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Indonesia is the largest palm plantation that reaches 32 million tonnes palm oil production per year with 84 million tones Palm Oil Mill Effluent (POME) as liquid waste. POME contains many organic substances. The quality of POME for its utilization is generally measured in COD which has range 30000 -100.000 ppm. Microbial convertion for biogas especially for bio-H2 enrichment, the active sludge was pretreated physically to suppress methanogenesis microbes. H2 Biogas production was conducted at pH 5-6. Additional 10% phosphate buffer was done in the beginning only. The production of H2 biogas was influenced by hydrostatic pressure in closed batch system. Inoculumsmedium ratio also influenced the H2 biogas productivity, reached 0.7 ml/ml POME with more than 50% H2. Scaling up anaerobic in 2.5 L working volume bioreactor, H2 biogas productivity reached 0.86 ml/ml POME by 10% inoculums because of no hydrostatic pressure. In bio-reactor, H2-CO2 in H2 biogas was affected by the amount of active sludge. In the beginning of H2 biogas, H2 reached 80%. However, at subsequence process, fed batch, with retention time 2.5 day and 3 days H2 biogas production, the active sludge was accumulated and caused the decreasing H2, finally only 46% at the 3rd day. The consortium tended to produce more CO2 as the result of primary metabolite rather than H2. Raising inoculums to level 15% improved productivity only in the beginning but H2 content was getting less, only 59%. Additional feeding would cause more accumulation sludge and more decreasing H2 content to 31% on the 3rd day. Thus, the ratio of active sludge and substrate availability must be controlled to gain optimum H2. Limited substrate will cause the direction of bio-conversion more in CO2 rather than H2.

Sei Pagar's palm oil mill (PKS Sei Pagar), PTPN V Riau processes fresh fruit bunch into crude palm oil(CPO). This processing also generates waste like empty fruit bunches (EFB), shells, fiber, and palm oilmill effluent (POME). POME has a high content of chemical oxygen demand (COD), approximately30,000-80,000 mg/L, which is usually fermented by bacteria. This fermentation mechanism can beused to produce biogas containing methane in a continuous stirred tank reactor (CSTR). Since POMEor organic materials for biogas production generally contain sludge, the biogas production processshould have an agitator to mix sediment in the base reactor and improve biogas production. Thisresearch aims to determine the agitator's specifications for the biogas pilot plant in PKS Sei Pagar,consisting of power type and type of stirrer include diameter calculation, geometry, and powercalculation. The agitator's power and geometry are determined based on input data from the datasheetreactor and the efficiency of the stirrer is calculated by Reynolds reynolds numbers. From thisresearch's calculations, an agitator geometry for the biogas pilot plant in PKS Sei Pagar had a length of0.875 m, a width of 0.7 m, and a height of 3.5 m. This research also obtained that the motor power resultwas 23.55 HP. The selection of motor power in the Biogas pilot plant's stirring process in PKS Sei Pagarshould have a standard agitator motor power of 25 HP.

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