Water Treatment Technologies

Flashcards for review

Microfiltration (MF)

Pore Size: 0.1 to 10 micrometers. Utilizes membranes to remove larger particles, bacteria, and suspended solids from liquids. Used as pre-treatment for reverse osmosis (RO) systems, Removal of suspended matter in water treatment.

Ultrafiltration (UF)

Pore Size: 0.01 to 0.1 micrometers. Uses membranes to filter out proteins, viruses, and colloids. Applied in water and wastewater treatment, decolouring (removal of larger molecules)

Nanofiltration (NF)

Pore Size: Approximately 0.001 micrometers. Features membranes that remove small organic molecules, multivalent ions, and some salts. Used in water softening, removal of specific contaminants, Pre-filtration for RO systems.

Reverse Osmosis (RO)

Pore Size: Below 0.001 micrometers. Employs semi-permeable membranes to remove nearly all dissolved salts, organic molecules, and microorganisms. Essential for desalination, producing high-purity water for industrial and medical use, and residential water purification.

Nanofiltration (NF) for Color Removal

Highly effective due to its ability to remove small organic molecules, including those responsible for color, thanks to its pore size of around 0.001 micrometers.

Combination of Ultrafiltration (UF) and Nanofiltration (NF)

Ideal for wastewater streams with high levels of particulates. UF acts as pre- treatment to remove suspended solids and larger organic molecules, protecting the NF membranes from fouling and improving overall efficiency.

Adsorption for Humic Acid Removal

Involves the attachment of humic acids to the surface of an adsorbent material, such as activated carbon or specific resins. Highly efficient, cost- effective, and versatile, making it a preferred choice for humic acid removal.

Cation Exchange

Involves the replacement of positively charged ions (cations) in water with other positively charged ions held by the resin. Cation exchange resins release hydrogen ions (H+) into the water, replacing cations such as calcium (Ca2+) and magnesium (Mg2+).

Anion Exchange

Involves the replacement of negatively charged ions (anions) in water with other negatively charged ions held by the resin. Anion exchange resins release hydroxide ions (OH-) into the water, replacing anions such as sulfate (SO4--) and carbonate (CO3--).

Ion exchange for sulfate ions (SO42-)

Sulfate ions are exchanged with other ions, such as chloride or hydroxide ions, on the exchange resin. Sulfate-selective ion exchange resins can effectively remove sulfate ions from water, providing high removal efficiency.

Granular Filtration (GF)

Pore Size: Not fixed; depends on the size of the granular media used (typically 15% of +/- 500 µm). Uses granular media such as sand, gravel, or activated carbon to physically filter out particulate matter and adsorb dissolved contaminants.

Potable water from sea water

For producing potable water from seawater, a combination of RO and MF/UF would be ideal. RO removes dissolved salts, while MF/UF removes larger particles and bacteria, ensuring high-quality drinking water

Activated carbon process

Filtration where water passes through a bed of activated carbon granules and adsorption where carbon's porous structure attracts and holds organic compounds, chlorine, and other pollutants.

Ion Exchange for Ammonium Removal

Ammonium ions (NH4+) are removed using a cation exchange resin. The resin is charged with sodium (Na+) or another suitable cation, which is exchanged with the ammonium ions in the water.

Nitrate Removal:

Nitrate ions (NO3-) are removed using an anion exchange resin. The resin is charged with chloride (Cl-) or another suitable anion, which is exchanged with the nitrate ions in the water.

Ions Exchanged in strong base anion exchange

In a strong base anion exchange process, negatively charged ions (anions) in the water are exchanged with hydroxide ions (OH-) or chloride ions (Cl-) that are pre-loaded onto the resin.

Regeneration of Resin

Regeneration is typically performed using a strong base solution, such as sodium hydroxide (NaOH) or potassium hydroxide (KOH). The regeneration solution displaces the captured anions from the resin, replacing them with hydroxide ions (OH-).

Polymer Cross-Linking in ion exchange

The polymer backbone of the resin beads is cross-linked to provide structural stability and to control the resin’s physical and chemical properties.

Ion exchange for Calcium Removal

Ion exchange is generally more efficient and cost- effective for this specific purpose, especially in applications like water softening