The threat of global warming due to CO 2 emissions has stimulated research into carbon sequestration and emissions reduction technologies. Alkaline scrubbing allows CO 2 to be captured as bicarbonate, which can be photochemically fixed by microalgae. The carbon concentrating mechanism (CCM), of which external carbonic anhydrase is a key component, allows the organisms to utilise this bicarbonate. In order to select a suitable strain for this application, a screening tool is required. The current method for determining carbonic anhydrase activity, the Wilbur and Anderson assay, was found to be unsuitable as a screening tool as the associated error was unacceptably large and tests on whole cells were inconclusive. This paper presents the development of a new, whole cell assay to measure inorganic carbon uptake and external carbonic anhydrase activity, based on classical pH drift experiments. Spirulina platensis was successfully used to develop a correlation between the specific carbon uptake (C) and the specific pH change (dpH). The relationship is described by: C (mmol C (g dry algae)-1 h-1) = 0.064 × (dpH). Inhibitor and salt dissociation tests validated the activity and presence of external carbonic anhydrase, and allowed correlation between the Wilbur and Anderson assay and the new whole cell assay. Screening tests were conducted on Spirulina platensis, Scenedesmus sp., Chlorella vulgaris and Dunaliella salina which were found to have carbon uptake rates of 5.76, 5.86, 3.86 and 2.15 mmol C (g dry algae)-1 h-1 respectively. These results corresponded to the species' known bicarbonate utilisation abilities and validated the use of the assay as a screening tool.

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Heap bioleaching operations are often faced with extended and unpredictable lag periods after inoculation, prior to the establishment of a stable oxidising environment, during which the heap is fully colonised or the inoculum overcomes the sub-optimal conditions resulting from acid agglomeration. Supplementation of laboratory scale (4kg ore) leach columns with soluble nitrogen, particularly as yeast extract, significantly reduced the lag time and promoted bacterial growth, resulting in a 50-95% increase in copper recovery post-inoculation. The effect of yeast extract addition to Acidithiobacillus ferrooxidans in controlled oxidation tests was investigated. Initial exposure of a stock culture to yeast extract resulted in a transient, dose dependent inhibition at concentrations of 0.5 g.l-1 and below. At 1.25 g.l-1 inhibition was complete over the time scale of the experiment. The inhibition phase was characterised by observable changes in cell morphology and ultrastructure. Despite the initial inhibition, the biomass yield at the end of the experiments was equivalent, or higher, in the presence of yeast extract. Cultures were adapted to growth on yeast extract as the sole nitrogen source and adapted cultures showed the highest rates of iron oxidation and cell growth, in the presence of 0.5 and 1 g.l-1 of yeast extract.