Exam 2 Flashcards
Why is filtration important and what is it used for?
Filtration separates suspended solids ands colloidal impurities from water by a porous medium. It’s important in the removal of small and fine constituents that can affect water.
What is the most common used filtration unit in the United States And Why?
Dual-media filter; higher flow rates without lost of effluent quality
What are some common problems with filtration units?
Clogging due to the filling of pores by particles; improper assembly
Why is back washing filters important?
Water flow rate is expanded, because particles are removed
Why do we soften? What constituents must be present for softening?
People object to the taste of hard water. Hard water resist soap treatments. Calcium carbonate and magnesium hydroxide are the main constituents of hard water.
How does softening and recarbonation work?
Softening removes ions of calcium carbonate and magnesium hydroxide into calcium to settle out of water. Recarbonation lowers the ph of water to create excess lime and carbonate precipitates.
How does the ph change during this process?why is CO2 used for ph adjustment?
Ph is increased to remove carbonate using lime
Ph is lowered a stable water to prevent corrosion in a water system.
Lime reacts with CO2 to produce calcium carbonate.
Why do we need rapid mix talks? What type of reaction occurs in a a rapid mix tank.
Chemicals need to be rapidly and almost instaneously mixed with coagulant for flocculation.
Chemical reaction takes place in the rapid mix tank.
Why do we need flocculation tanks ?
Flocculation removes suspended solids and pathogens.
What types of compounds are removed in coagulation/ flocculation ? What remains ?
Flocculation removes natural organic matter, pathogens, inorganics, arsenic, fluoride, and chemical phosphorus which are suspended in water. Fine pathogens and particles remain.
What is coagulant and how does it work?
A cation, normally aluminum or ferric iron which forms desired flocs to remove bacteria, solids, chemicals, and viruses.
What is occurring in sedimentation basins?
Velocity of water is lowered below the suspension velocity for particles to settle out of water by gravity.
What constituents are removed in the sedimentation tank?
Remove solid particles to prepare for clarification or thickening.
What are the characteristics of a bad settling tank?
Too shallow
Too deep
Too much accumulation
Which constituents are we most concerned about removing from a drinking water source?
Pathogens/ microorganisms , chemicals, inorganic solids
