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Guidelines
for Soakaway System
THE
SOAKAWAY SYSTEM
iv) Septic
Tank
Purpose:
To facilitate sedimentation and decomposition of small solid
particles. (Septic tanks are normally not required for poultry
farms because dry muck-out at poultry farms can achieve very
high levels of solids removal. Soakaway pits/trenches are
however necessary.)
Design
Considerations:
(a) Sufficiently
large to provide a minimum capacity for 3 days' storage of
wastewater, and to hold all the sludge likely to accumulate
between desludging. The required size is therefore determined
by the amount of water used during washing, the solids content
of the wastewater entering the tank (and therefore the amount
of solids remaining after dry muck-out) and the frequency
of desludging. Table 1 illustrates how the required capacity
for a pig farm can be affected by different operational practices.
For example, if the amount of water used in a pig farm is
15L/pig/day, with 80% of solids removed during dry muck-out,
and the tank is desludged once every 3 months, the required
capacity is about 0.15m3 per pig. Nevertheless,
a septic tank should not be smaller than 2.5m3
to enable ease of maintenance.
(b) Well
vented with a vent pipe to avoid accumulation of methane or
other obnoxious gases.
(c) Leak-proof.
(d) Covered
to prevent external deposition of solids or ingress of rain.
(e) Access
for mechanical desludging.
Table
1 Size of Septic Tank for Pig Farms with Different Operational
Practices
| Quantity
of washwater used (L/pig/day) |
Desludging
interval (month) |
Septic
tank size (m3 / pig) for different percentage
removal of solids during dry muck-out |
| 70% |
80% |
90% |
| 15 |
3 |
0.20 |
0.15 |
0.10 |
| 6 |
0.35 |
0.25 |
0.15 |
| 10 |
3 |
0.18 |
0.13 |
0.08 |
| 6 |
0.32 |
0.23 |
0.13 |
| 5 |
3 |
0.16 |
0.11 |
0.07 |
| 6 |
0.30 |
0.21 |
0.11 |
Maintenance
Requirement: Periodic sludge removal, at least once every
6 months but once every 3 months is normally expected.
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