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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 28 Documents
 1   2   3 
Sustainable Dyeing: Utilizing Natural Ketapang Colors for Shibori Products Widowati; Atika; Sholikhah, Roudlotus; Nurmasitah, Sita; Wahyuningsih, Sri Endah; Apriliana, Luthfiyah; Ayudianisa, Nadhifa Luthfihasna; Mutiara, Alma
Rekayasa Vol. 21 No. 1 (2023)
Publisher : Universitas Negeri Semarang

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.15294/rekayasa.v20i2.897

Abstract

The use of synthetic dyes in the textile industry produces wastewater with high potential for environmental pollution. Utilizing natural dyes from Ketapang leaves offers an alternative for reducing such wastewater and can be considered a sustainable dyeing method. According to data from the UNNES Conservation Development Agency, there are 5,170 Ketapang trees around the UNNES campus, indicating a plentiful supply for natural dye production. The purpose of this study is to explore the potential of Ketapang leaf dye in enhancing the aesthetic quality of Shibori products, specifically in terms of motif aesthetics and color direction. The research employs a quantitative approach with an experimental design, using a single variable. Data analysis was conducted through descriptive percentage statistics. The Shibori with the highest aesthetic value was produced using lime as a fixative, achieving a 95% rating (highly quality). Color direction analysis showed that each fixative produced different color outcomes: lime resulted in a Dijon color, alum produced a Corn color, and ferrous sulfate yielded a Seaweed color. Based on these findings, it can be concluded that natural dyes from Ketapang leaves contribute significantly to both motif aesthetics and color direction in Shibori dyeing, offering a sustainable and environmentally friendly alternative for textile production.
Compact Eyeshadow Preparations from Chiken Egg Shell and Rosella Flower Petals Extract (Hibiscus Sabdariffa L) as Natural Colorants and Preservatieves Agustin, Eny Widhia; Wara Dyah Pita Rengga
Rekayasa Vol. 20 No. 2 (2022)
Publisher : Universitas Negeri Semarang

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.15294/rekayasa.v20i2.2935

Abstract

Eyeshadow is used to give the eye dimension to look attractive, so the selection of eyeshadow materials needs to be considered to avoid side effects that can occur on the surface of the eyelids. Eyeshadow can be made from natural ingredients. One of the natural ingredients that can replace talcum chemicals is chicken eggshell powder because chicken eggshell powder contains a source of calcium that can nourish the skin. Rosella flower petal powder extract is also added as a natural colourant for manufacturing this compact eyeshadow powder. In addition to functioning as a colourant, Rosella flower petals contain anthocyanins and flavonoids, which have antioxidant and antibacterial properties. This study aims to determine the innovation process of chicken eggshell waste into Compact Powder Eyeshadow as decorative cosmetics by analyzing the feasibility of eyeshadow through organoleptic tests, pH tests, particle uniformity tests, specific gravity tests, and water content tests. This study's results show that formula III's physical quality with an extract concentration of 50% has good physical quality compared to other concentrations because the resulting colour is light. However, the colour resistance produced is the same as other formulas and does not last long.
Addition of Germicidal UV-C Radiation Equipment in the Sterilization Process to Extend the Shelf Life of Cow's Milk Wulansarie, Ria; Rusiyanto, Rusiyanto; Dino Alfian, Rangga; Diyah Ayu Utami, Kiki; Rahmah, Ladunia; Izza Arinanda, Miftakhul; Dyah Pita Rengga, Wara
Rekayasa Vol. 22 No. 1 (2024)
Publisher : Universitas Negeri Semarang

