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Simultaneous wastewater treatment and power generation with single chambered up-flow membrane-less microbial fuel cell
No full textDoctor of Philosophy in Environmental EngineeringMicrobial fuel cell (MFC) is a technology that can convert chemical energy into electrical energy from biomass. MFC is also one of the promising technology to generate sustainable green bioenergy. The development of MFC technologies have been expanded
to various application, such as wastewater treatment, specific inorganic pollutant treatment, sediment bioremediation and biosensor. This thesis addressed the potential of an up-flow membrane-less (UFML) MFC that used for wastewater treatment with an enormous variety of configurations and working parameters. The primary objective of this study is to examine the potential and the mechanism of the novel UFML MFC by using various carbon material as aqueous biocathode. Further investigation was
conducted to evaluate the effect of the biofilm formation on different carbon material surface morphology based on performance of power output and chemical oxygen demand (COD) reduction in UFML MFC. Carbon flake, Pt-loaded carbon paper, carbon plate and carbon felt were used as aqueous biocathode. The voltage output for the carbon flake cathode (384 ± 16 mV) was comparable to the Pt-loaded carbon paper cathode (399 ± 9 mV), which is unexpected. The COD reduction efficiency for all cathode materials at the anode region and effluent were achieved as high as 75% and 85%, respectively. The
surface area and surface morphology of the cathode material may influence the ability of
microbial attachment and electron transfer. The results suggested that the power
generation and the COD reduction were influenced by the cathode material. Besides,
UFML MFC was also used to further explore the potential and the mechanism between
biodegradation of Acid Orange 7 (AO7) and generation of bioelectricity. The
decolorization efficiency of AO7 was up to 96%. Overall voltage output was affected by
the increased dosage of AO7. However, the increased dosage of AO7 and continuous 24-
h flow could help to lower down the other anaerobic microbial activities and consequently
caused more available electrons which can be used by AO7 decolorization and electricity
generation. Furthermore, the decolorization of AO7 at cathode region indicated that the
oxygen and azo dye were both competed for electron acceptor. Based on the UV–visible
spectra analysis, the breakdown of the AO7 azo bond into more toxicity aromatic
compounds in anaerobic condition were confirmed. Nonetheless, these aromatic
compounds can be further degraded into short chain aliphatic acids and lastly
decomposed into carbon dioxide and water. In additional, the intermediates listed in the
proposed plausible biodegradation pathway were partially identified. These results
proved that the combination of anaerobic-aerobic in UFML MFC was able to completely
mineralize the AO7. Lastly, the new enhanced up-scaled UFML MFC (SUFML MFC)
was fabricated with innovative anode configuration (cube carbon felt and linked carbon
felt). This reactor was used to examine the overall performance of power output with
different hydraulic retention time (HRT) and electrode spacing distance. The results
proved that the linked anode was better in flow pattern and mass transfer, providing
overall better voltage output during stationary phase at all different HRT setup
Design, processing and properties of fly ash-based lightweight geopolymer using foaming agent for brick application
No full textDoctor of Philosophy in Materials EngineeringLightweight concrete reduces the overall self-weight of the structures resulting in the reduction of the foundation size, cost, and other specification. However, the conventional lightweight concrete production causes several environmental impacts and
produce low mechanical properties, so there is a clear need of searching and replacing for more efficient and durable alternatives beyond the limitations of the conventional lightweight concrete. Geopolymer represents a great opportunity to ensure greater
