Journal of Engineering in Agriculture and the Environment

PERFORMANCE EVALUATION OF A SINGLE STAGE FIXED DOME BIOGAS REACTOR ADAPTED FOR HUMAN WASTE TREATMENT AND BIORESOURCE RECOVERY

2025-06-03T08:13:58+00:00

A performance evaluation of three first generation fixed dome anaerobic reactors installed in Kenya was undertaken to understand emerging design and operational deficiencies and inform design and scheme management improvements. These reactors were designed for decentralized human waste treatment and bio-resources recovery. Scheme management and reactor design configuration were explored while sixteen operating and performance parameters were monitored over 42 weeks using standard wastewater measurement techniques. The study results showed treatment efficiencies ranging from 26% to 51% for physicochemical parameters and 44% to 80% for microbiological indicators. However, effluent quality consistently failed to meet than World Health Organization and Food and Agriculture Organization (WHO/FAO) standards. Notably, Total Suspended Solids (TSS) in the effluent ranged from 1,843 to 2,299 mg/L—substantially higher than typical raw wastewater levels of 155 to 330 mg/L (median ~250 mg/L)—indicating poor solids removal. Chemical Oxygen Demand (COD) levels were between 735 and 2,522 mg/L (higher than WHO limit: ≤250 mg/L), Electrical Conductivity (EC) reached 5,140 µS/cm (WHO/FAO limit: ≤700 µS/cm for unrestricted irrigation), while microbial contaminants E. coli (2,254–2,370 MPN/100 mL) and helminths (31–52 eggs/100 mL) far exceeded limits for restricted irrigation (<1,000 MPN/100 mL and ≤1 egg/L, respectively). Additionally, the microbial log reduction value (LRV) was only 0.3, well below the WHO recommended LRV > 2 for secondary treatment. These findings confirm the reactors’ inadequate pathogen attenuation and pollutant removal, limiting safe effluent reuse. Design flaws that include straight-line inlet-outlet pipe configuration, low hydraulic retention times (2–5 days), and operation under psychrophilic temperatures (27–28 °C resulted in dead zones and poor flow dynamics. Systems that received more diluted influent (e.g., Gachoire) performed slightly better than those handling concentrated waste (e.g., Kibera). Still, none achieved adequate treatment. The computed Treatment Index (TI) values—0.58 (Gachoire), 0.52 (Naivasha), and 0.46 (Kibera)—confirmed the reactors’ inadequacy in reducing both microbial and chemical pollutants. Bioresource recovery potential was however demonstrated, with daily nitrogen recovery of 496.2 kg and biogas production of 60 m³. The findings underscore that single-stage fixed dome systems adapted from livestock applications are inadequately suited for human waste treatment. Advanced modelling, adoption of baffled or hybrid designs and integration of dual-metric performance evaluation (percentage removal and absolute concentrations) are recommended to improve treatment efficiency, ensure safe reuse, and achieve environmental compliance in future deployments.

EFFECT OF DEFICIT IRRIGATION ON THE GROWTH PARAMETERS, YIELD AND WATER USE EFFICIENCY OF COMMON BEANS (PHASEOLUS VULGARIS L) UNDER FOLIAR SELENIUM APPLICATION

2025-10-15T08:55:03+00:00

Water scarcity remains a major constraint to sustainable crop production, particularly in arid and semi-arid regions. This study investigated the effects of foliar selenium (Se) application as water stress management strategy on common bean (Phaseolus vulgaris L.). It assessed growth and water productivity under Deficit Irrigation (DI). A greenhouse experiment was conducted at the Tatton Agricultural Park at Egerton University for one season using a randomized complete block design with three replicates. The experiment consisted of three irrigation regimes;100%, 70%, and 50% of crop evapotranspiration (ET_c) and four selenium concentrations (0, 0.5, 1.0, and 1.5 mg/L). The results revealed that full irrigation 100% ET_c and moderate water deficit at 70% ET_c, combined with foliar application of 1.5 mg/L Se, significantly (p < 0.05) improved growth and yield parameters. Further, water productivity was highest under the 70% ET_c and 1.5 mg/L by Se treatment, suggesting enhanced physiological efficiency and drought resilience. Selenium application mitigated the adverse effects of water stress by supporting plant metabolism, antioxidative defense, and stomatal regulation. Furthermore, the highest total pod yield (13177.8Kg/Ha) was obtained at 100% ETc combined with 1.5mg/L of foliar selenium, but statistically on pair with 70% ETc and 1.5mg/L of selenium concentration compared to the control treatment 100% ET_c and no foliar selenium application (8785.2Kg/Ha), while the lowest pod yield (2288.9Kg/Ha) was attained at 50% ET_c combined with no foliar selenium application. These findings demonstrate that supplying 70% ET_c with 1.5 mg/L of selenium concentration instead of full water requirement can be a good strategic approach to improving water use efficiency and sustaining common bean production under limited water availability. The study provides valuable insight for developing climate-smart irrigation practices thus contributing to sustainable water management.