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.15294/rekayasa.v22i1.6239

Abstract

Cow's milk provides essential human nutrients, including calcium, protein, and minerals. However, it is highly susceptible to bacterial contamination, which leads to rapid spoilage. Pasteurization is the most common method to process cow's milk, effectively reducing microbial levels. However, some heat-resistant bacteria can survive the pasteurization process, limiting its effectiveness in ensuring long-term milk safety. This study investigates the use of chemical engineering technology by combining pasteurization and UV-C radiation methods, either sequentially or simultaneously, to improve the effectiveness of milk sterilization. The use of combined techniques aims to leverage the strengths of both processes, achieving superior microbial reduction and extending milk shelf life. Different operating temperatures and radiation durations were tested to identify optimal processing conditions. The findings revealed that this combined approach achieved a significant bacterial reduction of 99.95%, decreasing the microbial count from an initial 1.9 × 10⁶ cfu/mL to 7.0 × 10² cfu/mL. Moreover, the shelf life of the milk was extended to five months, demonstrating the effectiveness of the hybrid method. The study also monitored the milk's acidity (pH) throughout the process, which remained within optimal conditions of 6.5 to 6.8. This indicates that the combined treatment does not compromise milk quality. Integrating pasteurization with germicidal UV-C radiation offers a promising alternative for milk sterilization, improving microbial control and significantly increasing the shelf life of cow's milk. The results suggest that this dual-method approach could be a valuable advancement in dairy processing, enhancing both safety and efficiency in the production and preservation of milk.
Seismic Vulnerability Microzonation Based on Dominant Frequency and Amplification Using the HVSR Method in Wedi, Changewaro (Klaten) and Gendangsari (Yogyakarta) Desi Mustami Limayukha, Desi Mustami Limayukha; Adhi, Mochamad Aryono Adhi; Wibowo, Nugroho Budi; Bilqis El Farsiyyi, Billqis El Farsiyyi; Elsa Fadlika Widyantari, Elsa Fadlika Widyantari; Ilqia Rahma, Ilqia Rahma; Rahmania Sofyana Ulya, Rahmania Sofyana Ulya
Rekayasa Vol. 20 No. 2 (2022)
Publisher : Universitas Negeri Semarang

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.15294/rekayasa.v20i2.9957

Abstract

The Yogyakarta region is prone to frequent earthquakes, highlighting the need for seismic vulnerability assessment and micro zonation analysis. This study aimed to evaluate the area's seismic vulnerability by utilizing microtremor methods to estimate dominant frequency, amplification, seismic vulnerability index, and shear wave velocity. Microtremor points were analyzed using the Horizontal Vertical Spectral Ratio method, with data processed through Geopsy software to obtain f0, A0, and H/V curves. The H/V curve was further inverted using Dinver software to derive ellipticity curves, ground profiles, and Kg values. The results revealed that the dominant frequency values ranged from 0.668 Hz to 18.271 Hz, with higher values prevalent. The soil types in the area were classified as type IV and type I, primarily consisting of older, hard sandy rocks and gravels. Amplification values ranged from 1.03 to 8.36, indicating low amplification levels and placing the area in zone 1. Kg values varied from 0.066 to 15.07 s²/cm, suggesting moderate seismic vulnerability. If an earthquake occurs, the region would experience shaking, though damage would be moderate. Vs30 values ranged from 179.64 m/s to 681.82 m/s, categorizing the soil as hard, dense, soft, or medium.
Site Effect Analysis in Prambanan District and Surroundings Using Shear Wave Velocity and Ellipticity Curve Method from Microtremor Data Rahmania Sofyana Ulya, Rahmania Sofyana Ulya; Adhi, Mochamad Aryono; Budi Wibowo, Nugroho; Desi Mustami Limayukha, Desi Mustami Limayukha; Elsa Fadlika Widyantari, Elsa Fadlika Widyantari; Bilqis El Farsiyyi, Billqis El Farsiyyi; Ilqia Rahma, Ilqia Rahma
Rekayasa Vol. 21 No. 1 (2023)
Publisher : Universitas Negeri Semarang

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.15294/rekayasa.v20i2.9962

Abstract

The shear wave velocity (Vs) is a crucial parameter for determining subsurface layers by averaging the Vs value to a depth of 30 meters, known as Vs30. This study aims to analyze the subsurface soil layers, calculate the Vs30 value, and assess the potential seismic site classifications in Kapanewon Prambanan and its surrounding areas. The research utilizes secondary microtremor data from 27 observation points in the form of MSD files. The microtremor data was processed using Geopsy software with the HVSR method to generate an H/V curve. This curve was further analyzed with the Ellipticity Curve method via Dinver software to obtain the Vs profile at various depths. The findings suggest that the subsurface layers in Kapanewon Prambanan are predominantly composed of hard, very dense soil, soft rocks, and solid rocks, based on the Vs30 values. The Vs30 distribution across the region ranges from 267.857 m/s to 1675.977 m/s, classified into site categories A, B, C, and D. However, the majority of the area falls under site classes B and C. These classifications indicate that the regions under B and C have a relatively lower potential for significant earthquake wave amplification. Nonetheless, attention should still be given to areas categorized under sites D and E, particularly for earthquake disaster mitigation efforts. This detailed Vs30 analysis provides critical insights for seismic assessments, regional planning, and mitigation strategies in Kapanewon Prambanan.
Optimizing Bio-Oil Yield from Pyrolysis of Spent Bleaching Earth for Liquid Fuel Production Okzani, Syahrial; Said, Muhammad; Bahrin, David
Rekayasa Vol. 22 No. 1 (2024)
Publisher : Universitas Negeri Semarang

