Mass balance analysis of two-phase AD indicated that off-gas (H2 and CO2) produced in acidogenic reactor represent up to 30% of the consumed substrate and under most circumstances, this part of energy was not utilized leading to low overall energy recovery. Hence, the objective of this study was to enhance overall energy recovery during two-phase AD of food waste through reutilization of acidogenic off-gas and to further optimize the processes through manipulating the metabolic pathways and controlling acidogenic off-gas production. In the first phase, feasibility of reutilizing acidogenic off-gas in methanogenic reactor and contribution of acidogenic off-gas to overall energy recovery was investigated. Acidogenic off-gas diversion increased the methane gas (CH4, 0.28 L/g VSadded) production up to 38.6%, of which ~8% was contributed by acidogenic off-gas. Both higher hydrolysis rate and COD production were also achieved with off-gas diversion. Metabolic pathway determines the distributions of intermediate soluble products, which constitute the quality of acidogenic leachate. Therefore, two experiments focusing on manipulating metabolic pathways were performed. Firstly, the effects of four levels of headspace pressures, 6-12 psi (T1), ~3-6 psi (T2), ~3 psi (T3) and ambient pressure (T4) were investigated. Mixed acids metabolic pathways prevailed in all the treatments with butyrate as the single major component. Then, four different levels of H2 partial pressure (PH2) were set the next experiment, self-generated PH2 (T1, control), 80% of H2 (T2), 60% of H2 (T3) and 0.04% of H2, while the headspace pressure was kept at 3.3 psi. Typical butyrate fermentation pathways dominated in T4 whereas mixed acid fermentation pathways were prevailing in the other three treatments. Because of the improved hydrolysis/acidogenesis and higher quality of acidogenic products, overall CH4 recovery in T4 (301.0 L/kg VSadded) was 44.6% higher than the control. In Phase III, strategies to enhance acidogenic off-gas production were investigated. First, four types of neutralization modes including daily pH adjustment of leachate to 6.0, methanogenic effluent recirculation, and initial addition of NaOH and lime separately at a dosage of 20.0 and 14.0 g/kg food waste, respectively, were investigated. Obviously, a H2 production rate of 3.0 and 2.1 L/d with lime and NaOH addition was much higher than 0.7 and 0.4 L/d with effluent recirculation and daily adjustment, respectively. Also, addition of alkali agents could enhance the COD leaching of food waste, especially with NaOH. A CH4 production of 11.24 L/d could be attributed to both the elevated leachate quality and the acidogenic off-gas with lime addition. Another experiment investigated the effect of different carbohydrate contents in the substrates on acidogenic H2 production. Anaerobic hydrolysis of wastes sourced from bakery (T1), Chinese-style restaurant (T2), western-style restaurant (T3) and wet market were performed in LBRs. Food waste collected from western-style restaurant with a carbohydrate content of 69.5% achieved the highest H2 production of 61.0 L/kg VSadded. The highest specific CH4 production rate at 0.42 L/gVSadded was also achieved with western restaurant food waste. Finally, the possible redirection of fluxes associated with shift of metabolic pathways from the experiment of PH2 was proposed. Significant increase in the production of butyrate in treatment T4 with PH2 of 3.3 psi × 0.04% indicated the channeling of electrons towards the production of butyrate. Dynamics of the microbial community were correlated with the distribution of metabolites. In T1 without external gas flushing, lactic acid fermentation was dominant during the initial 7-days. Accordingly, phylotypes affiliated to the genus Lactobacillus sp. were detected. A heterlatic fermentation pathway was observed in in both T2 and T4 during first four days, and thereafter the fermentation pathways shifted towards acetate and butyrate as dominant products, which were accompanied by changing the microbial community with phylotypes of Clostridium sp. and Bifidobacterium sp. becoming dominant. To conclude, reutilization of acidogenic off-gas by diversion to methanogenic phase is a promising strategy for enhancing overall energy recovery during two-phase AD of food waste. However, improvement of the short-lived acidogenic H2 production and H2/CO2 ratio needs further investigation.

Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology. / While biodiesel has the potential to resolve the energy crisis, its production is hampered by both feedstock and catalyst availability. The aim of this current study is to investigate the production of biodiesel from waste vegetable oil (WVO) as feedstock under heterogeneous catalysis, mediated by calcined eggshell ash. WVO, characterised by 9% free fatty acid (FFA) and 0.17wt% water content, was employed as feedstock in the biodiesel production via transesterification reaction. The composition of WVO was determined using Gas chromatography (GC) analysis. The eggshell was washed with distilled water to remove impurities, dried in an oven at 105°C, and then crushed into fine particle of 75μm, and finally, calcined in a muffle furnace at 800°C. The chemical properties of the catalyst were assessed as follows: 1) using X-ray diffraction (XRD) to determine the major component phase of the element; 2) using X-ray fluorescent (XRF) to determine the elemental composition of the eggshell ash; 3) using Brunauer Emmet Teller (BET) to define the structure, the surface area, pore volume and pore diameter of the eggshell ash; and 4) using SEM to show the morphology structure of the element. The XRD analysis performed on eggshell ash showed 86% CaO as a major component in the catalyst; the remaining 14% was composed of MgO, SiO2, SO3, P2O5, Na2O, Al2O3, K2O and Fe2O3, as obtained from XRF. The BET result of the catalyst prepared was characterised by large pore diameter (91.2 Å) and high surface area (30.7m2/g), allowing reactants to diffuse easily into the interior of the catalyst used

Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2016. / The generation of municipal solid waste has increased significantly due to the exponential population growth and it has become a global issue. Gasification technology, an alternative method for waste treatment is a thermochemical process where carbon-based material are exposed to an environment deprived in oxygen, was used for this project. The aim of this thesis is to study the gasification of plastic waste which is a potential alternative energy source using infrared heaters. To achieve this goal, fundamental studies have been numerically and experimentally conducted for an infrared gasifier and subsequently establishing the temperature profile for gasification using a small scale reactor. A detailed study on low density polyethylene was conducted using Infrared Spectrometry and thermal decomposition techniques such as Thermogravimetry and Differential Scanning Calorimetry were performed to establish the temperature at which plastic pellets sample used for this research gasify. The gasification behaviour of pelletized low density polyethylene (plastic pellets) was tested and three case studies were done to evaluate the most suitable temperature profile for the reactor to gasify the low density polyethylene at high temperature for less amount of time. Subsequently, the reactor model was simulated and results validate the use of reactor at an optimum temperature of 800 °C for a gasification process with less residue content. The reactor designed for this research is fully functional and validates the temperature behaviour predicted during simulation. The experimental results show infrared heaters are suitable for gas production using this gasification process.

Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology, 2017. / Energy security, environmental and economic issues have spurred the interest in pyrolysis of scrap tyres for the production of fuels and energy in South Africa. However, the application of the process on a commercial scale is being hampered by the high cost required to upgrade the comparatively low quality pyrolytic products as well as the high energy input. Further insights into the mechanisms of thermal degradation of rubber will assist to improve on the process economics for production of liquid hydrocarbons fractions suitable for use as transportation fuels and chemicals. This study developed a correlation to predict the contents of waste tyres that will be converted into hydrocarbons during pyrolysis from the proximate analysis data. The mechanism/kinetics of thermal degradation behaviour of waste tyres is also studied, in order to locate the optimal temperature that will maximize the yield of liquid hydrocarbons and other recoverable materials. Data from thermogravimetric analysis is used to determine the kinetic constants for the pyrolysis reaction over a temperature range of 500 °C - 750 °C. A relationship between the optimal temperatures and the volatile mater content depending on the desired products was obtained. This is necessary to eliminate thermal cracking of the pyrolytic oil into the non-condensable gas that will result from excessive temperature and the associated energy cost. Relationship to determine the kinetic equation constants is presented as a function of the volatile matter content. An inductor furnace batch reactor system is used to carried out the pyrolysis reaction, using Argon as the inert gas to provide the oxygen free environment required. The products are sent through a 2-stage condensers, the first operated at room temperature to collect the pyrolytic oil, and the second maintained at -5 oC to collect the condensable pyrolytic gases.

A review of literature on the subject of methane exploitation from landfill is presented in conjunction with the results of experiments concerning landfill gas extraction at the Grahamstown Landfill Site. A description of the LFG extraction system and the utilisation of LFG at the Grahamstown Landfill Site is included. Data concerning LFG enhancement parameters, LFG compositions and flow rates, refuse composition, LFG modelling, LFG pumping trials and the economics of LFG extraction and utilisation are presented. The indication is that LFG can be economically extracted and utilised as a heating fuel in South Africa.

Microbial fuel cells (MFCs) are a promising form of alternative energy capable of harnessing the potential energy stores in organic waste. The oxygen reduction reaction (ORR) forms an integral role in the generation of electricity in MFCs however it is also a potential obstacle in enhancing the performance of MFCs. Platinum, a commonly used catalyst for the ORR, is expensive and rare. Significant research has been conducted into developing alternative catalysts. Metallophthalocyanines (MPc) have garnered attention for use as catalysts. Iron phthalocyanine (FePc) has been shown to have catalytic activity towards the reduction of oxygen. Coupling of the catalyst to nanostructured carbon materials, such as multi-walled carbon nanotubes, has been observed to have several advantages as nanostructures have a high surface-to-volume ratio. In this study, we have attempted to assess the suitability of FePc, both its bulk and nanostructured form, as an oxygen reduction catalyst and acid functionalized multi-walled carbon nanotubes for use as a catalyst support using electrochemical techniques such as cyclic voltammetry and electrochemical impedance spectroscopy. We showed, for the first time, the catalytic nature of nanostructured FePc towards the ORR. Applying the data obtained from the electrochemical analyses, electrodes were modified using FePc and MWCNTs and applied to an Enterobacter cloacae-based MFC. Several operational parameters of the MFC, such as temperature and ionic strength, were optimized during the course of the study. We showed that optimized FePc:MWCNT-modified electrodes compared favourably to platinum-based electrodes in terms of power densities obtained in a microbial fuel cell.

