of about 20-30% is expected in large scale systems compared to a conventional de-humidification processes.

To read more about this technology please refer to:

1. The Potential Of Osmotic Membrane Dehumidification, Arthur Kesten, Jeffrey McCutcheon, Ariel Girelli and Jack Blechner, AIChE Annual Meeting/Conference, November 4, 2013.
2. Versatile Dehumidification Process and Apparatus, Kesten, A.S. and Blechner, J.N., U.S. Patent 7,758,671 B2, July 20, 2010.
3. Dehumidification Process and Apparatus, Kesten, et al, U.S. Patent 6,539,731 B2, April 1, 2003.

Filtering difficult biological solutions? Normally, using a thin membrane filter can pose serious questions:

• “How much liquid can I get through the filter?”
• “When will it clog?”
• “What if my solution is very critical to the project?"

Sterlitech Polyethersulfone (PES) membrane filters have a unique asymmetric pore structure that allows the user to take advantage of this feature; PES can be its own pre-filter and dynamically increase throughput!

Hold a sample piece of this material up to the light at an oblique angle, and you will see a glossy/shiny side, and a more matte/dull side. This sided-ness feature (representation below) is helpful in that the more open area (matte side) has larger entry pores compared to the glossy side; and it should face into the incoming liquid stream for the best results with particulate-heavy liquids. If you were to view an SEM image of the matte side, you may quickly notice the pores seem much larger than the stated pore size, this is normal! Each pore’s ability to capture particulates is not only a function of the outer diameter, but of the entire pore pathway through the filter. Each pathway constricts in diameter, turns sharp curves, and makes multiple intersections with other pore pathways. This feature is what gives PES its high level of water flow and particulate loading compared to many other absolute-rated filters of the same pore size.

This is especially helpful when filtering liquids from cell lysates, cell culture media, plasma, serum, sputum, surface water, seawater, river/pond water, and other liquids from a biological or pharmaceutical source. PES membranes bind very little protein and have a high degree of open area to facilitate fast filtering, even with most challenging particulate loads. If sterile filtering is needed, this is easily accomplished with the 0.2 µm pore size. This material was tested against ASTM method F838-05 for the removal of B. diminuta for a minimum 7-log reduction, and it passed very well.

Sterlitech offers PES filter discs, sheets, and roll stock in 0.03, 0.1, 0.2, 0.45, 0.65, 0.8, 1.2, and 5.0 micron pore sizes. Syringe filters for smaller volumes are also available in 0.2 and 0.45 micron and pre-sterilized syringe filters in 0.2, 0.45, and 0.8 microns. Not sure what pore size is needed or if your solution will work with PES? Get in touch with a Sterlitech technical representative at sales@stelitech.com for an informative and fast reply. Stay tuned for next month’s article on pore geometry as exposed by SEM imagery!

Sterlitech PES membrane filters can be seen here.

Q: What is membrane pre-conditioning and why is it recommended to pre-condition new flat sheet membranes prior to use in the bench scale filtration cells?

A: Membrane pre-conditioning is a filtration step generally done at a pressure equal to or higher than the test pressure using deionized water as the feed. During this process membrane pores are wetted and the membrane structure may go though compaction or swelling. These changes in the membrane affect both the permeate flux and the rejection values. Therefore, it is recommended to pre-condition the membranes prior to use in the bench scale filtration cells to ensure the membrane performs according to the specs provided by the manufacturer, in terms of both permeate flux and rejection values.

Q: How do you know if membrane is pre-conditioned?

A: It is recommended to filter deionized water through the membrane until the permeate flux reaches a relatively steady value. At this point deionized water can be replaced with feed solution and the test can start.

Nanostone 1812 Elements are being discontinued by the manufacturer. If you need assistance finding a suitable replacement product, please contact Sterlitech.

You can browse other 1812 elements that Sterlitech offers at the moment by clicking here.

Limited quantities of Nanostone Flat Sheet Membranes are still available; please contact us for more information.