PEMANFAATAN LIMBAH NASI BASI MENJADI BIOETANOL SEBAGAI BAHAN BAKAR ALTERNATIF

Abstrak Meningkatnya kebutuhan transportasi turut meningkatkan konsumsi bahan bakar sehingga menyebabkan kelangkaan. 10 tahun terakhir Indonesia mengalami penurunan produksi migas sehingga diperlukan energi alternatif seperti bioetanol. Masyarakat sering menyisakan limbah nasi yang mengandung karbohidrat dan bisa diubah menjadi alkohol. Penelitian ini bertujuan mengetahui perbandingan volume air, berat ragi dan waktu fermentasi untuk menghasilkan kadar bioetanol optimal serta pengujian karakteristik bioetanol. Penelitian ini menggunakan metode eksperimen dengan berat nasi basi 250 gram, volume air (750,1000,1250, 1500 ml), berat ragi (5, 7, 9, 11 gram) dan waktu fermentasi (3,4,5,6 hari) hingga diperoleh kadar bioetanol maksimal. Pembuatan bioetanol dilakukan dengan tahap sakarifikasi, fermentasi dengan saccharomyces cerevisiae serta distilasi suhu 78ºC. Setelah diperoleh kadar >95%, dilakukan pengujian karakteristik sesuai Keputusan Dirjend Energi Baru, Terbarukan dan Konservasi Energi Nomor 722K/10/DJE/2013. Data pengujian disajikan dalam bentuk tabel dan grafik disertai penjelasan secara distributif. Hasil penelitian menunjukkan bahwa perbandingan terbaik yaitu volume air 5000 ml, berat ragi 45 gram dan waktu fermentasi 5 hari dengan kadar bioetanol 29%. Selanjutnya dilakukan distilasi bertingkat untuk mencapai kadar 96,5% dengan penambahan silica gel 25 gram dan batu kapur 30 gram pada ujung kondensor sebagai penyerap kadar air. Hasil karakteristik bioetanol limbah nasi basi yaitu kadar bioetanol 96,5%, kadar metanol 0,00103%-v, kadar air 0,7726%-v, kadar tembaga 0,0067 mg/kg, keasaman sebagai asam asetat 2 mg/L, tampakan jernih, tidak ada endapan, kadar ion klorida 0 mg/L, kandungan belerang 50 mg/L, kadar getah 1,2 mg/100ml, nilai kalor 5724 kkal/kg, titik nyala 30°C, titik beku -50°C, densitas 0,808 gr/cm3, viskositas 3,5 cPs dan pH 7,55. Terdapat beberapa karakteristik yang melebihi standar Dirjen Energi Baru, Terbarukan dan Konservasi Energi Nomor 722K/10/DJE/2013 yaitu kadar belerang dan kadar air yang diduga karena pada alat distilasi mengandung berbagai unsur paduan logam serta bahan baku yang sudah mengandung kadar air tinggi yaitu 57%. Secara perhitungan ekonomis bioetanol limbah nasi basi lebih mahal dari pada bioetanol di pasaran karena proses pembuatannya masih skala kecil.   Kata Kunci: Bioetanol, saccharomyces cerevisiae, sakarifikasi, fermentasi, distilasi.  Abstract Increased of transportation needs also increase the fuel consumption so causing scarcity. In the last 10 years, Indonesia has decreased oil and gas production therefore it needs alternative energy such as bioethanol. Community activities often leaving waste stale rice containing carbohydrates and can be converted into alcohol. This research aims to knowing comparison of water volume, yeast weight, fermentation time to produce optimal bioethanol content and testing of bioethanol characteristic.This research uses experimental method with stale rice weight 250 gram with stale rice 250 grams, water volume (750, 1000, 1250, 1500 mililiters), yeast (5, 7, 9, 11 grams) and time fermentations (3, 4, 5, 6 days) to obtained a maximum bioethanol content. Bioethanol production is processed by the stage of saccharification, fermentation with saccharomyces cerevisiae and distillation at temperature of 78 ºC. After content of bioethanol obtained at >95%, conducted characteristic testing according to the decision of the new energy director general, renewable and energy conservation number 722K/10/DJE/2013. Test data results are presented in the form of tables and charts with distributive explanations. The research results showed that the best comparison of water is 5000 mililiters, 45 grams yeast and 5 days fermentation time with 29% bioethanol content. Furthermore multilevel distillation to reach levels of 96,5% with the addition of 25 grams silica gel and limestone 30 grams at the end of the condenser as absorbent moisture content. The result examination of bioethanol characteristic of stale rice waste that is bioethanol content 96,5%, methanol 0,00103%-v, water content 0,7726%-v, copper content 0,0067 mg/kg, acidity as acetic acid 2 mg/L, brightness, no sediment, 0 mg/L chloride ion content, 50 mg/L sulfur content, gum washed content 1.2 mg/100ml, heating value 5724 kcal / kg, flash point 30°C, pour point -50°C, density 0,808 gr/cm3, viscosity 3,5 cPs and pH 7,55. There are several characteristics that exceed the standard specified by the Director General of New Energy, Renewable Energy and Conservation No. 722K / 10 / DJE / 2013 that is the sulfur content and water content which is suspected because the distillation apparatus contains various elements of metal alloy and raw material which already contains high water content that is 57%. The econometric calculation of bioethanol from stale rice waste is more expensive than the bioethanol in the market because the process of manufacture is still small scale.   Keywords: Bioethanol, saccharomyces cerevisiae, saccharification, fermentation, distillation. &nbsp