| The
minimum requirements for grease trap design are: |
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| 1. |
Provide
sufficient capacity to slow down the passing wastewater,
giving greasy waste the opportunity to separate
out. A grease trap should be able to hold all the
kitchen wastewater entering it during times of maximum
water use for a period of 20 minutes. A grease trap
connected to a single sink should not be smaller
than 250 litre (55 gallons) capacity. A larger grease
trap is used if more than one fixture is connected.
Check the size of an existing grease trap or determine
the approximate size of a new grease trap by following
the instructions given on Page
3. |
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| 2. |
The
length of the trap should be equal to between 1.3
and 2.0 times the total depth. Note that usually
the grease trap contents occupy 2/3 of the total
depth; the top 1/3 of the trap is head space. Do
not include wall and cover thickness in the length
and depth measurements if the grease trap is built
of concrete. |
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| 3. |
The
surface area of the trap (the length times the width
in square millimeters) should be equal to between
1000 and 2000 times the total depth measured in
millimeters. Again, do not include wall and cover
thickness in measuring a concrete trap. |
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| 4. |
Prevent
wastewater entering the grease trap from mixing
up the top greasy waste layer. A baffle should be
present at the trap inlet (see centre
pages) to slow down the incoming wastewater
and keep it separate from the top waste layer.
The inlet pipe should end in a 90o downwards bend
so that incoming wastewater enters the trap at least
100 mm below the water surface. The inlet pipe SHOULD
NOT terminate above the liquid surface such that
wastewater drops into the trap. |
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| 5. |
Allow
access to the trap for maintenance so that all covers
can be lifted and accumulated material removed from
both the top and bottom of the trap. Except for
very large grease traps, the total depth of liquid
should never exceed 1200 mm. A sampling hole with
appropriate cover must also be provided if the opening
for maintenance access does not also give access
to the grease trap outlet. |
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| 6. |
Provide
necessary safety features. All grease traps must
be vented. Under-floor grease traps and grease traps
with over 1000 litre capacity must be provided with
a prominent sign to show location, to indicate both
total and liquid depth, and the maximum allowable
thickness of the greasy waste layer (30%). Warning
signs and safety barriers are to be deployed whenever
these traps are opened. |
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