The Botany Groundwater Treatment plant was constructed in 2005 as part of the project to remediate groundwater contaminated with chlorinated hydrocarbons. The chlorinated hydrocarbons are removed by air stripping before further treatment steps to enable re-use of the water. Off-gases from the stripping process are treated by thermal oxidation, yielding a weak acid stream which is recycled to the stripping process to prevent iron fouling.

The stripping process has been plagued by fungal fouling since it began operation, despite initially operating at pH 2.7. Manual cleaning was required on a fortnightly basis. The aeration, low pH, and presence of chemical reducing agents limits the use of standard chlorine disinfection. Metal based and organic biocides were screened without success. Increased pH proved most effective, but limited in practice by iron precipitation replacing biomass as the foulant. Operation at pH 4.5-5 was found to be the optimum, but manual cleaning was still required monthly, presenting a significant occupational health risk as well as maintenance costs.

Chlorine dioxide was proposed as a biocide, as it can be applied over a wide range of pH, and is significantly more effective against biofilms than chlorine. Despite being a dissolved gas, it is much less volatile than chlorine, and hence was considered feasible. A trial of chlorine dioxide dosing was conducted with dramatic success. A full scale system was installed and commissioned, with chlorine dioxide produced by the acidification of sodium chlorite solution, thus utilising the waste acid from the thermal oxidation process.