Full Scale Tubular Bioreactor for Hydrogen Sulphide Removal

The Wairakei geothermal power station situated in Taupo in the North Island of New Zealand was commissioned in 1958. Condensing water and geothermal steam condensate containing hydrogen sulphide is discharged to the Waikato River. Environmental concerns over sulphide aquatic toxicity in the river were considered when discharge permit conditions were reviewed in 2007. New discharge limits for the power station came into effect in August 2012, requiring the mass emission of hydrogen sulphide in the condensing water to be reduced from current levels of approximately 10,300kg/week to 2,800kg/week, with a further reduction to 630kg/week from 2016. This required a hydrogen sulphide concentration reduction from 1000mg/m3 to less than 60mg/m3 in a cooling water flow of 17m3 /s. An innovative tubular biofilm reactor was developed, leading to construction of a full scale plant in 2012. The full scale bioreactor consists of 1890 parallel 100mm diameter x 200m length pipes with a total length of 378km, believed to be the largest tubular biofilm reactor in the world at the time of construction.