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PublicationAdsorption of Hydrogen Sulphide using zeolite ZSM–5 for the enhancement of fermentative biohydrogen production( 2024)Biohydrogen production from mixed fruit waste (MFW) is a renewable energy source. However, the presence of highly toxic and corrosive hydrogen sulphide (H2S) might reduce performance and limit energy conversion equipment use. Adsorbents including zeolites, biochar, and activated carbons have become popular for treating harmful gases like H2S. Thus, the research examined the feasibility of employing ZSM-5 zeolite for H2S adsorption as an activating agent to improve biohydrogen quality from thermophilic condition. A suspension rich in carbohydrate from MFW was used at initial concentration 5 g/L during the fermentation process was conducted in a thermophilic anaerobic closed bioreactor (TACB) at an initial pH 6 and temperature 60 ℃. Hydrogen-producing bacteria via the butyric acid fermentation route were the most prevalent microbes in biohydrogen generation. Volumetric biohydrogen yield and substrate degradation efficiency was 22511.60 mL and 85% per total carbohydrate, respectively obtained in the experiments performed. The biogas that was produced had undergone adsorption process on zeolite ZSM-5. The effect of dosage of adsorbents and reaction temperature on the hydrogen yield and H2S removal investigated. The hydrogen yield after adsorption process increased from 89% to 92.78%. The optimum dosage and reaction temperature for H2S adsorption were 0.8 g (0.00889 mg/g) and 25 ℃ (0.00890 mg/g), respectively. The zeolite was subjected to consecutive regeneration and adsorption cycle where H2S adsorption capacities of 0.00890 mg/g were maintained for 3 cycles demonstrating reusability and stability of the sorbents. However, the adsorption capacity starts reducing at the fourth cycle. The H2S removal on zeolite ZSM-5 was the best represented by Avrami kinetics model showing that H2S were adsorbed via multiple adsorption pathways with multilayer adsorption on heterogenous surface. The adsorption is physical adsorption, exothermic, increasingly random, and non-spontaneous. Intra-particle diffusions were found to critically control the rate of adsorption. Higher H2S adsorption capacity and regenerability shown by fibrous zeolite in this this study confirmed its applicability as an alternative sorbent in enhance biohydrogen quality under thermophilic conditions.
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PublicationRecycling of municipal solid waste incineration ash as raw material in cold-bonded lightweight aggregate( 2021)This study focusses on the development of new lightweight aggregate (LWA) that eventually have comparable properties with existing natural aggregate which is granite. The main objective of this study is to examine potential use of recycled municipal solid waste incineration (MSWI) ash as raw material in LWA production with a method of cold-bonded pelletization process. The ashes are collected from Cameron Highland Incineration Plant, Malaysia that can be divided into bottom ash (BA) and fly ash (FA). The properties of BA and FA are studied by means of X-Ray Fluorescence (XRF), Scanning Electron Microscope (SEM) and apparent density test. The LWA is denoted as bottom ash lightweight aggregate (BALA) and fly ash lightweight aggregate (FALA). Both BALA and FALA have experienced two different curing process for 28 days namely room-room (RR) and room-water (RW) curing conditions. The percentage of BA and FA used in this study were 10 %, 20 %, 30 %, 40 % and 50 % of partial cement replacement and the size of aggregate is fixed between 10 mm to 20 mm with circular shape. The properties of BALA and FALA produced in this study is examined including loose bulk density, water absorption, aggregate impact value (AIV) and specific gravity. Other physical properties including colour and texture are also being investigated. Potential use of BALA and FALA in concrete is investigated by selecting optimum samples of both aggregates to be incorporated in the manufacturing of semi-lightweight aggregate concrete (SLWAC). 30 specimens of SLWAC were produced having water-cement ratio of 0.5 and percentage of aggregate replacement is fixed at 20 %. Characteristics of SLWAC were examined including workability, density, water absorption, capillary water sorption, ultra-pulse velocity (UPV), compressive strength and permeability. Distribution of BALA and FALA in SLWAC is examined through cut-section of concrete. From the results of LWA it is clearly seen that 20 % BA and 20 % FA were the best percentage of ash used to produce good quality LWA. Loose bulk density of BALA selected is 739.53 kg/m3 with water absorption 20 % and AIV 13.94 %. Meanwhile, for FALA, optimum percentage is as follows; loose bulk density 716.72 kg/m3, water absorption is 19.7 %, AIV 13.80 % and specific gravity 1.670. However, for SLWAC, the results show that by incorporating BALA and FALA in the concrete improved the workability of concrete. The obvious impact due to the reduction of loose bulk density in LWA can be evident by the reduction of apparent density of SLWAC. Compressive strength of FASLWAC is comparable with NWC. Well-distributed BALA and FALA in concrete specimens is believed to contribute to the properties of SLWAC.
