School of Natural Sciences

INVESTIGATION OF THE OCCURRENCE, BIOSORPTION, AND PHYTOREMEDIATION OF SELECTED ENDOCRINE DISRUPTING CHEMICALS FROM WASTEWATER USING MORINGA OLEIFERA AND EICHHORNIA CRASSIPES

2026-07-09T10:08:34Z

INVESTIGATION OF THE OCCURRENCE, BIOSORPTION, AND PHYTOREMEDIATION OF SELECTED ENDOCRINE DISRUPTING CHEMICALS FROM WASTEWATER USING MORINGA OLEIFERA AND EICHHORNIA CRASSIPES Ngeno, Emily Chelangat Endocrine disrupting chemicals (EDCs) cause adverse health effects to biota. They are not effectively removed by conventional wastewater treatment options and advanced methods are costly. This study investigated the levels, mass loadings, removal efficiency, and associated ecotoxicological risks of selected EDCs, namely, dibutyl phthalate (DBP), diethylhexyl phthalate (DEHP), dimethyl phthalate (DMP), linuron (LNR) and progesterone (PGT) in wastewater, sludge, and untreated dry biosolid (UDBS) samples from twelve wastewater treatment plants (WWTPs) in nine major towns in Kenya. Analysis was done using high-performance liquid chromatography coupled with triple quadrupole mass spectrometry (HPLC-MS/MS). All the wastewater influents had quantifiable levels of EDCs with DBP being the most abundant (37.5%) with a mean range of 4.3 ̶ 9.7 μg L-1. DEHP was the most abundant in sludge and accounted for 48.2% ranging between 278.7 and 9243.5 ng g-1 dry weight (dw). In the UDBS samples, DEHP was also the most abundant (40%) of the total EDCs detected with levels ranging from 78.8 ̶ 3938.5 ng g-1 dw. The average removal efficiency per pollutant was as follows: DMP (98.7%) > DEHP (91.7%) > PGT (88.3%) > DBP (77.9%) > LNR (72.2%). The mass loadings were as high as 373.3 g day-1 of DBP in WWTPs in densely populated cities. DEHP and PGT had their Risk Quotients (RQs) > 1, posing a high risk to biota. DMP, DBP, and LNR posed medium risks as their RQ values were between 0.1 and 1. Removal of these toxicants was carried out via adsorption using chemically activated fat-free powdered Moringa oleifera seed biomass (MOSB) which was pretreated, characterized, and used as a low-cost biosorbent for the abstraction of PGT and LNR from synthetic wastewater. The process parameters, contact time, pH, adsorbate concentration, temperature, and adsorbent dosage were set and optimized using central composite design (CCD) and response surface methodology (RSM) in Design Expert Software. For biosorption of both PGT and LNR, the proposed model was quadratic. The optimum parameters for PGT adsorption to MOSB were: 86.8 min, 500 µg L-1 adsorbate concentration, 298 K and 0.1 g adsorbent dosage while for LNR were: 154 min, 500 µg L-1 adsorbate concentration, 298K and 0.1 g adsorbent dosage. pH was not a significant factor in the removal of both PGT and LNR. The kinetics, isotherms, and thermodynamics were analyzed further using OriginPro. The equilibrium data were best described by the Langmuir isotherm for PGT and Sips model for LNR, with maximum monolayer adsorption capacities of 135.8 µg g-1 and 144.0 µg g-1, respectively. Adsorption kinetics followed pseudo-first order (PFO) for PGT and pseudo-second order (PSO) for LNR predicting physisorption and chemisorption rate-determining steps, respectively. The thermodynamics functions (PGT: ΔG < 0, ΔH = -9.3 kJ mol-1 and ΔS = +44.2 J mol-1 and LNR: ΔG < 0, ΔH = -10.3 kJ mol-1 and ΔS = +41.5 J mol-1) confirmed that the adsorption of PGT and LNR onto MOSB was a spontaneous and exothermic process with randomness and affinity experienced at the surface of the adsorbent. The adsorption mechanism was non-electrostatic and may have involved π-π interactions. The results from this study show that the MOSB is a promising alternative for an ecofriendly, low-cost biosorbent that can effectively remove PGT and LNR from aqueous solutions. Phytoremediation of LNR and PGT using Eichhornia crassipes was also carried out. The concentrations of EDCs abstracted using phytoremediation were however below the quantification levels.

