15.
b
d
Fly larvae assist in the biological action, provided the infestation does not
16.
a
b
17.
c
18.
d
19.
a
c
20.
Secondary sedimentation.
Note: An exception is the intermittent sand filter,
21.
5
22.
23.
a
c
f
h
24.
25.
a
26.
c
27.
28.
a
29.
a
e
maintenance than conventional plants, but they do require maintenance.
They can be as efficient as conventional, but they are not necessarily more
MD0161
2-65