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What to do with the fruit residue from oil palm seeds: refine it into bio-ethanol or use it as fertilizer?

When oil is harvested from the seeds of the oil palm tree, the fruit residue can be used to make bio-ethanol. However, it can also be used as a fertilizer on palm tree plantations; which option is best for the environment? Edi Wiloso compared the two green options at the Institute of Environmental Sciences Leiden (CML). His PhD defence is scheduled for 29 October.

A wet mass

De vrucht van de oliepalm

Once the oil has been pressed from the seeds of oil palm fruit, you’re left with a wet mass of fruit residue. The oil is used in margarine, deep frying oil, potato crisps, taco crisps, sauces, biscuits and is even used to make soaps. In Indonesia, the world’s largest producer of palm oil, the idea was raised to turn the residue into ethanol, a green alternative for fossil fuels. However, Wiloso’s research shows that this isn’t always the best option for the environment.

Higher yields through fertilisation

De vruchten zitten bij honderden tot duizenden bijeen in een dichte, tot 25 kg zware tros
Hundreds of fruit in a single 25 kilo fruit bunch.

The residue is currently usually returned to the plantations, where it are used as fertilizer. Nutrients leak into the ground, where they are absorbed by the trees. But when the residue is used for bio-fuels, the fertility of the soil decreases, which in turn affects the yields. In time, larger plantations will be necessary to compensate and to sustain production levels. Synthetic fertilizer could be used as an alternative, but is the green energy worth the substitution?

Life cycle analysis

To compare the options, Wiloso developed a method to measure the environmental impact of both products – green energy and green fertilisation. This included various aspects such as greenhouse gases and carbon dioxide emission. He used life cycle assessment, an approach that maps the environmental impact of a product throughout the course of its existence, from harvesting the materials, to processing, and use. This requires a lot of custom measuring, because the crucial characteristics differ per product. Wiloso included all possible applications for oil palm fruit residue in this study. The residue isn’t just suitable as a green fertilizer or as a bio-fuel; it can also be used as a source for fibres that are used in the production of mattresses or in the food industry.

Geoogste trossen op een plantage
The harvest.

Not a single clear result

The current process, in which the residue is returned to the plantations and used as fertilizer, turns out to be the most environmentally friendly process in most situations. Wiloso: ‘But this isn’t always the case, as the local situation influences the results; this means that every location needs to be analysed separately. Upon returning to Indonesia, Wiloso wants to promote the life cycle assessment method in the palm oil industry to make production more environmentally friendly.

CML was the best option

Wiloso works at the Research Center for Chemistry of the Indonesian Institute of Sciences (LIPI, Puspiptek, Indonesia). The production of bio-ethanol from harvest residues has been on the agenda of the institute since 2010. Wiloso was asked to study the environmental impact of the use of palm oil residue. ‘I was checking out different universities online, looking for the best location to study this issue. I soon found myself on the website of the CML.’ He also founded the Indonesian Life Cycle Assessment Network in 2014.

Edi Iswanto Wiloso ‘Development of life cycle assessment for residue-based bioenergy’ on 29 October 2015.

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