Utilizing Palm Oil Mill Waste for Co-Production of Biogas and Microalgae Biomass

Abstract

In 2013 Indonesia produced about 28 million ton/year of CPO. This large CPO production has an impact on liquid waste called as Palm Oil Mill Effluent (POME) and Empty Fruit Bunches (EFB). About 80 million ton of POME and 32 million tons of EFB are produced per year. Open anaerobic pond (conventional treatment) is widely used to reduce COD and BOD content from POME emits uncontrolled CO2 and CH4, which are the main greenhouse gasses and harmful for the environment. POME has high content of COD (50000-100000 mg/L) and BOD (25, 000 mg/L) and this is a potential for biogas production. Due to the C/N ratio of POME (6.5) is far below optimal C/N ratio for biogas production using anaerobic digester (between 20 and 30), combining high C/N ratio (60) EFB with POME is predicted to improve the biogas production. The effluent of anaerobic digester containing rich nutrients such as Nitrogen, Phosphor and Kalium are potential for plant or microalgae growth. This experiment used two types of reactor, which are batchly operated in the room condition: (i) a 13L-UASB (Up-flow Anaerobic Sludge Blanket) reactor made of PVC and (ii) 1.5L tube reactors made of PET (Poly Ethylene Terephthalate) plastic. Adding EFB into POME was proven to increase biogas production. The results indicate that the higher EFB composition the faster the biogas formation is. Based on this result, the conversion factor (volume base) of the mixture of POME and EFB into biogas is range from 13 to 47 %. The highest conversion is 47 % from ratio 7.5 of POME to 1 EFB. Based on this result it can be concluded that ratio 7.5 of POME to 1 EFB generated high volume of biogas and methane content. This research also shows significant increase in biomass production of spirulina when biogas was fed into POME medium. Total produced biomass on POME medium with biogas is double than that on POME medium without biogas. This increase could be due utilization of CO2 content in the biogas as a carbon source by Spirulina sp.