Septic
In rural areas where houses are
spaced so far apart that a sewer system would be too expensive to
install, people install their own, private sewage treatment
plants. These are called septic tanks.
A septic tank is simply a big concrete or
steel tank that is buried in the yard. The tank might hold 1,000
gallons (4,000 litres) of water. Wastewater flows into the tank at
one end and leaves the tank at the other. The tank looks something
like this in cross-section:
.
| A |
From Home |
| B |
Scum
layer |
| C |
Fairly clear
water |
| D |
Sludge |
| E |
Exit to trench or
sewer |
In this picture, you can see three
layers. Anything that floats rises to the top and forms a layer
known as the scum layer. Anything heavier than water sinks to form
the sludge layer. In the middle is a fairly clear water layer.
This body of water contains bacteria and chemicals like nitrogen
and phosphorous that act as fertilizers, but it is largely free of
solids.
Wastewater comes into the septic
tank from the sewer pipes in the house, as shown
here:
A septic tank naturally produces
gases (caused by bacteria breaking down the organic material in
the wastewater), and these gases don't smell good. Sinks therefore
have loops of pipe called P-traps that hold water in the lower
loop and block the gases from flowing back into the house. The
gases flow up a vent pipe instead -- if you look at the roof of
any house, you will see one or more vent pipes poking
through.
Grease Interceptors
Grease traps or interceptors are
passive devices required by municipalities to stop grease, fat,
oil, wax or debris from entering the city's sanitary sewer
system.
Such materials cause blockages in
the system, which cause backups and overflows. Traps and
interceptors are designed to separate greasy materials from
wastewater so that they can be removed before they enter the sewer
system.
All restaurants, caterers, school
cafeterias and other commercial cooking facilities must avoid
discharging grease into the municipal sewer system.
Grease interceptors must receive
wastewater from all contributory sources, such as pot sinks,
dishwashers, floor drains and mat washing area drains before
draining to the sanitary sewer system.
Typical building codes require all
such new or rebuilt facilities to install a grease interceptor to
pre-treat grease entering a sewer. All units should be fitted with
a standard final-stage sample box. Interceptors must typically be
sized for at least a 30 minute peak wastewater flow detention time
from all contributory sources.
On occasion, a grease trap will be
required in place of an interceptor. Traps are typically required
to have a rated flow capacity sufficient for the same 30-minute
flow time.
The link below shows how
similar grease traps are to septic systems, grease traps normally
have several baffle plates to separate the sections. To take a
look at several different designs click on the link below.
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