Utilisation of DOBE: Palm oil mill waste as organic fertiliser

M. Haryati and M. Theeba

Abstract
Depleted oil bleaching earth (DOBE) is a waste discharge from spent bleaching earth (SBE) processing facilities of palm oil refineries. This material is acidic (pH <5.0) and hydrophobic. Currently, DOBE is disposed to landfills, thereby posing environmental hazard due to its intrinsic properties. A study was undertaken to de-oil DOBE by composting with palm oil mill effluent (POME) only, POME mixed with commercial microbes, and commercial microbes only to eliminate the acid reactivity and DOBE hydrophobic property. The study found that the results produced by POME were as good as those by commercial microbes. The C/N ratio and oil content for DOBE pile added with POME alone decreased from 58.8 to 9.5 and from 8.5% to 0.5%, respectively. A field trial comparing composted DOBE against three conventional organic fertilisers showed that composted DOBE performed as good as those conventional organic fertilisers. Further research is needed to establish whether frequent usage of composted DOBE will lead to the reduction of soil pH. Whilst using liquid POME to treat DOBE into an organic fertiliser is virtually cost-free, the composting process helps solve the problem with DOBE disposal.

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