K.A. Third

CANON and Anammox in a gas‐lift reactor

Anoxic ammonium oxidation (Anammox) and Completely Autotrophic Nitrogen removal Over Nitrite (CANON) are new and promising microbial processes to remove ammonia from wastewaters characterized by a low content of organic materials. These two processes were investigated on their feasibility and performance in a gas-lift reactor. The Anammox as well as the CANON process could be maintained easily in a gas-lift reactor, and very high N-conversion rates were achieved. An N-removal rate of 8.9 kg N (m(3) reactor)(-1) day(-1) was achieved for the Anammox process in a gas-lift reactor. N-removal rates of up to 1.5 kg N (m(3) reactor)(-1) day(-1) were achieved when the CANON process was operated. This removal rate was 20 times higher compared to the removal rates achieved in the laboratory previously. Fluorescence in situ hybridization showed that the biomass consisted of bacteria reacting to NEU, a 16S rRNA targeted probe specific for halotolerant and halophilic Nitrosomonads, and of bacteria reacting to Amx820, specific for planctomycetes capable of Anammox.

The role of iron-oxidizing bacteria in stimulation or inhibition of chalcopyrite bioleaching

A series of bacterial and chemical leaching experiments were conducted to clarify contradictory reports in the literature regarding the role of bacteria in the bioleaching of chalcopyrite. Tests containing a high bacterial concentration showed inhibited leaching, even lower than non-inoculated controls. However, when bacterial cells were washed before inoculation, it was apparent that it was not the bacterial cells but rather the chemical species introduced with them that influenced the leaching rate. In addition, the results of comparative tests with 0.1 M ferrous sulphate or ferric sulphate showed that copper was leached from the ore 2.7 times faster in leach solutions containing ferrous ion, suggesting that ferric ions inhibit chalcopyrite dissolution. The results indicated that the chalcopyrite dissolution rate is strongly dependent on the reduction potential (Eh) in solution, and that this parameter is far more influential than the number or activity of bacterial cells. These results imply that the role of bacteria may only be stimulatory when the prevailing electrochemical conditions are also favourable.