City │ Preventive Work │ Any Unusual
│ │ Conditions
│ │ with Which
│ │ Your
│ │ Department
│ │ Has to
│ │ Contend?
├────────────────┬──────────┬───────────┤
│What Effort, If │Is Cost of│ Do Police │
│ Any, Made to │ Cleaning │and Health │
│ Secure │Considered│Departments│
│ Cooperation of │ in │and Courts │
│Public to Reduce│Selecting │Cooperate? │
│ Street Litter? │ Kind of │ │
│ │Pavement? │ │
│ │ │ │
│ │ │ │
│ │ │ │
│ │ │ │
│ │ │ │
│ │ │ │
─────────────┼────────────────┼──────────┼───────────┼─────────────
Buffalo │By ordinance. │No. │Yes. │None.
Beacon │Waste cans. │No. │Yes. │No.
Binghamton │ │ │ │
Cincinnati │Through press │No. │Yes. │Land slides
│ and clean-up │ │ │ and floods.
│ campaigns. │ │ │
Cambridge │Clean-up Week. │No. │Yes. │No.
Chicago │ │ │Yes. │
Camden │Education │ │ │
│ campaign │ │ │
│ cooperating │ │ │
│ with civic │ │ │
│ organizations.│ │ │
Columbus │ │ │ │
Cleveland │ │ │ │
Cortland │ │No. │Some. │Some lanes in
│ │ │ │ rear of
│ │ │ │ stores used
│ │ │ │ for dumping
│ │ │ │ papers.
Dunkirk │ │ │ │
Denver │ │ │ │
Elmira │Waste cans used.│Not much. │Yes. │No.
Fall River │No. │No. │No. │No.
Grand Rapids │ │ │ │
Hudson │ │Yes. │Yes. │Existence of
│ │ │ │ alleys.
Jamestown │ │ │ │City very
│ │ │ │ hilly.
Kansas City │Superintendent │No. │Yes. │No.
│ arrests │ │ │
│ violators. │ │ │
Kingston │ │ │ │
Los Angeles │ │ │ │
Louisville │Yes. │ │Yes. │
Lowell │ │Yes. │Very │
│ │ │ little. │
Lynn │ │ │No. │Papers from
│ │ │ │ refuse
│ │ │ │ collectors.
Lackawanna │Clean-up │Yes. │Yes. │No.
│ campaign. │ │ │
Little Falls │None. │To some │No. │
│ │ extent. │ │
Milwaukee │Publicity and │ │Yes. │No.
│ circulars. │ │ │
Middletown │Placed cans for │Yes. │Yes. │No.
│ paper. Through│ │ │
│ press. │ │ │
Mechanicville│Police │ │Yes. │No.
│ department and│ │ │
│ waste cans. │ │ │
New York City│Anti-litter │ │Yes. │Construction
│ League │ │ │ work; push
│ Educational │ │ │ carts.
│ work. │ │ │
New Orleans │ │ │ │
New Bedford │ │ │ │
Newark │Police │No. │Yes. │No.
│ department and│ │ │
│ public │ │ │
│ schools. │ │ │
Norwich │Very little. │No. │No. │No.
New Rochelle │Yes, by │Yes. │Yes. │No.
│ ordinance. │ │ │
Niagara Falls│Placing waste │Yes. │Yes. │No.
│ cans. │ │ │
Newburgh │Through press, │ │ │
│ cans provided,│ │ │
│ hand-bills │ │ │
│ distributed in│ │ │
│ business │ │ │
│ section. │ │ │
Oakland │Distribute │Yes. │Only in │None.
│ cards, │ │ extreme │
│ enforcements │ │ cases. │
│ of ordinance │ │ │
│ prohibiting │ │ │
│ dumping of │ │ │
│ refuse in │ │ │
│ streets. │ │ │
Oswego │Use waste cans. │ │ │No city
│ │ │ │ garbage or
│ │ │ │ ash
│ │ │ │ collection;
│ │ │ │ people dump
│ │ │ │ on back
│ │ │ │ streets.
