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Hydranautics E-Newsletter
May 2007
Greetings, Valued Friends and Customers
As we face a new fiscal year brimming with opportunity, we at Nitto Denko-Hydranautics are excited about the future. Operating on leading-edge technology platform, ND/HY has a highest-class share of the world market for RO membrane elements making ultrapure water for industrial and clean water for public utilities applications. We have a particularly high achievement record in the fields of ultrapure water production, seawater desalination and wastewater reclamation - our achievements are coupled with our commitment to Hydranautics 5 governing values: Innovations, Flexible Solutions, Real Relationships, Global Responsibility and Unwavering Integrity.
Nitto Denko-Hydranautics provides total solutions to customers in the water treatment membranes field not only through our RO membrane elements business but also by accelerating business development and product line-up expansion in the fields of pretreatments applications of microfiltration (MF), ultrafiltration (UF), and now membrane bioreactors (MBRs).
Please enjoy this newsletter - we invite you to get to know our company, our people and our products better. Learn about our new offices in the United Arab Emirates and India, read about Hydranautics at Ulu Pandan - the fourth and final plant in the history-making Singaporean water recycling effort, brush up on your reverse osmosis chemistry and even find out how you can help children around the world get better access to clean water.
With warmest regards,
Upen Bharwada
COO
R.O. U - Teaching a curious world about Reverse Osmosis Chemistry... one Dalton at a time.
This month’s fundamental factoids…
Alkalinity
primarily of carbon dioxide (CO2), bicarbonate (HCO3-), and carbonate (CO3--) and hydroxides. Naturally occurring alkalinity is the earth’s natural buffering system in that small doses of strong acids (e.g. acid rain) react with alkalinity and result in relatively small changes in pH. Between pH 6.2 and pH 10.1, bicarbonate is the dominant species. Above pH 10.1, carbonate is the dominant species. Most naturally occurring water sources have a pH between 6 and 8.4, so the alkalinity is the form of bicarbonate. Alkalinity, especially in boiler water, can be reported as M-Alkalinity and P-Alkalinity. M-Alkalinity measures the Total Alkalinity in a water in terms of "ppm as calcium carbonate" based on an acid titration to a pH of 4.2 using a Methyl orange indicator endpoint. P-Alkalinity measures the amount of bicarbonate, carbonate and hydroxyl alkalinity based on an acid titration to a pH of 8.2 using a Phenolphthalein pink indicator endpoint.
Composite polyamide membranes are manufactured in two distinct steps. First, a polysulfone support layer is cast onto a non-woven polyester fabric. The polysulfone layer is very porous and is not semipermeable; that is it does not have the ability to separate water from dissolved ions. In a second, separate manufacturing step, a semipermeable membrane skin is formed on the polysulfone substrate by interfacial polymerization of monomers containing amine and carboxylic acid chloride functional groups. This manufacturing procedure enables independent optimization of the distinct properties of the membrane support and salt rejecting skin. The resulting composite membrane is characterized by higher specific water flux and lower salt passage than cellulose acetate membranes. Polyamide composite membranes are stable over a wider pH range than cellulose acetate membranes. However, polyamide membranes are susceptible to oxidative degradation by free chlorine, while cellulose acetate membranes can tolerate limited levels of exposure to free chlorine. Compared to a polyamide membrane, the surface of cellulose acetate membrane is smooth and has little surface charge. Because of the neutral surface and tolerance to free chlorine, cellulose acetate membranes will usually have a more stable performance than polyamide membranes in applications where the feed water has a high fouling potential, such as with municipal effluent and surface water supplies.
Sodium (Na)
A monovalent cation. The solubility of sodium salts is high and does not cause a RO scaling problem. Sodium, in seawater, is the prevalent cation. Dietary sodium levels can range from 2000 mg/l for low-sodium diets to 3500 mg/l for average consumption levels. The US EPA has set a DWEL (Drinking Water Equivalent Limit) of 20 mg/l for potable water but is reevaluating the limit as too low. Daily consumption of 2 liters (0.53 gallons) of water with 100 mg/l of sodium would be only 200 mg. A relatively "hard water" with 10 grains per gallon (171.2 mg/L) of hardness (as calcium carbonate) results in only an additional 79 mg/L of sodium when softened.
Frequently Asked Questions
1- The conductivity of the product water has gone up sharply but the flows and pressures have not changed considerably. What is wrong?
In most cases the problem is related to sealing failures such as in-between elements, disconnects at the end caps or rolled o-rings at either position resulting in disconnects. The first step in determining the problem is to profile the system to determine which vessel is producing the poor quality water. Once this is determined the operator should probe the vessel (see Technical Service Bulletin 114) to determine the location of the problem. From this information the necessary connections can be repaired and o-rings can be replaced as necessary. As well, the proper shimming can be completed (see Technical Service Bulletin 109).
2- How long can new elements be stored?
For new, sealed elements there is no set storage life. As long as they are stored in the proper environment (see Technical Service Bulletin 108) the elements should be good to use at any time. It is important however to check the elements from time to time while in storage to insure an airtight seal and the lack of any noticeable biological growth. However, Hydranautics’ warranties and return policies have time limits. Contact your sales representative for details.
3- What type of rejection can be expected for specific elemental species? Rejection of various ions depends on feed composition, ion concentration, ion state, membrane type, temperature, pH, recovery and system flux. To estimate specific ion rejection customers should use Hydranautics’s IMSDesign projection software which can be downloaded for free from our website.
NOTE: No data can be guaranteed without pilot studies and/or contractual obligation.
Questions or comments?
Please forward to lgalloway@hydranautics.com