Large- and medium-scale palm oil mills produce copious volumes of liquid waste from the sterilizer, clarifying centrifuges and hydrocyclones. This effluent must be treated before discharge to avoid serious environmental pollution.
Liquid waste treatment involves anaerobic fermentation followed by aerobic fermentation in large ponds until the effluent quality is suitable for discharge. In some of the palm oil mills the treated effluent is used on the farm as manure and source of water for irrigation. The sludge accumulating in the fermentation ponds is periodically removed and fed to the land.
To manage the amount of oil entrained in the effluent, while at the same time improving the efficiency of oil recovery, the large mills use de-watering and decanting centrifuges at various locations in the process line.
When it comes to liquid waste management most traditional processors and small-scale palm oil processors do not adhere to any environmental protection practices. The environmental awareness level of the operators in this industrial area is low. Indeed much is desired of the hygiene of most facilities. Traditional processors operate so close to nature that they simply return liquids to the surrounding bushes. The discharged quantities are so small that the ground easily absorbs the waste matter and the operators have not yet seen their activities as injurious to their surroundings.
However in the more organized intermediate technology mills sludge from the clarifying tanks are carried in buckets or rudimentary gutters to sludge pits dug in the nearby bushes. When the sludge pit begins to give off a bad odour the pit is filled in and another one dug for the purpose. Charcoal from the cooking fires is dumped into the pits to absorb some of the odour.
Sometimes the oil in the sludge pit is recovered and mixed with fibre to make a fire-starting cake called ‘flint’.
It has been observed that when the small-scale mill operators empty their sludge on the surrounding bushes the bushes slowly die. Operators say they use the sludge as a herbicide to clear their surroundings. It is, however, time to develop simple inexpensive aqueous pollution control systems for small-scale operators.
Environmental pollution considerations in small-scale palm oil milling need concentrated attention as this industrial segment assumes greater importance. It is hoped that as more educated people come into the industry they will bring increased awareness and a greater commitment to adopt improved environmental management practices in their operations.