Ogdensburg │ │ │ │
Philadelphia │Pamphlets │In general│To some │Overloaded
│ distributed. │ way. │ extent. │ wagons,
│ Rubbish cards │ │ │ storekeeper
│ distributed, │ │ │ sweeping
│ lectures to │ │ │ dust into
│ school │ │ │ street.
│ children. │ │ │
│ Place waste │ │ │
│ cans. │ │ │
Providence │ │ │Yes. │
│ │ │ │
Rochester │ │ │ │
Rensselaer │ │No. │Yes. │No.
Reading │ │ │ │
Richmond │ │ │ │
│ │ │ │
St. Louis │Placing metal │Yes. │ │
│ refuse boxes │ │ │
│ on sidewalk. │ │ │
San Francisco│Place dirt cans │ │Yes. │
│ and paper │ │ │
│ cans. │ │ │
Salt Lake │Enforcement of │ │Yes. │
City │ ordinances. │ │ │
Springfield │ │ │ │
Seattle │Through the │ │Yes. │Many hills.
│ press. │ │ │
Scranton │ │ │ │
Troy │ │ │ │
Utica │ │ │ │
Washington │Placing waste │No. │Yes. │
│ paper boxes, │ │ │
│ police │ │ │
│ regulation. │ │ │
─────────────┴────────────────┴──────────┴───────────┴─────────────
─────────────┬───────────────────
City │Disposal of Sweepings
│
│
│
│
│
│
├─────────┬─────────
│ Average │ Average
│ No. of │Amount of
│Cu. Yds. │Sweepings
│ of │Collected
│Sweepings│ at Each
│per 1,000│Cleaning
│Sq. Yds. │
│ of Area │
│ Cleaned │
│ │
│ │
│ │
│ │
─────────────┼─────────┼─────────
Buffalo │ │
Beacon │ │
Binghamton │ │
Cincinnati │ .24│ Yes.
│ │
│ │
Cambridge │ │ Yes.
Chicago │ .079│ .079
Camden │ │
│ │
│ │
│ │
│ │
Columbus │ │
Cleveland │ │
Cortland │ │
│ │
│ │
│ │
│ │
Dunkirk │ │
Denver │ │
Elmira │ │
Fall River │ │
Grand Rapids │ │
Hudson │½ cu. yd.│
│ │
Jamestown │ .053│
│ │
Kansas City │ │
│ │
│ │
Kingston │ │
Los Angeles │ │
Louisville │ │
Lowell │ │
│ │
Lynn │ │
│ │
│ │
Lackawanna │ │
│ │
Little Falls │ │
│ │
Milwaukee │ │
│ │
Middletown │ │
│ │
│ │
Mechanicville│ │
│ │
│ │
New York City│ 28.6 per│ .029 cu.
│ yr.│ yds.
│ │
│ │
New Orleans │ │ Yes.
New Bedford │ │
Newark │ │
│ │
│ │
│ │
Norwich │ │
New Rochelle │ 119 cu.│
│ yds.│
Niagara Falls│ │
│ │
Newburgh │ │
│ │
│ │
│ │
│ │
│ │
Oakland │ │
│ │
│ │
│ │
│ │
│ │
│ │
│ │
Oswego │ │
│ │
│ │
│ │
│ │
│ │
│ │
Ogdensburg │ │
Philadelphia │ .17│ .23 cu.
│ │ yds.
