http://reposit.library.du.ac.bd:8080/xmlui/xmlui/handle/123456789/196 2026-11-11T03:14:49Z http://reposit.library.du.ac.bd:8080/xmlui/xmlui/handle/123456789/4918 Citric Acid and Gypsum Production from Wastes Biomass and Industrial By-products Using Microbial Fermentation A Ahmmed, Hd. Razu The economic potential of microbial citric acid (CA) production is substantial due to its wide-ranging applications in the beverage, food, detergent, cosmetic, and pharmaceutical industries. In Bangladesh, the majority of CA demand is met through imports, while annual consumption is increasing steadily at a rate of 3.5–4%, underscoring the need for sustainable domestic manufacturing alternatives. Large-scale production must therefore adopt eco-friendly processes that utilize readily available and inexpensive agro-industrial byproducts, while ensuring high production yields. CA is predominantly produced via microbial fermentation using Aspergillus niger. The present study aimed to optimize citric acid production from sugarcane molasses employing A. niger (F-81) strain under submerged fermentation, with gypsum as a byproduct. The concentration of CA in the fermentation broth was determined using the Marier–Boulet method. Maximum production was observed in the pretreated molasses sample (12.49 mg/ml), compared to the non-pretreated counterpart (7.3 mg/ml), under identical fermentation conditions (10 days, 2% inoculum size, and an initial pH of 5.6). These findings demonstrate the significance of substrate pretreatment in enhancing yield. The production rate of CA is influenced by multiple factors, including regulatory genes of A. niger, pH, temperature, inoculum size, substrate concentration, and the presence of heavy metals, which warrant further investigation. In addition, citric acid biosynthesis was evaluated using six indigenous fungal strains (FS1–FS6) isolated from soil, cultured under standardized fermentation conditions with 5% molasses as the carbon source, at an initial pH of 6.0 and ambient temperature (30ºC). The produced citric acid was isolated through precipitation method using calcium hydroxide and sulfuric acid, in which gypsum was found as a by-product. Citric acid and gypsum production was confirmed via FTIR analysis. Among the isolates, FS2 exhibited the highest and most consistent productivity, yielding 0.93 mg/ml 1.09 mg/ml and 1.11 mg/ml after 5 days, 7 days and 10 days of incubation, respectively. Moderate production was observed in FS5 (0.55–0.61 mg/ml) and FS3 (0.51–0.61 mg/ml), whereas FS1 (0.41–0.60 mg/ml) and FS4 (0.32–0.40 mg/ml) displayed comparatively lower yields. FS6 was the least productive, reaching only 0.14 mg/ml by day 10. Overall, the results identify A. niger (F-81) strain as the most promising candidate for industrial-scale citric acid production under the tested conditions in Bangladesh. This thesis is submitted for the degree of Master of Philosophy. 2026-10-19T00:00:00Z http://reposit.library.du.ac.bd:8080/xmlui/xmlui/handle/123456789/4796 Non-metal Doped TiO2 Nanocomposites for the Removal of Nuclear Waste from Water Hassan, Md. Mehedi This study focuses on the synthesis and evaluation of non-metal doped titanium dioxide (TiO2) nanoparticles for the potential remediation of radionuclide-contaminated water. Undoped TiO2 and doped TiO2, e.g., B-doped TiO2 (B–TiO2), C-doped TiO2 (C–TiO2), N-doped TiO2 (N–TiO2) were successfully prepared by the sol-gel method. The resultant nanoparticles were thoroughly characterized by XRD, FESEM, EDX, TEM, FTIR, UV–Vis spectroscopy, DLS, zeta potential measurement, and AAS to study their structural, morphological, optical, and adsorption properties. Furthermore, batch adsorption and photocatalytic experiments using adsorbents were conducted to assess their efficiency in radionuclide removal. While attempting to extract radioactive isotopes from water, real radionuclides were not implemented due to safety, cost, and facility constraints. Instead, the nonradioactive analogs—cobalt, iodine, manganese, and zinc (which have similar radioisotopes, such as 60Co2+, 131I-, 54Mn2+, and 65Zn2+)—were employed, due to their similarity with the radioactive elements. XRD results revealed that both the doped and undoped TiO2 were crystalline anatase, and B-doping led to the formation of a small amount of the rutile phase. Both SEM and TEM images showed that the morphology and particle dimension were influenced by doping, with the smallest average particle size being reached for C–TiO2. The adsorption capacity was evaluated using iodine adsorption and the removal of metal ions. The C–TiO2 and N–TiO2 nanocomposites were found to show excellent adsorption properties among the doped samples, which may be due to a higher surface area and improved surface chemistry. The findings indicate that non-metal doping can enhance the photocatalytic and adsorption activity of TiO2. Thus, these materials are promising candidates for treating radioactive wastewater. This thesis is submitted for the degree of Master of Philosophy. 2026-03-03T00:00:00Z http://reposit.library.du.ac.bd:8080/xmlui/xmlui/handle/123456789/4642 Effect of fillers on the performance of surface modification of plywood with epoxy acrylate by UV radiation This thesis is submitted for the degree of Master of Philosophy. 2025-05-26T00:00:00Z http://reposit.library.du.ac.bd:8080/xmlui/xmlui/handle/123456789/4641 Removal of arsenic from contaminated tube well water Haque, Md. Mozaharul This thesis is submitted for the degree of Master of Philosophy. 2025-05-26T00:00:00Z