Basic water-quality treatment facts Which set of statements about boiling, lime softening, pH effects, and bacterial survival is collectively correct?

Introduction / Context:
Basic water-quality control employs physical, chemical, and biological mechanisms. Disinfection, softening, and pH adjustment are routine interventions that influence microbial survival and scaling/corrosion tendencies.

Given Data / Assumptions:

• Boiling pertains to point-of-use emergency treatment.
• Lime softening refers to chemical precipitation that removes carbonate hardness and, with soda ash, part of the non-carbonate hardness.
• Excess lime raises pH and shifts carbonate equilibrium.
• Many waterborne bacteria are sensitive to high pH.

Concept / Approach:
Boiling achieves thermal inactivation of vegetative bacteria and many pathogens. Lime (CaO/Ca(OH)2) addition precipitates calcium as CaCO3 and magnesium as Mg(OH)2 under appropriate conditions, thus reducing hardness. Overdosing lime increases pH significantly. Elevated pH (above ~9.5) is hostile to many bacteria, complementing disinfection processes but not replacing them entirely.

Step-by-Step Solution:

Verification / Alternative check:
Jar tests and plant operations confirm pH rise with lime and the softening reactions; public health guidance recognizes boiling as effective emergency disinfection.

Why Other Options Are Wrong:
Choosing any single statement ignores the fact that all listed statements are accurate in their scope.

Common Pitfalls:
Assuming lime alone removes all permanent hardness (soda ash is often needed), and assuming high pH alone ensures complete pathogen safety without contact time or residual disinfectant.

Final Answer:
All the above