Production Of Biogas And Fatty Acids Phase Behaviour From Palm Oil Mill Effluent Via Thermophilic And Mesophilic Anaerobic Suspended Growth Degradation Process
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Date
2015-04
Authors
YEE SHIAN, WONG
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Abstract
The anaerobic degradation of palm oil mill effluent (POME) was carried out under thermophilic (550C) and mesophilic (350C) temperature in anaerobic suspended growth closed bioreactors (ASGCB). The termophilic and mesophilic ASGCB were operated by a series of continuous experiments using feed flow-rates of 0.58, 0.70, 0.88, 1.17 and 1.75 liters of raw POME wastewater per day, which correspond to hydraulic retention time (HRT) of 24, 20, 16, 12 and 8 days. The COD reduction efficiency of the thermophilic and mesophilic ASGCB was in the range of 90.90% - 83.58% and 89.66% - 79.83%, respectively, between the HRT 8 days and 24 days. The pH for both ASGCB were in the range of 8.05 to 7.74 and 7.80 to 7.35. High amounts of biogas were produced from 19.86 L biogas/day to 64.56 L biogas/day and 17.79 L biogas/day to 46.76 L biogas/day, respectively. The daily methane gas production were from 14.92 L CH4/day to 44.54 L CH4/day and from 12.92 L CH4/day to 30.81 L CH4/day, respectively, in the thermophilic and mesophilic ASGCB. The methane gas content ranged from 75.11 % to 68.99 % and 72.50 % to 65.90 % for both ASGCB. The thermophilic and mesophilic ASGCB followed the acidogenesis, acetogenesis, methanogenesis and sulphidogenesis process of degrading the POME wastewater. The acidogenesis and acetogenesis anaerobic degradation occurred in the early stage of anaerobic degradation of POME wastewater. In the acidogenesis stage, the palmitic acids of POME wastewater were degraded to short chain fatty acid such as acetic, propionic butyric and iso-butyric
acids. The acetogenesis anaerobic degradation took place to breakdown the propionic, butyric and iso-butyric acids to the sole end product of acetic acid. Lastly, the acetic acids were converted to methane and carbon dioxide in the methanogenesis process. Mass balance, reaction rate equation and Monod models were followed in both ASGCB in order to determine the kinetic coefficients. The kinetic coefficients for the thermophilic ASGCB produces the following biological kinetic coefficients: YG (0.364 gVSS/ g COD), b (0.103/day), μmax (0.58/day), Ks (31.90 g COD/L) , Θc (1.72 day) and YCH4 (0.45 L CH4/ CODreduction), respectively. The kinetic coefficients for the mesophilic ASGCB produces the following biological kinetic coefficients: YG (0.357 gVSS/ g COD), b (0.073/day), μmax (0.36/day), Ks (27.60 g COD/L) , Θc (2.78 day) and YCH4 (0.34 L CH4/ CODreduction), respectively. The value of YCH4 of 0.45 L CH4/ g CODreduction and 0.34 L CH4/ g CODreduction for thermophilic and mesophilic ASGCB are so far the highest methane yield for POME wastewater in the anaerobic degradation process.
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Production Of Biogas And Fatty Acids Phase Behaviour From Palm Oil Mill Effluent Via Thermophilic , And Mesophilic Anaerobic Suspended Growth Degradation Process