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

The preparation of bovine 19s thyroglobulin by agarose-gel filtration

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A systematic, functional genomics, and reverse vaccinology approach to the identification of vaccine candidates in the cattle tick, Rhipicephalus

In the post-genomic era, reverse vaccinology is proving promising in the development of vaccines against bacterial and viral diseases, with limited application in ectoparasite vaccine design. In this study, we present a systematic approach using a combination of functional genomics (DNA microarrays) techniques and a pipeline incorporating in silico prediction of subcellular localization and protective antigenicity using VaxiJen for the identification of novel anti-tick vaccine candidates. A total of 791 candidates were identified using this approach, of which 176 are membrane-associated and 86 secreted soluble proteins. A preliminary analysis on the antigenicity of selected membrane proteins using anti-gut antisera yielded candidates with an IgG binding capacity greater than previously identified epitopes of Bm86. Subsequent vaccination trials using recombinant proteins will not only validate this approach, but will also improve subsequent reverse vaccinology approaches for the identification of novel anti-tick vaccine candidates.The Red Meat Research Development Trust, University of Pretoria Research Development Programme, and the Technology and Human Resources for Industry Programme.http://www.elsevier.de/ttbdishb201

Evaluation of the ASTERTM process in the presence of suspended solids

The ability to recycle and reuse process water is a major contributing factor toward increased sustainability in the mining industry. However, the presence of toxic compounds has prevented this in most bioleaching operations. The ASTERTM process has been used for the bioremediation of cyanide (CN) and thiocyanate (SCN−) containing effluents at demonstration and commercial scale, increasing the potential for recycling of the treated effluent. The process relies on a complex consortium of microorganisms and laboratory tests have shown that the biomass retention, in suspended flocs or attached biofilm, significantly improved SCN− degradation rates. The current research evaluated the process performance in the presence of suspended solids (up to 5.5% m/v) ahead of implementation at a site where complete tailings removal is not possible. Experiments were performed in four 1 l CSTRs (with three primary reactors in parallel at an 8 h residence time, feeding one secondary reactor at a 2.7 h residence time). Stable operation at the design specifications (5.5% solids, 100 mg/l SCN− feed, effluent SCN− 57 mg/l/h was achieved, despite no obvious floc formation. Microbial ecology studies (16S rRNA clone library) revealed reduced diversity relative to reactors operated without suspended solids

Comparison of the VersaTREK blood culture system against the Bactec9240 system in patients with suspected bloodstream infections

BACKGROUND: To evaluate the VersaTREK (TREK Diagnostic Systems, Cleveland, Ohio) blood culture system against the Bactec9240 (BD Microbiology, Cockeysville, MD), for the recovery of bloodstream pathogens. METHODS: Venous blood from patients with suspected bacterial sepsis was evenly distributed into bottles of each system. Positive signals were recorded and bottles processed onto standard media for organism recovery. False positive signals were regarded if no organisms were seen on Gram stain and no growth was observed. RESULTS: 177 bottles were available for analysis; the Bactec9240 system yielded 43 positive, 134 negative results and no false positive signals. The VersaTREK system had 58 positive signals with 14 being false positives. CONCLUSIONS: In our setting with high background burden of immuno-compromised patients, the VersaTREK system compared favourably with the Bactec9240 in recovering blood stream aerobic and facultative anaerobic pathogens from patients with suspected bacterial sepsis. A concern is the high false positivity rate. Due to its versatility to accommodate small and large workloads as well as using smaller volumes of blood, this system may establish itself as a useful alternative for the recovery of bloodstream pathogens

Comparative microarray analyses of adult female midgut tissues from feeding Rhipicephalus species

The cattle tick, Rhipicephalus microplus, has a debilitating effect on the livestock industry worldwide, owing to its being a vector of the causative agents of bovine babesiosis and anaplasmosis. In South Africa, co-infestation with R. microplus and R. decoloratus, a common vector species on local livestock, occurs widely in the northern and eastern parts of the country. An alternative to chemical control methods is sought in the form of a tick vaccine to control these tick species. However, sequence information and transcriptional data for R. decoloratus is currently lacking. Therefore, this study aimed at identifying genes that are shared between midgut tissues of feeding adult female R. microplus and R. decoloratus ticks. In this regard, a custom oligonucleotide microarray comprising of 13,477 R. microplus sequences was used for transcriptional profiling and 2476 genes were found to be shared between these Rhipicephalus species. In addition, 136 transcripts were found to be more abundantly expressed in R. decoloratus and 1084 in R. microplus. Chi-square analysis revealed that genes involved in lipid transport and metabolism are significantly overrepresented in R. microplus and R. decoloratus. This study is the first transcriptional profiling of R. decoloratus and is an additional resource that can be evaluated further in future studies for possible tick control.The Red Meat Research Development Trust Gauteng Department of Agriculture and Rural Development,University of Pretoria Research Development Program, and the National Research Foundation’s Technology and Human Resourcesfor Industry Program (Grant No. TP2010072300035).http://www.elsevier.com/locate/ttbdishb201

