A very common way to treat wastewater in both rural areas
and urban systems is with a septic tank or cesspool, sometimes coupled with a
filtration system added. The septic tank removes sediment and floating solids
from the black water absorption system. It then filters and treats the
clarified effluent from the septic tank.
Removing solids from wastewater protects the soil absorption
system against clogging and premature failure. At the same time removing solid
matter, the septic tank digestion also allows a portion of the solid matter to
remain and stores the undigested portion.
Operation of Septic Tanks
Solids from septic tanks are removed by decantation, by
stopping residual water in the tank, allowing them to sink and for the sediment
layer to float away the impurities. For this separation to occur, residual
water in the tank must be stopped for a minimum of 24 hours.
Up to 50 percent of the solids retained in the tank will decompose.
The remaining solid matter is accumulated in the tank.
The silt continues to accumulate at the bottom of the septic
tank while the septic system is used, without any intervention. Properly
designed wells have a safe space for the accumulation of at least three years
of silt. When the level of silt goes beyond this point, wastewater has less
time to separate solids from the water before it leaves the tank, so the
process stops performing effectively.
While silt levels rise, more solid material enters the
filtration area. If silt accumulates too long, no separation of solids from
water and sewage can occur directly in the filtration area. To prevent this,
the tank must be emptied of silt, usually with a pump of a special vehicle for
emptying Septic Tanks.
The deadline for emptying a septic tank depends basically on
the:
- Capacity of the septic
tank
- Amount of wastewater
(related to family size)
- Volume of solids in the
wastewater
Cleaning a Septic Tank
It is highly recommended to hire a specialised company,
which empties by pumping and transporting the sludge from septic tanks. This is
because certain standards must be met. The resulting waste should be monitored
to ensure cleaning is done properly. To remove all the material from the tank,
you have to disperse the solid layer and mix the layers of silt and the liquid
part of the tank to facilitate emptying as much as possible.
As usual, this is alternatively achieved by removing the
water from the tank with a pump and pressure from the bottom of the tank. The
septic tank should be cleaned through the central manhole and not by inspection
ports, as this may damage certain parts essential for its proper functioning.
