Judul: Produksi Bioetanol dari Hidrolisat Pati Singkong Racun dengan Fermentasi Repeated-batch oleh Saccharomyces cerevisiae Terimobilisasi pada Ampas Singkong
Abstrak: Produksi bioetanol secara curah oleh sel mikroba bebas memiliki kelemahan, yaitu produktivitas dan efisiensi yang relatif masih rendah. Di samping itu, produksi bioetanol berbasis pati singkong menghasilkan ampas singkong yang belum dimanfaatkan secara optimal. Oleh karena itu, dalam penelitian ini sel Saccharomyces cerevisiae diimobilisasi dengan menggunakan ampas singkong. Penelitian ini bertujuan mengkaji proses produksi bioetanol dari pati singkong secara repeated-batch oleh Saccharomyces cerevisiae terimobilisasi pada ampas singkong. Metode penelitian ini terdiri atas ekstraksi pati, pembuatan hidrolisat secara enzimatis, perlakuan terhadap ampas singkong oleh HCl 3% (v/v), imobilisasi Saccharomyces cerevisiae pada ampas singkong, serta fermentasi secara repeated-batch. Pada penelitian ini diperoleh rendemen pati sebesar 26.20% (b/b) serta efisiensi konversi pati menjadi hidrolisat sebesar 36.89% (b/b). Penggunaan ampas singkong hasil perlakuan oleh HCl 3% (v/v) telah mampu mengimobilisasi sel sebanyak 1.76x1011 sel per gram carrier. Fermentasi secara repeated-batch oleh Saccharomyces cerevisiae terimobilisasi pada ampas singkong dengan kadar total gula awal 140 g/L menghasilkan etanol berkadar 42.72-63.66 g/L, produktivitas 1.78-2.66 g/L/jam, persentase konversi gula sebesar 90.80-95.74%, yield sebesar 0.33-0.47 g etanol/g gula, serta efisiensi sebesar 65.91-93.13%. Hasil penelitian ini menunjukkan metode imobilisasi yang digunakan memiliki kestabilan yang baik, serta didapatkan produktivitas bioetanol, persentase konversi gula, dan efisiensi tinggi dengan fermentasi secara repeated-batch.
Keyword: Bogor Agricultural University, Institut Pertanian Bogor, IPB, Bioethanol, Cassava bagasse, Fermentation, Repeated-batch, Saccharomyces cerevisiae

Judul: Fermentasi Repeated-batch Menggunakan Saccharomyces cerevisiae Terimobilisasi pada Ampas Singkong untuk Produksi Bioetanol
Abstrak: Bioetanol is ethanol produced from biomass containing sugar, starch or cellulose through fermentation by microorganisms, one of them is Saccharomyces cerevisiae. Improvement of ethanol production can be done by using immobilized cell. The potency of cassava bagasse is big, but has not been optimally utilized, so in this research it was used as a carrier for imobilization. This research is aim to study bioethanol production from cassava starch in repeated-batch fermentation by S. cerevisiae immobilized on cassava bagasse. Research method consists of starch extraction, starch hydrolysis, cassava bagasse treatment by HCl 3% (v/v), immobilization of S. cerevisiae on cassava bagasse, and fermentation by repeated-batch method. The resulting yield of starch was 25.10% (w/w) and conversion efficiency of starch to hydrolyzed starch was 98.94%. The total cell of S. cerevisiae which adsorp on the surface of the carrier was 0.75 x 1011 sel/g carrier. Selection of the best ratio of carrier to the media fermentation found in the ratio of 6% which produced ethanol concentration of 49.23-68.75 g/L, productivity 2.05-2.86 g/L/h, yield 0.40-0.50 g/g, sugar conversion 83.16-99.86%, and efficiency 78.20-97.02%. The resulting ethanol concentration was 42.72-63.66 g/L, productivity 1.78-2.66 g/L/h, sugar conversion 90.80-95.74%, yield 0.33-0.47 g/g, and efficiency 65.91-93.13%. Selection of the best sugar concentrations have been observed through repeated-batch fermentation with 10 cycles. The research showed that best sugar concentration was obtained by using 160 g/L and ethanol produced was 71.91 g/l. This research showed that imobilized cells can improve productivity by 2-3 times in comparison with the fermentation by using free cells.
Keyword: Saccharomyces cerevisiae, repeated-batch, fermentation, cassava bagasse, bioethanol

Judul: Metrik Einstein (Anti-) Self-Dual Berdimensi Empat dengan Metode Cartan
Abstrak: Gravitational field equation can be formulated in differential forms (differential geometry), which describes gravity as a manifestation of the curvature of space-time. Curvature of space-time is characterized by a metric that satisfies the gravitational field equation. With differential forms it can be formulated the (anti-) self-dual Einstein equation, which is a modification of the Cartan structure in (anti-) self-dual basis. Calculation of (anti-) self-dual metric with (anti-) self-dual Einstein equation is simpler than the calculation using Christoffel symbols.
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