Idea Transcript
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RINGKASAN WIDYA FATRIASARI. Produksi Gula Pereduksi melalui Rekayasa Proses Pra-perlakuan Bambu Betung (Dendrocalamus asper (Schult.f)). Dibimbing oleh WASRIN SYAFII, NYOMAN J WISTARA, KHASWAR SYAMSU dan BAMBANG PRASETYA. Lignin dan struktur kristalin selulosa merupakan faktor pembatas utama pada proses konversi bahan berlignoselulosa menjadi gula pereduksi. Dalam rangka meningkatkan aksesibilitas enzim maka perlu dilakukan modifikasi struktur lignoselulosa dengan proses pra-perlakuan. Praperlakuan ramah lingkungan yang menarik dikembangkan diantaranya praperlakuan biologis dan gelombang mikro dalam medium air. Penggunaan pra-perlakuan tunggal (biologis atau gelombang mikro) pada bambu betung dengan hidrolisis asam-gelombang mikro untuk memperbaiki rendemen gula hidrolisis enzimatis belum pernah dilaporkan sebelumnya. Selain itu, kombinasi pra-perlakuan secara biologis-gelombang mikro merupakan alternatif untuk memperbaiki rendemen gula, sehingga proses hidrolisisnya lebih efisien. Hal ini mengingat lebih optimalnya aktivitas degradasi lignin, pelarutan hemiselulosa, pelunakan substrat dan peningkatan porositasnya. Bambu termasuk dalam kelompok rumput-rumputan yang berpotensi dijadikan alternatif bahan bioenergi. Beberapa hal yang mendasarinya adalah produktivitas biomasanya tinggi, mudah dan cepat diproduksi, ketersediaanya melimpah, tumbuh dengan baik pada unsur hara yang minim dan kandungan holoselulosanya tinggi. Bambu ini tumbuh tersebar terutama di Asia dan bambu di Indonesia menempati tempat ketiga setelah Tiongkok dan India. Bambu betung merupakan salah satu jenis bambu terpenting di Indonesia yang berpotensi dikembangkan. Bambu ini memiliki morfologi dan kandungan komponen kimia cukup baik untuk dikonversi menjadi bioetanol. Pengaruh pra-perlakuan tunggal (biologis atau gelombang mikro) dan kombinasi biologis-gelombang mikro dalam mengubah struktur selulosa dan lignin bambu betung menjadi fokus dalam penelitian ini. Pengaruh perubahan karakteristik bambu setelah pra-perlakuan tersebut kemudian dihubungkan dengan kinerja hidrolisis enzimatis dan asam-gelombang mikro. Perbandingan peningkatan rendemen gula pereduksinya terhadap kontrol dan antar pra-perlakuan tunggal dan kombinasi juga didiskusikan. Selain itu juga dicoba untuk memperbaiki kinerja hidrolisis asamgelombang mikro dengan penambahan karbon aktif. Penelitian ini terdiri dari enam tahap penelitian yaitu penelitian tahap 1, 2, 3 untuk menganalisis perubahan karakteristik lignin dan selulosa selama pra-perlakuan biologis menggunakan jamur pelapuk putih, T.versicolor (tahap 1), pra-perlakuan gelombang mikro dalam medium air (tahap 2), kombinasi pra-perlakuan secara biologis-gelombang mikro (tahap 3). Berdasarkan penelitian tahap 1 dan 2 diperoleh kondisi pra-perlakuan terpilih dilanjutkan dengan kombinasi pra-perlakuan biologis dan gelombang mikro. Indikator utama penentuan kondisi pra-perlakuan terpilih dari kehilangan berat, kehilangan lignin dan selulosa dan hemiselulosa,
selektifitas delignifikasi, perubahan struktur kristal selulosa alomorf, dan indeks kristalinitas bahan. Penelitian pada tahap 4, 5 dan 6 dimaksudkan untuk memperoleh informasi kinerja hidrolisis enzimatis dan asam-gelombang mikro dari kondisi pra-perlakuan biologis dan gelombang mikro terpilih serta kombinasi kedua pra-perlakuan tunggal. Parameter kunci untuk mengevaluasi kinerja hidrolisis pada penelitian tahap ini meliputi rendemen gula pereduksi, nisbah hidrolisis dan senyawa coklatnya. Pengaruh penambahan katalis karbon aktif sebagai adsorber inhibitor selama proses hidrolisis asam-gelombang mikro juga dikaji pada tahap ini. Hasil penelitian menunjukkan bahwa inkubasi selama 30 hari dalam praperlakuan biologis terpilih sebagai kondisi terbaik dengan indikator selektifitas delignifikasinya yang tinggi. Kondisi pra-perlakuan gelombang mikro terpilih adalah iradiasi selama 5, 10 dan 12 menit (330 W) serta 5 menit (770 W) dengan mempertimbangkan tingkat kehilangan berat dan kehilangan