Faced with rising energy costs, forest industries have been seeking ways to better utilize wood residues for fueling plant operations. A major problem with this fuel is its high moisture content when produced from green trees, which seriously reduces the heat of combustion. In light of this a study was conducted to determine the moisture content, drying rates, and fuel value of logging residues produced in three of Virginia's physiographic zones. Samples were taken from the residues at intervals over a two year period to monitor moisture and fuel value changes under a variety of environmental conditions. It was concluded that these residues (tree tops, branches, and cull trees) had become dry enough for fuel use after as little as one or two months of field-drying in a suitable location. In other situations, drying rates were too slow to consider the method a viable alternative. The main factors affecting the field drying process were found to be size of the residue, geographic location, and season. / Master of Science

The current energy crisis is exponentially growing and widening the chasm between demand and supply. Biofuels such as ethanol not only provide greener alternatives to fossil fuels but have been shown to reduce emissions from vehicles, improving air etc. Biofuel production from sources such as cellulose is believed to be more sustainable due to its low cost, vast availability in nature and sources such as industrial plant waste can be put to good use. However, due to the absence of a low-cost technology to overcome its recalcitrance, a concept called Consolidated Bioprocessing (CBP) has been put forward which proposes to integrate the production of saccharolytic enzymes, hydrolysis of the carbohydrate components to sugar molecules, and the fermentation of hexose and pentose sugars to biofuels into a single process. The present study involves development of cellulolytic E. coli strains towards cellodextrin assimilation by employing an energy-saving strategy in cellulose metabolism through the phosphorolytic cleavage of cellodextrin mixture produced as cellulosic degradation products.

This study investigated the commissioning and maintenance of a Pennells two-tank bioreactor system with specific reference to its application in rural areas of KwaZulu- Natal, South Africa to treat sewage and generate biogas. The septic tank configuration was installed in a community which lacked electricity and domestic waste disposal. An artificial wetland was constructed at the outlet of the system to facilitate further treatment. Inefficient operation and maintenance of the system occurred due to various social/community-related problems which are typical of a field- and community-based project of this nature in a rural region of a Third World African country. These problems affected both maintenance and digester performance. The Pennells system was characterized by incomplete anaerobiosis which limited methanogenesis. Despite this, and attendant problems of low temperatures and elevated pH values, COD removal resulted. Laboratory-scale batch cultures, in conjunction with fluorescence and scanning electron microscopy, were used to identify a suitable anaerobic digester sludge for inoculation purposes. Perturbation experiments with locally used detergents and toxic compounds demonstrated the inimical effects of these agents. In contrast, low concentrations of penicillin and tetracycline promoted methanogenesis. Further analysis with light, fluorescence and scanning electron microscopy identified the acidogens as the predominant bacterial species, whilst fluorescence microscopy confirmed the absence of methanogens in the bioreactor. / Thesis (M.Sc)-University of Natal, Pietermaritzburg, 1997.

This thesis examined the conversions of biomass and biomass components to petrochemicals and total aliphatic gasoline like products. There are three major projects of the thesis. Since biomass is very complicated, to understand the thermal decomposition pathways of biomass, the pyrolytic behaviors of various biomass components including lignin and cellulose under different reaction were investigated in the first phase. Due to complexity and limited volatility, the thermal decomposition products from biomass bring insurmountable obstacles to the traditional analysis methods such as GC-MS, UV and FT-IR. Therefore, precise characterization of the whole portion of thermal decomposition products has significant impacts on providing insight into the pyrolysis pathways and evaluating the upgrading processes. Various NMR methods to characterize different functional groups presented in liquid and solid pyrolysis products by 1H, 13C, 31P, 2D-HSQC and solid state 13C-NMR were introduced in the second phase. Nevertheless, the major drawback towards commercialization of pyrolysis oils are their challenging properties including poor volatility, high oxygen content, molecular weight, acidity and viscosity, corrosiveness and cold flow problems. In situ upgrading the properties of pyrolysis oils during thermal conversion process by employing zeolites has been discussed in the third phase. The further hydrogenation of pyrolysis oils to total aliphatic gasoline like products by heterogeneous catalysis in “green medium” – water has also been examined in the third project.