Palm oil is the main plant oil in the world. Most production is found in the Far East. Oil palm cultivation and oil processing are potentially large sources of Greenhouse Gas (GHG) emissions. Improving GHG impacts of palm oil production by generating biogas from palm oil mill effluent can help to reduce emissions while generating additional energy and income for (small-scale) farmers and plant owners.
Palm oil production in Indonesia could generate 91 million ton of sludge and wastewater (Palm Oil Mill Effluent, or POME), a potential source of GHG emissions. POME is generated from different fractions in the palm oil extraction process:
• Condensate from bunch sterilization
• Water phase or sludge from oil clarification centrifuges
• Water from the hydro-cyclone used in separation
POME, containing large amounts of organic material, is a suitable feedstock for digestion. Capture of POME methane could reduce 80% of the common GHG emissions of traditional palm oil production chains. This can lead to improved economic returns of milling and increased smallholder and middlemen incomes.
POME anaerobic digestion generates biogas that can be used as energy source to produce steam required in the sterilisation of the fruits. It also generates digestate, a suitable fertiliser for oil palm land. Digestion can occur in capped pond systems or special tanks.
The use of a digester tank has major advantages:
• Prevention of spontaneous methane production from open ponds
• Enhanced biogas yields, replacing fossil fuels in steam production
• Reduction of odour problems
• Generation of digestate, replacing artificial fertilisers
• Reduction of N2O emissions
• Suitable to construct on any kind of soil
(Anaerobic) Digestion tanks of a ‘one size fits all´-type lack the ability to adjust to variations in POME composition which is bound to vary as large variations may occur in pH (ranging from 2.5 to 4.8), COD (range between 14,200 and 42,300) and ammonia-nitrogen (ranging between 10 and 80 mg/l).
Smart process control
Experiences with POME anaerobic digester tank systems so far are mainly limited to Asia and Africa while capped ponds are more common in Latin America. Realization of high biogas yields require flexible digester management which can adjust to variations in POME composition. A smart process control and monitoring system is proposed to monitor conditions in the digester. This allows continuous response to variations in organic matter contents, pH etc. Dedicated micro-organisms can provide enhanced biogas yields. Under these conditions, the tank contents can be much smaller than would be the case in a ‘one size fits all’ scenario.
Anaerobic digestion of palm oil wastewater (POME) reduces spontaneous methane production (from open ponds) while the gas that is generated can replace more fossil energy than open or capped pond systems. This reduces GHG emissions and offers income benefits to farmers and plant owners. Digestate can be used to recycle valuable nutrients and replace costly fertilisers, further improving the palm oil carbon footprint and economic result.
Smart process control and monitoring is proposed to respond to changes in POME composition and conditions for digestion following variations in fruit composition and oil-harvesting efficiency. Vital indicators of the digestion process will to be monitored in order to enhance biogas yields.