Date of Award
Master of Science (MS)
Civil and Environmental Engineering
This study assesses the impact of clayey materials’ properties on biofilm formation within the context of point-of-use water treatment systems such as ceramic water filters (CWFs). CWFs were manufactures using clayey materials from different countries by mixing with sawdust and water, and then fired in a kiln. Due to the influence of clayey properties on the quality and duration of CWFs, this study focused to establish a standardization process for clayey selection criteria for ceramic filter factories around the world. To do this, well-established geosciences, environmental and geotechnical engineering methodologies were used. Physical characteristics of clayey materials can be determined through grain size analysis, and liquid limit and plastic limit tests. Mineralogical composition can be determined using X-ray diffraction (XRD) analysis. ICP-MS analysis identifies metals in sawdust fired ashes. Pseudomonas Fluorescens Migula was used as model organism to assess biofilm formation on both clayey materials and CWFs.
Three clayey materials from Guatemala, Canada, and Guinea-Bissau were selected for this study. The Guatemalan clayey belonged to poorly-graded sand with silt contains four identifiable minerals: quartz, muscovite, montmorillonite and albite, and its CWF contains quartz, muscovite, and albite. The Canadian clayey was mainly made of quartz, muscovite, and kaolinite and defined as poorly-graded sand, however, its CWF contains quartz, muscovite and hematite. The clayey material from Guinea-Bissau contains quartz, kaolinite, dickite, and montmorillonite and belongs to poorly-graded sand, and its CWF was made of quartz and hematite, respectively. The average biofilm formation coverages for Guatemala, Canada, and Guinea-Bissau clayey materials were 20.02% ± 6.65%, 19.27% ± 4.59%, and 9.88% ± 5.01%, respectively, while average biofilm formation coverages for Guatemala, Canada, and Guinea-Bissau CWFs are 13.08% ± 4.12%, 10.39% ± 5.05%, and 8.50% ± 5.35%, respectively. 11 elements including Na, Mg, K, Cr, Mn, Fe, Co, Ni, Cu, Zn, and As were identified and quantified in sawdust ashes after firing process. High concentrations of Cr, Ni, Cu, Zn metals in general hinder biofilm formation, while Na, Mg, and Fe can accelerate biofilm formation, thus incorporation of ash can impact final CWF bulk geochemistry. Compared to previous studies, our study showed similar trends when P. fluorescens were used on diverse materials; biofilm formation on Canada clayey material containing kaolinite was higher than on Guinea-Bissau clayey material, which contained montmorillonite. Moreover, in Guatemala clayey, albite contained Na+, which can be exchanged with H+ in the culture medium to increase bacterial attachment on the positively charged mineral surface. Muscovite has a high bacterial adhesion, which promotes biofilm formation in Guatemalan and Canada clayey materials. Montmorillonite decreases biofilm formation in Guinea-Bissau clayey material, but does not play a decisive role in Guatemalan clayey material. Heavy metals in sawdust ashes have the potential to lower biofilm formation on CWFs in general, when compared to initial materials—this is supported at least for Guatemalan and Canadian samples. Our data suggest that the presence of muscovite in the CWF material causes significant differences in biofilm coverage, as shown by pairwise analysis of (1) Guatemalan (+ muscovite) and Guinea-Bissau (- muscovite) CWFs and (2) Canadian (+muscovite, +hematite) and Guinea-Bissau (- muscovite, + hematite) CWFs. However, the small observed differences of biofilm formation between clayey material and CWF of Guinea-Bissau cannot be fully explained by heavy metal loading through firing with ash incorporation or montmorillonite loss coupled to hematite ingrowth, due to initially lower biofilm coverage on related clayey material.
This study showed the importance of the determination of mineral composition of clayey materials for the manufacturing of CWFs. Mineral composition have an important effect on the promotion or hindrance of biofilm formation, therefore impacting the performance of CWF.
Zhang, Yichen, "Development of Ceramic Water Filter Clays Selection Criteria" (2017). Open Access Master's Theses. Paper 1070.
Available for download on Saturday, July 28, 2018