Water filtration

Water filtration

A widely used method for purifying water is filtration. The process of water filtration is effectuated by the introduction of a physical barrier to contaminants present in the water. The rationale is to prevent a certain group of contaminants in the water to pass through. This is also referred to as the level of filtration. The barrier introduced is called the filtering media. Selection of the optimal filtration media and method go hand in hand with an analysis of  the composition of the Feed Water and the required composition of the Effluent water.

The most common used parameter(s) for analysis of the (in)-organic quality of water are:
  • Total Dissolved Solids (TDS): A measure for the total amount of organic and in-organic substances present in the water.
  • Total Suspended Solids (TSS): The amount of particles in the water, measured by the dry weight of the particles (in mg/L), when filtered to a certain cut-off size (2 micron).
  • Turbidity: Is the haziness of water, visible for the eye due to dissolved particles in the water.
  • pH-value range: Is a measure for the alkalinity (higher pH values) or the acidity (lower pH values).    
  • Conductivity: Is an indicator for the salinity, it actually measures how well electricity travels through water.
  • Salinity: Is a measure of the level of salt –ions present in the water.
  • Total Dissolved Salts (TDS): A Measure for salinity and equals the sum of all measured ions (cations & anions).
  • Hardness (as CaC0₃): Total hardness is a measure for the presence of calcium and magnesium. Hard water has a tendency to create film and is associated with scale formation.
  • Alkalinity (as CaCO₃): Is an indicator of the buffering capacity of the water, or the ability of the water to resist change in pH value upon addition of acids.
Besides the before mentioned the following individual values are important:

Calcium (Ca), Magnesium (Mg), Sodium (Na), Potassium (K), Boron (B), Bicarbonate (HCO₃) and Carbonate (CO₃²¯), Sulfate (SO₄), Chloride (Cl), Nitrate (NO₃-N), Phosphorous (P), Iron (Fe), Zinc (Zn), Copper (Cu), Manganese (Mn), Arsenic (As), Barium (Ba), Nickel (Ni), Cadmium (Cd), Lead (Pb), Chromium (Cr) and Fluoride (F).   

Another measure widely used is the permeability of the filter media. This relates to the extent that contaminants are allowed to pass through. Or alternatively, filtered out of the water. Membrane filtration is the best option to use as filtering media. Main advantage is that  membrane filtration is very precise, membrane selection based on their permeability has excellent results to reach composition of the effluent water.

 

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