This paper presents an experimental investigation on using mixed culture for immobilization and co-immobilization for hydrogen production. The shape and diameter of the beads were investigated. Hydrogen was produced from 10 g.L 1 glucose in anaerobic batch using immobilized mixed culture with extrusion dripping method. The alginate concentrations as immobilization material were 1%, 2%, and 3%. The mixed culture had three different biodigester sources consisting of cow dung, tofu waste, and fruit waste. The pretreatment of each mixed culture was acidification and enrichment. Then the mixed culture were mixed with immobilization material and inserted into a syringe, then dropped into 0.1M CaCl 2 . Activated carbon was added to alginate (coimmobilization) with ratio 1:1. The results showed that bead using 1% and 2% alginate concentrations were a pear-shaped. The highest concentration of hydrogen (mol H 2 /mol glucose) was 0.029 for immobilized beads with 2% alginate concentration and the lowest hydrogen (molH 2 /mol glucose) was 0.009 for immobilized beads with 3% alginate concentration. Acetic acid was the most dominant.

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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.

Bioethanol is an environmentally benign renewable energy commonly obtained from glucose fermentation using Saccharomyces cerevisiae. The purposes of this study are to investigate the effects of time, temperature, pH, immobilized yeast cell loading, beads reuse during ethanol production through batch fermentation of glucose derived from oil palm empty fruit bunches by S. cerevisiae immobilized on Na-alginate beads and to compare the performance of fermentation using immobilized yeast cells and that of using a free cell system. The results revealed that time, temperature, pH, yeast mass and beads reuse significantly affected the ethanol and final glucose concentrations. As expected, a maximum ethanol concentration was obtained from fermentation using immobilized yeast cells at 30 °C, pH 5, and immobilized yeast cell loading of 0.75 g for 48 hours. However, fermentation with a free cell system at the same conditions resulted in lower ethanol yield. The highest ethanol concentration of 88.125 g/L with a productivity of 1.84 g/L·h was achieved from the second cycle fermentation using of immobilized cells beads. The results suggest that an immobilized cell system exhibits great potential applications for improved ethanol production due to its ability to sustain the stability of cell activity, reduce contamination tendency, and protect yeast cells from any possible inhibitions.

The synthesis of γ-valerolactone (GVL), a versatile precursor in the manufacture of high-value chemicals such as polymer plasticizer, solvent, jet fuel, and, agrochemicals, has been targeted by many research groups. In this study, we report the catalytic performance of iron-modified palladium supported on titanium oxide (denoted as Pd(5.0)-Fe(5.0)/TiO2; 5.0 was the loading amount of Pd and Fe, respectively) in the selective hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) in stainless-steel batch reactor system. Pd(5.0)-Fe(5.0)/TiO2 catalyst was synthesized by a simple hydrothermal method at 150°C for 24 h, then followed by reduction with H2 at 500°C for 3 h. The X-ray diffraction (XRD) patterns of Pd(5.0)-Fe(5.0)/TiO2 before and after reduction showed the formation of metallic Pd at 2θ = 40.34° and 47.2° corresponding to Pd(111) and Pd(200), respectively. The hydrogenation of LA to GVL effectively occurred in the H2O solvent, whereas in 2-propanol the formation of ester was the main side product. The highest yield of GVL (52.5%) was obtained over Pd(5.0)-Fe(5.0)/TiO2 catalyst at a temperature of 170 °C, initial H2 pressure of 4.0 MPa, solvent H2O 3 ml at a reaction time of 7 h. The yield of GVL slightly increased to 63.3% when the reaction time was prolonged to 15 h.

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.