Treatment of palm oil steriliser condensate by an anaerobic process

Abstract

In a conventional palm oil mill, the mixed effluent (POME) contains a mixture of steriliser condensate, separator sludge and hydrocyclone waste. The mixed POME is treated by anaerobic, aerobic/facultative processes before it is discharged. In a palm oil mill using a decanter, steriliser condensate is the main liquid effluent generated. The steriliser condensate was found to be easily treatable by a simple anaerobic process at ambient temperature. A BOD removal efficiency of more than 90% could be achieved. The process seemed to attain optimum operating conditions at a BOD loading of 1·8 kg per cubic metre per day with a hydraulic retention time of 15 to 16 days. Despite the low pH of the steriliser condensate, no pH adjustment was required at steady state. The Volatile Fatty Acid to alkalinity ratio was found to be a good control index. It was quick and simple to determine. The ratio was always below 0·3 for healthy digestion. About 21 cubic metres of biogas was generated for every cubic metre of steriliser condensate digested. The kinetic model developed by Lawrence & McCarty (1976) was used to determine various coefficients. The values of k, Ks, Y, kd and Θ c m were found to be 2·09 per day, 13 770 mg litre −1, 0·358 mg VSS per mg BOD, 0·041 per day and 2·2 days, respectively.