Abstract Production of organic acids from palm oil mill effluent during continuous anaerobic treatment

A.R. NorAini¹, M.A. Hassan^1*, Y. Shirai², A.B. Ariff¹ and M.I.A. Karim¹

¹Department of Biotechnology, Faculty of Food Science and Biotechnology, Universiti Putra Malaysia,
43400 UPM Serdang, Selangor, Malaysia.
²Department of Biochemical Engineering and Science,
Faculty of Computer Science and Systems Engineering, Kyushu Institute of Technology, Iizuka,
Fukuoka 820 8502, Japan.

(Received 4 March 1999 / Accepted 11 October 1999)

Abstract.
We have previously reported on the anaerobic treatment of palm oil mill effluent (POME) to produce organic acids as raw materials for PHA (polyhydroxyalkanoates) production (Hassan et al, 1997a). This study focused on optimisation of organic acids production as part of an integrated zero emission system. Optimisation of organic acids production was performed by continuous fermentation at four different retention times of 2.5, 5, 7.5 and 10 days until steady states were achieved. POME was mixed with an equal amount of anaerobic sludge in a 12 liter stirred tank bioreactor. The pH was controlled at 7.0 to produce organic acids, particularly acetic and propionic, from POME. Total organic acids produced were 7.7 to 9.6 g/L for 2.5, 5 and 7.5 days retention times. More than 75% of the chemical oxygen demand (COD) removal could be achieved during anaerobic treatment at 5, 7.5 and 10 days retention times. The best retention time was 5 days which produced 9.53 ±1.28 g/L of total organic acids with 11700 mg/L COD and 77% COD removal at steady state. After separation of the organic acids in the treated effluent by ion exchange chromatography, the residual COD was less than 100 mg/L which met the effluent standard set for the industry by the Department of Environment of Malaysia. The results obtained in this study establishes the possibility of integrating organic acids production from POME either within its conventional wastewater treatment system or in the zero emission system.

Keywords: Palm oil mill effluent, anaerobic treatment, organic acids, continuous culture