38 Organic waste recycling: technology and management
Nuts and fresh fiber are then separated to recover the nuts which are
subsequently cracked to produce kernels for sale. The pressed fiber and some of
the shells are usually burnt as fuel in the steam-raising boiler.
The extracted crude oil, consisting of a mixture of oil, water and some fine
solid materials, is passed through a vibrating screen to remove the solid matters.
Hot water is often added in this operation. A clarification tank is used to
separate the oil by gravity and the oily sludge settles at the bottom. The clarified
oil is further purified in a vacuum dryer prior to being pumped to a storage tank.
The oil sludge, after straining and desanding, is centrifuged to recover the oil
which is returned to the clarifier. The sludge is discharged into an oil trap, where
further oil is recovered by heating the sludge with steam prior to discharge of
the sludge to a waste treatment facility.
With respect to Figure 2.4, the sources of wastewater and sludge generated
during palm oil milling are given below.
- Sterilizer's condensates, cleansing of the sterilizers and floor washing at the
sterilizer station. - Floor washing and desanding of the press station.
- Steam condensates
- Steam condensates
- Hydrocyclones discharge
- Steam condensates
- Turbines cooling water and steam condensates
- Boilers blowdown
- Overflow and backwash water of the water softening plant
- Floor washing of the oil room
- Wastewaters discharged from various units in the oil room
- Overflow from the vacuum dryers
- Oil trap discharge
A general mass balance of various products generated from a palm oil mill plant
is shown in Figure 2.5. It is seen that of the 100 tons fresh fruit bunches (FFB)
processed, about 21 tons of palm oil and 6 tons of palm kernel will be produced.
Other miscellaneous by-products can be used as animal feed, fertilizer, and boiler
fuel.