Charlottenburgh Park are trialling a new system which sees old tyres being used as a treatment for sewage. Around 25,000 tyres in 30 truckloads have been used to create a pilot project to treat wastewater.

Normally, the tyre chips would head to landfill. However, these chips have instead been shipped to the park to help filter sewage. The chips act as a habitat for bacteria that convert nutrients in the park visitors waste into harmless compounds such as carbon dioxide. The system should be able to filter around 30,000 litres of sewage a day – that’s approximately the amount of sewage that 10-20 residential homes produce.

The treatment site covers around an acre of land and is divided into three systems – two of the systems are using the tyre chips and it is predicted that the tyre chip system will imitate the biological processes found in wetland. The third system uses a traditional gravel based system and this acts as a standard by which to measure the two tyre chip systems.

It is anticipated that the project will be cheaper to run that it’s alternatives – long white pipes allow oxygen to travel deep into the material passively, doing away with the need for expensive mechanical pumps. Oxygen is essential in the process because it allows the bacteria needed to thrive. Iron scraps are dotted around in the tyre chips to help absorb phosphorous and discourage the growth of algae (which use up the free oxygen).

The project has cost around $500,000 including a grant of $150,000 from the Ministry of Environment’s Best in Science research partnership program. The grant allows the system to be monitored over the next three years to measure how effective the new system is in comparison to more traditional methods. If successful, the project has the potential to be scaled upwards and used in larger projects such as in other parks or in municipal waster water plants.

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