sustainability in the construction industry especially for the use of industrial waste such as fly ash. This research focuses on the preparation of fly ash-based lightweight geopolymer using superplasticizer as foaming agent. The superplasticizer (Polyoxyethylene alkyether sulfate) was prepared using pre-formed method by combination with water and air pressure. The effects of geopolymeric synthesis parameters such as the NaOH concentration (6 M, 8 M, 10 M, 12 M and 14 M), ratio of foaming agent to water (1/10, 1/20, 1/30 and 1/40) by volume, ratio of foam to geopolymer paste (0.5, 1.0, 1.5 and 2.0) by volume, curing temperature (40 °C, 60 °C, 80 °C and 100 °C) and curing time (6, 12, 24 and 48) hours on the lightweight geopolymer paste that affect the mechanical and microstructure properties were studied in detailed. The compressive strength, water absorption, density, were studied to determine the mechanical properties of lightweight geopolymer. The thermal insulation properties was investigated through the effects of thermal conductivity, thermal diffusivity, and specific heat of lightweight geopolymer at different ageing time (3, 7, 28, 60 and 90) days. The microstructure properties of lightweight geopolymer were tested by using Scanning Electron Microscope. The results indicated that the lightweight geopolymer have an optimum NaOH concentration of 12 M, with highest compressive strength of 15.2 MPa at 7 days, an optimum ratio of foaming agent to water (1/10) and ratio of foam to geopolymer paste (1.0) with highest strength of 16.6 MPa (7 days), optimum curing temperature (80 °C) and curing time (24 hours) showed the highest strength and lowest density of 15.6 MPa and 1400 kg/m3, respectively. The thermal conductivity and thermal diffusivity of lightweight geopolymer are substantially lower with value of 0.63 W/mK to 0.83 W/mk and 0.26 mm2/s to 0.35 mm2/s, respectively. A potential new lightweight construction material can be produced by using low cost of foaming agent and easy to process for addition to geopolymer paste. The fly ash-based lightweight geopolymer produced in this work exhibit compressive strength in accordance to the standard for masonry lightweight applications at considerably lower curing temperature (80 °C)
A study of multilayer solar cells performances using gallium arsenide (gaAs) and silicon (Si)
No full textMaster of Science in Microelectronic EngineeringThe present low efficiency of solar cells is due to the incomplete use of the solar spectrum. Since different semiconductor materials have different band gaps, it responds separately to different parts of the solar spectrum and therefore, it is possible to put several layers in a series. The multilayer solar cell has been extensively studied with the hope of improving the good efficiency and low-cost for future trends. A substrate layer which consists of Gallium Arsenide (GaAs) and Silicon (Si) will give different characteristic band gap energy, which causes it to absorb light most efficiently at a certain color and more precisely, to absorb electromagnetic radiation over a portion of the spectrum. Since Gallium Phosphide (GaP) is one of the favored material for solar
cell, the GaP semiconductor is chosen to absorb nearly the entire solar spectrum, thus
generating electricity from as much of the solar energy as possible. Improvement of
solar cell efficiency with selected material composition are very important from
economical and technological aspects. The improvements are made to Gallium
Phosphide (GaP) solar cell by introducing doping such as Indium (In) and Aluminium
(Al) into the GaP structure. The results are produced for single layer and dual layer to
observe the effectiveness of the material used and also included the result for multilayer
structure. For single layer, the efficiency of the GaAs solar cell is 11.32 % , 2.13 % for
Silicon and 5.89 % for GaP solar cell. In multilayer InxGa1-xP cells, the highest
efficiency obtained from InxGa1-xP/ GaAs at x=0.7 with the efficiency of 13.23 % and
for InxGa1-xP/ Si, the efficiency obtained is 13.12 % at x=0.7. For AlxGa0.5-xIn0.5P cells,
the highest efficiency obtained from AlxGa0.5-xIn0.5P/ GaAs, which is 36.99 % and for
AlxGa0.5-xIn0.5P/ Si solar cell, the efficiency obtained is 35.63 %, both at x=0.4. As an
improvement, the highest efficiency is 43.42 % for AlxGa0.5-xIn0.5P/ GaAs and 37.11 %
for Alx Ga0.5-xIn0.5P/ Si, at x=0.4 for both by having Anti-Reflective Coating (ARC)
using Zinc Oxide (ZnO) on top of multilayer cells