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.15294/rekayasa.v20i2.10398

Abstract

Spent Bleaching Earth is an industrial waste generated primarily from vegetable oil processing and contains     20-40% oil by weight, which poses a fire hazard due to the risk of spontaneous combustion. Commonly, Spent Bleaching Earth is processed using extraction methods with solvents like n-hexane, methanol, or steam. However, transforming SBE into liquid fuel via pyrolysis remains underexplored. This research aims to convert into liquid fuel through pyrolysis. The process was conducted at 600 °C for 90 min, resulting in pyrolysis oil with a density of 992.8 kg/m³, a viscosity of 31.21 cSt, a calorific value of 40.63 MJ/kg, and a flash point of 36 °C. Additionally, the oil contained 21.18% phenol compounds. The remaining material from the process, including char, constituted 54% of the original spent bleaching earth mass. These results demonstrate the feasibility of using pyrolysis to convert into a valuable liquid fuel, offering a sustainable approach to manage this hazardous industrial waste while producing energy-rich byproducts. This study underscores the potential of pyrolysis as a waste-to-energy solution and a safer alternative to traditional disposal methods for Spent Bleaching Earth.
Impact of Stroke Length Variation on Speed Efficiency in an Authomatic Tofu Extract Filtering Machine Saputro, Danang Dwi; Pangestu, Wahyu Dwi
Rekayasa Vol. 20 No. 2 (2022)
Publisher : Universitas Negeri Semarang

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.15294/rekayasa.v20i2.11941

Abstract

In the tofu industry, especially at the home-scale "Tahu Pak Muhson," production remains largely manual, with traditional filtering methods. To enhance efficiency, a machine was designed to filter tofu juice, incorporating various crankshaft step lengths to optimize performance. This study aims to assess the impact of different step lengths on filtration time, tofu yield, and quality. Using a descriptive experimental research method with a quantitative approach, the independent variable is crankshaft stroke length (140, 200, 260 mm), while dependent variables include filtration time, yield, and tofu quality. The control variable is a consistent 10kg soybean input. Results indicate that a 260mm stroke length provided the quickest filtration, averaging 524.3 s, compared to 726 s for 140mm and 620 seconds for 200 mm. Yield for the 140mm stroke was 46%, 45.5% for 200mm, and 44.5% for 260 mm. Tofu quality showed minimal variation across different lengths, although the 260 mm stroke length produced tofu with a slightly coarser texture and a faster smell development. The findings demonstrate that step length impacts filtering efficiency and yield, with potential implications for tofu production scalability.
Design and Construction of a Leisure Boat Bottom Glass Prototype as An Underwater Panorama Tourism Ride in Karimunjawa Aryadi, Widya; Bahatmaka, Aldias; Karnowo, Karnowo; Rumondang, Juwita Ria; Rumapea, Fedrik Immanuel; Kurniawan, Ahmad Khusom; Kusuma, Anwar Widjaya; Hidayat, Indra Nurul
Rekayasa Vol. 22 No. 1 (2024)
Publisher : Universitas Negeri Semarang

