No abstract

No abstract

The need to remove or recover metal ions from industrial wastewaters is both financially and environmentally driven, financially in terms of cost savings through metal reuse or sale, and environmentally as heavy metal toxicity can affect organisms throughout the food chain, including humans. Current removal strategies are mainly based on physico-chemical techniques such as filtration, chemical precipitation and solvent extraction. All these "conventional" technologies have raised issues of efficacy when faced with low metal concentrations, high start-up or operating costs and low metal selectivity. Conversely, metal removal using biological and membrane processes is becoming more widely accepted as new evidence is gathered highlighting their lower cost, ease of operation, selectivity and efficacy. Precipitation of metal ions using biogenic hydrogen sulphide, produced by sulphate-reducing bacteria, is not a new technique, and is used by a small number of industrial installations worldwide. While this process has disadvantages such as the hazardous nature of the gas, the advantages inherent in utilising this source of sulphide are greatly enhanced when used in combination with membrane bioreactor technology. Initial studies have shown that the sulphate-reducing bacterial bioreactor coupled with a membrane can remove up to 90% of the metal ions present in an aqueous solution.

The process of platinum group metal (PGM) refining can be up to 99.99% efficient at best, and although it may seem small, the amount of valuable metal lost to waste streams is appreciable enough to warrant recovery. The method currently used to remove entrained metal ions from refinery wastewaters, chemical precipitation, is not effective for selective recovery of PGMs. The yeast Saccharomyces cerevisiae has been found capable of sorbing numerous precious and base metals, and is a cheap and abundant source of biomass. In this investigation, S. cerevisiae was immobilised using polyethyleneimine and glutaraldehyde to produce a suitable sorbent, capable of high platinum uptake (150-170 mg/g) at low pH (<2). The sorption mechanism was found to be a chemical reaction, which made effective desorption impossible. When applied to PGM refinery wastewater, two key wastewater characteristics limited the success of the sorption process; high inorganic ion content and complex speciation of the platinum ions. The results proved the concept principle of platinum recovery by immobilised yeast biosorption and indicated that a more detailed understanding of the platinum speciation within the wastewater is required before biosorption can be applied. Overall, the sorption of platinum by the S. cerevisiae sorbent was demonstrated to be highly effective in principle, but the complexity of the wastewater requires that pretreatment steps be taken before the successful application of this process to industrial wastewater.

No abstract