16. The filtration unit is used:
As a means of disposal without surface effluent.
As secondary treatment, following primary settling.
To clarify digester supernatant for recycling to trickling filters.
In lieu of primary settling tanks, to filter out nonfiltrable residue.
17. Activated sludge is:
An inert, biologically stable substance recovered from primary settling tanks.
A septic, highly volatile substance in which anaerobic decomposition is taking
A biologically active material containing numerous organisms and organic
material in various stages of decomposition.
Sludge from primary settling tanks which has been activated by the addition
of anaerobic bacteria to aid in the digestion process.
18. How does activated sludge differ from sludge from primary settling tanks?
Primary sludge is only 95 percent water, where as activated sludge is 99.9
Primary sludge is relatively odorless, while activated sludge has a pungent,
Primary sludge is inactive, stable material, while activated sludge is active,
Primary sludge consists mainly of settleable solids, whereas activated sludge
contains large quantities of dissolved fine organic matter that have been
absorbed by the sludge.