PALM OIL FACTORY EFFLUENT TREATMENT BY
ANAEROBIC DIGESTION IN LAGOONS
Alan Southworth, Production Controller
Guthrie Research Chemara
Seremban, Kuala Lampur
Malaysia
INTRODUCTION
The main purpose of this paper is to report on the design, installation and start-up
of a pretreatment system for palm oil factory effluent using anaerobic digestion in
lagoons.
For those not familiar with the crop some background information is also provided
on the oil palm, the palm oil extraction process and Malaysian Government requirements
for effluent disposal.
THE OIL PALM
The oil palm (Elaeis guineensis jacq.) is indigenous to west and central Africa but is
now grown as a plantation crop in many tropical areas of the world. In 1978 Malaysia
had about 0.75 million hectares under oil palm cultivation and is currently the largest
exporter of oil palm products.
The oil palm produces fresh fruit bunches (FFB) throughout the year, although
there are considerable monthly fluctuations in yield. The average yield in Malaysia is
about 23 metric tons FFB/hectare for mature palms.
Palms are planted at a density of around 135 per hectare and each palm will produce
about 9 or 10 fruit bunches per year. Bunches weigh between 10 and 32 kg; the average
is about 19 kg. An average bunch contains 1000 fruit which each consist of a fleshy
mesocarp enclosing a nut. Palm oil is extracted from the mesocarp and palm kernels
from the nut. Palm oil forms about 22% of the weight of the bunch and palm kernels
about 4.5%. The overall yield of palm oil per mature hectare is therefore approximately
5 metric tons and of palm kernels 1 metric ton.
THE PALM OIL EXTRACTION PROCESS
In Malaysia, FFB are processed in central factories to extract crude palm oil which is
sold to edible oil refiners for conversion into products such as cooking oils, margarines,
etc. Palm kernels are also extracted and sold to seed crushers to produce palm kernel oil.
Palm oil extraction factories vary in capacity from throughputs of 10 metric tons FFB
per hour to 60 metric tons FFB per hour. A simplified flow diagram of the oil extraction
process is shown in Figure 1. Only small amounts of effluent are generated in the palm
kernel extraction process; this is not shown in the diagram. The process is in four stages-
sterilization, stripping, digestion/pressing and clarification.
Sterilization
In this stage FFB is subjected to a steam treatment in horizontal cylindrical pressure
vessels. Steam pressures of two atmospheres are used for about 75 minutes for each
charge. Charges of between 10 and 20 metric tons FFB per sterilizer are normally used.
The purposes of sterilization are:   (a) To loosen individual fruit from bunches; (b) To
inactivate an enzyme which produces free fatty acids in palm oil; and (c) To soften the
fruit mesocarp for further processing.
421