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 consumption of oxygen and evolution of carbon dioxide for heterotrophic carbon catabolism can be used to assess microbial activity. In the case of autotrophic bioleaching bacteria, carbon dioxide is used as a carbon source resulting in the consumption of both oxygen and carbon dioxide. The use of such respirometry techniques at high temperatures (up to 80 degrees C) for the investigation of bioleaching Archaea, however, poses particular difficulties. At these elevated temperatures, the solubility of oxygen into the liquid phase is particularly poor. This work details specific methods by which high temperature constraints are overcome while monitoring the activity of thermophilic 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 oxygen concentrations on microbial oxygen consumption rates. The relative rates of oxygen and carbon dioxide consumption are also illustrated during the oxidation of a chalcopyrite concentrate. In addition, this paper details generic methods by which respirometry data can be used to quantify inhibitory effects of a compound such as Na(2)SO(4). The further use of such data in predicting minimum hydraulic reactor retention times for continuous culture bioleaching reactors, as a function of concentration of potentially inhibitory compounds, is also demonstrated.

Empirical model for the autotrophic biodegradation of thiocyanate in an activated sludge reactor.

AIMS: The aim of this investigation was to develop an empirical model for the autotrophic biodegradation of thiocyanate using an activated sludge reactor. METHODS AND RESULTS: The methods used for this purpose included the use of a laboratory scale activated sludge reactor unit using thiocyante feed concentrations from 200 to 550 mg x l(-1). Reactor effluent concentrations of <1 mg x l(-1) thiocyanate were consistently achieved for the entire duration of the investigation at a hydraulic retention time of 8 h, solids (biomass) retention of 18 h and biomass (dry weight) concentrations ranging from 2 to 4 g x l(-1). A biomass specific degradation rate factor was used to relate thiocyanate degradation in the reactor to the prevailing biomass and thiocyanate feed concentrations. A maximum biomass specific degradation rate of 16 mg(-1) x g(-1) x h(-1) (mg thiocyanate consumed per gram biomass per hour) was achieved at a thiocyanate feed concentration of 550 mg x l(-1). The overall yield coefficient was found to be 0.086 (biomass dry weight produced per mass of thiocyanate consumed). CONCLUSION: Using the results generated by this investigation, an empirical model was developed, based on thiocyanate feed concentration and reactor biomass concentration, to calculate the required absolute hydraulic retention time at which a single-stage continuously stirred tank activated sludge reactor could be operated in order to achieve an effluent concentration of <1 mg x l(-1). The use of an empirical model rather than a mechanistic-based kinetic model was proposed due to the low prevailing thiocyanate concentrations in the reactor. SIGNIFICANCE AND IMPACT OF THE STUDY: These results represent the first empirical model, based on a comprehensive data set, that could be used for the design of thiocyanate-degrading activated sludge systems.