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An antiscalant is a special formulated chemical that is dosed into liquids, primarily water, to inhibit the formation of inorganic scales in supersaturated conditions. Antiscalants achieve this through three primary mechanisms:
Threshold Inhibition: This type of antiscalants introduces ions that interfere with the precipitation of scale forming compounds such as calcium carbonate and calcium sulfate and delays the crystallization of these compounds.
Crystal Modification: This type of antiscalant adsorbs onto nucleated crystals, or initially formed scales that are subatomic in size. The strong negative charge of the antiscalant disrupts the positive charge on the crystal slowing crystal growth and significantly alters its natural size and shape due to charge imbalance.
Dispersant: Some antiscalants have dispersant properties as well, effectively preventing any particles in suspension from adsorbing onto the membrane surface.
As water compositions and treatment processes will vary, the need for a variety of antiscalants is needed to achieve the required scale inhibition. Typical antiscalants include:
Phosphonate Chemistry Antiscalants: This type of antiscalant chemistry is effective at inhibiting common scale forming species such as calcium carbonate and are commonly used in membrane and thermal based desalination processes. Phosphonate based antiscalants are highly efficient at threshold inhibition, making them suitable for various water and wastewater treatment applications where supersaturation is likely to occur.
Polymeric Antiscalants: Ideal for complex scale formations, polymeric antiscalants can address multiple types of scaling, including calcium, magnesium, and silica-based compounds. Polymeric antiscalants are especially valuable in environments with high silica levels.
Formulated blends of multiple antiscalant chemistries deliver the best of both worlds, leveraging synergistic effects to maximize recoveries and optimize system performance.
Antiscalant is dosed just prior to any membrane, thermal or other processes that concentrate dissolved salts, such as reverse osmosis (RO), nanofiltration (NF), multi effect distillation (MED), multi stage flash distillation (MSF) or membrane distillation (MD). Injecting the antiscalant upstream of the feed pump ensures thorough mixing, allowing the product to be evenly distributed for optimal scale control.
When acids are being dosed in conjunction with an antiscalant, the antiscalant should be injected far enough downstream of the acid dosing location such that the acid is sufficiently mixed before coming in contact with the antiscalant. Strong acids may hydrolyze or degrade some antiscalants.
Antiscalant dosing is determined by using the feedwater chemistry, which can be provided by a reputable analytical laboratory and then entering dissolved solid concentrations into our scaling projection software. It’s important to ensure a representative feedwater sample is analyzed to ensure proper antiscalant dosage. Often times water qualities change over time or operating conditions are adjusted, requiring dosage re-evaluation.
Our antiscalant products are typically dosed neat or 100%, but can be diluted if required. Please contact us prior to diluting our products.
Membrane elements should be cleaned immediately when one of the following occurs:
NOTE: Normalization software can be obtained from the membrane manufacturer or contact out technical support for assistance.
The type of specialty cleaner required depends greatly the foulant being removed from the membrane element. The best way to perform a chemical clean is first to determine what type(s) of fouling has occurred, by looking at recent normalize operating data and comparing with matrix below. A more accurate method of determine the nature of the foulant is to remove a lead and tail element for autopsy and analytical analysis.
Membrane cleaning can require multiple chemical solutions as there may be multiple types of foulant. When there are multiple foulants the order in which the chemical cleans are being performed is critical in removing the foulants, and determining the order of which chemicals to use may be through trial and error. It is commonly thought to perform a high pH cleaning followed by a low pH cleaning, but this sequence of cleaning will not be effective for all cases.
Another method in determining which chemicals are best to use is to submit fouled elements for chemical cleaning studies. The results can provide valuable insight directing the most beneficial chemical product(s) and sequencing, if multiple cleaning products are required.
TerraMar Tech has specialty chemical cleaners for all membrane products. For additional information, please contact our technical support.
Foulant Matrix
Cause | Location | Stage Differential Pressure | Feed Pressure | Salt Passage | TerraMar Cleaner |
Scale – CaCO3, CaPO4 | Last stage tail elements | Moderate Increase | Slight increase | Marked increase | TerraClean 100L or P |
Scale – CaSO4, BaSO4, SrSO4 | Last stage tail elements | Moderate Increase | Slight increase | Marked increase | TerraClean 200L or P |
Reactive Silica or CaF2 | Last stage tail elements | Normal to decreased | Increased | Normal to increased | TerraClean 300L or P |
Biological Fouling | All stages | Marked increase | Marked increase | Normal to increased | TerraClean 200L or P |
Organic Fouling | All stages | Gradual increase | Increased | Decreased | TerraClean 200L or P |
Colloidal Fouling | First stage lead elements | Gradual increase | Gradual increase | Slight increase | TerraClean 200L or P |
Metal Oxides (e.g. Fe, Mn, Al, Zn) | First stage lead elements | Rapid increase | Rapid increase | Rapid increase | TerraClean 100L or P |
The most effective parameters for cleaning membrane products are; cleaning chemical product(s) selection, cleaning chemical concentration, cleaning solution temperature, cleaning chemical contact time and cleaning chemical solution recirculation flow rate and flow path. Each membrane product will have guidelines for cleaning flow rate and flow path. Typical chemical cleaning parameters for spiral wound elements is in the table below. Consult our chemical cleaning products specification sheet for details on chemical concentration.
Spiral Wound Element Cleaning Matrix
Spiral Wound Element Diameter (in.) | Cleaning Recirculation Flow Rate/Vessel (gpm) | Maximum Stage Pressure Drop (psi) | Maximum Pressure Drop per Element (psi) | Typical pH Range (≤40°C) for Polyamide Products | Cleaning Solution Temperature (°C) |
2.5 | 3 – 5 | 60 | 13 | 2 – 11 | 40 |
4 | 8 – 10 | 60 | 15 | 2 – 11 | 40 |
8 | 35 – 45 | 60 | 15 | 2 – 11 | 40 |
TerraMar offers a comprehensive range of specialized chemicals and tailored solutions developed to maximize membrane system performance. By leveraging our innovative solutions and extensive industry experience, customers can improve system recovery, minimize downtime, and extend membrane life. Benefit from TerraMar's experience, rely on our solutions, and elevate your system performance to new heights.
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