Judul: Process engineering of cassava pulp hydrolysis using microwave heating for ethanol production
Abstrak: Cassava pulp is a potential source of carbohydrates. In this work, characteristics of the cassava pulp were analyzed and validity of microwave irradiation for hydrolysis of carbohydrates, especially starch present in the cassava pulp, was estimated as a non-enzymatic saccharification technique. The hydrolysis was performed in water and acid medium. In addition, the role of activated carbon in the microwave-assisted hydrolysis was also evaluated. An optimization of the hydrolysis was conducted using Central Composite Design (CCD) and was analyzed using Response Surface Methodology (RSM). Fermentation of cassava pulp hydrolysates produced from microwave-assisted acid hydrolysis was performed to those added with activated carbon (25% w/w) and those without activated carbon by Saccharomyces cerevisiae. There were two types of activated carbon, which have different adsorption properties, used in this experiment. Results of the cassava pulp characterization shows that the starch granules in the cassava pulp were trapped in biomass matrices, so that the starch was harder to hydrolyze than the free starch, such as that in tapioca flour. Microwave-assisted hydrolysis of cassava pulp can be completed in less than 15 minutes in water medium, and less than 10 minutes in acid medium. The addition of activated carbon improved hydrolysis of cassava pulp starch in water medium with suppression of formation of the secondary decomposed materials. The highest glucose yield obtained from cassava pulp was 46% of dry matter or 52% of theoretical, which was about 60% higher than the one without the addition of activated carbon. On the contrary, the addition of activated carbon decreased the glucose yield when the hydrolysis was performed in acid medium (0.5% H2SO4). The glucose yield could reach 80.8% of dry matter or 91.5% of theoretical yield when no activated carbon was added in the acid medium. The estimated optimum condition for cassava pulp hydrolysis under microwave irradiation was using 0.88% sulfuric acid with 9 minutes of heating time, which resulted in 85% of theoretical glucose yield and 140 g/L glucose concentration. At the end of the fermentation the ethanol yield and concentration obtained in the samples treated with activated carbon (0.41-0.43 g ethanol / g glucose consumed; 34-35 g/L) were lower than that not treated with activated carbon or those treated with activated carbon which was added after hydrolysis (0.48 g ethanol / glucose consumed; 38- 39 g/L). However, the fermentation was completed very much faster in the hydrolysates treated with the activated carbon which has a high adsorption capacity than in that not treated with activated carbon or those treated with activated carbon of low adsorption capacity. Therefore, ethanol productivities (0.44-0.55 g/L/h) of the former were higher than the latter (0.28-0.34 g/L/h).
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Judul: Delignifikasi Kulit Singkong sebagai Bahan Baku Bioetanol dengan Metode Alkali dan Pemanasan Microwave
Abstrak: Indonesia menduduki peringkat keempat sebagai negara produsen singkong terbesar dengan jumlah produksi sebesar 20 juta ton per tahun. Sebanyak 15-20% per kilogram singkong merupakan limbah berupa kulit singkong yang mengandung pati dan memungkingkan untuk dikonversi menjadi alternatif energi seperti bioetanol. Proses produksi bioetanol dilakukan melalui tahap pretreatment/delignifikasi, hidrolisis, fermentasi, dan pemurnian. Proses pretreatment dilakukan untuk mendapatkan kandungan selulosa yang akan digunakan dalam proses hidrolisis. Pretreatment dapat dikombinasi seperti penggabungan metode secara fisika (pemanasan microwave) dan kimia (larutan alkali). Penggunaan metode alkali dan pemanasan microwave akan meningkatkan kadar selulosa dan menurunkan kadar lignin yang lebih baik dibandingkan dengan metode yang lain. Larutan alkali yang digunakan yaitu NaOH karena memiliki sifat yang sesuai apabila dikombinasikan dengan pemanasan microwave. Delignifikasi