WSP09153

• File Number: 8041
• Description: Section D General Studies-NPDES/Water Quality
• Date: 7/10/1958
• Title: Water Quality Studies-Pollution-Where We Stand on Pollution Control
• Water Supply Pro - Doc Type: Publication

c!)~! 3'J

In pollution discharged, degree of treatment and type of secondary process

Degree % %
at 1940 1945 1949 1957 Change Change
Treatment '45-157 '49-157
- -
Number ot Plants
Minor 49 60 54 41 -317 -24.1
Primary 2,669 2,629 3,019 2,730 -3.5 -9.6
Intermediate {2630} 96 107 100 2.0 -6.5
Secondary , 2,799 3,050 4,647 66.0 52.4
Total 5,560 5,766 6,230 7,516 29.9 20.7
Estimated Population Served (Millions)
Minor 3.3 4.3 3.9 1.6 -56.4 -51.7
Primary 15.1 17.2 17.2 25.7 49.5" 49.1
Intermediate /22.2} 3.8 3.6 5.6 48.6 54.2
Secondary 21.7 26.1 43.3 100.0 66.1
Total 40.6 47.0 50.8 76.4 63.1 50.5

2 Secondar treatment is on :ihar rise

tion abatement programs, all of the dat,l
ore the subject of a spccial PHS study
to be reported at a later date.
Table 2 points up the sharp rise in
secondary treatment construction since
]945. Some 43.3 million persons served
by complete treatment represent 57%
of the trealed population and 44% of
the sewered population (98.4 million).
Significantly, there ha\'e been decreases
since 1949 in the number of plants in
all categories otner than secondary.

Estimated Population
Type at Treatment Served (Millionsl
...!lli.. Jill... ~
Chemical Treatment 4.0 5.3 7.3
Activated Sludie 10.5 11.6 25.0
Trickling Filter Standard Rote {8.4 } 6.8 11.3
TricklinQ Filter HiQh Rote 0.7 6.5
intermittent Sand Filter .0.9 1.0 0.9
Applicatian to Land 0.9 1.3 2.0
LOQoons 0.2 2.4
3 Activated slud e is drawing awa

Table 3 gives striking evidence of the
increasing popularity of the activated
sludge process. But transcendent as its
position has become, the greltest per-
c.entage increase during 194,-1957 was
for lagoons. or stabilization ponds. The
lIumber of ponds increased from -!-5 to
631; fhe\' are concentmtcd in the
smaller communities and the \Vest.
Note that the data in T3ble 3 arc
Ilot additive. In all the other sum-
maries shown. \I/here a plant incorpo-

secondary and sludge handling processes

rates two or more processes, it has been
arbitrarily assigned to the predominant
tl'pe. In Table 3. the full population
of dual process plants has heen assigned
in both places. Thus. tot,l of the 1957
columns less chemic<l] tre3tment is -!-S.l
million, compared to 43.4 million for
st'condarv treatment in T,lb1c 5. The
exact population served hy e<"lch type of
secondary plant lies somewhere between
the two, though much closer to the
smaller figure.

Number Estimated Percent at Number at Est. Pop.
PrOClss Served
pracess of Pop. Served Estimated Plants Usillll (Millions)
Population
Plants (Millions) Served Chlorinotion 2,216 37.8
- Grit removal 1,~61 51.7
Activated sludge SludQI processsinQ
Mechanical aeration 259 0.9 2.1
Diffused air 284 20.2 46.5 Septic tonk 1,120
Others 46 3.7 8.5 Imhoff tanks 2,759
Trickling filters Stage dlQe.tion 272
Standard rote 1,870 9.3 21.6 Separate digestion 2,790
High rate 812 6.0 13.8 Drying bed. 5,342
Sand filters 394 0.8 1.9 LaQoons 167
Land application 340 1.0 2.3 Mech. dewoterinQ 197
Oxidotion ponds 430 0.8 1.8
Other' f.. Unknown 212 ~ --.!1. No organized method 1,781
Tofoi 4,647 43.4 100.0 Miscellaneous 226
5 Activated sludge redominates in bi cities 6 Chlorination, rit removal, slud e

Table 5 shows the activated sludge
process is used in 589 plants serving
24.8 million persons. This type pre-
dominates in cities over 25,000 popula-
tion. There are considerable differences
in process use <llTIong the various basins.
For example, in the L<lke Erie basin
almost 55% of the plants (by number)
are activated sludge, while in the Colo-
rado River basin the corresponding fig-
ure is only 5.2%.

The diffused air method of actuated
sludge is quite uni\'er~<"I1.
The figures shown in Table 6 for
chlorination comprise 29.5% of all
treatment plants and 49.5% of the
population served. In 1945, compara-
ble qnantities were 21.8% and 34.2%,
respectively. The latest figures represent
increases of 75.6% in plants ming and
136% in population served.
For grit rel11ov31, the figures shown

represcnt increases from 1945 to 1957 of
107% in number of plants so equipped
~1I1d 86% in population served.
While 1,781 plants do not report
any organized method of sludge de-
\\'aterihg. it is probable that some have
drying units that have not been re-
ported to state officials. The majority
01 the 1.781 plants are small Imhoff or
septic tank plants.