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The Best PhD Thesis in the Faculties of Dentistry, Engineering, Medicine and Science (University of Hong Kong), Li Ka Shing Prize,1993-1995 / published_or_final_version / Civil and Structural Engineering / Doctoral / Doctor of Philosophy

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published_or_final_version / abstract / toc / Civil Engineering / Doctoral / Doctor of Philosophy

Biotechnology of sulphate reducing bacteria has developed rapidly in recent years with the recognition of their extensive and diverse biocatalytic potential. However, their application in a number of areas has been constrained due to problems including poor cell retention within the continuous bioprocess reactor environment, and contamination of the treated stream with residual organic feed components and cell biomass. These problems have so far excluded the application of biological sulphate reduction in the treatment of ‘clean’ inorganic waste streams where components such as sulphate, acidity and heavy metal contamination require treatment. This study investigated the effective immobilisation of sulphate reducing bacterial cultures and proposed that the disarticulation of the electron donor and carbon source supply using such systems would create the basis for their application in the treatment of ‘clean’ inorganic waste streams. A functional and stable sulphate reducing culture was selected and following evaluation using a number of techniques, was immobilised by encapsulation within a calcium-alginate-xanthum gum membrane to give robust capsules with good sulphate reduction activity. The concept of disarticulation was investigated in a swing-back cycle where the carbon source was excluded and the electron donor supplied in the form of hydrogen gas in a continuous up-flow capsule-packed column reactor. Following a period of operation in this mode (4-12 days), the system was swung back to a carbon feed to supply requirements of cell maintenance (2-3 days). Three types of synthetic ‘clean’ inorganic waste stream treatments were investigated, including sulphate removal, neutralisation of acidity and heavy metal (copper and lead) removal. The results showed: • Sulphate removal at a rate of 50 mg SO₄²⁻L/day/g initial wet mass of capsules during three 4-day cycles of electron donor phase. This was comparable to the performance of free cell systems; • Neutralisation of acidity where influent pH values of 2.4 and 4.0 were elevated to above pH 7.5; • Copper removal of 99 and 85 % was achieved with initial copper concentrations of 2 and 60 mg/L respectively; • Percentage lead removal values of 49 and 78 % were achieved; This first report on the application of the concept of capsular immobilisation and disarticulation in the treatment of ‘clean’ inorganic waste streams will require future studies in order to extend the development of the full potential of the concept.

This study was carried out to gain knowledge of the degradation processes in an anaerobic environment of pre-treated waste for different degrees of pre-treatment and the evolution of waste pre-treatment by forced aeration. Pre-sorted MSW (MSW) was pretreated by composting for 16 weeks in a laboratory scale using forced aeration. Oxygen concentrations were maintained at 15-18% of oxygen in air for the first 8 weeks and 10-15 % for the later 8 weeks. The ambient temperature was kept constantly between of 20-35 QC. Representative samples of waste from the reactor were collected every fortnight wherein analysis and full characterisation on the solid matter (C/N ratio, TS and VS, R17, Biogas) and on the eluate (BOO, COD, TOC, TKN, Conductivity, pH, NOx and NH3)) were conducted. The process showed a sharp increase in temperature in the first 6 weeks, ranging from 30- 70 QC indicating a period of high biological activity, a decrease from day 30 to day 50 from 70 to 30 QC and a consistent decrease throughout the later days of the process from 35-25 QC. The sharp increase in temperature signifies a period of maximum biological activity, where readily biodegradable material decomposes as well as some of the resistant materials pointing out the success and efficiency of the forced aeration process. For the first 25 days in an anaerobic environment, waste pre-treated for four weeks was the most active, indicated by a large volume of gas produced. For the MSW pre-treated for 8, 10, 12 and 16 the volume of gas produced remained basically similar throughout the length of the experiments. CH4 production in an anaerobic reactor shows an increasing trend for all degrees of stabilisation up to 6 weeks, after that the gas production and quality deceases and is comparable to the remaining degrees of treatment. A gradual decrease in concentration of key parameters (organics) analogous to the European limit in Europa (1998), were observed after 5 weeks pre-treatment. The study highlighted that the highest efficiency of pre-treatment is achieved in 6 to 8 weeks and, therefore it is not recommended to prolong the treatment any further. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2007.

