36 Organic waste recycling: technology and management
Table 2.9 UMERa values of tapioca starch wastewater in g/kg root (Thanh 1984)
Wastewater
Characteristics A B C D Combined
First-grade factory(Figure 2.2)^
COD 0.69 55.2 6 - 61.9
BOD 5 0.33 26.5 2.9 - 29.8
Suspended solids 0.54 10.5 3.7 - 15.7
Dissolved solids 4.91 46.3 9.6 - 60.8Second-grade factory(Figure 2.3)^
BOD 5 1.8 44.8 2.1 2.1 48.8
Total solids 3.1 102.8 2.2 2.2 109.2
Suspended solids 3.1 83.5 0.6 0.6 87.2
a UMER = unit mass emission rate
2.3.2 Palm oil industry
Palm oil is basically a vegetable oil used mainly for human consumption. It is semi-
solid, edible oil, extracted from the pulpy portion of the fruit wall of the palm fruit.
The palm plants seem to have originated in the Guinea coast of West Africa and are
now Malaysia's second most important crop. Almost all the palm oil produced in
Malaysia and Thailand is used for margarine and other edible purposes. Due to the
high oil prices, there has been increased use of palm oil to produce bio diesel in
those countries that have oil palm plantation.
Extraction process
A general process flow diagram of a palm oil mill is shown in Figure 2.4. The
freshly cut fruit bunches, delivered to the mill, are first loaded in cages mounted on
rails and run directly into a horizontal sterilizer where steam is used to heat the
fruits to about 140 °C at a pressure of 2.5 - 3.5 kg/cm^2 (35-45 psi) for 50 to 75 min.
The purpose of this sterilization is to de-activate the enzymes responsible for
the break-down of oil into free fatty acids and to loosen the fruits from the
stalks. Thereafter, the sterilized bunches are fed into a rotary-drum threshing or
stripping machine, which separates the fruit from the bunches. The empty
bunches drop into a conveyor belt that carries them into an incinerator and are
burnt into ash, whereas the loose fruits are converted into a homogenous oily
mash by a series of rotating arms (digester). The digested mash is then fed into a
press for the extraction of crude oil (nuts must not be broken at this stage of the
process).