An investigation into the fundamental understanding of an activated sludge bioremediation process and optimisation of thiocyanate and cyanide destruction

Cyanide (CN) is used in the gold mining industry to dissolve gold from free milling, complex and refractory gold containing ores. Processing sulphide containing refractory ores using biooxidation as a pre-treatment has become increasingly important due to the depletion of free milling ores. The reaction of CN with reduced sulphur species during the cyanidation process results in the formation of thiocyanate (SCN), often at relatively high concentrations (> 5 000 mg/L). The SCN and residual free CN are deported with the tailings as components of the liquid fraction. The concentration of SCN often exceeds the legislated discharge specification, necessitating on-site treatment, while water would also require treatment before on-site recycling and reuse. Biological degradation of CN and particularly SCN in these effluents provides an alternative to the more traditional processes such as SO2 treatment or UV destruction. The traditional destruction processes focus on breaking the chemical bonds, through physical or chemical means, thereby converting the toxic CN and SCN species to less toxic compounds. These processes generally suffer from high reagent cost, incomplete removal of CN and particularly SCN species and the generation of by-products which require further treatment. A number of microorganisms are capable of utilising CN and SCN as a source of sulphur, nitrogen and carbon, as well as generating energy from their oxidation. Additional removal of metal-CN complexes may be achieved by adsorption to the cell surface or extracellular polymeric substances secreted by the cells. The activated sludge tailings effluent remediation (ASTERTM) process was developed for the biological treatment of especially SCN, but also free CN and metal-cyanide complexes, such as CuCN and Zn(CN)2. The basic ASTERTM technology consists of an aerated reactor, in which SCN and CN species are oxidised and a settler to facilitate the recovery of water and potentially biomass. The desire to expand the commercial application of the technology necessitated a more complete, fundamental understanding of the ASTERTM process and required focused, in-depth research. This research aimed to define the viable operating window for SCN destruction, as well as optimising practical SCN and CN destruction process conditions. The ASTERTM process relies on a complex microbial community, so understanding the community structure and metabolic potential for SCN and CN destruction, further enhanced the fundamental and mechanistic understanding of this bioprocess. The research contributed to the fundamental understanding of this technology and enhanced the commercial application thereof. The first step in defining the operating window was to investigate the effect of feed SCN concentration on the SCN destruction ability of the mixed microbial community. Experiments were conducted at feed SCN concentrations ranging from 60- 1 800 mg/L. Complete SCN destruction was achieved across the range at ambient temperature. The maximum SCN destruction rate was 15.7 mg/L.h at an initial SCN concentration of 1 400 mg/L. Temperature was investigated in the range of 10-45°C with an initial SCN concentration range of 60-180 mg/L. A maximum SCN destruction rate of 17.4 mg/L.h was measured at 35°C, with an initial SCN concentration of 180 mg/L. A wide pH range (pH 5.0-10.0) was tolerated, with optimal performance recorded at pH 7.0. This evaluation identified not only the optimum operating pH, but also highlighted the negative impact of a sudden pH change on the efficiency of SCN destruction. Residual SCN concentrations below 1 mg/L were achieved in all cases, which would allow for discharge or recycling of treated water. Floc (sludge) formation was observed in experiments with high initial SCN concentrations and indicated a possible stress response during these batch experiments. Floc (sludge) formation were taken as microbial cells imbedded within extracellular polymeric substances and not only an aggregate of cells. Evaluating the maximum potential for SCN destruction and optimising the operating conditions and system configuration was investigated using continuous reactor experiments. A maximum SCN destruction rate of 87.4 mg/L.h (2 098 mg/L.d) was achieved at a feed SCN concentration of 1 000 mg/L and eight hour hydraulic retention time (HRT) during these experiments. The formation of substantial amounts of sludge was observed, with attachment to the reactor surfaces. The maximum feed SCN concentration, where substantial destruction was measured, was at 2 500 mg/L, achieving a practical SCN destruction rate of 972 mg/L.d. Significant inhibition of microbial inactivity was observed beyond this feed SCN concentration. The microbial community was able recover performance, within six days, after an extended period (54 days) of inactivity when the feed concentration was reduced from 3 500 mg/L SCN to 1 000 mg/L. The nature of the accumulated biofilm did not appear to change during the