350 ENVIRONMENTAL HEALTH
These are essential fi rst steps to ensure that the proposed con-
struction will meet the community, state and national goals and
objectives.
Water Quality Standards The purpose of stream and other
surface water quality standards is to protect, improve where
needed, and maintain the highest practicable water quality
for certain specifi ed best uses. Such uses are usually grouped
under “public water supply,” “bathing and recreational,”
“fi shing, aquatic life and wildlife,” and “natural drainage,
agricultural and industrial water supply.” In general, sludge
deposits, solid refuse, fl oating solids, oils, grease, and scum
are not allowed under any uses. Waters are also required to
be free from organic and inorganic chemical or radiologic
constituents in concentrations or combinations which would
be harmful to human, animal, or aquatic life for the speci-
fi ed water use. For sources of drinking water supplies, the
sewage and industrial waste treatment before discharge to
a stream is such that with conventional (coagulation, sedi-
mentation, rapid sand fi ltration) water treatment the Public
Health Service Drinking Water Standards are not exceeded.
For sources of drinking water with chlorination treat-
ment alone, the maximum permissible average most prob-
able number (MPN) of coliform bacteria per month should
not exceed 50 per 100 ml with not more than 20% of the
samples exceeding 240. With coagulation, rapid sand fi ltra-
tion, and chlorination the average MPN should not exceed
5000 with not more than 20% of the samples exceeding 5000.
Fecal coliforms should not exceed 20% of the total coliform
counts. For sources of water for bathing and other contact
recreation uses the average MPN should not exceed 2400 (or
1000) per 100 ml with not more than 20% (or 10%) of the
samples exceeding 5000 (or 2000). The fecal coliform count
(log mean) should not exceed 200 with not more than 10%
of the samples collected during any 30-day period exceeding- In all cases the coliform counts should be interpreted in
the light of a sanitary survey and related factors.
Water quality standards also specify a minimum dis-
solved oxygen content of 5.0 mg/l for trout waters, 5.0 or
4.0 mg/l for non-trout waters and a minimum 2.0 or 3.0 mg/l
for any other waters. Similar standards as above are used for
marine waters. If waters are used for shellfi sh harvesting for
direct human consumption, the coliform bacteria shall not
exceed a median MPN of 70 per 100 ml and not more than
10% of the samples shall ordinarily exceed 230.
Effl uent Standards It should be obvious that the realistic
compliance with water classifi cation standards requires con-
trol over all sewage and industrial wastewater discharges to
the classifi ed waters. In Britain, the Ministry of Housing and
local government reaffi rmed in 1966 the Royal Commission
“General Standard” as a “norm” for sewage effl uents, i.e.,
5-day BOD 20 mg/l and suspended solids 30 mg/l with a
dilution factor of 9 to 150 volumes in the receiving water-
course having not more than 4.0 mg/l BOD. A higher effl u-
ent standard of 10 mg/l BOD and suspended solids may be
required if indicated.^21 In any case, sewage and industrial
waste effl uents should not contain any matter likely to render
the receiving stream poisonous or injurious to fi sh, or if used
for drinking water supply injurious to man.
Wastewater Treatment The need for wastewater treatment
can be better justifi ed for aesthetic, economic, recreation,
and fi sh reasons rather than for reasons of reduction of health
hazards. Treatment of sewage and industrial wastes does not
usually remove the need for nor reduction in required treat-
ment for drinking water. On the contrary, greater emphasis
needs to be placed on the improvement and maintenance
of drinking water quality. The increasing urbanization and
industrialization has and will continue to result in the dis-
charge of viruses, organic, and inorganic chemicals, which
are not readily removed by conventional water treatment,
and whose long-term health effects are not yet known. Many
people may be misled into thinking that money and effort
spent in stream pollution abatement justifi es relaxation of
effort, money to be spent and support for drinking water
treatment. Nothing could be further from the truth!
Wastewater treatment usually involves screening and
sedimentation for primary treatment. When followed by oxi-
dation and disinfection it is given secondary treatment. If
secondary treatment plant effl uent is passed through a sand
fi lter, oxidation pond, or some combination of chemical
treatment and fi lters plus chlorination, in which additional
organic and inorganic materials are removed, together with
bacteria, protozoa and viruses, then it would be receiving
tertiary treatment. Some possible combinations of sewageTABLE 6
Sewage-treatment plant unit combinations and effi cienciesTreatment plantTotal % reduction—approximateSuspended
solidsBiochemical oxygen
demandSedimentation plus sand fi lter 90–98 85–95
Sedimentation plus standard
trickling fi lter, 600 lb BOD per
acre-foot maximum loading 75–90 80–95
Sedimentation plus single stage
high rate trickling fi lter 50–80 35–65a
Sedimentation plus two stage
high rate trickling fi lter 70–90 80–95a
Activated sludge 85–95 85–95
Chemical treatment 65–90 45–80
Pre-aeration (1 hr) plus
sedimentation 60–80 40–60
Plain sedimentation 40–70 25–40
Fine screening 2–20 5–10
Stabilization, pond aerobic 70–90
Anaerobic laboon 60–70 40–70a No recirculation. Effi ciencies can be increased within limits by controlling
organic loading, effi ciencies of settling tanks, volume of recirculation, and
the number of stages: however, effl uent will be less nutrifi ed than from
standard rate fi lter, but will usually contain dissolved oxygen. Filter fl ies
and odors are reduced. Study fi rst cost plus operation and maintenance.
From Environmental Sanitation, Joseph A. Salvato, Jr., John Wiley & Sons,
Inc., New York, 1958.C005_009_r03.indd 350C005_009_r03.indd 350 11/18/2005 10:24:50 AM11/18/2005 10:24:50 AM