hemiselulosa. Pra-perlakuan menyebabkan struktur matriks lignoselulosa menjadi lebih terbuka, lunak serta terjadi pemisahan antar serat dan menyebabkan lebih tereksposnya selulosa. Terjadi penurunan intensitas absorbansi gugus fungsional setelah pra-perlakuan meskipun pada umumnya tidak terdapat perubahan gugus fungsi yang teridentifikasi. Hilangnya sebagian lignin setelah pra-perlakuan didukung dengan adanya penurunan intensitas gugus aromatik lignin dengan syringil lebih rendah dibandingkan dengan guaiacyl. Terjadi penurunan intensitas pada pola difraksi sinar X dan pra-perlakuan menyebabkan indeks kristalinitas bahan meningkat terkait dengan hilangnya bagian amorf yaitu lignin dan hemiselulosa dan efek hornifikasi terkait dengan kondisi pengujian sampel. Transformasi struktur kristal selulosa alomorf dari monoklinik menjadi triklinik terjadi pada semua pra-perlakuan. Rendemen gula pereduksi hidrolisis enzimatis pada ketiga jenis praperlakuan dibawah 5% per bambu awal, meskipun terjadi peningkatan dibandingkan dengan kontrol. Rendemen ini dapat diperbaiki dengan hidrolisis asam-gelombang mikro. Penggunaan konsentrasi asam 1% direkomendasikan untuk digunakan dalam hidrolisis asam-gelombang mikro pada bambu. Peningkatan rendemen tertinggi terhadap kontrol dihasilkan pada proses hidrolisis gelombang mikro selama 12.5 menit dari hasil kombinasi pra-perlakuan biologis (inokulum 5%) dan gelombang mikro (5 menit, 330 W) yaitu sebesar 8.4 kali (16.65% per bambu awal). Rendemen ini lebih rendah dari rendemen gula pereduksi tertinggi dari pra-perlakuan gelombang mikro selama 12.5 menit (330 W) yaitu sebesar 25.81% per bambu awal dengan peningkatan rendemen terhadap kontrol 6.2 kali. Penambahan karbon aktif dalam hidrolisis asam-gelombang mikro hanya berpengaruh terhadap efek penghambatan pembentukan senyawa inhibitor yaitu senyawa coklat namun rendemen gula pereduksinya menurun. Kata kunci: bambu betung, pra-perlakuan biologis dan gelombang mikro, lignin, selulosa, hidrolisis asam-gelombang mikro, karbon aktif
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SUMMARY WIDYA FATRIASARI. Reducing Sugar Production through Pretreatment Process Engineering of Betung Bamboo (Dendrocalamus asper (Schult. f)). Under the supervision of WASRIN SYAFII, NYOMAN J WISTARA, KHASWAR SYAMSU, BAMBANG PRASETYA. Lignin and crystalline nature of cellulose are major recalcitrance in the conversion of lignocellulosic materials to reducing sugar. Pretreatment of raw material is required to improve enzyme accessibility into the lignocellulosic structure . Many pretreatment methods have been developed including that of environmental-friendly pretreatments such as biological and microwave pretreatments in water. In general, lignocellulosic conversion into bioethanol is carried out with single pretreatment and then proceeded with enzymatic hydrolysis. However, low yield of reducing sugar frequently resulted from the method. The pretreatment sequences of biological-microwave could be useful to improve the yield of hydrolysis. Biological-microwave pretreatment was thought to bring about lignin degradation, hemicelluloses removal, substrate softening and an increase of substrate porosity. These effects will possibly improve the hydrolysis performance of lignocellulosic based materials. Bamboos belong to the graminae family and are potential alternative for bioenergy production. The potentials are indicated by the facts that bamboo retains high biomass productivity, fast and readily grown, highly available, capable of growing well in marginal land and high in hollocellulose content. Bamboos mainly grow in Asia including Indonesia. The country is ranked the 3rd after China and India in bamboo plantation. Betung bamboo is the most important species in Indonesia. The species morphologically and chemically suitable for the bioethanol production. This research was aimed to evaluate the effect of single (biological and microwave) and combined (biological-microwave) pretreatments on lignocellulosic substrates to the structural change of the substrate cellulose