EVALUATION OF BIOGAS GENERATION FROM PINEAPPLE PROCESSING WASTE

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The generation of biogas, an alternative source of energy, from pineapple waste, was investigated on a laboratory scale using simple single-stage digesters of 1 liter. The digesters were fed on a batch basis with the slurry of fresh pineapple waste mixed with cow dung as an inoculum in two portions. In one portion, pineapple waste was mixed with cow dung in a ratio of 1:1 while in the other, in a ratio of 2:1 respectively. The characteristics of pineapple waste (Moisture Content (MC), Volatile Solids (VS), Total Solids (TS) and Hydrogen ion concentration (pH)) were determined before feeding into the digesters. MC, VS and TS were determined using standard methods and the pH was determined using a pH meter (Mettler-Toledo AG). Various neutralizing reagents (5.0 M sodium hydroxide (NaOH) solution, 0.25 M ammonium hydroxide (NH4OH) solution and 1.0 M sodium hydrogen carbonate solution (NaHCO3)) were added to the waste to raise its pH (4.7) to neutral (7.0) for some samples and to 9.0 for other samples at the start of the process. The digesters were placed in a water bath maintained at 35 0C using an emersion thermostat (E100 LCE 0221-10-01144) and the volume of the generated gas was measured every day at 4:00 pm using the down displacement method where the volume of water displaced is equal to the volume of gas generated. Results showed that, pineapple waste has 81.62% Moisture Content (MC), 95.83% Volatile Solids (VS), 18.38% Total Solids (TS) and Hydrogen ion concentration (pH) of 4.7. Results also revealed that, the anaerobic digestion of pineapple waste has a retention time of about 20 days for digesters maintained at 35 0C. On average, 1 kg of slurry with a mixing ratio of 2:1 (pineapple waste: cow dung) and the pH initially set to 9.0 generates 0.01 m3 of biogas with a methane content of 68.35% while that with the pH initially set to 7.0 generates 0.007 m3 of biogas with a methane content of 35.7%. Furthermore, results revealed that,1 kg of slurry with a mixing ratio of 1:1 (pineapple waste: cow dung) and pH initially set to 9.0 generates 0.012 m3 of biogas with a methane content of 60.2% while that with the pH initially set to 7.0 generates 0.008 m3 of biogas with a methane content of 27.7%. It was therefore concluded that, pineapple waste is capable of generating biogas with a methane content of up to 68.35% if its pH is set to 9.0 using ammonium hydroxide solution at the start of the process. Thus, for calculations involving techno-economic feasibility, a mixing ratio of 2:1 (with a pH of 9.0) was considered since it generated biogas with the highest methane content. (1.676Mb)

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MULIGI, RONALD

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http://hdl.handle.net/20.500.12281/4236

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