Browsing by Author "Molalign Emirie Hailu"

Now showing 1 - 1 of 1
  • No Thumbnail Available
    Item
    Advanced Oxidation Process–Driven Degradation of Selected Emerging Contaminants in Wastewater Using Titanium Oxide- Based Photocatalytic Nanocomposite Materials
    (Addis Ababa University, 2026-02) Molalign Emirie Hailu; Zebene Kiflie; Shimelis Kebede (Co-Advisor)
    Wastewater treatment plants are increasingly recognised as secondary sources of emerging contaminants due to the limitations of conventional treatment technologies. This study assessed the physicochemical characteristics of influent and effluent from the Kality Municipal Wastewater Treatment Plant (KMWWTP) in Ethiopia and evaluated its performance in removing nutrients, heavy metals, and selected pharmaceuticals. Influent and effluent analyses were conducted following APHA standard methods, while heavy metals were quantified using ICP-MS. The plant demonstrated partial compliance with the WHO and USEPA standards, with low removal efficiencies for total nitrogen, total phosphorus, and several heavy metals. Notably, concentrations of Ni, Cd, Pb, and As increased after treatment. Pharmaceuticals detected in the effluent using LC-MS/MS - including amoxicillin (2.54 μg L⁻¹), ciprofloxacin (2.43 μg L⁻¹), ibuprofen (8.21 μg L⁻¹), carbamazepine (0.82 μg L⁻¹), and caffeine (1.24 μg L⁻¹)-confirmed the persistence of emerging contaminants in treated wastewater. To address these challenges, a visible light–active triple KBN–doped TiO2 nano photocatalyst was synthesised via the sol–gel method and optimised operation parameters using the Box–Behnken design (BBD). Boron (B) – to titanium (Ti) molar ratio, calcination temperature, and calcination time were selected as synthesis variables, while potassium (K) and nitrogen (N) doping ratios were kept constant at 2%K and 5%N, respectively. Characterisation using XRD, FTIR, BET, SEM-EDX, XPS, and UV-Vis revealed that calcination temperature and boron doping concentration significantly influenced the crystallinity, surface area, electron transfer properties, and photocatalytic activities of the materials. The optimised photocatalyst achieved a surface area of 66.48 m2 g-1 and 84.3% ciprofloxacin (CIP) degradation, with the quadratic regression models showing high predictive accuracy (R2 > 0.98). Building on this optimisation, a novel KNB@TiO2@rGO nano photocatalytic composite was synthesised through sol–gel processing, followed by hydrothermal deposition of TiO2 nanoparticles on reduced graphene oxide. Comprehensive characterisation, including XRD, FTIR, XPS, SEM-EDS, UV–Vis, and photoluminescence (PL), confirmed successful composite formation with enhanced charge separation efficiency. The composite achieved 99.21% CIP degradation and 75.09% total organic carbon (TOC) removal under visible light (950 W m⁻²). The influence of co-existing ions showed mild inhibition by Mg2+ and Ca2+, enhancement by Cl⁻, NO3⁻, and HCO3⁻ and suppression by SO42-, PO43- and humic acid (HA). Electron spin resonance and radical scavenging tests confirmed the formation of •OH, O2•-, and 1O2 reactive oxygen species, and using UPLC – MS/MS identified the intermediate byproducts and proposed the plausible degradation reaction pathways To further enhance performance, peroxymonosulfate (PMS) activation was integrated with the photocatalytic process, forming the KBN@TiO2@rGO/PMS system. This ternary system achieved complete (100%) CIP degradation and 74.23% TOC removal within 90 minutes, outperforming TiO2/PMS and pristine TiO2. The improved activity was attributed to synergistic effects from ternary (K, B, N) doping, rGO-mediated electron transfer, and PMS activation, which collectively promoted the generation of both radical (•OH, O2•-, SO4•-) and non-radical (1O2) species. Response Surface Methodology optimised operational conditions (pH 8.17, 101.2 min reaction time, 0.13 g L⁻¹ catalyst, and 9.99 mg L⁻¹ CIP), predicting 100% CIP degradation and 75.91% TOC removal with 100% desirability. Overall, this work highlights the inadequacy of conventional wastewater treatment plants for removing persistent pollutants in Kality municipal wastewater treatment plant effluents and demonstrates the strong potential of advanced photocatalytic systems, particularly the KBN@TiO2@rGO/PMS composite, for efficient and sustainable degradation of emerging contaminants across diverse water matrices.