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PublicationThe influence of alkali and alkaline earth metals on RU/YSZ catalyst for catalytic and electrochemical promotion of Carbon Dioxide Methanation( 2020)Carbon dioxide (CO₂) is the major contributor of global greenhouse gas (GHG) emissions, leading to an increase in the global temperature. CO₂ utilisation is a sensible approach to mitigate the CO₂ emission while conserving the carbon resources. One of the ways to utilise CO2 is through hydrogenation process which allows efficient conversion of CO₂ into value added fuels like methane (CH4). In this study, catalytic hydrogenation of CO₂ into CH4 and carbon monoxide (CO) was investigated over a ruthenium catalyst film supported on 8 mol% yttria-stabilised zirconia pellet (Ru/YSZ), externally modified with several alkali and alkaline earth metal species i.e. sodium (Na), potassium (K), calcium (Ca) and magnesium (Mg) at low coverage (0.16%) between 250-400°C in a single chamber reactor. A stronger promotion of the catalytic activity and product selectivity of the methanation reaction was observed in the Ru/YSZ system modified with alkali metals i.e. Na and K. Of these, a higher catalytic activity was observed for Ru/YSZ modified with K at low coverage (0.16%), attributed to the smaller Ru crystallite size which results in higher Ru catalyst dispersion. The Ru-K/YSZ system at varied K coverage (0.16-16%) was further investigated in terms of the reaction kinetics. The calculated order of methanation reaction with respect to H2 and CO₂ concentrations indicated an Eley-Rideal mechanism for the Ru sample, in which one of the reactants (CO₂) needs to adsorb, while the other reacts directly from the gas phase, but this changed at higher potassium coverage (16%), to a Langmuir-Hinshelwood mechanism where reaction depends on both reactants’ adsorption as both have weak chemisorption. The increase in the activation energy with higher potassium coverage may be due to the increase in the intrinsic activity barrier on the catalyst because of the presence of metal species which blocked the active surface sites. On the other hand, a higher potassium coverage was in favour of CO production possibly due to weaker adsorption of CO₂. Electrochemical promotion of CO₂ methanation mainly shows an inverted-volcano type promotional behaviour with strong non-faradaic rates except for CO production at 16% K (volcano type). A synergistic effect, in which reaction rate is higher than that caused by addition of K and polarisation can be observed at 16% K, indicating that both K and oxygen species spillover onto the catalyst react favourably to some extent to promote CO₂ methanation.
