Development of a fluidized bed solid state fermenter for the conversion of palm kernel cake as poultry feed
Solid state fermentation (SSF) which involves growth of microorganism on moist solid substrates in the absence of free flowing water, has gained renewed attention over submerged fermentation for specific applications. During the SSF process in fermenter, there are three main engineering problems enc...
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| Format: | Thesis |
| Language: | English English |
| Published: |
2007
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| Subjects: | |
| Online Access: | https://eprints.ums.edu.my/id/eprint/6883/1/24%20PAGES.pdf https://eprints.ums.edu.my/id/eprint/6883/2/FULLTEXT.pdf https://eprints.ums.edu.my/id/eprint/6883/ |
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| Summary: | Solid state fermentation (SSF) which involves growth of microorganism on moist solid substrates in the absence of free flowing water, has gained renewed attention over submerged fermentation for specific applications. During the SSF process in fermenter, there are three main engineering problems encountered such as the removal of metabolic heat from the substrate, diffusion of O2 and moisture through the substrate, and heterogeneity of the substrate and inoculum. A fluidized bed fermenter in which the particles move independently like a fluid was proposed to conduct SSF of PKC. Hydrodynamic studies showed that the experimental Umf for 8551µm, 655IJm and 363IJm PKC particles were 0.340 m/s, 0.205 m/s and 0.080 m/s, respectively, where as the Urnf calculated using Wen and Yu correlation was 0.206 m/s, 0.131 m/s, and 0.043 m/s. The discrepancy between experimental and theoretical values most probably due to the breakage of the PKC particles and the presence of shells with different density. Heat transfer studies have also been carried out. The results showed that the heat loss from PKC to air was very fast and increased with increase of air velocity. In contrary, heat loss from PKC to air was increased with decrease in air relative humidity and bed height. Throughout the study, rapid heat transfer from PKC to air was experimentally observed within the first 150 seconds with a temperature drop of 30°C. This indicated that the excellent heat transfer between palm kernel cake and air allows solid state fermentation of PKC without accumulation of metabolic heat in the fermenter. A mathematical model for heat transfer between PKC and fluidizing medium was proposed which can predict the experimental data quite satisfactorily within an average error of ± 15%. Apart from heat removal, water adsorption on PKC from air to bed was carried out. It showed that the increase of adsorbed water in PKC was proportional to air relative humidity and inversely proportional to superficial air velocity. The maximum moisture content adsorbed by PKC under fluidization conditions was around 10% (on dry basis). For SSF operation, 10% moisture content was too low for microbial growth. Therefore, a water dropping system was installed to add water on PKC to maintain the moisture content at required level. A mathematical model for mass transfer between PKC particle and fluidizing air was proposed which can predict the experimental data quite satisfactorily. Finally, the effect of superficial air velocity on SSF of PKC was studied in the prototype fermenter, which can be operated as fluidized bed and packed bed, using fungal strain Aspergillus flavus. The strain was isolated from PKC sample. The maximum increase of reducing sugar concentration was at 0.17 m/s. It increased about 28%, from 14.55 mg mannose/g dry PKC to 18.63 mg mannose/g dry PKC. Meanwhile, the hemicellulose content reduced about 10%. |
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