Tropical Environment, Biology, and Technology

Sustainable Concrete Production through Partial Cement Replacement Using Fly Ash and Rice Husk Ash

Thu, 29 Jan 2026 00:00:00 +0000

This study explores the utilization of fly ash and rice husk ash as supplementary cementitious materials to partially replace ordinary Portland cement (OPC) in concrete production. The increasing environmental impact of cement manufacturing, particularly its contribution to carbon dioxide emissions, has driven the search for alternative materials that promote sustainability without compromising performance. Fly ash and rice husk ash, both industrial and agricultural by-products, possess pozzolanic properties that enhance the mechanical and durability characteristics of concrete when properly incorporated. This paper reviews their chemical composition, particle morphology, and the effects of replacement levels on compressive strength, workability, and long-term durability. Additionally, the study discusses challenges such as variability in ash quality, optimal replacement percentages, and curing conditions that influence performance outcomes. By integrating these waste materials into concrete, significant environmental and economic benefits can be achieved, including reduced landfill disposal, conservation of natural resources, and lower greenhouse gas emissions. The findings highlight the potential of fly ash and rice husk ash as sustainable cement substitutes, supporting the development of eco-friendly construction materials aligned with green building standards and circular economy principles. This research contributes to advancing sustainable practices in the construction industry and provides insights for future studies focused on optimizing mix design, performance enhancement, and large-scale application of alternative cementitious materials.

Long-term Evaluation of Constructed Wetland Efficiency for Domestic Wastewater Treatment under Temperate Climatic Conditions in Beijing, China

Zeyuan Liu, Le Hien, Le Duc Anh Tuan, Nguyen Thi Xuyen — Tue, 09 Jun 2026 00:00:00 +0000

This study evaluated the long-term performance of a constructed wetland (CW) system for domestic wastewater treatment under temperate climatic conditions in Beijing, China. The system, with a capacity of 400 m³/day serving approximately 3,500 people, was monitored over four years. The results showed stable treatment performance, with average effluent concentrations of COD 30.04 ± 8.49 mg/l, BOD₅ 10.53 ± 3.12 mg/l, TSS 8.87 ± 3.38 mg/l, TN 12.34 ± 2.88 mg/l, TP 0.54 ± 0.16 mg/l, and NH₄⁺ 4.85 ± 1.15 mg/l, all meeting the Chinese discharge standard GB 18918-2002 (Level IB). Removal efficiencies were higher for organic matter and TSS (up to 76.49% and 84.52% in summer) than for nutrients (TN 66.62%, TP 55.61%, NH₄⁺ 49.68%). Seasonal variation significantly affected performance, with winter efficiencies decreasing to 57.87% (COD) and 41.50% (NH₄⁺). Correlation analysis indicated that temperature was the dominant factor (r = 0.637–0.638, p < 0.01), while influent characteristics had moderate effects (r = 0.405–0.479). These results demonstrate that CW systems provide a stable and effective solution for decentralized wastewater treatment, although optimization is required to improve performance under low-temperature conditions.

Evaluation of Rural Domestic Wastewater Treatment Using a Hybrid Constructed Wetland with Three Flow Configurations

Xiaojuan Feng, Xingjie Wang, Bui Thi Van Nga, Nguyen Thi Xuyen — Mon, 25 May 2026 00:00:00 +0000

This study evaluated the performance of a hybrid constructed wetland (CW) system consisting of horizontal subsurface flow (HF), vertical subsurface flow (VF), and free water surface (FWS) units for domestic wastewater treatment under rural conditions. The system was operated at two hydraulic loading rates (HLR) of 5 and 10 cm/day to assess treatment efficiency under different operational scenarios. Results showed high removal efficiencies for organic matter and nitrogen, with average BOD₅ and NH₄⁺-N removal reaching approximately 82.6–84.8% and 85.7–88.2%, respectively. Total suspended solids (TSS) removal ranged from 67.1% to 83.8%, while total coliform removal exceeded 98%. However, phosphorus removal remained low and unstable (14.2–17.2%), indicating the need for improved substrate materials. The performance of HF units varied depending on plant species, with Caladium bicolor demonstrating superior BOD₅ removal efficiency. The integration of HF and VF units, combined with intermittent feeding, enhanced nitrification–denitrification processes and improved nitrogen removal. Overall, the study demonstrated that the hybrid CW system was an effective, low-cost, and sustainable solution for domestic wastewater treatment in rural areas without requiring recirculation.

