Water quality and treatment Knowledge-Based Download PDF

Questions

1. 1.

   In environmental water quality assessment, what does Biochemical Oxygen Demand (BOD) primarily measure?

   • A) The quantity of dissolved oxygen consumed by aerobic microorganisms while decomposing organic matter in a water sample.
   • B) The total mass of oxygen needed to chemically oxidize all organic and inorganic substances using a strong chemical oxidant.
   • C) The equilibrium concentration of gaseous oxygen that remains dissolved in water at a specific temperature and atmospheric pressure.
   • D) The concentration of dissolved oxygen required to precipitate soluble divalent metal ions during preliminary aeration.
2. 2.

   In municipal water treatment, the lime-soda ash process is frequently utilized to decrease mineral hardness. What is the primary chemical role of adding hydrated lime, $\text{Ca(OH)}_2$, during this softening process?

   • A) To oxidize dissolved ferrous iron and manganese into settleable oxide flocs.
   • B) To selectively adsorb synthetic organic compounds and chlorinated disinfection by-products.
   • C) To supply supplemental sodium ions that undergo reversible ion exchange with multivalent cations.
   • D) To neutralize bicarbonate alkalinity and precipitate dissolved calcium as calcium carbonate.
3. 3.

   In municipal drinking water purification, what is the primary role of passing clarified water through a bed of granular activated carbon (GAC)?

   • A) Inactivating enteric pathogenic viruses and bacteria through strong chemical oxidation
   • B) Adsorbing dissolved organic compounds, synthetic micropollutants, and taste- and odor-causing molecules
   • C) Neutralizing negative surface charges on suspended mineral colloids to promote rapid aggregation
   • D) Precipitating dissolved calcium and magnesium ions out of solution to reduce total hardness
4. 4.

   In municipal drinking water treatment, what is the primary purpose of maintaining a measurable residual concentration of free chlorine throughout the distribution network?

   • A) To prevent microbial regrowth and protect against secondary contamination during transit to consumers
   • B) To continuously precipitate dissolved heavy metal ions as insoluble chloride salts
   • C) To degrade synthetic microplastics into non-toxic gaseous by-products
   • D) To adjust and buffer the water pH to prevent the corrosion of distribution pipes
5. 5.

   In municipal drinking water treatment, what is the primary role of adding aluminum sulfate to raw water during the coagulation stage?

   • A) To oxidize dissolved organic pollutants and eliminate microbial pathogens
   • B) To neutralize negative surface charges on suspended colloidal particles, allowing them to aggregate into settleable flocs
   • C) To increase water hardness and elevate dissolved oxygen levels for biological filtration
   • D) To precipitate dissolved chloride and sulfate ions as insoluble mineral scales