│ │
│ │
│ │
│ │
│ │
│ │
│ │
Providence │ │
│ │
Rochester │ │
Rensselaer │ │
Reading │ │
Richmond │ │
│ │
St. Louis │ │
│ │
│ │
San Francisco│ │
│ │
│ │
Salt Lake │ │
City │ │
Springfield │ │
Seattle │ │
│ │
Scranton │ │
Troy │ │
Utica │ │
Washington │ │
│ │
│ │
│ │
─────────────┴─────────┴─────────
─────────────┬──────────────────────────────────────────
City │Disposal of Sweepings
│
│
│
│
│
│
├──────────────────────────────────────────
│ Method of Disposal
│
│
│
│
│
│
│
│
├────┬──────┬──────────┬──────────┬────────
│ On │ Used │ Sold for │ Price │ Total
│City│ for │Fertilizer│ Charged │ Yearly
│Dump│Filler│ │ │Receipts
─────────────┼────┼──────┼──────────┼──────────┼────────
Buffalo │Yes.│Yes. │ │ │
Beacon │ │ │Yes. │Contract. │ $137.00
Binghamton │ │ │ │ │
Cincinnati │Yes.│ │ │ │
│ │ │ │ │
│ │ │ │ │
Cambridge │ │ │ │ │
Chicago │Yes.│Yes. │ │ │
Camden │ │ │ │ │
│ │ │ │ │
│ │ │ │ │
│ │ │ │ │
│ │ │ │ │
Columbus │ │ │ │ │
Cleveland │Yes.│ │ │ │
Cortland │Yes.│Yes. │ │ │
│ │ │ │ │
│ │ │ │ │
│ │ │ │ │
│ │ │ │ │
Dunkirk │Yes.│ │ │ │
Denver │Yes.│ │ │ │
Elmira │ │Yes. │ │ │
Fall River │Yes.│ │ │ │
Grand Rapids │ │ │ │ │
Hudson │Yes.│Yes. │ │ │
│ │ │ │ │
Jamestown │ │ │ │ │
│ │ │ │ │
Kansas City │Yes.│ │ │ │
│ │ │ │ │
│ │ │ │ │
Kingston │ │ │ │ │
Los Angeles │ │ │Yes. │ │
Louisville │Yes.│ │ │ │
Lowell │Yes.│ │Yes. │ │
│ │ │ │ │
Lynn │Yes.│ │ │ │
│ │ │ │ │
│ │ │ │ │
Lackawanna │Yes.│ │ │ │
│ │ │ │ │
Little Falls │Yes.│ │Yes. │ │
│ │ │ │ │
Milwaukee │Yes.│ │ │ │
│ │ │ │ │
Middletown │Yes.│ │ │30¢. for │
│ │ │ │ 1½ yds. │
│ │ │ │ │
Mechanicville│ │Yes. │ │ │
│ │ │ │ │
│ │ │ │ │
New York City│ │Yes. │ │ │
│ │ │ │ │
│ │ │ │ │
│ │ │ │ │
New Orleans │ │ │ │ │
New Bedford │ │ │ │ │
Newark │ │Yes. │ │ │
│ │ │ │ │
│ │ │ │ │
│ │ │ │ │
Norwich │Yes.│Yes. │ │ │
New Rochelle │Yes.│ │ │ │
│ │ │ │ │
Niagara Falls│Yes.│ │ │ │
│ │ │ │ │
Newburgh │Yes.│ │ │ │
│ │ │ │ │
│ │ │ │ │
│ │ │ │ │
│ │ │ │ │
│ │ │ │ │
Oakland │Yes.│Yes. │ │ │
│ │ │ │ │
│ │ │ │ │
│ │ │ │ │
│ │ │ │ │
│ │ │ │ │
│ │ │ │ │
│ │ │ │ │
Oswego │Yes.│ │ │ │
│ │ │ │ │
│ │ │ │ │
│ │ │ │ │
│ │ │ │ │
│ │ │ │ │
│ │ │ │ │
Ogdensburg │ │ │ │ │
Philadelphia │Yes.│Yes. │ │ │
│ │ │ │ │
│ │ │ │ │
│ │ │ │ │
│ │ │ │ │
│ │ │ │ │
│ │ │ │ │
│ │ │ │ │
│ │ │ │ │
Providence │Yes.│Yes. │ │$2.00 per │
│ │ │ │ cord. │
Rochester │ │ │ │ │
Rensselaer │Yes.│Yes. │Yes. │No. │
Reading │ │ │ │ │
Richmond │Yes.│Yes. │Yes. │15¢. per │
│ │ │ │ load. │
St. Louis │Yes.│Yes. │ │ │
│ │ │ │ │
│ │ │ │ │
San Francisco│Yes.│ │ │ │
│ │ │ │ │
│ │ │ │ │
Salt Lake │Yes.│Yes. │ │ │
City │ │ │ │ │
Springfield │Yes.│ │Yes. │No. │
Seattle │Yes.│Yes. │ │ │
│ │ │ │ │
Scranton │ │ │ │ │
Troy │ │ │ │ │
Utica │ │ │ │ │
Washington │Yes.│Yes. │ │ │
│ │ │ │ │
│ │ │ │ │
│ │ │ │ │
─────────────┴────┴──────┴──────────┴──────────┴────────
NOTE: Seattle and Denver are the only cities which report that they
clean their sidewalks. Denver limits its work to the business district.
