published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

Present day society generates large volumes of waste that present an environmental hazard when disposed of in landfills. As our population grows, so does the volume of waste generated and hence the threat to our environment. One method of reducing harmful emissions in landfills is the mechanical-biological pretreatment of waste prior to landfilling. The purpose of this dissertation is to investigate the degree of stabilization of waste in shallow landfills (simulated by test cells) with particular focus on biogas production and quality. Municipal waste was composted in aerobic, open windrows for periods of eight and sixteen weeks. Five test cells, designed and operated according to the PAF model (Pretreatment, Aeration and Flushing) were constructed at the Bisasar Road landfill site. These cells were used to simulate large scale municipal landfill sites. They were filled with fresh and pretreated waste and were used to monitor the dynamics of prolonged aeration and degradation of waste over a period of six months. The cells were monitored on a weekly basis while being aerated. Two flushing events were conducted at the beginning of the passive aeration. Gas emissions were also monitored by recording the methane, carbon dioxide and oxygen volumes per volume of air in probes strategically placed in each cell. These results were then analysed to assess the effect of mechanical-biological pretreatment of municipal solid waste on the emission quality of sanitary landfills and the appropriateness of prolonging the aeration in shallow landfills, as often used in sub-tropical countries. It was found that the design of the test cells was appropriate for the landfilling and stabilization of waste that was aerobically treated. After six months in the test cells, analysis of the waste from each cell showed that the waste was completely degraded. The PAF model, when applied to shallow landfills, is very effective in stabilising waste and would be appropriate for a sub-tropical climate. Waste that is pretreated, placed in shallow landfills, initially flushed and then aerated over a six month period was fully stabilized. The requirement for such treatment would be relatively small amounts of waste, a wet climate and the availability of open space for shallow landfills. This method, therefore, would be very appropriate in a South African context. The major problem with this method may be the generation of large quantities of leachate which will have to be treated and disposed of in an environmentally safe manner. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2006.

This study proposed and evaluated a waste-to-resource strategy for beneficially using solid waste as ceramic raw materials. The sludge generated from waterworks and sewage treatment processes contains significant amounts of aluminum and iron, and the industrial sludge is enriched with high metal content. The hazardous metals in waste sludge may lead to metal bioaccumulation and cause adverse effects for ecosystem. This study aims to stabilize copper- and zinc-laden sludge in commonly available ceramic products, and to beneficially use waterworks and sewage sludge to incorporate waste metals. The study was first investigated by sintering simulated metal-laden sludge with Al-rich (γ-Al2O3, -Al2O3, kaolinite, mullite) and Fe-rich (Fe2O3) precursors. Secondly, the practicability of recycling Cu-bearing electroplating sludge as a part of ceramic raw materials was evaluated through thermal interaction with Al-rich precursors. Furthermore, the potential of using water and sewage treatment works sludge to stabilize metals were also examined. Sintering procedures were carried out within 650-1450 oC for 3 h, and phase transformations were studied using X-ray diffraction (XRD) with the quantification technique of Rietveld refinement analysis. The formation of CuAl2O4 spinel was initiated at 650 oC using γ-Al2O3, and the maximum copper transformation reached 80%. The copper incorporation into CuAl2O4 started at 850 oC and reached 95% in -Al2O3 system. The growth of CuAl2O4 was found at 750 oC using kaolinite, but at 900 oC in mullite system. The maximum copper transformation for both kaolinite and mullite reached ~80%. With CuAl2O4, decomposing, the formation of CuAlO2 predominated in alumina systems, but CuO and Cu2O were found in kaolinite and mullite systems. When using Fe2O3, the CuFe2O4 with tetragonal structure was observed at lower temperatures, and the cubic CuFe2O4 became predominant at 1000 oC. The formation of ZnAl2O4 spinel started at 750 oC in γ-Al2O3 system and at 950 oC in -Al2O3 system, respectively. The zinc transformation completed in both γ-Al2O3 and -Al2O3 systems at higher temperatures. The coexistence and competition between ZnAl2O4 and Zn2SiO4 were found using kaolinite and mullite. The increase of temperature to 1350 °C resulted in complete zinc transformation to ZnAl2O4 in mullite system. Through leaching tests, aluminates and ferrites were found to be superior to oxide and silicate phases in immobilizing hazardous metals. The leachates of aluminates and ferrites exhibited the behavior of incongruent dissolution, and the Zn2SiO4 leachate showed congruent dissolution. The CuAl2O4 spinel was observed when sintering Cu-laden electroplating sludge with aluminate precursors. The copper leachability decreased with CuAl2O4 developing and the lowest copper concentration in leachates was within the optimal temperature range for CuAl2O4 generation. Both copper and zinc were successfully incorporated into the spinel structure using waterworks sludge, and the cubic CuFe2O4 became the main component when using sewage sludge to stabilize copper. Overall, this study demonstrated a promising process to stabilize hazardous metals in waste materials, such as sludge, ash, and slag, through sintering with the inexpensive ceramic precursors. This may provide an avenue for economically reduce the environmental hazards of toxic metals by reliably blending them into the marketable ceramic products. / published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

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