TM 5-814-8
Table 6.4.
Summary of primary and biological wastewater treatment processes
Major Treatment
Preliminary
Application
Treatment Steps
Equipment. Required
Purpose
Unit Process
Almost all domestic waste-
Screening and usually grit
Primary sedimentation tank
Remove settleable suspended
Primary Sedimentation
A.
removal .
waters. Must precede trick-
with sludge collecting
inorganic and organic solids.
ling filter. Does not have
mechanism and skimming
to precede activated sludge,
device.
but usually most economical
method of reducing BOD and
suspended solids.
Removal of carbonaceous
Must have primary treat-
Trickling filter, settling
Trickling Fil ter Systems
Biologically convert dis-
B.
BOO. Under certain environ-
ment.
tank and sludge collector,
solved and nonsettleable
mental conditions may
recirculation pumps (high
organic material and
achieve considerable nitri-
rate units), and piping.
remove by sedimentation.
fication.
Removal of carbonaceous
Usually primary treatment
Aeration tank, aeration
Biologically convert dis-
Activated Sludge System
c.
BOO. Usually little nitrifica-
although not necessary.
equipment, settling tank,
solved and unsettleable
tion unless designed for long
sludge collector, sludge
suspended organic material
solids retention time.
return pumps, and piping.
and remove by sedimenta-
tion.
Small facilities where ade-
Earthen pond with inlet
None.
Ponds
D.
Combines the purposes of
quate land area is available.
and outlet structures.
primary and secondary
Good for intermittent waste-
biological treatment as
water discharge, but will
well as sludge treatment
not meet U.S. EPA-defined secon-
and disposal into one unit
dary treatment standards.
process.
Where ammonia conversion
Usually secondary treat-
1. Suspended Growth
Vitrification
Biologically oxidize
E.
or nitrogen removal is
ment; although in many
System - vitrification
(Nitrogen Conversion)
ammonia to nitrates.
required.
cases with proper design
tank, aeration equipment,
and operation, nitrifica-
settling tank and sludge
tion can be part of
collector. sludge return
secondary treatment.
pumps, and piping.
2. Tricklinq Filter
System - low-rate filter,
settling tank and sludge
collector.
3. Rotating Biological
Contactor System -
several RBC stages, set-
tling tank and sludge
collector.
Where complete nitrogen
Most be preceded by
1. Suspended Growth
F.
Biological removal of
Denitrification
removal is required and
vitrification step.
system - denitrification
nitrogen by reduction
vitrification facilities
tank with mixing equip-
from nitrates to nitrogen
are installed. Potential
ment, final settling tank
gas.
for combining with fil-
with sludge collection
tration step is good.
equipment, return sludge
pumps and piping, chemical
feed system, and possibly
small aerated basin for
release of nitrogen gas.
2. Columnar System -
structure containing media
similar to deep bed filter
(gravity or pressure sys-
tem), backwash and chemi-
cal feed equipment.
wastewater treatment is limited to granular car-
Hydraulic loadings and bed depth are
bon. Both upflow and downflow carbon contractors
important design parameters, but contact
time is the most important factor in
can be used. Upflow units more efficiently utilize
carbon systems.
carbon since counter-current operation is closely
For some domestic and certainly all in-
approached. Downflow contractors are used for
dustrial applications, treatability studies,
both adsorption and some suspended solids filtra-
(laboratory and pilot scale) must be con-
tion. Dual-purpose downflow contractors offset
ducted. This is essential since the carbon
capital cost at the expense of higher operating
removes the dissolved trace organics
costs. The following basic factors should be
from wastewaters by a combination of
considered when evaluating an activated carbon
adsorption, filtration and biological degra-
system (l)(127):
dation. Treatability studies will assist in
--To avoid clogging, the influent total sus-
evaluating these factors to optimize de-
pended solids concentration to the acti-
sign criteria for the particular wastewater
vated carbon unit should be less than 50
under consideration.
mg/L.
c. Chemical oxidation.
6-15
Previous Page
