Sodium alginate is the polymer matrix most commonly used for the immobilization of cells, enzymes, and microalgae for various purposes. One of the bead immobilization preparations is the droplet extrusion method in which CaCl2 is the adsorbent. However, the use of CaCl2, which is a cross-linking agent, can increase alginate susceptibility. Therefore, this review aims to provide an overview of the application of immobilized cells in the form of reused beads for the production of biohydrogen and bioethanol, as well as beads for removing heavy metals from wastewater, and removing potassium from vinasse. Meanwhile, the immobilized cells used were cow dung, Saccharomyces cerevisiae (S. cerevisiae), and D. subspicatus. All reported applications have shown that the initial bead shape of the drip extrusion method was spherical. However, over time the alginate beads become eroded due to repeated use. Round beads occurred when using 2% alginate concentration and the performance was optimum compared to 1% and 2% of alginate concentrations even though the cross-linked concentrations varied.

One of the microalgae that can be potentially used to produce bioethanol is Chlorella vulgaris, as it is rich in carbohydrates. However, the carbohydrates in C. vulgaris cannot be converted directly into ethanol. This study aimed to investigate the chemical and enzymatic hydrolysis of C. vulgaris, which is subsequently followed by fermentation. The catalysts used in the chemical hydrolysis were hydrochloric acid, sodium hydroxide, and potassium hydroxide, while the enzymes used were the mixture of alpha-amylase + glucoamylase, alpha-amylase + cellulase, and alpha-amylase + glucoamylase + cellulase. The hydrolysate obtained from chemical hydrolysis was fermented through Separate Hydrolysis Fermentation (SHF), while the one from enzymatic hydrolysis was fermented through Simultaneous Saccharification and Fermentation (SSF), in which both processes used S. cerevisiae. After undergoing five hours of enzymatic hydrolysis (using alpha-amylase + glucoamylase), the maximum glucose concentration obtained was 9.24 ± 0.240 g/L or yield of 81.39%.  At the same time and conditions of the substrate on chemical hydrolysis, glucose concentration was obtained up to 9.23 + 0.218 g/L with a yield of 73.39% using 1 M hydrochloric acid. These results indicate that chemical hydrolysis is less effective compared to enzymatic hydrolysis. Furthermore, after 48 hours of fermentation, the ethanol produced from SHF and SSF fermentation methods were 4.42 and 4.67 g/L, respectively, implying that producing bioethanol using the SSF is more effective than the SHF method.

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Dioscorea esculenta or known as gembili in Indonesian is a tuber that can grow easily in almost tropical areas. Gembili is one of the important food sources in the tropical regions. It contains 22.44% carbohydrate which makes it very potential to be developed into tuber flour. This study aims to improve the quality of gembili flour by assessing the effect of several parameters such as oxidation time, the ratio of slurry, and agent concentration on swelling power level. The optimum condition of the oxidation process was at the ratio of slurry 10% with 2% of H2O2 concentration and 60 min operation time that presented the swelling power level of 7 (g/g). Therefore, this swelling power of gembili flour complies with American wheat standards.

S. platensis is a microalga that contains carbohydrate composition of 30.21% which makes it potential to be used as raw material for ethanol production. Hydrolysis of S. platensis is the first step for converting its carbohydrates into monosaccharides. The second step is fermentation of monosaccharides into ethanol. This research aims to study the effect of temperature and microalgae concentration on the hydrolysis of S. platensis using sulfuric acid as catalyst. This research was conducted using 300 mL sulfuric acid of 2 mol/L, hydrolysis temperatures of 70, 80 and 90 °C, and microalgae concentrations of 20, 26.7, and 33.3 g/L. The effect of temperature is significant in the hydrolysis of S. platensis using sulfuric acid. At microalgae concentration of 20 g/L and hydrolysis time of 35 minutes, the higher the temperatures (70, 80, and 90 °C), the more the glucose yields would be (8.9, 13.5, and 22.9%). This temperature effect got stronger when the hydrolysis was running for 15 minutes. Every time the hydrolysis temperature increased by 10 °C, the glucose yield increased by 13.0% at microalgae concentration of 33.3 g/L. At temperature of 90 °C and time of 35 minutes, the higher the microalgae concentrations (20, 26.7, and 33.3 g/L), the higher the glucose yields would be (25.5, 27.7, and 28.2%). The highest glucose concentration obtained was 2.82 g/L at microalgae concentration of 33.3 g/L, temperature of 90 °C, and time of 35 minutes.