The objectives of this research were to study biogas production and COD removal efficiency of wastewater from palm oil mill industry using Anaerobic Baffled Reactors (ABR). The research used the 3- and 4-compartment of ABR (3C and 4C). Two ABR reactors volume were 10 liters each. Wastewater from palm oil mill, with COD concentration of 133,010 mg/l, suspended solids of 27,000 mg/l and pH 4.4, was fed to both reactors. The organic loading rate (OLR) at the beginning of the study was 2.5 kg COD/m3-day. Then, organic loading rates of the feed were increased to 5.0, 10.0, 15.0, 20.0, 25.0, 30.0, 35.0 and 40.0 kg COD/ m3-day respectively. The results showed that the system has good performance in treating wastewater with high concentration and producing high volume of biogas. For the 3C reactor, average COD removal was about 83.23±10.10%. For the 4C reactor, average COD removal was about 82.45± 9.47%. Biogas production rates for the reactor 3C and 4C were 15.80 and 15.25 l/day respectively. Average biogas production potential for the experiment were 770.16 and 778.27 ml biogas / g COD removed, respectively. At organic loading rates from 10.0 to 25.0 kg COD/ m3-d, The 3C reactor had better performance. The 3C and 4C reactors possessed average efficiency for oil and fat at this organic loading rate range at 77.34% and 72.19% respectively. But at high organic loading rate range of 30.0 to 40.0 kg COD/ m3-d, the 4C reactor provided better removal efficiency. Average removal efficiency of oil and fat for this loading range was 49.17% and 56.48% respectively. In conclusion, two ABR reactors were effective for COD removal and biogas production similarly. They exhibited slightly different efficiencies in terms for oil and grease removal. The COD removal efficiency is the highest at the first compartment and decreased gradually along the rest of compartments . The experimental results can be further applied for the wastewater from industries that contains with high concentration of oil and COD.