and lignin. The changes were then used to explain the performance of the enzymatic and microwave assisted acid hydrolysis. The hydrolysis performance of single pretreatment, combined pretreatment and control (hydrolysis of the untreated sample) were compared. In the present works, the effect of activated carbon addition to the performance of the microwaveassisted acid hydrolysis was also studied. The present study was carried out in six stages. The 1st, 2nd and 3rd stages were aimed to evaluate the characteristics of lignin and cellulose after biological pretreatment with white rot fungi (Trametes versicolor), microwave pretreatment in water, and combined biological-microwave pretreatment, respectively. The resulting substrates from the best pretreatment conditions of the 1st and 2nd stages were selected for the biological-microwave pretreatment. Major indicators of the best pretreatment condition were weight loss, the removal of lignin, hemicellulose and cellulose, delignification selectivity, cellulose allomorph and crystallinity index of materials.
The 4th and 5th stages were aimed to determine the performance of enzymatic and microwave-assisted acid hydrolysis of the selected biological and microwave pretreatments. The 6th stage was aimed to determine the performance of the enzymatic and microwave-assisted acid hydrolysis on the resulting substrate of the combined pretreatment. The hydrolysis performance was evaluated based on the yield of reducing sugar and the formed brown compound. The effect of activated carbon addition in the microwave-assisted acid hydrolysis was also discussed. Based on its delignification selectivity, biological pretreatment for 30 days incubation was considered the best condition. The best condition of microwave pretreatment based on weight loss and hemicelluloses removal was found with irradiation power of 330 W for 5, 10, and 12 minutes, and with irradiation power of 770 W for 5 minutes. Pretreatments brought about a more exposed and open structure of cellulose and fiber disintegration. Following pretreatment, a decreasing peak intensity of FTIR spectra were found, but no change in the functional group was identified. Decreasing peak intensity was indicative to the decreasing of the lignin aromatic ring, in which the content of syringyl moieties was lower than that of guaiacyl moieties. Pretreatment increased the crystallinity of the substrate and was thought due to the removal of amorphous lignin and hemicelluloses components, as well as the occurrence of hornification due to substrate drying during X-ray examination. Both single and combined pretreatments transformed the cellulose monoclinic structure into the cellulose triclinic structure. The reducing sugar yield of enzymatic hydrolysis of substrate from all method of pretreatment was higher than that of control, but was less than 5% of the initial substrate weight. The yield improved when microwaveassisted acid hydrolysis was applied. A 1% acid concentration was recommended in microwave-assisted acid hydrolysis of bamboo. The highest reducing sugar yield of the microwave-assisted acid hydrolysis of the combined pretreated substrate was 16.5 % of the initial weight of the substrate or 8.4 fold of its control yield. The hydrolysis was carried out with 12.5 minutes microwave irradiation of the substrate pretreated with 5% inoculum of TV proceeded with 330 W microwave irradiation power for 5 minutes. On the other hand, the highest reducing sugar yield of the microwave-assisted acid hydrolysis of the microwave pretreated substrate was 25.81% of the initial weight of substrate or 6.2 fold of its control. The substrate was irradiated for 12.5 minutes at the power of 330 W. Activated carbon addition in the microwave-assisted acid hydrolysis merely influenced the formation of inhibitor compound such as brown compound. Activated carbon addition, in fact, reduced the reducing sugar yield.
Keywords: betung bamboo, biological and microwave pretreatment, lignin, cellulose, microwave-assisted-acid hydrolysis, activated carbon