All cities report they do not dump sweepings in manholes. All cities
except Salt Lake City and Norwich report they sprinkle streets preceding
sweeping. Cambridge, San Francisco, and Springfield, Mass., are the only
cities which report they do not have sprinklers precede squeegee
machines.
-----
Footnote 1:
On account of favorable weather conditions and the necessity of
economising very little machine brooming is done.
Footnote 2:
One-tenth of it cleaned four times daily. Two-fifths once a day. One-
half once a week.
Footnote 3:
Flushing only.
Footnote 4:
Hand cleaning, flushing and squeegeeing.
Footnote 5:
Not including alleys.
Footnote 6:
Flushing only.
Footnote 7:
Hand and machine sweeping and flushing.
Footnote 8:
Entire year.
Footnote 9:
Sweepers patrol streets from one to ten times daily.
Footnote 10:
Also includes machine sweeping, cleaned periodically.
Footnote 11:
Also includes machine sweeping—per year.
Footnote 12:
43,341 loads in year; 85% 2 cu. yds. each and 15% 3 cu. yds. each.
Footnote 13:
Four of these on the average will be sub-foremen at $3.50, and the
other laborers at $2.50 for 8 hours. These men are also under the
supervision of four district deputies at $125 a month each. These
district deputies have many other duties.
Footnote 14:
Length of day eight hours, unless otherwise noted.
Footnote 15:
For water and oil.
Footnote 16:
.045 foot frontage for 40 foot street.
.055 foot frontage for 50 foot street.
.065 foot frontage for 60 foot street.
Footnote 17:
City also paid for water and hydrant rental $25,329.88
Footnote 18:
Based on street 30 feet wide and sprinkled twice daily for 150 days.
Footnote 19:
Railroad company furnishes electric power and use of tracks for car
sprinkler and power flusher. City pays for car.
Footnote 20:
City furnishes two men and company motormen and conductor. City owns
sprinklers.
Footnote 21:
Including 10% of cost of machinery for depreciation and repairs and
4½% interest on machinery.
Footnote 22:
Trolley car flusher.
Footnote 23:
Per 1,000 sq. yds.
Footnote 24:
Does not include depreciation and interest.
Footnote 25:
On city work only. Does not include amount paid to contractor.
Footnote 26:
Includes cleaning drains and gutters and inlets, cleaning under small
highway bridges and removing fallen trees from roadway.
Footnote 27:
One square equals 540 ft. including salaries and wages, cost of new
appliances, repairs and maintenance of appliances and all other
overhead charges.
Footnote 28:
Includes depreciation and repairs, but not general supervision.
SEWAGE DISPOSAL
EFFICIENCY OF PROCESSES USED BY AMERICAN CITIES—OPINIONS OF AUTHORITIES—
EXPERIMENTS WITH NEW METHODS.
Recognition of the necessity for the proper disposal of sewage is now
quite prevalent in most American communities, whether large or small. In
many sections the problem has become vital, and as the population
increases, it is only a matter of time when all will be compelled to
solve the problem, for its importance grows in direct proportion to the
rapid increase in inhabitants. The continued concentration of population
makes it increasingly difficult and expensive for a municipality to
secure and maintain a pure water supply and forces community activity
for protection against disease germs. It also causes the demand for the
improvement of the esthetic condition of bodies of water within or near
a city’s boundaries. Many states have already recognized the conditions
due to these nuisances and have enacted strict legislation with a view
to preventing the pollution of streams and other bodies of water, for
the protection of water supplies, surface and underground, and for the
elimination of disease germs accompanying sewage. States and even
nations have realized that sewage disposal is more than a local problem.
