In the mid-1990s, several pilot plants were constructed at Wairakei to either improve the operational and economic performance of the power station or to mitigate the environmental effects of discharges to the Waikato River. The results of the following investigations are discussed: (1) fluid flow dynamic effects on silica scaling; (2) production of silica sols of predetermined particle size to evaluate the potential for generating commercial grade silica products; (3) use of "sulfur oxidising bacteria" for the abatement of dissolved hydrogen sulphide in cooling water; (4) removal of arsenic from separated geothermal water; (5) steam line condensate corrosion: and (6) measurement and modelling of steam scrubbing in Wairakei's long steamlines. (c) 2008 Elsevier Ltd. All rights reserved.