Is it necessary to re-inoculate a heap that increases in temperature?

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The microbiology of bioheaps is more complex than that for stirred tank reactors for treating sulfide minerals due to the presence of gradients of not just temperature but also pH, nutrients, oxygen and metals etc. Due to these different niches it is an important consideration to ensure that bioheaps contain sufficient biodiversity for microorganisms to inhabit all of the available niches [1]. To ensure that there is an even distribution of the microorganisms is complex and bioheap inoculation has been patented.

In theory, it would not be necessary for a bioheap to be re-inoculated as it heats up due to exothermic biological and chemical reactions as microorganisms are likely to be present in the environment in low numbers that will be able to grow at higher temperatures, especially those that are able to produce spores. However, it is highly likely that bioleaching will proceed after the heap increases in temperature with a shorter lag phase if it is inoculated with thermophiles, although the actual time saving is unknown. If the bioheap is to be inoculated it would be likely that microorganisms already present capable of growth at lower temperatures will persist, particularly in the outer areas of the heap.


  1. Rawlings & Johnson (2007) The microbiology of biomining: development and optimization of mineral-oxidizing microbial consortia. Microbiology 153: 315-324
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