Water Hardness Quiz

Study Notes

Hard water contains dissolved calcium (Ca+2) and magnesium (Mg+2) ions.
Hardness is measured in milligrams per liter (mg/L) or parts per million (ppm) as calcium carbonate equivalents.
Hard water makes it difficult to form lather with soap; the Ca+2 and Mg+2 ions react with the soap to form an insoluble scum.
Hardness can be temporary or permanent
Temporary hardness is caused by bicarbonates of calcium and magnesium; it can be removed by boiling.
Permanent hardness is caused by chlorides and sulfates of calcium and magnesium; it cannot be removed by boiling but requires softening agents.

Hardness is determined by the EDTA (ethylenediamine tetraacetic acid) method.
Hardness of water is determined by titrating a known quantity of water with a standard EDTA solution, using EBT indicator.
EDTA reacts with Ca+2 and Mg+2 ions to form a stable complex, which is colorless.
When all the Ca+2 and Mg+2 ions have reacted, the indicator changes color from blue to wine red.

BFW is the water used for boilers, which generate high-pressure steam for power generation, heating, sterilization, and drying.
BFW quality directly affects boiler performance and efficiency.
BFW should have a minimal amount of dissolved impurities including oxygen, total hardness, iron, copper, silica, and alkalinity.
Impurities in BFW can cause scale formation (CaCO3, CaSO4, MgCO3, MgSO4) leading to low boiler efficiency, fuel wastage, and potential for explosion.
Sludge formation (MgCl2, MgCO3, MgSO4, CaCl2) can lead to blockage of boiler components and impact efficiency.

Priming involves water droplets carryover into steam lines.
Foaming results in excessive persistent bubbles in the boiler.
Both are caused by contaminants in boiler feed water, improper boiler construction, and excessive water level.
Priming is avoided by removing contaminants, proper boiler design, and slow steam discharge.
Foaming is avoided by using antifoaming agents, removing oils, greases, clay, and suspended particles.

Internal treatment is carried out inside the boiler to soften the water.
Common methods include:
- Complexation: using complexing agents like polyphosphates to prevent scale formation.
- Calgon (Sodium Hexametaphosphate) Treatment: using Calgon to prevent scale formation by binding calcium and magnesium ions.
- Carbonate Treatment: using sodium carbonate (Na2CO3) to precipitate out calcium and magnesium as carbonates.

Ion exchange resins are used in the softening process to remove Ca+2 and Mg+2 ions from water.
The two main types of ion exchange resins are cation and anion exchange resins.
Cation exchange resins replace calcium and magnesium ions with sodium ions.
Anion exchange resins remove anions like chloride and sulfate ions.

RO is a membrane-based process used to purify water by separating solutes from water.
A semi-permeable membrane allows passage of water molecules while blocking salts and other contaminants.
RO is effective in removing dissolved salts, organic matter, and microorganisms from water.

ED is a membrane-based process used to separate ions from water using an electric potential.
The semi-permeable membranes are selective for either positive or negative ions.
ED is effective in removing salts and other ionic contaminants from water.

The most common disinfection method for water uses Chlorine (Cl2).
Chlorine is effective in killing microorganisms but can lead to taste and odor problems in water.
Chloramine (ClNH2) is an alternative to chlorine, offering a safer and more stable disinfectant.