The Allconnex Water treatment plants provide wastewater treatment for Gold Coast, Logan and Redland districts.
Treatment plants differ tremendously in the amount of wastewater they can treat, and the quality of the outputs they can produce. While differing in complexity and the technology that they use, most treatment plants are based on a combination of physical and biological processes, that are described below:
Please refer to the Glossary for further explanation of unfamiliar terms.
Inlet works
As wastewater enters a treatment works, it is pumped from a wet well under the inlet building into the screenings and grit removal areas. It passes through screens to remove larger solid material such as paper and objects. The inlet screening is followed by grit removal to remove sand, stones and other non-biodegradable items such as fruit seeds.
Primary sedimentation
A primary sedimentation tank or primary clarifier may be used to remove heavier suspended solids in the wastewater.
As well as reducing the aeration requirements and the size of the biological reactor required, this material collected in this type of tank can be fermented and used as biodegradable material for the biological nutrient removal processes downstream.
Such a tank may also be used to help manage overflows in the event of higher than average flow periods.
Biological reactor
Biological treatment is generally based on two treatment methods; oxidation ditches and bioreactors. Both use natural micro-organisms to break down the waste products using both aerated and un-aerated cycles.
Oxidation ditches
Oxidation ditches are primarily used to reduce the organic material and nitrogen in the wastewater. They tend to use surface aerators to provide the oxygen required. While this process also achieves some phosphorus reduction, this is only due to the uptake by the micro-organisms.
Bioreactors
A biological nutrient removal (BNR) reactor or bioreactor is a tank that involves more complex aeration control and more circulation and movement of the large volumes of wastewater. The bioreactor is able to reduce phosphorus levels more effectively than an oxidation ditch.
Final clarifiers
Final clarifiers separate the solid and liquid portions of the flow leaving the oxidation ditches and bioreactors. Part of the solid material that settles in these tanks is returned to the system to maintain a viable population of micro-organisms.
Final clarification process is very important in managing the biological load that a treatment plant outputs into the environment.
Sludge treatment
Micro-organisms left over from the biological system constitute the 'sludge' at a wastewater treatment works. After excess water is removed from the sludge, these solids are then disposed and the water is further treated.
Disinfection
At this point, the wastewater still contains bacteria and other micro-organisms which may be harmful to human health.
These must be removed or reduced to non-harmful levels before the final product leaves the wastewater treatment plant, either for discharge into a river or for beneficial re-use.
Chemical Dosing
A bioreactor will reduce the concentration of phosphorus - however as this is a purely biological method and it can produce inconsistent results, dependent upon wastewater quality, temperature and aeration control. Chemicals such as ferric salts and alum may be used to provide a more consistent result.
For further information on the treatment process please view the 
Wastewater treatment process brochure (987kb).