Browsing by Author "John Chagu"

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Effects of phosphoric acid concentration on properties of activated carbon from Strychnos spinose fruit shells
(Nature, 2026) John Chagu; Alinanuswe Joel Mwakalesi
The accumulation of agricultural wastes in the environment is an emerging challenge. Their thermochemical conversion to activated carbon represents an efficient form of utilization that minimizes the secondary pollution caused by conventional treatment methods, such as incineration and landfilling. This study reports the synthesis and characterization of activated carbon from an affordable, abundant, and underutilized source of Strychnos spinosa fruit shells. The activated carbon was prepared through chemical activation using phosphoric acid of different concentrations (30%, 60%, 100%, and 150%), followed by physical activation at 500 °C for 4 h. The influence of the activating agent concentrations on the properties of activated carbon, such as yield, moisture content, ash content and iodine number, was studied. Additionally, X-ray diffraction, scanning electron microscopy, Brunauer–Emmett–Teller and Infrared spectroscopy techniques were used to study characteristics of activated carbon. The results showed that the yield of activated carbon increased from 25.33% to 29.2% as the concentration of phosphoric acid increased from 30% to 150%. The increased acid concentration also increased the moisture content, ash content and iodine number of the activated carbon. The highest iodine number of 999 mg/g was obtained for the activated carbon with the surface area of 507.373 m²/g impregnated with 150% phosphoric acid. Similarly, the SEM images revealed larger pore sizes for activated carbon produced using 150% phosphoric acid compared to those produced using 30%, 60% and 100% phosphoric acid. The findings demonstrate that phosphoric acid concentration influences the properties and performance of the Strychnos spinosa fruit shell activated carbon.
Unveiling the hidden risks: heavy metal concentrations in soil and vegetables irrigated with Kalobe wastewater stabilization ponds, Mbeya, Tanzania
(Journal of Food Protection, 2025-10) Azaria Stephano Lameck; Dickson Mlelwa; John Chagu; Victor Sanga; Melkizedeck Hiiti Tsere; Gisandu K. Malunguja; Alinanuswe Joel Mwakalesi
This study evaluated the concentrations of heavy metals in wastewater, soil, and tomatoes and Napa cabbage irrigated with efuent from the Kalobe Wastewater Stabilization Pond (KWWSP) in Mbeya, Tanzania. Human health risks were assessed using Chronic Daily Intake (CDI), Target Hazard Quotient (THQ), Hazard Index (HI), and Target Cancer Risk (TCR) indices. The results showed that cadmium (Cd) in all ponds was below the FAO/ WHO permissible limits, while lead (Pb) and chromium (Cr) were below detection levels. Heavy metals in soil were found in the order of Pb (5.95 mg/kg) > Cr (0.63 mg/kg) > Cd (0.25 mg/kg), all within FAO/WHO acceptable limits, indicating suitability for agricultural use. Cd levels in Tomatoes (0.14 mg/kg) and Napa cab- bage (0.40 mg/kg) exceeded permissible limits. Cr levels in the Tomato and Napa Cabbage were 1.87 and 2.10 mg/kg, respectively, and were close to the safety threshold, suggesting health concerns with long-term consumption. Cd exposure through vegetable intake was within but near acceptable limits, while Cr exposure, particularly for Napa cabbage, exceeded recommended safety thresholds. This resulted in elevated noncarcino- genic risks (THQ and HI > 1) and carcinogenic risks (TCR above the USEPA’s acceptable range). These ndings suggest that consuming wastewater-irrigated Tomatoes and Napa cabbage may pose human health risks. Continuous monitoring of heavy metals, safe irrigation alternatives, and cropping restrictions using inade- quately treated wastewater is essential to safeguard public health and long-term environmental sustainability.