Tapioca processing from cassava produces abundant solid wastes. If left untreated, it potentially increases greenhouse gas emissions from the decomposition of organic matter. These gas emissions are known to accelerate global climate change. Tapioca solid waste (TSW) has high starch and cellulose content, making energy recovery possible through conversion to bioethanol. This research aimed to produce bioethanol from TSW by a co-fermentation method of baker’s and local tapai yeast. The research was conducted through multi-stages of enzymatic hydrolysis, followed by fermentation, then distillation. The hydrolysis produces hydrolyzate with a relatively high reducing sugar concentration. The ethanol fermentation results were optimally achieved in 48 h, namely substrate fermented by tapai yeast first for 24 h, followed by the addition of baker’s yeast and fermentation time to 48 h. This proces produced the highest yield and bioethanol concentration, almost 2 times higher than fermentation using baker’s or tapai yeast only. This results suggested that TSW can be used for bioethanol production by co-fermentation of baker’s and tapai yeast method. TSW usage will reduce global warming, bioethanol production can be widely applied in various fields replacing fossil fuel, thus has the potential to reduce global warming and global climate change.

Organic sulfur compound of fossil fuel are too resistant to be removed by the conventional desulfurization processes. This study aimed to investigate the best growth conditions of Agrobacterium tumefaciens strain LSU20 on desulfurized of dibenzothiophene (DBT) compound in the n-tetradecane as model of oil. The experiments were performed with the medium two-phase system, aqueous phase: mineral salt sulfur free (MSSF) medium and the oil phase: n-tetradecane containing 200 ppm of DBT in the ratio of oil/water (1: 5). The culture of LSU20 that has been aged 4 days (OD660 5) of 0.1 ml inoculated in a test tube containing 5 mL of MSSF medium and 1 ml model of petroleum, grown at temperature variations incubation as follows: 33°C, 37°C, 41°C, 45°C, and 49°C; variations in the initial pH of medium: pH 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, and 8.0; and variations of carbon sources such as glucose, sucrose, glycerol and citric acid. The experiments were conducted using a water bath shaker at 150 rpm for 96 hours of incubation. The results showed that the highest rate of degradation of DBT by LSU20 occurs at a temperature of 37°C, media pH of 7 and glucose as the carbon source, ie with the growth rate reached 0.91 (OD660) and DBT compounds degraded until 76.9% (w/v).

Currently the supply of fossil energy is running low; besides, it contributes very significantly to environmental pollution and climate change. Therefore, it is necessary to develop new and renewable alternative energy, one of which is bioethanol. One of the potential raw materials used in bioethanol production is sugarcane bagasse which is an abundance of agricultural waste. This study aims to determine the concentration of Na-alginate and the density of cell suspension with the best activity and stability of immobilized Saccharomyces cerevisiae ATCC 9763 cells in the bioethanol production process. This research is an experimental study using a randomized block design (RBD) with a factorial pattern consisting of two factors, namely the first factor is the concentration of Na-alginate and the second factor is the concentration of cells suspension in making immobilized S. cerevisiae cells. The first factor consists of 5 levels, namely 0%, 2%, 3%, 4%, and 5% (w/v). The second factor consisted of 3 levels, namely cells with OD660 20, 25, and 30. The parameters observed were the activity of immobilized S. cerevisiae cells including several variables, namely reducing sugar content, pH, and ethanol content. The stability of immobilized S. cerevisiae cells was seen from the level of cell turbidity (OD660 nm). The results showed that the concentration of Na-alginate, the concentration of S. cerevisiae cells, and the interaction between treatments had a very significant effect on the activity and stability of immobilized S. cerevisiae cells. The treatment of Na-alginate 2% (w/v) with cell density 25 was able to produce ethanol with a higher level of 63.87 ppm compared to treatment with 0% Na-alginate (free cells) with the level of cell density 25 was 56.97 ppm.

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