Comparison of Piggery Wastewater Treatment after the Biogas Process by Cyperus alternifolius and Ipomoea aquatica in a Vertical Subsurface Flow Constructed Wetland System in Vietnam

Bui Thi Van Nga, Chao Rong — Wed, 25 Feb 2026 00:00:00 +0000

Vertical subsurface flow constructed wetlands (VSF CWs) have been widely applied as an eco-friendly solution for treating livestock wastewater. This study compared the treatment performance of Cyperus alternifolius and Ipomoea aquatica planted in VSF CWs treating piggery wastewater after biogas digestion. Two laboratory-scale VSF CW systems (50 × 50 × 50 cm) with identical media configuration and operational conditions were operated in an intermittent mode with a hydraulic retention time of 3 days over 20 treatment cycles. The VSF CW planted with C. alternifolius consistently exhibited higher removal efficiencies for all monitored parameters compared with the system planted with I. aquatica (p < 0.05). The average removal efficiencies of the papyrus-based system reached 74.2 ± 3.1% for COD, 85.8 ± 3.4% for TSS, 70.9 ± 4.1% for TN, 75.1 ± 5.5% for NH₄⁺–N, and 64.7 ± 7.9% for TP, with most effluent concentrations complying with the Vietnamese discharge standard QCVN 62:2025/BTNMT (Column B). In contrast, the VSF CW planted with water spinach achieved lower treatment efficiencies, with average removal rates of 53.9 ± 2.6% for COD, 80.5 ± 5.6% for TSS, 54.6 ± 5.6% for TN, 57.0 ± 8.6% for NH₄⁺–N, and 44.5 ± 13.1% for TP, and did not consistently meet discharge limits for nitrogen and phosphorus.

Vulnerability Assessment of Rodriguez, Rizal towards the development of a Community-Engaged Flood Risk Management System

Jeffrey Bancifra — Fri, 12 Jun 2026 00:00:00 +0000

Rodriguez (Montalban), a municipality in the Philippines located on the southern slope of the Sierra Madre Mountain Range, is characterized by predominantly mountainous terrain, with approximately 83% of its land consisting of uplands, hills, and steep slopes. Despite these extensive upland areas, most urbanized zones are situated in flood-prone locations. Climate change has further exacerbated flood risks by increasing the intensity and frequency of precipitation events. This study assessed the vulnerability of communities in selected barangays of Rodriguez, Rizal, using a combination of Geographic Information System (GIS) mapping, the Hydrologic Engineering Center’s River Analysis System (HEC-RAS), surveys, and Key Informant Interviews (KIIs), alongside considerations of social engagement and the thematic areas of the National Disaster Risk Reduction and Management Framework (NDRRMF). The findings indicate that Rodriguez exhibits a moderate level of flood vulnerability, with flood risk management measures being predominantly reactive rather than preventive. Residents identified deforestation, particularly quarrying activities, as the primary contributor to flooding, whereas the Local Government Unit (LGU) identified urbanization as the main driver. However, these perspectives are not mutually exclusive. Furthermore, HEC-RAS simulations revealed that areas with steeper slopes and locations adjacent to deforested zones experience higher flood velocities than other parts of the floodplain. Motivations for community engagement in flood risk management were largely influenced by perceptions of good governance (35.57%) and shared values (33.08%), while financial incentives for key volunteers were found to have only a marginal influence (12.31%). Based on these findings, the study developed the FLOOD GATES (Flood Governance Anchored in Transparency and Engaged Society) System, a community-engaged flood risk management model designed for mainstreaming within LGUs. By integrating technical hydrological data with community-generated inputs, the FLOOD GATES System facilitates proactive participation across all phases of flood risk management, including prevention, mitigation, preparedness, response, and rehabilitation. The model also enhances adaptive capacity by promoting transparency, accountability, and community empowerment.

Epiphytic Biomass And Chlorophyll-a Concentration – Relations In Seagrass Leaves Enhalus acoroides In Sanur Waters, Bali

Mon, 20 Apr 2026 00:00:00 +0000

Seagrass beds are important coastal ecosystems that functioned as primary producers and habitats for various marine biota; however, their persistence was vulnerable to environmental pressures. One of these pressures was the increase in epiphytic biomass on seagrass leaves, which had the potential to inhibit photosynthesis. This study aimed to assess the condition of Enhalus acoroides seagrass cover and to analyze the relationship between epiphyte biomass and chlorophyll-a concentration in seagrass leaves in the waters of Sanur, Bali. This study was based on seagrass ecological theory, the role of epiphytes, and chlorophyll-a as an indicator of seagrass physiology and productivity. The research methods included field observations using line transects and quadrats, measurement of seagrass cover, analysis of chlorophyll-a in seagrass leaves using spectrophotometric methods, and calculation of epiphyte biomass using gravimetric methods. The results showed that Enhalus acoroides seagrass cover in Sanur waters was classified as moderate to dense, with water quality conditions that still supported seagrass growth. The relationship between epiphyte biomass and chlorophyll-a concentration indicated a weak negative correlation, in which an increase in epiphyte biomass tended to be followed by a decrease in chlorophyll-a. The findings of this study indicated that epiphytes had the potential to reduce the photosynthetic efficiency of seagrass, although their influence was also affected by local environmental factors.