In every case it is an inter-community problem, in some it is inter-
state and in a few the question must be settled by national governments.
Even those communities which have not already provided a proper method
of disposal of their sewage know that it must be done sooner or later,
and many are preparing for it either by making a preliminary study, by
preparing tentative plans, by reconstructing their sewerage systems or
planning new extensions with that end in view, or by shaping their
financial programs so that the community will be prepared to assume the
financial burden when the necessity becomes imperative.
The quantity of harmful waste produced by a community is surprisingly
small in comparison with the disastrous effects it may produce. All
authorities agree that in cities provided with an abundant water supply
sewage contains less than one-tenth of one per cent. of foreign
substances. This organic matter and the products of its decomposition
the Massachusetts State Board of Health has found rarely exceed one-half
of one per cent. of the sewage. George W. Fuller, consulting sanitary
engineer, says that 99.9 per cent. of sewage is ordinarily pure water
and that even much of the remainder is harmless matter of a mineral
nature. The experience of George S. Webster, Chief Engineer of the
Bureau of Surveys and of the Philadelphia Sewage Testing Station, with
sewage works, indicates that on an average 1,000 persons produce per
annum forty-five tons of dry sludge matter, or the solid part of the
sewage after treatment; and the United States Census Bureau reports that
the volume of sewage discharged daily during the year per person is 164
gallons. Yet the small amount of decomposing matter must be properly
treated for it is that which gives sewage its offensive character and
power to cause disease.
The proper solution of the sewage disposal problem involves first, the
construction of a sewerage system that will remove the sewage from the
community completely and as rapidly as possible, and secondly, the
construction of a disposal plant at which the sewage can be treated in
such a way that when it is discharged into the body of water it will not
cause a nuisance and disease.
The Sewerage System
There are two types of sewerage systems in use, the separate and the
combined. In the former the storm water is removed in one set of pipes
and the domestic sewage in another. The combined system removes both in
the same set of pipes. In deciding which system to adopt three factors
must be first considered, the cost, the topography of the city and the
method of disposal. The general conclusions of sanitary engineers at
present regarding the relative merits of the two systems are that either
is satisfactory from a sanitary point of view when properly constructed,
that the separate system is usually best for suburban districts not
closely built up and for all communities where the sanitary sewage
requires treatment, and that often a combination of the two systems can
be used to advantage. Most engineers point to the advantage of combined
sewers in narrow streets and congested districts where only one pipe and
one house connection are required.
The belief has been expressed by John H. Gregory, consulting engineer,
that as a general proposition the cost of building a combined system is
less than that of constructing a separate system, especially where the
territory to be served is more or less closely built up and streets
paved. In suburban territory, not closely built up and where storm water
is easily and quickly diverted into natural water courses, he believes
the separate system will in general cost less, for then only sanitary
sewers need to be built first, the storm water sewers being deferred for
years or only such drains constructed as are immediately required. When
there are steep grades and relatively high velocity all authorities
agree with Gregory that it is advisable to build combined sewers, even
though the development of the territory may hardly be such as to require
the removal of the storm water.
Discussing the merits of the two systems so far as they affect the cost
of disposal Clark P. Collins, sanitary engineer, concludes that
generally speaking “it is unwise to dilute sewage with storm water and
to befoul storm water with sewage in the attempt to remove both by the
same underground channel.” Gregory has expressed the opinion that if
sewage is to be discharged into a body without treatment the combined
system will offer the simplest and cheapest solution of the problem.