period of limited SCN destruction activity. Calculation of specific SCN destruction rates was not possible due to the nature of the sludge and heterogeneous dispersion of microbial members. Biomass (cells embedded in the EPS sludge) loading experiments showed SCN destruction rates increased with an increase in biomass loading, but this relationship was not proportional. A 25-fold increased biomass concentration resulted in only a 2-fold increase in destruction rate, suggesting a mass transfer limitation. The sludge most likely offers protection against unfavourable conditions, such as high residual SCN concentrations, by presenting a mass transfer barrier, resulting in an SCN concentration gradient across the sludge matrix. This enhances the robustness of the process and would facilitate rapid recovery in the case of a system upset at commercial scale. This research is the first to demonstrate the effective removal of SCN in the presence of suspended tailing solids, under conditions well suited for commercial application. The maximum SCN destruction rate achieved was 57 mg/L.h in the presence of 5.5% (m/v) solids. Sludge formation was not observed in the reactors containing solids, despite substantial sludge formation under similar operating conditions in the absence of solids, most likely due to shear-related effects. Fluctuations in pH, due to the nature of the solid material, were identified to negatively impact reactor performance and pH control was required. Moreover, the type of solid particle was found to influence the SCN destruction rate showing a need for adaptation not only to the presence of solids but also to various types of solids that are to be treated. Treatment of residual CN in solution is critical to ensure safe disposal or recycling of water. Treatment of SCN and CN was successfully demonstrated at feed concentrations up to 2 000 and 50 mg/L, respectively. The presence of residual CN (0.5 mg/L) prevented complete destruction of SCN, while complete SCN destruction was measured in the absence of CN under identical conditions. A range of reactor configurations were investigated and the optimum system required biomass retention, by means of attached biomass and complete destruction of any residual CN prior to SCN destruction. Conversion of SCN-S to SO4-S was stoichiometrically proportional in solution, while the majority of the liberated nitrogen appeared to be assimilated. Pre-colonisation of the reactor with attached biomass is beneficial and removed the need for a solid-liquid separation unit, reducing the potential footprint of the process. Additional treatment capacity could be created by operation of reactors in series. The diversity of the microbial community responsible for destruction of especially SCN were shown to be far more extensive than initially expected. Initial molecular characterisation of the microbial community selected for 185 representatives of bacterial 16S rRNA genes, of which 106 non-identical genotypes were sequenced. In contrast, for the reactor containing solids, only 48 representatives were selected and 30 genotypes were sequenced. Bacteria implicated in SCN destruction in the reactor containing suspended solids were members from the genera Bosea, Microbacterium and Thiobacillus. In the absence of solids, members capable of SCN destruction were identified from genera including Thiobacillus and Fusarium. High-throughput genome sequencing, followed by sequence assembly confirmed the dominance of Thiobacillus spp. Metabolic predictions indicated the autotrophs, gaining energy from the oxidation of reduced sulphur intermediates produced during SCN destruction were the dominant community members. The potential for ammonium oxidation and denitrification within the microbial community was identified during analysis of the metabolic potential, based on the metagenomic sequence data. These would be required for complete remediation of wastewater. The data generated during the research led to the development of a conceptual model to describe the evolution of system performance. Following inoculation with planktonic culture the SCN destruction is performed by the planktonic microbial community. An increased residual SCN concentration results in floc formation and the colonisation of reactor surfaces by attached biofilm. A concomitant decrease in planktonic cell concentration was observed, while SCN destruction rates increased. The extracellular material provided a matrix for biomass retention, resulting in high cell concentrations, and provided some protection against high SCN concentrations by providing a barrier to mass transfer. The attached biofilm developed to the point where overall SCN degradation rates may become limited by reduced oxygen penetration. The research presented in this thesis has been used to inform the design and operation of the ASTERTM process at commercial scale, specifically with respect to the benefits of attached biomass and the demonstration that the process can be used in the presence of suspended solids. The latter has been particularly important in applications where the available footprint is constrained

