The Council plans to initially reduce the bacteria to bathing standards before discharge to the Estuary. This means bacteria levels will be well inside accepted guidelines once the wastewater is in the Estuary. Although chemical disinfection has never been used to treat Christchurch wastewater, there is some justification that technically and economically it should be considered. However with the large quantities of chlorine required to purify wastewater and with growing concerns about the resulting impact this can have on the environment, alternative methods of disinfection are becoming more attractive and viable. Ozone is an effective and clean method of disinfection, but very expensive.
Electrocution is another disinfectant.
Standard UV systems usually require a clear liquid, relatively free of suspended solids to effectively kill bacteria. Wastewater high in suspended solids is much less easy to treat with UV or requires a higher input of power to achieve the desired result. UV disinfection of wastewater is normally carried out directly after the treatment plant and before entry to the ponds where wastewater has a low concentration of suspended solids. However new UV technologies have been developed recently that can be more effective in algae-laden water. The advantage of disinfecting after the wastewater has been through the ponds is that the bacteria deposited in the ponds by birds can also be killed.