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Rekayasa: Jurnal Penerapan Teknologi dan Pembelajaran
Published by Universitas Negeri Semarang
ISSN : -     EISSN : 25276964     DOI : https://doi.org/10.15294/rekayasa
Core Subject : Education,
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REKAYASA journal publishes exciting articles from all fields of research and Engineering Science. The journals primary focus is on research practice and engineering processes utilizing biomass or factory waste. The engineering journal is an open-access peer-reviewed journal that publishes articles from all areas of Engineering and Science research.
Arjuna Subject : Umum - Umum
Articles 3 Documents
 1 
Search results for , issue "Vol. 23 No. 1 (2025)" : 3 Documents clear
Optimization of Water-in-Biodiesel  Emulsification of Palm Oil by Ultrasonic Method using  Respons Surface Methodology Fauzi, Dinda Adelia; Kusumaningtyas, Ratna Dewi; Widyastuti, Catur Rini; Veny, Harumi
Rekayasa Vol. 23 No. 1 (2025)
Publisher : Universitas Negeri Semarang

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.15294/rekayasa.v23i1.31831

Abstract

Palm oil biodiesel offers a renewable alternative but has high viscosity and density. Emulsifying biodiesel with water reduces these drawbacks and lowers nitrogen oxide (NOx) emissions. This study aims to optimize the emulsification process of water-in-biodiesel emulsion made from palm biodiesel (B100) using an indirect ultrasonic method and the response surface methodology approach with a Box-Behnken design. Three main independent variables were examined: hydrophilic-lipophilic balance values (6, 7.5, and 9), water concentrations (9%, 12%, and 15% v/v), and surfactant concentrations (5%, 7%, and 9% v/v) with a combination of Tween 80 and Span 80 as surfactants. The experimental process involves the synthesis of biodiesel from palm oil through transesterification with the help of 100W ultrasonic power for 15 minutes at room temperature. The analysis was carried out on three main parameters: density, viscosity, and water droplet size on water-in-biodiesel. The results of laboratory tests and statistical modeling show the three independent variables have a significant effect on the physical properties of water-in-biodiesel. The optimization resulted in the best conditions at a hydrophilic-lipophilic balance value of 6.11, water concentration of 9.06%, and surfactant concentration of 5%, with density characteristics of 859.95 kg/m³, kinematic viscosity of 4.44 mm²/s, and average water particle size of 4.46 μm, values close to conventional diesel fuel standards. This study confirms that the indirect ultrasonic method and respons surface methodology-based optimization are effective in improving the performance and character of water-in-biodiesel, potentially becoming a reference for the development of environmentally friendly renewable energy based on palm oil.
Performance Test of Methylene Blue Degradation Using TiO₂–Graphene Oxide Composite Synthesised from Coconut Shells Heltina, Desi; Fesya Putri, Andini; Fauziyah, Hidayatul; Peratenta Sembiring, Maria; Amri, Amun; Tao Jiang, Zhong
Rekayasa Vol. 23 No. 1 (2025)
Publisher : Universitas Negeri Semarang

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.15294/rekayasa.v23i1.32529

Abstract

Industry produces textile liquid waste which contains dangerous compounds such as methylene blue which can damage the environment. One effective method to overcome this problem is to use a TiO2 nanocomposite-based photocatalyst modified with Graphene Oxide (GO). GO is obtained from the synthesis of coconut shells, which is a biomass waste. This research aims to synthesize and display the performance of a TiO2/Graphene Oxide composite photocatalyst from coconut shells in degrading methylene blue. The TiO2/Graphene oxide nanocomposite synthesis method begins by carbonizing coconut shells to form graphite. Carbonization removes volatile compounds and produces a rich carbon structure, which is the initial requirement for the formation of GO. Synthesis of GO from graphite using the Hummer method. Synthesis of TiO2/Graphene oxide composite using a solvothermal process with various GO mass ratios. The performance of the photocatalyst was tested for degradation using methylene blue. Analysis of the TiO2/Graphene Oxide Composite using XRD, FTIR, SEM, BET characterisation and UV-Vis Spectrophotometer. The results show that at GO of 15%, the composite showed the highest surface area and optimal anatase crystallinity, resulting in the best degradation efficiency (70%). Graphene Oxide is synthesized from coconut shell biomass waste. This research shows that the TiO₂–Graphene Oxide composite has high efficiency in degrading dangerous synthetic dyes from textile industry wastewater through an efficient photocatalytic mechanism. This composite application is an application of technology that contributes directly to achieving the Sustainable Development Goals (SDGs), especially SDG 6 (Clean Water and Adequate Sanitation), through the development of sustainable, efficient and environmentally friendly waste processing technology.
Design and Performance Evaluation of a Soybean Filtration Machine Utilizing an Electric Motor and Low-Torque Gearbox Nur Fatta, Muhammad Affa; Dwi Saputro, Danang; Hidayat, Hanif
Rekayasa Vol. 23 No. 1 (2025)
Publisher : Universitas Negeri Semarang

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.15294/rekayasa.v23i1.19394

Abstract

The traditional soybean filtration process in small- and medium-scale tofu industries remains inefficient due to labour-intensive operations, inconsistent extract quality, and high processing time. Manual pressing methods often result in reduced extract yield, uneven texture, and contamination risks. Therefore, this study aims to design and evaluate a soybean filtration machine powered by an electric motor and a low-torque gearbox, with the goal of improving efficiency, hygiene, and mechanical reliability. The research employed a Research and Development approach using the Four-D model: define, design, develop, and disseminate. A 0.5 hp electric motor was integrated with a 1:20 ratio gearbox to achieve stable rotational motion for the reciprocating filter system. The mechanical analysis indicated a total working force of 613.725 N, a motor torque of 61.37 Nm, and an output torque of 1,105 Nm after accounting for efficiency. The system demonstrated low structural deflection (0.405 mm) and a high safety factor of 3.81, confirming robust mechanical integrity. Experimental testing yielded a filtration efficiency of 93% and an average flow rate of 1.2 L/min, showing a 70–80% reduction in processing time compared to manual filtration. The feasibility assessment resulted in an 88.63% approval rating from operators, classifying the machine as highly feasible. Overall, the designed system effectively improves productivity, ergonomics, and product consistency in soybean-based food processing.

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