Continuous production of organic acids from palm oil mill effluent with sludge recycle by the freezing-thawing method

Abstract

The performance of the anaerobic treatment of palm oil mill effluent for organic acids production at a short retention time of less than 5 days was assessed by incorporating a sludge recycle system with no pH control except by adding calcium carbonate. The system could be operated successfully for a 3.5-day retention time at pH 5. The sludge solids in the treated effluent were separated by a freezing-thawing technique and it was partly recycled back to the reactor. The thawed clarified POME solution contained a low SS of 2,200-3,500 mg/L. The organic acids production with a concentration of 10-14 g/L was essentially similar to the treatment for a 5-day retention time without a sludge recycle. Hence by incorporationing a sludge recycle system with the freezing-thawing method, the retention time for the treatment could be reduced without affecting without the organic acids generation.