Among the principal objections to the combined system when the sewage is
treated are the increase it causes in the volume of liquid which
necessarily requires a larger plant and expenditure, the changes it
causes in the character of the sewage which complicates operation of the
plant, and the frequency with which it causes the flow of sewage to
exceed the maximum of the plant, thereby making it necessary to
discharge untreated sewage into the stream. With a combined system all
kinds of trade wastes must be run through the disposal plant, whether
they are offensive or not; automatic devices, which should be avoided
whenever possible, are necessary between the combined and intercepting
sewers to limit the amount of flow; a greater amount of grit is
deposited at the disposal works unless in the separate system the first
wash of the street is intercepted. The New York State Board of Health
advocates the separate system.
In constructing, extending or reconstructing a sewerage system it is
well to bear in mind that even though a city has not at present a
disposal plant, the time will come in all probability when increased
population will compel the treatment of its sewage by some process. It
may, therefore, be more economical eventually to make present plans so
that when disposal does come the sewerage system will make possible the
most economical operation of the disposal works. Gregory’s conclusion as
recently expressed in an address is that “other things being equal,
especially as more and more attention is being given to sewage disposal,
the separate system seems to offer greater advantages.”
All engineers advocate good ventilation for sewers and gradients that
will develop self-cleansing velocities, so as to reduce gas trouble and
to deliver the sewage as fresh as possible to the disposal works. The
best practise, according to reports of the State Boards of Health, show
that these velocities should be not less than two feet per second in
separate systems and two and one-half feet in combined systems. In some
instances where it has been necessary to reduce the gradients because of
the expense of obtaining steeper ones, a velocity of one foot per second
has been found to be satisfactory; but in such instances sewers must be
well constructed and flushed. Most trade wastes require a higher
velocity to prevent deposits.
The Degree of Purification of Sewage
Before determining the proper method of disposal the first point to be
settled by a city is the degree of purification desired or needed for
both the present and the future. The decision is dependent upon three
factors: the self-purifying capacity of the stream or body of water into
which the effluent—liquid portions of the sewage run off after
treatment—is to be discharged and its utilization for water supply,
bathing, etc., the character and amount of the sewage and the possible
future growth not only of the city itself, but also of the communities
bordering on the stream. While there have been some demands for the
absolute sterilization of sewage, many sanitarians believe that any
artificial method of sewage treatment will not esthetically render the
final effluent fit for ingestion, and practically all authorities agree
that final discharge of sewage need not be in this perfect condition.
This seems to be based on logical reasoning when one considers that all
waterways are necessarily polluted to some extent. John Duncan Watson,
of Birmingham, England, contends that the complete elimination of
bacteria is prohibitive inasmuch as it is beyond the limits of the
reasonable demands on the purse. Robert Spurr Weston, member of the
American Society of Civil Engineers, at one time reminded an audience
that the proper place to protect the water consumers against disease is
at the water works and not at the sewage disposal plant. Authorities are
in general agreed that sewage should be disposed of as the stream
demands, and that local conditions should determine degree of
purification required. Standards of purity have been studied by many
societies and various suggestions have been made. All agree that the
sewage after treatment should not deteriorate the stream into which it
flows. Watson advocates under certain conditions an effluent that will
not putrefy on being kept for seven days at a uniform temperature of 80
degrees F. and that does not contain more than three parts per 100,000
of suspended solid matter.
Generally speaking the suspended matter should be removed, the
conditions near the point of discharge be inoffensive and the water be
not impaired for purposes of manufacture and pleasure. When a city is
located on the seashore or near a large lake or stream the screening out
of the heavy particles before the sewage is discharged together with
dilution will prevent active decomposition and putrefaction of the
sewage the body of water receives and the esthetic senses of the
community will not be offended. On small bodies of water and when the
water is used for drinking and manufacturing purposes or for bathing or
shellfish the conditions usually demand not only a non-putrescible
effluent but also one that is free from harmful bacteria or one that is
highly purified like that from sand filters.
