Rekayasa proses hidrolisis ampas tapioka menggunakan pemanasan gelombang mikro untuk produksi etanol

Abstract

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).