STOCHASTICMODELLINGOFPREDATOR-PREYDYNAMICSINA THREE-PATCHECOSYSTEMWITHOPTIMALHARVESTING

2026-04-16T13:16:40Z

STOCHASTICMODELLINGOFPREDATOR-PREYDYNAMICSINA THREE-PATCHECOSYSTEMWITHOPTIMALHARVESTING Mayabi, Lucian Talu Predator-prey interactions play a pivotal role in shaping ecological dynamics, and understand ing these interactions is critical for sustainable resource management and effective conservation. Existing literature predominantly focused on deterministic models incorporating optimum har vesting policy involving two ecosystems or less. Moreover, while stochastic models had been employed to account for randomness and uncertainty in ecological interactions, these studies were often limited to single-patch ecosystems. The stochastic dynamics of predator prey models involving more than two ecosystems had been given little attention in literature yet they are crit ical in conservation and resource management. Therefore, this research developed a stochastic predator-prey model with optimum harvesting for three patches namely “cages” which are within a lake, containing a predator-prey system involving large Nile perch as predators and smaller fish as prey. The dynamics of the prey population could transfer from one cage to the other. The study aims to investigate how randomness and harvesting controls affect population stability and sus tainability. Stability analysis of the deterministic part was carried out in order to study the long term behaviour of solutions around equilibrium points. Stability analysis of the stochastic model was done using stochastic Lyapunov function method assessing its impact on the system dynam ics. Numerical analysis was done to explain the analytic approach. From the results, when ei < 1 (ei is the predator’s efficiency in converting prey into a new predator), the lyapunov function, V(t), stays bounded indicating stochastic stability, and when ei > 1, V(t) grows without bound indicating that the system is unstable. An optimal control problem was formulated to derive harvesting functions that maximize resource utility while maintaining a sustainable ecosystem employing the Pontryagin’s Maximum Principle. From Numerical simulation, prey populations remained viable when the harvesting rates were maintained below ν1 = 0.02, ν2 = 0.02, and ν3 =0.02, and noise intensities were controlled at σ = 0.10, and σ = 0.90. The findings high light the impact of human activities, particularly harvesting, on ecosystem balance. They also contribute to conservation biology, fisheries management, and mathematical ecology, providing insights for sustainable resource management and effective conservation strategies.

THE STRUCTURES OF MATRICES AND INDICES OF ZERO DIVISOR GRAPHS OF 3,4-RADICAL ZERO COMPLETELY PRIMARY FINITE RINGS

2026-04-16T13:14:33Z

THE STRUCTURES OF MATRICES AND INDICES OF ZERO DIVISOR GRAPHS OF 3,4-RADICAL ZERO COMPLETELY PRIMARY FINITE RINGS Ndago, Frank Omondi A zero divisor graph of the ring R is a graph whose vertices are entirely from the set of zero divisors of the ring and two vertices of the graph are adjacent if and only if their product is zero. The study of zero divisor graphs is important for it provides a better way of relating graph geometry to matrix conformations and formulation of encryption algorithms in coding therefore fundamental in interpretation of patterns, maps and networks in computer programs and modelling. Reasonable research has been done concerning zero divisor graphs of commutative rings with identity 1 ̸ = 0, however the generalization of the structures of the matrices of zero divisor graphs is still not extensive in the existing literature. Much of the recent works on zero divisor graphs of finite commutative rings have been restricted to the algebraic properties of the graphs such as colouring, girth, spectral radii and classification in terms of their completeness up to isomorphism. This has left the characterization of finite commutative rings via the structures of the matrices and indices of their graphs fairly untouched. In particular, matrices and indices of the zero divisor graph Γ(R) of finite commutative rings of 3-radical zero and 4-radical zero have not been characterized. This research has determined and investigated the properties of the matrices and indices of Γ(R) of finite rings R with unique maximal ideal J(R) such that J(R)3 = (0) and J(R)2 ̸ = (0); J(R)4 = (0) and J(R)3 ̸ = (0). It has also established the singularity and the relationship that exist between the eigenvalue multiplicities in the spectrum to the nullity of the graphs. We have validated the construction of these classes of rings using idealization procedure and the zero divisor graphs drawn from the isolated zero divisors using the Tikz Software. The matrices have been formulated from the graphs using standard definitions and the Mathematica software applied in investigating some of their algebraic properties. The results of this study can find an application to networking such as Google PageRank algorithms, developing more improved codes for better graph interpretation in operation systems. It will also advance the ring classification problem by revealing the interplay between ring theory, graph theory and linear algebra therefore contributing fundamentally to the literature of advanced algebra