A new window of opportunity for TAVI

This short report features the role of multi detector computer tomography (MDCT) in imaging the ascending aorta to assess the feasibility of a transaortic access route for transcatheter placement of an Edwards SAPIEN XTTM aortic valve

First experience with the Edwards SAPIEN transcatheter aortic valve implantation (TAVI). Data from the Western Cape, South Africa

Background: Transcatheter aortic valve implantation (TAVI) is an exciting new technology that was launched in South Africa in October 2009 for the treatment of aortic stenosis in patients at high risk for conventional surgery. We report our initial experience with TAVI in the Western Cape, South Africa. Methods: 70 patients with severe symptomatic aortic stenosis underwent TAVI with the Edwards SAPIEN device (26 via transapical approach and 44 via transfemoral) at Panorama and Vergelegen Mediclinic hospitals in the Western Cape. All implants were performed by a team consisting of 2 cardiothoracic anaesthesiologists, 2 cardiothoracicsurgeons, 2 cardiologists and an echo expert. Results: Patients were at high risk with a mean age of 80 years and a mean logistic EuroSCORE of 26. The acute procedural success rate was 97% with two acute deaths. At 30 days, there were a total of 5 deaths. Major vascular complications were seen in 6 cases (9%). Only one stroke was seen during the follow-up period. Conclusions: With a multidisciplinary team approach and careful patient selection, TAVI can be performed by a high volume centre in South Africa with results comparable to international published outcomes

First case of trans apical implantation of an aortic valve in a patient with dextrocardia

We describe the clinical presentation and implantation procedure of the first transcatheter aortic valve implantation described in a patient with dextrocardia

Analysis of the microbial community associated with a bioprocess system for bioremediation of thiocyanate- and cyanide-laden mine water effluents

Gold extraction by cyanidation from refractory gold ores results in the formation of thiocyanate- and cyanide-contaminated wastewater effluents that must be treated before recycle or discard. Activated sludge processes, such as ASTER™, can be used for biodegradation of these effluent streams. The destruction of these compounds is catalyzed by a mixed microbial culture, however, very little is known about the community composition and metabolic potential of the thiocyanate- and cyanide-degrading microorganisms within the community. Here we describe our on-going attempts to better understand the key microorganisms, within the ASTER™ bioprocess, that contribute to the destruction of thiocyanate and cyanide, and how this knowledge relates to further process optimisation

The Archaeofauna from Xaro on the Okavango Delta in northern Botswana

We report on the fauna from the sites of Xaro 1 and Xaro 2 located on the Okavango Delta in northern Botswana. Carbon isotopes from two human graves at Xaro Lodge located approximately 500 m south of Xaro 1 suggest an economy oriented toward wild plants, fish and game similar to that of the modern baNoka, or ‘River Bushmen’. The faunal remains from Xaro 1 and 2 corroborate this suggestion.Pottery from the Early Iron Age, radiocarbon dates from the Later Iron Age, and glass beads from the European trade indicate there were two occupations at both sites, one belonging to the 18th and 19th centuries and an earlier one containing ceramics consistent with a first millennium AD date. The fauna from both occupations is dominated by fish and Chelonia (likely tortoise or terrapin). The people also hunted a variety of game animals, most of which are associated with aquatic conditions. Sheep remains were recovered from the later occupation of Xaro 1.http://www.journals.co.za/ej/ejour_nfi_ditsong.htmlam2013cp201

An investigation into the effects of preleach time period, nitrogen supplementation and iron concentration on bioleaching performance

Includes abstract.Includes bibliographical references (leaves 69-75).Bioleaching has developed into a very important process for the recovery of valuable metals, particularly from low grade copper ores due to the ever increase in demand. A lag phase is present during the start-up phase of heap bioleach operations characterised by a low degree of microbial colonisation, a low ferrous iron oxidation rate and low microbial proliferation rates, ultimately resulting in a poor copper recovery rate

Die struktuurbepaling en totaalsintese van die antikankerverbinding dolastatien 3

D.Sc. (Chemistry)Please refer to full text to view abstrac

Metodologie vir die sintese van chirale tiofeenderivate

M.Sc. (Chemistry)Please refer to full text to view abstrac

Hyperbaric oxygenation : a general review with special consideration of the surgical applications

Thesis (M.D.) -- University of Stellenbosch, 1966.Full text to be digitised and attached to bibliographic record