There seems to be a general agreement among sanitary engineers that the
condition of the river below where the effluent joins it is a safe guide
and should be the ruling factor in determining the degree of
purification desirable. Authorities, however, are not agreed as to
whether the standard of cleanliness should be based solely on chemical
analysis or on a mixed standard taking into consideration the appearance
of the water and its physical, chemical and bacterial conditions, as has
been demonstrated by the Metropolitan Sewage Commission of New York. One
expert in answer to the question propounded by the Commission based the
standard solely on chemical analysis, but none of those whose views were
sought was willing to accept the dissolved oxygen test as an all
sufficient criterion of the condition of the water. One considered that
the oxygen should be regarded as a reliable index of the cleanliness of
the water only when dealing with the condition of gross pollution and
only when in conjunction with observations of the appearance and
physical conditions of the water. One of them would not have a standard
of cleanliness based solely upon analysis of any kind and all were
agreed that the standard of cleanliness should not rest upon the effect
of the polluted water upon health.
After having decided on the degree of purification the next step in the
solution of the problem is to select the process of treatment best
adapted with local conditions to produce the results at the lowest cost
and without nuisance. No specific rules can be laid down for the
selection of the best process for all communities. Domestic wastes offer
the least difficulty, but they are usually complicated with the presence
of trade or street wastes or both. Features difficult to overcome may
then be produced. Then also, the character of the sewage varies greatly
with the season, days and even hours. This is due to the habits of the
people, to climatic conditions and to the amount and character of trade
and industrial wastes and to the amount of water used and allowed to
infiltrate. A cannery, creamery, tannery, brewery, strawboard factory,
wool scouring shop, dyeing and cleaning works may discharge its wastes
so that during a certain period the character of the sewage be entirely
changed. Knowledge of these conditions and changes are necessary to plan
a successful disposal plant. Each community has its own problem, and
while there are certain general conditions that should be considered,
each case is more or less unique. Charles G. Hyde, consulting engineer
of the California State Board of Health, has summed up the situation in
this statement: “It is folly to suppose that because one town can
dispose of its sewage successfully in some certain fashion, another town
can adopt the same method with a certainty of securing equally
satisfactory results. Sewage differs widely in character, not only as
between towns but in a given town.”
Processes of Treatment
The processes for treating sewage may be divided into three main groups—
the preliminary or preparatory, the main or final, and disinfection.
The processes in the preliminary or preparatory group remove more or
less of the solids, especially the suspended matter, but the effluent,
or liquid that is discharged into the stream, is chemically unstable and
will decompose and putrefy. These are the simplest methods of treatment,
and, except when sewage is discharged into very large bodies of water
where it is desired only to improve the esthetic condition or where the
water is capable of rapid self-purification, at least one of these
processes is used in combination with some other form of treatment in
the next group. The preliminary processes are dilution, screening
(coarse or fine), plain sedimentation, straining or roughing filters,
chemical precipitation, slate beds, colloidal tanks, septic tank
treatment, and single contact beds.
The main or final processes are more complex. These remove a substantial
proportion of the dissolved and suspended matter. The effluent is
generally stable. When any one of these processes is used it is
customary to provide some preliminary treatment. The processes in this
group are double contact beds, trickling (also called percolating),
sprinkling filters, intermittent sand filtration and broad irrigation or
sewage farming.
In the third group is the process of disinfection, either by hypo-
chlorite of lime or liquid chlorine. Some authorities call this third
group the finishing process and preface two others, secondary settling
tanks and secondary filters. The chemical elements of this group destroy
the bacteria, especially the disease producing kind, and are used in
combination with one or more of the processes in the other two groups to
produce a highly purified effluent.
Several other processes have been developed within the last few years.
The electrolytic process is now being used in a few American cities, and
has been included in almost all of the experiments now being made by
municipalities. The activated sludge process has been adopted by two
large cities, Milwaukee, Wis., and Houston, Texas, and two small cities,
San Marcos, Texas, and Escanaba, Mich., and is being tested in at least
eighteen others, among them Baltimore, Cleveland and Brooklyn. Jersey
City, N. J., has tentatively adopted the activated sludge process.
Another process, known as the Miles Acid Sludge Process, is being
experimented with by the city of Boston.