SYNCHROTRON-BASEDIN-SITUANDEX-SITUINVESTIGATIONOF PEROVSKITEFORPHOTOVOLTAICAPPLICATIONS

2026-04-16T13:10:27Z

SYNCHROTRON-BASEDIN-SITUANDEX-SITUINVESTIGATIONOF PEROVSKITEFORPHOTOVOLTAICAPPLICATIONS Shatsala, Elly Miller The advancement of perovskite-based optoelectronic devices hinges on overcoming their intrinsic instability challenges. Synchrotron-based techniques have been widely employed to characterize various materials, including the structural and interactive properties of perovskite crystals and their complexes, using ex situ, in situ, and operando approaches. Grazing Incidence Wide-Angle X-ray Scattering (GIWAXS) and Small Angle X-ray Scattering (GISAXS) studies have revealed inherent crystal peaks in perovskite films through both in situ and ex situ methods. This thesis investigates the crystallization dynamics, humidity resilience, and defect passivation strategies of triple cation (Cs₀.₀₅(FA₀.₈₃MA₀.₁₇)₀.₉₅Pb(I₀.₈₃Br₀.₁₇)₃) perovskite thin films, along with co passivation strategies applied to Cs₀.₁FA₀.₉PbI₃ using phenylethylammonium chloride (PEACl) and 2,8-Bis(diphenylphosphoryl)dibenzo[b,d]furan (PPF), aiming to enhance structural, optical, and electronic properties for efficient photovoltaic applications. A comprehensive experimental approach was adopted, combining solvent engineering, anti-solvent optimization, and co-passivation strategies. Film fabrication and degradation behaviors were characterized using synchrotron-based in situ and ex situ GIWAXS techniques, micro-X-ray diffraction (μ-XRD), photoluminescence (PL) spectroscopy, UV-Vis absorption spectroscopy, Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray Spectroscopy (EDS) for detailed analysis. Results reveal that 5% cesium incorporation into triple cation perovskites yields superior crystal structures, minimizing δ-perovskite phase and PbI₂ formation while enhancing humidity resistance. Solvent treatments, particularly with ethyl acetate (EA) and chlorobenzene (CB), influenced grain size, surface morphology, and film smoothness. Co-passivation of Cs₀.₁FA₀.₉PbI₃ with PEACl and PPF slowed crystallization kinetics, regulated grain orientation, suppressed non-radiative recombination centers, and stabilized the thermodynamically favorable α-perovskite phase. GIWAXS data confirmed the evolution of highly oriented 2D/3D mixed-phase architectures with enhanced c-axis unit cell alignment. Surface and elemental analysis demonstrated uniform passivant distribution, stronger Pb–O bonding, and reduced ion migration pathways. Photo-physical studies showed narrowed PL peaks, bandgap tuning, and reduced trap densities. This work establishes a strategic framework for achieving high-quality, stable perovskite films, laying the foundation for fabricating full solar modules at MMUST Materials Research Laboratory. The outcomes also pave the way for future collaborations, contributing toward the commercialization of perovskite photovoltaics with power conversion efficiencies exceeding 40%. Additionally, ongoing work involving robot automation and Machine Learning for high-throughput experiments at the Advanced Light Source, along with the development of a new multimodal spin-coater design to eliminate overheating and mechanical wobbles, is expected to further enhance beamline studies for perovskite, polymer, and battery research.