dilakukan dengan memberikan variasi konsentrasi NaOH 0,5 M, 0,75 M, dan 1 M dan variasi lama waktu paparan panas microwave 5, 10, dan 15 menit. Hasil variasi pretreatment diuji secara statistik menggunakan rancangan acak lengkap. Secara statistik, peningkatan konsentrasi larutan NaOH dan lama waktu paparan panas microwave memberikan pengaruh nyata untuk kandungan selulosa dan lignin. Konsentrasi NaOH dan waktu paparan microwave terbaik adalah 1 M dan 15 menit. Perbandingan data sebelum dan setelah pretreatment menunjukkan bahwa metode tersebut memenuhi syarat pretreatment lignoselulosa., Indonesia is the fourth-largest producer of cassava with a total production of 20 million tonnes per year. Up to 15-20% per kilogram of cassava is waste in the form of cassava peel, which contains starch and allows it to be converted into alternative energy such as bioethanol. The process of bioethanol production is carried out by stages of pretreatment/delignification, hydrolysis, fermentation, and purification. The pretreatment process is carried out to obtain the cellulose content that will be used in the hydrolysis process. Pretreatment can be combined, for example by combining physical (microwave heating) and chemical (alkaline solution) methods. Using alkaline methods and microwave heating will increase cellulose content and reduce lignin content which is better than other methods. The alkaline solution used is NaOH because it has suitable properties when combined with microwave heating. The delignification was carried out by varying the concentration of 0,5 M, 0,75 M and 1 M NaOH and the exposure time to microwave heat was 5, 10 and 15 minutes. The results of the pretreatment variation were tested statistically using a complete block design. Statistically, the increase in the concentration of the NaOH solution and the duration of exposure to microwave heat had a significant effect on the cellulose and lignin content. The best NaOH concentration and microwave exposure time were 1 M and 15 minutes. Comparison of the data before and after pretreatment shows that the method meets the requirements of lignocellulosic pretreatment.
Keyword: alkaline, bioethanol, cassava peel, delignification, microwave heating

Judul: Teknik penentuan posisi bintang berdasarkan pelat foto overlapping
Abstrak: Bintang adalah salah satu objek langit yang menarik untuk diamati. Untuk itu, pengetahuan tentang posisi bintang sangat diperlukan. Posisi bintang di langit dapat dihitung melalui foto bintang. Fotografi astronomi atau astrometri merupakan ilmu yang mempelajari metode untuk menentukan posisi bendabenda langit seperti bintang berdasarkan pelat foto (Kamp, 1967). Sebuah pelat foto berisi citra bintang-bintang yang sudah diketahui posisinya berdasarkan katalog dan citra bintang-bintang yang belum diketahui posisinya. Posisi bintang yang ada di katalog dinyatakan dengan (a,3). Bintang yang belum diketahui posisinya lebih banyak jumlahnya daripada bintang yang sudah diketahui posisinya. Citra bintang pada pelat foto berupa sebuah titik dalam bentuk tetap. Posisinya pada pelat merupakan hasil pengukuran pada bidang kartesius dan dinyatakan dengan (1;,fl). Hasil pengukuran tersebut kemudian direduksi menjadi koordinat terukur (x,y). Hubungan antara (a,3) dan (x,y) didekati dengan sebuah deret dengan konstanta-konsranta deret merupakan konstanta pelat. Nilai konstanta pelat diperoleh dengan menggabungkan hasil pengukuran posisi bintang pada masing-masing pelat menjadi sebuah persamaan normal (Jefferys, 1963). Hasil akhir dari gugus persamaan normal tersebut dijabarkan dalam bentuk nOlasi matriks partisi dan berupa sebuah sistem persamaan linier Ax = b di mana A adalah matriks jarang, dan x merupakan konstanta pelar yang akan dicari nilainya. Untuk menyelesaikan sistem persamaan linier terse but digunakan metode transformasi given. Konstanta pelat yang sudah diperoleh dengan menyelesaikan sistem persamaan linier di atas, kemudian disubtitusi ke sebuah persamaan untuk memperoleh posisi bintang yang tidak tercantum dalam katalog. .
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