Browsing by Author "Douglas Mushi"

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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.
Commiphora swynnertonii-derived silver nanoparticles significantly enhance the selectivity of the medium for isolating fungal species
(Springer, 2026-02) Celina Ntibigwahake; Alinanuswe Mwakalesi; Eliapenda Elisante Mariki; Douglas Mushi
Silver nanoparticles (Ag-NPs) were synthesized using an eco-friendly and economically feasible procedure from the root bark of the medicinal plant Commiphora swynnertonii, with optimized physicochemical variables in the reaction medium. The formation of Ag-NPs was visually monitored by a color change in the reaction mixture and confirmed by various analyses, including UV-Vis spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The synthesized Ag-NPs were tested for their antimicrobial properties and applied to enhance the detection and selective isolation of fungal species on potato dextrose agar (PDA). The optimal synthesis conditions for Ag-NPs were found to be at 60 °C, pH 9, 0.004 M AgNO₃, 40 mL of C. swynnertonii root bark extract, and a reaction time of 10 min. Under these conditions, the Ag-NPs exhibited a maximum absorption peak at 413 nm, spherical shapes, and an average size of 40 ± 15 nm. EDX analysis confirmed the presence of a substantial amount of silver in the synthesized nanoparticles, while FT-IR analysis identified functional groups on their surfaces derived from the root bark of C. swynnertonii. The Ag-NPs demonstrated enhanced antimicrobial activity against Gram-positive and Gram-negative bacteria (MIC, 0.058 mg/mL) compared to filamentous and non-filamentous fungi (MIC, 0.116 mg/mL). PDA without Ag-NPs supported bacterial and fungal growth, whereas PDA with Ag-NPs completely inhibited bacterial outgrowth while permitting fungal outgrowth. This study underscores the potential of C. swynnertonii root bark extract for synthesizing antimicrobial Ag-NPs with applications in controlling pathogenic bacteria and improving the detection sensitivity and selectivity of fungal growth media, particularly PDA.
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.