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.15294/rekayasa.v22i1.13881

Abstract

The lack of proper tourism infrastructure often limits the potential of marine ecotourism. In Karimunjawa, coral reef tourism is a major attraction. However, accessibility remains an issue, especially for visitors who cannot swim or dive. This research focuses on the design and construction of a glass-bottom leisure boat prototype to provide a safe and immersive underwater panorama experience. This study falls within naval architecture and marine engineering, addressing the challenge of designing a stable, efficient, and safe tourism vessel. A key concern in ship design is balancing hydrodynamic efficiency with stability. While monohull boats are common, their transverse stability is relatively low. To overcome this, a catamaran hull configuration was chosen for better stability, larger deck space, and reduced resistance. The prototype was constructed with dimensions of 21.81 m in length, 2.63 m in height, and 7.51 m in width, featuring a glass-bottom viewing area to enhance the tourism experience. Hydrodynamic performance analysis showed an average increase in resistance of 12.39307 N as speed increased, demonstrating the vessel’s efficiency. The construction and testing process confirmed that the catamaran hull improves passenger safety, minimizes capsizing risk, and enhances the underwater viewing experience. This research contributes to sustainable marine tourism by introducing an innovative tourism ride that allows visitors to explore the underwater beauty of Karimunjawa without requiring diving skills. The successful design and construction of this prototype provide a model for future eco-aafriendly tourism vessels.
Ultrafiltration Technology for Batik SME Wastewater Treatment: Column-Based Materials with Zippers for Plant Irrigation Water Supply Zakia, Maulida; Mahatmanti, F. Widhi; Wati, Safna Rahma; Rahmalia, Berliana Putri; Rengga, Wara Dyah Pita
Rekayasa Vol. 22 No. 2 (2024)
Publisher : Universitas Negeri Semarang

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.15294/rekayasa.v22i1.17184

Abstract

Textile batik wastewater discharged into drains can contaminate groundwater and harm ecosystems and human health. This study focuses on reducing hazardous heavy metals in sewage through physical and chemical filtration. Heavy metals in the wastewater can poison aquatic organisms, disrupt food chains, and contaminate water sources. The goal is to analyze the heavy metal content, pH, and colour of batik wastewater to make it safe for plant irrigation. The filtration process uses silica sand, activated carbon, and zeolite for mechanical filtration and ion exchange. Ultrafiltration is added to remove fine particles, heavy metals, and organic matter more effectively while resisting fouling. These materials are placed in zipper bags for easy replacement and regeneration. The wastewater passes through a filtration column consisting of two tanks: Tank 1 for fresh wastewater and sedimentation, and Tank 2 for overflow from Tank 1. Tests were conducted for Cr, Cu, Pb, and Zn using AAS, pH with a universal pH meter, and colour through organoleptic analysis. Cr levels initially exceeded quality standards, while Cu, Pb, and Zn were within safe limits. After filtration, reductions of Cr, Cu, Pb, and Zn were 81%, 8%, 22%, and 85%, respectively. The pH decreased from 10–11 to 7–8, and water color improved from murky greenish-brown to clearer. The results demonstrate the potential of ultrafiltration in reducing heavy metals, stabilizing pH, and improving water clarity. Wastewater treated through this process meets safety standards and can be used for plant irrigation.
Evaluation of Effectiveness and Benefits of iRAP and Bina Marga Methods for Road Safety Assessment on the Karanglo-Bts. Kota Batu (Karang Ploso) Segment Devayanti, Shafira; Machsus, Machsus; Khoiri, Mohamad
Rekayasa Vol. 22 No. 1 (2024)
Publisher : Universitas Negeri Semarang

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.15294/rekayasa.v22i1.18056

Abstract

According to Road Safety (2002), traffic accidents result from vehicles, humans, road environments, and their interactions. Addressing these issues is crucial for improving road safety, particularly for operational roads and those under maintenance, to prevent recurring accidents in the same locations. This study examines the effectiveness and benefits of two road safety assessment methods: the iRAP ranking analysis method and the Bina Marga ranking analysis method. The Karanglo–Batu City Border (Karang Ploso) road segment, spanning 7.99 km, was selected as the study area. Both methods analyze five key accident types: roadway departure, head-on collisions due to loss of control or overtaking, intersection accidents, and accidents at property access points. Factors influencing these accidents include probability, severity, operational speed, external traffic, and median traversability, with star ratings assigned based on the Star Rating Score (SRS). The iRAP method, utilizing the iRAP Demonstrator application, yielded an SRS score of 8.92 (3 stars), while the Bina Marga method, using manual calculations as per the Road Environment and Safety Guidelines Number 06/P/BM/2024, produced a score of 7.13 (3 stars). After implementing rehabilitation recommendations, both methods improved the score to 2.78 (4 stars). Effectiveness values were 35.68 for iRAP and 31.69 for Bina Marga, both categorized as effective. Post-improvement, the effectiveness value was 12.36, categorized as very effective. The iRAP method demonstrated higher direct benefits, particularly in data input, sampling, and implementation, making it more suitable for precise safety assessments.

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