Browsing by Author "Alinanuswe J. Mwakalesi"

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Adsorption kinetics of picloram on chitosan‑modified Strychnos pungens fruit shell activated carbon
(Springer, 2025-09) Liberatus J. Mpaka; Alinanuswe J. Mwakalesi
Activated carbon (AC) fabricated using Strychnos pungens fruit shells (biowaste) and encapsulated in a chitosan biopolymer (CHO) was applied for the removal of picloram from aqueous solutions. The synthesized activated carbon-chitosan beads (ACCHO) were characterized using Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), Infrared spectroscopy (IR) and Emmett Teller (BET) surface area analysis. The findings demonstrated the successful encapsulation of AC to produce ACCHO with both crystalline and amorphous properties. The application of ACCHO for picloram removal was affected by solution pH, adsorbent dosage, and initial picloram concentration. The efficiency increased with adsorbent dosage, reaching an optimum at 40 g/L. Similarly, efficiency increased as pH increased from 2 to 6, but declined at pH 8. Optimal conditions of pH 6, 40 g/L ACCHO dosage and 50 mg/L picloram produced 88% removal efficiency. The picloram adsorption kinet- ics best fitted the pseudo-first order (PFO) model. Langmuir and Freundlich adsorp- tion isotherms provide a good description of the picloram adsorption process. The adsorption mechanism on ACCHO was postulated to involve multiple interactions caused by electrostatic and weak forces of attraction. The results of the current study suggest that ACCHO can be used as a potential adsorbent for removing picloram and similar chemicals from contaminated water.
Antimicrobial silver nanoparticles derived from Synadenium glaucescens exhibit significant ecotoxicological impact in waste stabilization ponds
(Springer, 2024-08) Alinanuswe J. Mwakalesi; Douglas Mushi
In recent years, there has been an exponential increase in the production of silver bionanoparticles due to their widespread commercialization and technological applications. However, there is limited understanding of the impact of silver bionano- particles on biological agents commonly used in wastewater treatment, particularly in waste stabilization ponds (WSPs). This study aimed to synthesize new silver nanoparticles (sg-AgNPs) from Synadenium glaucescens root using an environmen- tally friendly method and optimized biosynthesis parameters, and evaluate their antimicrobial activity and ecotoxicological impact on WSPs using standardized approaches. The average primary sizes of the sg-AgNPs in the five samples were not significantly different (P > 0.05), indicating the effectiveness of the eco-friendly method and the importance of optimal biosynthesis conditions. Analysis from UV–Vis spectroscopy, energy-dispersive spectroscopy (EDX), transmission electron microscope (TEM), and X-ray diffraction (XRD) confirmed that sg-AgNPs exhibited typical characteristics of green silver nanoparticles. Furthermore, sg-AgNPs showed strong antimicrobial activity (MIC, 0.012–0.094 mg/ml) against gram-positive bacteria (Escherichia coli), gram-negative bacteria (Staphylococcus aureus), non-filamentous fungi (Candida albicans) and filamentous fungi (Aspergillus niger). While the Synadenium glaucescens root proved to be a valuable precursor for produc- ing effective antimicrobial sg-AgNPs, the introduction of sg-AgNPs into WSPs significantly impacted algal chlorophyll-a production and survival of ostracod population. These results shed light on the ecotoxicological risks of sg-AgNPs for WSPs organisms and highlight the suitability of algae and ostracods as model organisms for ecotoxicological studies in WSPs.