SENSOR BASED CHARACTERIZATION OF SOIL PROPERTIES FOR SUNDARBAN

2025-10-15T09:39:45+00:00

Sensor-based characterization of soil properties is inevitable due to the tedious, expensive, and time-consuming nature of traditional laboratory-based soil testing. This study focused on characterizing the soil properties of Indian Sundarban at depths of 0cm–20cm, 20cm–50cm, and 50cm–100cm using a PXRF, a Nix Pro color sensor, and a USB soil microscope. The soil samples belonged to mudflats in the intertidal zone and abandoned shrimp ponds. The soil samples were analyzed via Wet Digestion and Dry combustion for organic carbon (OC), total carbon (TC), and bulk density (BD). The average OC, TC, and BD at 0cm–20cm were 7.69 t/ha, 8.74 t/ha, and 1150 kg/m³, respectively. At 20cm–50cm, it was 11.73 t/ha, 13.08 t/ha, and 1239 kg/m³, respectively; 17.733 t/ha, 20.083 t/ha, and 1196 kg/m³, respectively, at 50cm–100cm. Modeling of OC, TC, and BD via multiple linear regressions was validated using R² and RMSE. PXRF produced satisfactory results, with BD (R² = 0.928; 0.9431; 0.998), SOC (R² = 0.9785; 0.9297; 0.9726), and TC (R² = 0.9938; 0.9619; 0.987). The Nix Pro color sensor with RGB, CIEL*A*b, and CMYK color spaces BD (R² = 0.3769; 0.4786; 0.3894), SOC (R² = 0.649; 0.3029; 0.4314), and TC (R² = 0.4932; 0.2603; 0.5518). USB microscope with RGB color space underperformed, while similar performance sequence was observed using RMSE. Also, soil data was spatially analyzed to assess variability across three depths.

EMPLOYING BINARY LOGISTIC REGRESSION ANALYSIS TO MODEL THE EFFECT OF DIFFERENT TREATMENTS ON QUALITY OF FRENCH BEANS (PHASEOLUS VULGARIS) PRODUCE

2025-10-15T10:48:07+00:00

French beans (Phaseolus vulgaris L.) is a significant agricultural product in developing countries, contributing to economic development, employment, and exports. Despite extensive research on French bean farming in Kenya, limited attention has been given to factors influencing produce quality. This study employed a binary logistic regression model to evaluate the effect of slope, soil deposition, and different mulching materials: Farmers’ Practice (no mulch), polymer mulch, tea leaves mulch, and grass mulch on French bean quality in Ol’ Lessos Ward, Nandi Hills Sub-County, Kenya. Quality was defined as the absence of disease incidence. Field experiments measured slope percentage, soil deposition (g), yield (kg/plant), and disease incidence across treatments. Results revealed that slope alone had no significant effect on quality, but mulching significantly reduced soil deposition, increased yield, and lowered disease incidence compared to Farmers’ Practice. Polymer mulch recorded the highest yields and lowest soil deposits, while tea leaves and grass mulches also improved performance. Logistic regression analysis yielded a Cox and Snell’s R²was 0.14 and Nagelkerke’s R²was 0.63 and the Nagelkerke R² which adjusts Cox and Snell’s value to a scale ranging from 0 to 1 was 0.628, suggested that the model had a strong explanatory power and a good overall fit. The findings underscore the critical role of mulching materials in enhancing French bean quality, independent of slope effects. Adoption of mulching, particularly polymer mulch, is recommended for sustainable production and improved marketability.

ENGINEERING ACCESSIBILITY IN NAIROBI CITY BY ROAD TRANSPORT INFRASTRUCTURE IN THE FACE OF CLIMATE CHANGE DILEMMA

2025-10-15T11:32:44+00:00

Globally, climate change continues to present a monumental dilemma in all sectors of the economy. In the urban road transport system, it has become a norm that short distances between places end up consuming longer hours of travel by motorists on rainy days. This prolongation of travel time is occasioned by flooding risks. This makes places inaccessible. Accordingly, this study aimed at improving the accessibility of Nairobi city neighborhoods during wet weather. This informs the reason for use of the term, “engineering accessibility” which simply means to reduce travel time during wet weather between destinations. The study leverages the theory of infrastructure resilience in an attempt to extract developmental data in terms of mapping in the GIS Software environment, the incremental strides in road network lengths and tracing the incremental building footprints over the time scales covering years; 2000,2010,2020 and 2024.Secondly, rainfall data was sourced from KMD open source database that assisted in the development of flood map profile over the same time scale in HEC-RAS software. In the year 2000, built up area covered,50km squared, and the road network totaled 9630km.The worst flood depth recorded around Ojijo road in the period was 0.63m.In 2024,built up area was 83km²,road length was 14,720 and the flood depth at the same location was 1.83.This was the worst as exhibited in figure 3.In conclusion, the study has highlighted the need to mainstream resilience in storm water drainage system by deploying a continuous action plans.