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PublicationRemoval of Nitric oxide (NO) by selective catalytic reduction over modified oil palm empty fruit bunch fibres (EFB)( 2021)Nitric oxide (NO) is one of the primary air pollutants emitted from combustion which could lead to many other global environmental problems such as acid rain and photochemical smog. Due to the associated risks, continuing effort to study the NO removal from industrial sources are necessary especially at low temperature. This work aims to investigate the NO removal by selective catalytic reduction (SCR) using activated carbon originated from oil palm empty fruit bunch fibres (EFB) as support material. The activated carbon (EFBC) was prepared by one stage chemical activation using phosphoric acid (H3PO4) and carbonized at temperature between 400-550°C for 4 hours. Higher carbonization temperature led to pore enlargement and resulted in lower NO adsorption capacity. The EFBC was then impregnated with metal additives i.e. copper (Cu), nickel (Ni) and iron (Fe) oxides/salts via wet incipient impregnation, and calcined at 400°C. Introduction of 5 wt.% CuO was found to be slightly more favourable for NO removal in comparison to the other two metals, and CuO at higher loading (10-20 wt.%). The physical and chemical properties of EFB and modified samples were characterized with surface area and pore analysis, proximate analysis, surface morphology and surface chemistry. The increase in the initial NO concentration and reaction temperature investigated between 300-1000 ppm and 100-300 ºC, respectively, were found to improve NO removal by both EFBC and CuO/EFBC. EFBC was also found to exhibit better performance in dissociative NO removal, with higher N2 production, while higher reaction temperature increased N2 production of EFBC from 13.99 % (100oC) to 62.56 % (300oC). The NO adsorption of both EFBC and CuO/EFBC at 100°C was best fitted to Sips isotherm, indicating the heterogenous nature of the adsorbent surface. On the other hand, the adsorption kinetic data of NO for both EFBC and CuO/EFBC were best fitted to Avrami kinetic model, suggesting that the NO adsorption were mainly governed by surface attachment and diffusional process. The NO adsorption data also fitted well with the intra-particle diffusion model via intraparticle diffusion and film diffusion. The reaction was endothermic in nature and nonspontaneous, involving both physisorption and chemisorption routes. The former route was mainly assisted by the physical characteristics such as higher surface area and smaller pore size while the latter were influenced by the surface chemistry on the carbon surface. Further hydrogen pre-treatment of CuO/EFBC at 600-700oC resulted in better specific surface area and pore properties, introduced more basic surface groups and induced the presence of smaller crystallite CuO, Cu2O and Cu3P, leading to higher metal dispersion favourable for NO removal. The research outcome will contribute to knowledge in NO removal and useful for post-combustion applications, especially for small medium industries who cannot afford high-temperature NO removal technologies.
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PublicationSimultabeous removal of colour, organic compounds and nutriens from synthetic wastewater containing Azo dye using aerobic-anaerobic baffled constructed wetland reactor( 2020)This thesis presents an improved approach on the simultaneous removal of colour, organic compounds, and nutrients from wastewater containing azo dye by using multiple zoned aerobic and anaerobic baffled constructed wetland reactors. Conventional constructed wetlands lack the provision of sequential aerobic and anaerobic treatment which is essential in the treatment of azo dyes, nutrients and organic compounds. An aerobic and anaerobic constructed wetland reactor is operationally and economically advantageous to adopt in the treatment of wastewater containing azo dye since the combination of these processes has the capability to mineralize organic compounds, decolourize colour from dye, aerobically nitrify and anaerobically denitrify nutrients in the wastewater. Acid Red 27 (AR27) was chosen as the model pollutant due to the wide usage and harmful nature which may cause adverse effects in human and animals besides being classified as an endocrine disruptor. The first part of this study involves the investigation of the performance of this system for nitrogen and organic compounds removal. The second part comprises of the introduction of AR27 into the system and the effects of AR27 on the performance of the system. Final part of the study revolved around the detailed analysis of the complete decolourization and mineralization of AR27. Besides that, a degradation pathway was proposed based on that analysis. The Aerobic - Anaerobic Baffled Constructed Wetland Reactors (ABCW) comprises of 5 vertical baffles that ensures an upward and downward flow within the system, which provides a longer treatment pathway through the wetland media. The ABCW reactor were planted with P.australis, where the hydraulic retention time was set to 1 day and fed with synthetic wastewater containing AR27. Intermediate aeration was supplied to control the aerobic and anaerobic zones within the system to enable the pollutants to pass through a series of sequential aerobic and anaerobic treatment. Performance of the ABCW was evaluated in terms of COD, NH4 +, NO3 - removal, decolourization and mineralization. Aerobic and anaerobic conditions were monitored through the ORP profiles while mineralization of organic compounds and proposed degradation pathway was conducted by several detailed analyses. The ABCW reactors demonstrated good performance in the simultaneous removal of colour, organic compounds, and nutrients, as COD removal ranged from 88 to 98%; NH4+ removal ranged from 93 to 98%; achieved 100% colour removal and complete mineralization of AR27 metabolites. This performance of the ABCW could be attributed to the long pathway travelled by the wastewater hence increasing contact time of pollutants with microbes and rhizomes. The synergistic effect of the combination of rhizomes, microbes and supplementary aeration also played an important role in the high performance of the ABCW reactor.