To address the adverse effects of ammonia in leachate-impacted stormwater, Timaru District Council (TDC) engaged Pattle Delamore Partners Ltd (PDP) to design an effective treatment solution. The key project objectives were to develop a solution that:
- Mitigates the impact on aquatic ecology.
- Requires minimal supervision and maintenance.
- Has a low capital and operational cost.
PDP’s solution was a nitrifying trickling filter (NTF), constructed on the embankment of a historic landfill and the bank of a stormwater pond. The NTF design used locally sourced rock to provide a medium for biofilm growth, with gabion baskets forming the structure’s walls. This created an aesthetically pleasing feature visible from a nearby public walkway.
Since its commissioning in September 2020, the NTF has achieved a 93% reduction in ammoniacal nitrogen, lowering concentrations to an average of 0.55 g/mÑ. Additionally, it contributed to a 16% reduction in total nitrogen and improved the clarity of the stormwater pond through natural coagulants from the biofilm.
The success of the first NTF led to the design of a second filter in 2023. This project was nominated for Water NZ’s Stormwater Project of the Year at the 2024 National Stormwater Conference, demonstrating its environmental impact.
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