Development of respirometry methods to assess the microbial activity of thermophilic bioleaching archaea

Respirometry methods have been used for many years to assess the microbial activity of mainly heterotrophic bacteria. Using this technique, the consum ption of oxygen and evolution of carbon dioxide for heterotrophic carbon ca tabolism can be used to assess microbial activity. In the case of autotroph ic bioleaching bacteria, carbon dioxide is used as a carbon source resultin g in the consumption of both oxygen and carbon dioxide. The use of such res pirometry techniques at high temperatures (up to 80 degreesC) for the inves tigation of bioleaching Archaea, however, poses particular difficulties. At these elevated temperatures, the solubility of oxygen into the liquid phas e is particularly poor. This work details specific methods by which high te mperature constraints are overcome while monitoring the activity of thermop hilic Archaea using a Micro-Oxymax respirometer (Columbus Instruments). The use of elevated headspace oxygen concentrations, in order to overcome low oxygen solubility, is demonstrated as well as the effect of such elevated o xygen concentrations on microbial oxygen consumption rates. The relative ra tes of oxygen and carbon dioxide consumption are also illustrated during th e oxidation of a chalcopyrite concentrate. In addition, this paper details generic methods by which respirometry data can be used to quantify inhibito ry effects of a compound such as Na2SO4. The further use of such data in pr edicting minimum hydraulic reactor retention times for continuous culture b ioleaching reactors, as a function of concentration of potentially inhibito ry compounds, is also demonstrated. (C) 2001 Elsevier Science B.V. All righ ts reserved.