Treatment of palm oil mill effluent by anaerobic ponds in PT SMART plants, Indonesia

In the process of the extraction and separation of palm oil, liquid effluents are generated and form a final effluent called POME (Palm Oil Mill Effluent). POME is a high-strength effluent rich in organics and minerals. It classically accounts for 60 to 70% of the tonnage of the total fresh fruit bunches processed or 3 times the quantity of produced oil. Before land application in oil palm fields, POME is treated in anaerobic ponding systems to stabilize its organic load. Although the anaerobic ponding system is the most popular treatment system adopted in Malaysia and Indonesia, its impacts are not very well known. A sampling campaign and analysis of effluents in inlet/outlet of the ponding system on two oil mills were carried out in 2002/2003. During the one year period it allowed us to characterize the raw and treated POME and also study the performances and impacts of the ponding system. Under the climatic conditions in Riau, Sumatra, the POMEs in the the anaerobic ponds in PT SMART oil mills were diluted by some 20% by the rains. In these conditions and taking into account the dilution rate, the mean hydraulic retention time of the two systems were 201 and 411 days. The organic loading rates of the two systems were very low reaching 0.12 and 0.29 kg COD.m-3. day-1. The high levels of COD (80 to 90%) and BOD5 (95%) removal efficiencies would lead to significant greenhouse gas emissions. Suspended particles agglomeration and decantation caused minerals and metals retention inside the ponds. The agronomic value of the treated POME was improved from the organic point of view but its nutient contents were unbalanced for direct application as fertilizer. Improvements of the ponding system were proposed to reduce environmental risks.