Colorimetric sensing of mercury in aqueous solutions using silver nanoparticles prepared from synadenium glaucescens root aqueous extract
(MDPI, 2023-03) Alinanuswe J. Mwakalesi; Magori J. Nyangi
Mercury contamination from various anthropogenic activities has been a recent global problem. Thus, developing cheap and efﬁcient techniques for sensing mercury is signiﬁcant for protecting humans and other organisms. The sensing of mercury using silver nanoparticles fabricated using phytochemicals extracted from Synadenium glaucescens roots (SYR) is reported. The successful synthesis of silver nanoparticles (SYR-AgNPs) was conﬁrmed by a strong plasmon resonance in the UV-Vis spectrum at 420 nm due to oscillations of electrons in the silver nanoparticles. The potential use of fabricated silver nanoparticles for the sensing of mercury ions from aqueous solutions was investigated. The prepared silver nanoparticles displayed a high selectivity for detecting mercury against other divalent metal ions (Hg2+ , Ba2+ , Ca2+ , Co2+ , Cu2+ , Fe2+ , Mg2+ , Ni2+ , and Pb2+ ). The addition of mercury changed the SYR-AgNPs’ color to colorless, and the observed change in color was proportional to mercury concentration. The application of silver nanoparticles for the sensing of mercury displayed a detection limit of 11.3 µM. Therefore, the ﬁndings in the current study indicate that the prepared SYR-AgNPs can serve as a potentially sensitive and selective readily available method for sensing mercury ions in environmental samples. The method can be useful in advancing the application of green technology for sensing heavy metals from environmental samples.
Green synthesis and characterization of silver nanoparticles from aqueous extract of harrisonia abyssinica fruits
(MDPI - Engineering Proceedings, 2025-03) Alinanuswe J. Mwakalesi; Emmy S. Lema
The synthesis of silver nanoparticles using phytochemical reducing agents is the most preferred technique because of its low cost and environmental friendliness. Conse- quently, there are several reports published on the synthesis of silver nanoparticles using extracts from leaves, barks, roots, and fruit peels. However, information on the use of fruit extracts for the synthesis of silver nanoparticles is limited. Thus, the green synthesis of sil- ver nanoparticles (HAF-AgNPs) using phytochemicals extracted from Harrisonia abyssinica fruit (HAF) is reported in the current study. The silver nanoparticles were synthesized through chemical precipitation and characterized using UV-Vis spectrophotometry, trans- mission electron microscopy (TEM), energy-dispersive X-ray (EDX), and X-ray diffraction analysis (XRD). The ﬁndings showed that fabricated HAF-AgNPs were crystalline and spherical, and exhibited a strong UV-absorption band at 420 nm. The appearance of a peak at 3 keV in the EDX spectrum indicated metallic silver atoms in the fabricated nanoparticles. The fabricated nanoparticles exhibited antibacterial activity against Gram-positive (Staphy- lococcus aureus) and Gram-negative (Escherichia coli) bacterial strains. The antibacterial activity was stronger for Staphylococcus aureus (MIC = 5 µg/mL) compared to Escherichia coli (MIC = 10 µg/mL). The preliminary ﬁndings from the current study suggest that the nanoparticles prepared from the extract could serve as a potential antibacterial agent against Gram-positive and Gram-negative bacteria.
Unexpected heroes: invasive macrophytes boost performance of faltering waste stabilization ponds
(Water Practice & Technology, 2026) Liberatus J. Mpaka; Alinanuswe J. Mwakalesi; Douglas Mushi
Waste stabilization ponds (WSPs) are a widely used technology for removing organic matter and pathogens from wastewater. However, their effectiveness is often hindered by hydraulic overload, sludge accumulation, and the proliferation of invasive macrophytes–the impacts of these challenges are not fully understood. In this study, standard methods were used to assess WSPs under these operational challenges for the removal efﬁciency of physical, nutrient, and organic pollutants, as well as faecal indicator bacteria (FIB); the extent of macrophyte occupancy; and the level of FIB colonizing invasive macrophyte − 3− roots. Results indicated high removal efﬁciencies (73.38–99.67%) for turbidity, total nitrogen, NO− 3 , NO2 , NH3, PO4 , BOD5, total coliforms, Escherichia coli, enterococci, and Clostridium perfringens, whereas total dissolved solids, electrical conductivity, and total phosphorus showed considerably lower removal (33.5–45.2%). Signiﬁcant correlations (r = 0.47–0.96, P < 0.05) were found between the removal efﬁciencies of physical, nutrient, and organic pollutants, as well as FIB, and macrophyte occupancy. Furthermore, high densities of FIB colonizing the macrophyte roots suggest that these roots may have positively contributed to the performance of the WSPs. The ﬁnal efﬂuent complied with East African standards for all pollutants except turbidity, BOD5, and FIB. This study reveals that ignoring WSP maintenance signiﬁcantly compromises treatment performance, with potential implications for public health, and underscores the role of macrophytes in enhancing the performance of faltering WSPs.