36. The activated sludge process is sometimes referred to as
A. fluid bed biological oxidation system
B. fixed-bed biological oxidation system
C. turning bed biological oxidation system
D. none of the above
37. BOD stands for
A. Biochemical oxygen demand
B. British oxygen demand
C. British oxygen depletion
D. Biological oxygen depletion
38. When temporary hard water is boiled, one of the substances formed is
A. calcium bicarbonate
B. calcium sulfate
C. hydrogen chloride
D. carbon dioxide
39. Zeolite softening process removes both temporary and permanent hardness of the water. In this process, the calcium and magnesium present in water are precipitated as
A. insoluble carbonates
B. insoluble zeolites
C. insoluble chlorides
D. insoluble sulfates
40. The methods used for biological treatment are
A. lagoon
B. activated sludge process
C. oxidation ditches
D. all of these