Transcript Sewage Treatment/Cultural Eutrophication

Sewage Treatment/Cultural
Eutrophication
SEPTIC TANKS
Septic tanks are used in areas where there are no combined sewers.
Septic tanks
(cesspools) must be
emptied each year.
Old tanks can crack
and leak coliform
bacteria into
surrounding soil,
groundwater, and
surface waters.
Figure 9-28
Page 196
Septic tank with
manhole (for cleanout)
Household
wastewater
Non-perforated pipe
Distribution box (optional)
Gravel or
crushed
stone
Drain
field
Vent pipe
Perforated pipe
SEWAGE TREATMENT
• Sewage treatment
means removing
impurities so that the
remaining waste water
can be safely returned
to the surface waters
(river, bay, ocean) and
become part of the
natural water cycle
again.
• sewage treatment
separates solids from
liquids by physical
processes and purifies
the liquid by biological
and chemical processes
PRIMARY TREATMENT
• solids like wood,
paper, rags and
plastic are removed
by screens, washed,
dried and taken
away for safe
disposal at a
licensed waste tip.
Grit and sand, which
would damage
pumps, are also
removed by settling
tanks and disposed
of in a similar way.
PRIMARY TREATMENT
• the remaining solids are separated
from the liquid by passing the sewage
through large settlement tanks, where
most of the solid material sinks to the
bottom. About 70% of solids settle out
at this stage and are referred to as
sludge. The sludge is used on farms
after further treatment called sludge
treatment.
SLUDGE TREATMENT
•
Sludge is an excellent soil conditioner and is used as a fertilizer on
farmland. However, it needs additional treatment to make it suitable. This
treatment is called anaerobic digestion and takes place in large, enclosed
tanks. NYC sludge has too many heavy metals (Hg, Pb, Cd, Cu) and may
not be used as a soil amendment for food resources in NY State.
•
The rate of digestion is increased by heating the sludge to a temperature
where naturally occurring bacteria (microorganisms) respond to these
comfortable conditions and feed on other bacteria. On cooling, the well-fed
bacteria die off, and the sludge is suitable for use on agricultural land.
•
A by-product of the sludge digestion process is methane gas. This can be
burned to produce electricity. The electricity can be used to heat more
sludge or to provide heat and light for the treatment works. Sometimes more
energy is produced than is required. The surplus is sold to local electric
companies.
SECONDARY TREATMENT
• a biological process which relies
on naturally occurring
microorganisms acting to break
down organic material and purify
the liquid.
• In a simple sewage treatment
process, micro-organisms are
encouraged to grow on stones
over which the sewage is trickled.
They feed on the bacteria in the
sewage and purify the water.
These treatment units are called
percolating filters.
SECONDARY TREATMENT
•
The rate of this process
can be increased by
pumping air into tanks of
sewage where the aerobic
digesters float freely and
feed on the bacteria.
These treatment units are
called aeration tanks.
•
Following either form of
secondary treatment, the
waste water is settled in
tanks to separate the
biological sludge from the
purified waste water.
Secondary
Primary
Bar screen
Grit
chamber
Settling tank
Aeration tank
Settling tank
Chlorine
disinfection tank
To river, lake,
or ocean
Raw sewage
from sewers
(kills bacteria)
Sludge
Activated sludge
Air pump
Sludge digester
Sludge drying bed
Disposed of in landfill or
ocean or applied to cropland,
pasture, or rangeland
(Sludge cake or pellets)
TERTIARY TREATMENT
• Extra treatment is
needed to give the
waste water a final
"polish". This is known
as tertiary treatment.
Various methods may
be used, including sand
filters, reed beds or
grass plots (artificial
treatment wetlands).
Disinfection, using ultra
violet light to kill
bacteria, is another
method, and is being
used at a number of
coastal sewage
treatment plants.
Rotating Drum Treatment
Sand Filtration
Carbon Filtration
There are two principal
mechanisms by which
activated carbon removes
contaminants from water;
absorption, and catalytic
reduction, a process
involving the attraction of
negatively charged
contaminant ions to the
positively-charged
activated carbon. Organic
compounds are removed
by absorption and residual
disinfectants such as
chlorine and chloramines
are removed by catalytic
reduction.
IMPACTS FROM ORGANIC WASTE
8 ppm
8 ppm (mg/L)
POLLUTION FROM SEWAGE
SEWAGE:
•poses a threat to public health because it carries disease-causing agents
(cholera bacteria, hepatitis, Eschericia coli (coliform bacteria).
•Causes nutrient-loading (organically-rich) into surface waters.
•Causes an increase in BOD (biological oxygen demand) or BOD5 over five
day period, which causes a decrease in
MONITORING SEWAGE
Standard test for for total coliform
(TCOL) and fecal coliform (FCOL)
bacteria. The number of colonies
formed are counted.
STANDARDS: (EPA)
1.
Drinking Water – 1 coliform
bacteria:100 mL of water
2.
Swimming Water – 200 coliform
bacteria: 100 mL of water
DISPOSAL OF SEWAGE
SLUDGE
1.
ANAEROBIC DIGESTION – anaerobic bacteria break down organics into
methane gas (NH4) and CO2. Methane is trapped and used to heat the
digester to 95F.
END PRODUCT = Soil conditioner for gardens (humus).
2. FERTILIZER – sludge is rich in plant nutrients and can be dried (pelletized) and
sold as a fertilizer.
PROBLEM: Combined sewer (industrial, residential and storm water combined may be high in heavy metals and PCB’s
(NYC SLUDGE!)
WATER POLLUTION
CONTROL LAWS
1988 – Ocean Dumping Ban Act – barred ocean dumping of sewage sludge at
the 200 mile marker. All cities were in compliance by 1988 EXCEPT for NYC,
who were permitted to dump until June, 1992.
1972 – Water Pollution Control Act – EPA established regulations for the
discharge of pollutants in the USA. It gave the EPA authority to implement
pollution control programs and set ambient water quality standards for all
contaminants entering surface waters. It also funded the construction of
sewage treatment plants.
WATER POLLUTION
CONTROL LAWS
• The Federal Water Pollution Control Act
was amended in 1977 and came to be
known as the Clean Water Act. The ACT
does NOT address water quantity or
groundwater, ONLY water quality. Initially
addressed point source, since the 1980’s
has come to address nonpoint source
issues as well.
WATER POLLUTION
CONTROL LAWS
• Great Lakes Critical Programs Act, 1990,
put in place part of the Great Lakes Water
Quality Agreement between the USA and
Canada. This law required the EPA to
establish water quality criteria to address
29 toxic pollutants with maximum levels
that are safe for humans, wildlife, and
aquatic life.
WAYS TO REDUCE CULTURAL
EUTROPHICATION
• Advanced waste treatment (sewage and industrial)
• Regulate detergents cleaning products for phosphates.
They have been regulated since the 1970’s on Long
Island!
• Promote soil conservation and preservation of wetlands
to capture and filter pollutants before they enter surface
waters.
• Regulate fertilizer, pesticide, agricultural and livestock
runoff to control Nitrogen, phosphate, and PAH’s.
• Create policies and economic incentives
for doing these things!