Gene expression profiling of adult female tissues in feeding Rhipicephalus microplus cattle ticks

The southern cattle tick, Rhipicephalus microplus, is an economically important pest, especially for resource-poor countries, both as a highly adaptive invasive species and prominent vector of disease. The increasing prevalence of resistance to chemical acaricides and variable efficacy of current tick vaccine candidates highlight the need for more effective control methods. In the absence of a fully annotated genome, the wealth of available expressed sequence tag sequence data for this species presents a unique opportunity to study the genes that are expressed in tissues involved in blood meal acquisition, digestion and reproduction during feeding. Utilising a custom oligonucleotide microarray designed from available singletons (BmiGI Version 2.1) and expressed sequence tag sequences of R. microplus, the expression profiles in feeding adult female midgut, salivary glands and ovarian tissues were compared. From 13,456 assembled transcripts, 588 genes expressed in all three tissues were identified from fed adult females 20 days post infestation. The greatest complement of genes relate to translation and protein turnover. Additionally, a number of unique transcripts were identified for each tissue that relate well to their respective physiological/biological function/role(s). These transcripts include secreted anti-hemostatics and defense proteins from the salivary glands for acquisition of a blood meal, proteases as well as enzymes and transporters for digestion and nutrient acquisition from ingested blood in the midgut, and finally proteins and associated factors involved in DNA replication and cell-cycle control for oogenesis in the ovaries. Comparative analyses of adult female tissues during feeding enabled the identification of a catalogue of transcripts that may be essential for successful feeding and reproduction in the cattle tick, R. microplus. Future studies will increase our understanding of basic tick biology, allowing the identification of shared proteins/pathways among different tissues that may offer novel targets for the development of new tick control strategies.The Red Meat Research Development Trust, University of Pretoria Research Development Programme and the Technology and Human Resources for Industry Programme, South Africa. Additional funding and student support was obtained from the National Research Foundation of South Africa.http://www.elsevier.com/locate/ijpar

New approaches in the diagnosis and treatment of latent tuberculosis infection

With nearly 9 million new active disease cases and 2 million deaths occurring worldwide every year, tuberculosis continues to remain a major public health problem. Exposure to Mycobacterium tuberculosis leads to active disease in only ~10% people. An effective immune response in remaining individuals stops M. tuberculosis multiplication. However, the pathogen is completely eradicated in ~10% people while others only succeed in containment of infection as some bacilli escape killing and remain in non-replicating (dormant) state (latent tuberculosis infection) in old lesions. The dormant bacilli can resuscitate and cause active disease if a disruption of immune response occurs. Nearly one-third of world population is latently infected with M. tuberculosis and 5%-10% of infected individuals will develop active disease during their life time. However, the risk of developing active disease is greatly increased (5%-15% every year and ~50% over lifetime) by human immunodeficiency virus-coinfection. While active transmission is a significant contributor of active disease cases in high tuberculosis burden countries, most active disease cases in low tuberculosis incidence countries arise from this pool of latently infected individuals. A positive tuberculin skin test or a more recent and specific interferon-gamma release assay in a person without overt signs of active disease indicates latent tuberculosis infection. Two commercial interferon-gamma release assays, QFT-G-IT and T-SPOT.TB have been developed. The standard treatment for latent tuberculosis infection is daily therapy with isoniazid for nine months. Other options include therapy with rifampicin for 4 months or isoniazid + rifampicin for 3 months or rifampicin + pyrazinamide for 2 months or isoniazid + rifapentine for 3 months. Identification of latently infected individuals and their treatment has lowered tuberculosis incidence in rich, advanced countries. Similar approaches also hold great promise for other countries with low-intermediate rates of tuberculosis incidence

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

n Ondersoek na die invloed van hipervitaminose A op beengroei, die endokrine sisteem en die bloedsyfer asook die moontlike sinergisme en antagonisme van vitamines A, B en D

Proefskrif (M. Sc. Fisiologie) -- Universiteit van Stellenbosch, 1948.Full text to be digitised and attached to bibliographic record