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy Johannesburg 2012 / Wastes from mining operations usually contain a suite of pollutants, among them cyanide and its complexes; heavy metals; metalloids and radionuclides. The pollution plume can affect public health through contamination of drinking water supplies, aquatic ecosystems and agricultural soils. As such, waste management and remediation has become an important integral component of mining. Conventional chemical and physical methods are often expensive and ineffective when the pollutant concentrations are very high, so the challenge of developing cost-effective materials with high adsorption efficiencies for pollutants still remains. This research was dedicated to the development of biosorbents with high metal loading capacity for the remediation of mine wastewater, namely: zeolite/bentonite functionalised with microbial components such as histidine, cysteine, sorbitol and mannitol; zeolite/bentonite functionalised with Penicillium-simplicissimum and zeolite-alginate complex generated by impregnating natural zeolite into alginate gel beads. The ability of the fresh water algae, Oedogonium sp. to remove heavy metals from aqueous solutions in batch systems was also assessed. Optimum biosorption conditions for the removal of Co, Cu, Cr, Fe, Hg, Ni, Zn and U (in a single-ion and multi-ion systems) were determined as a function of pH, initial concentration, contact time, temperature, and mass of biosorbent. An increase of adsorption capacity was observed following modification of natural zeolite/bentonite by microbial components with a maximum adsorption capacity obtained at low pH. The FTIR results of the developed biosorbents showed that the biomass has different functional groups that are able to react with metal ions in aqueous solution. Immobilisation of fungi (Penicillium-simplicissimum) on zeolite/bentonite yielded biomass of 600 mg g-1 (10-fold higher than the non-immobilised one) at a pH 4, showing the potential of this sorbent towards remediation of AMD-polluted mine sites. The maximum uptake of metals ions (in a multi-ion system) was higher and constant (40-50 mg g-1) in the inactive fungal biomass (heat-killed) from pH 2 to 7. The uptake of U and Hg increased significantly in the zeolite/bentonite-P.simplicissimum compared to their natural forms due to the presence of the N-H, S-H and COO- groups. iii The pseudo second-order adsorption model was found to be more suitable in describing the adsorption kinetics of metal ions onto biomasses in single- and multi-ion systems with the sorption of nickel being controlled by film diffusion processes (with the coefficient values of 10-7 cm2 s-1). The thermodynamic parameters showed that the adsorption onto developed biosorbents was feasible and spontaneous under the studied conditions. The calculated values of the loading capacities in column adsorption for the natural zeolite/bentonite as well as zeolite/bentonite-P.simplicissimum were close to those obtained in the batch tests, mainly for U and Ni. The bed depth service time model (BDST) was used successfully to fit the experimental data for Ni and U adsorbed on the natural zeolite. This suggested a linear relationship between bed depth and service time, which could be used for scale-up purpose. The developed biosorbents could be regenerated using 1 mol L-1 HNO3 solution for potential re-use. The total decrease in biosorption efficiency of zeolite-Penicillium simplicissimum after five cycles of adsorption-desorption was ≤ 5% which showed that zeolite/bentonite-Penicillium simplicissimum had good potential to adsorb metal ions repeatedly from aqueous solution. On applying it to real wastewater samples, the zeolite-P. simplicissimum biosorbent removed 97% of the metals. Penicillium sp. immobilisation enhanced the potential and makes it an attractive bioremediation agent. The zeolite-alginate sorbent exhibited elevated adsorption capacities for metals. This showed potential for use of such a system for remediation purposes. It also provides a platform to explore the possibility of using zeolite in conjunction with other polysaccharide-containing materials for heavy metal removal from wastewaters. The results obtained in this study have shown that zeolite and bentonite are good supports for biomass. The biofunctionalised zeolite/bentonite systems have potential in removal of heavy metals from wastewaters.

Studies were carried out from July 1988 to August 1989 to assess the growth and winter survival of water hyacinth, Eichhornia crassipes (Mart.) Solms, in treatment of secondary domestic wastewater in Tucson, Arizona. Percent of surviving overwintered plants for the following frost protection treatments from November 1988 to March 1989 was: 25 (control), 48 (plastic tarps), 70 (sprinklers), 34 (fog) and 76 (greenhouse). Both control plants and protected plants had longer roots at the effluent end of the ponds than the influent ends during winter months. Greenhouse-protected plants had greater root and entire plant lengths, and greater fresh and dry weights. Dry weight per unit area (kg m⁻²) was higher for greenhouse plants though all protected plants showed decline in dry weight per unit area with temperatures below 10 C. Qualitative observations indicated that protected plants showed less chlorosis and necrosis from low temperatures than control plants, however, plants in all frost protected treatments experienced low temperature stress. Aphids were seen in some of the ponds throughout the study and contributed to severe lamina and petiole damage.