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 CaCl₂is 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), andD. 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.

As a response to the increasing demand for ethanol as a renewable energy source, the design of a bioreactor to facilitate efficient glucose fermentation by Saccharomyces cerevisiae is very essential. Although a number of mathem atical models that gave some parameters used for bioreactor design can be found in the literature, only a few models were designated for fermentation using immobilized S. cerevisiae. This study aimed to develop an unstructured fermentation kinetics model based on the mass transfer phenomena and the Monod equation to describe the rate of glucose consumption, glucose concentration on the bead surface, yeast cell growth, and ethanol concentration. Four ordinary differential equations obtained from the model development were solved simultaneously using fourth order Runge-Kutta with the help of MATLAB software. The accuracy of the model was verified with the experimental data collected from the relevant literature with the average error (%) of the variation of loading yeast mass, pH, and temperature were 5.12–10.08, 3.63–7.95, and 5.35–11.87, respectively. Seven adjustable kinetic parameters were also successfully obtained for a quantitative description of bioethanol production from fermentation of glucose employing S. cerevisiae immobilized on sodium alginate beads. The simulation results proved that the proposed model can accurately predict the concentration of glucose and ethanol in the fermentation broth, concentration of glucose on the alginate beads surface, and yeast cell concentration. Hence, the model can be potentially applied for the design of a larger scale batch bioreactor for glucose fermentation using S. cerevisiae immobilized on sodium alginate beads for ethanol production.

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.

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.

Biohydrogen production via dark fermentation is a prospective renewable energy technology. In the process, reused of immobilized mixed culture is very important as their activities greatly influencehydrogen production. The aim of this work was to evaluate the reuse of alginate beads affecting the biohydrogen production for 45 days. This study in batch reactor were performed using glucose 10 M as substrate, alginate and activated carbon as immobilization matrix materials, chicken eggshell as buffer, and cow dung biodigester as mixed culture. Hydrogen and pH on fermentation product are investigated by gas chromatography (GC) technique and pH meter, respectively. The colony diameter on immobilized and co-immobilized mixed culture was observed using optical microscope and colony diameter was measured using Image-Pro Plus Software v4.5.0.29. The surface morphology of immobilization and co-immobilization beads were determined using scanning electron microscope (SEM). The results showed that the colonies growth observed using optical microscopy or SEM was apparent only in the immobilization of mixed culture. The average growth and diameter of colonies per day were 90 colonies and 0.025 mm, respectively. The weight of beads and pH during the 45-day fermentation process for bead immobilization of mixed culture were 1.32–1.95 g and 6.25–6.62, correspondingly, meanwhile, the co-immobilizations of the mixed culture were 1.735–2.21g and 6.25–6.61, respectively. In addition, the average hydrogen volume of glucose fermented using an eggshell buffer and reusing the immobilization and co-immobilization beads was 18.91 mL for 15 cycles.©2020. CBIORE-IJRED. All rights reserved

The availability of fossil energy is dwindling, so renewable fuels are the alternative choices, one of which is bioethanol. To increase the purity of the ethanol produced via the fermentation process, activated carbon (AC) was made from durian (Durio zibethinus) peel. The steps for making AC consist of carbonization (300 °C and 400 °C), chemical activation using phosphoric acid (10–40%), pyrolysis (700 °C and 800 °C), and neutralization. The results showed that the maximum surface area (326.72 m²/g) was obtained from 400 °C carbonization, 800 °C pyrolysis, and activation using a 40% phosphoric acid solution. Other characteristics are the surface area of 326.72 m²/g, pore radius of 1.04 nm, and total pore volume of 0.17 cc/g with phosphate residue in the form a P₂O₅ molecule of 3.47% by weight, with COOH, OH, CO, C=C, C=O, P-OC, and Fe-O groups with wavenumbers (cm⁻¹), respectively, of 3836, 3225, 2103, 1555, 1143, and 494. The AC also demonstrated the highest number of carbon (86.41%) upon detection using EDX, while XRF analysis verified an average carbon content of 94.45 wt%. The highest ethanol adsorption efficiency (%) and the lowest yield (%) of AC (%) were 90.01 ± 0.00 and 23.26 ± 0.01. This study shows that durian peel has great potential as the raw material for the activated carbon manufacture of ethanol adsorbents.