The Marton Wastewater Treatment Plant (WWTP) faced persistent odour problems due to high nitrogenous waste from local industry, which caused the primary receiving pond to become anaerobic. Despite the Rangitikei District Council spending $150,000 annually on mechanical aeration, the issue remained unresolved by 2009.

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Design Approach

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Floating treatment wetland (FTW) pontoons were installed as an anaerobic digestion cover (ADC) over the settlement pond. These pontoons scrubbed odours by forcing them through the biofilm on plant roots. An ammonia-free buffer around the pond’s edge was added to maintain plant cover, despite high levels in the water.

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Outcomes

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The FTW cover immediately controlled odour and increased the pond temperature, which boosted plant growth and digestion. Additionally, biochemical oxygen demand (BOD) levels dropped from 450 to 80 gm/m³, and total suspended solids (TSS) decreased from 400 to 70 gm/m³.

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This innovative use of floating wetlands was a world-first and has provided a lasting solution to the odour problem.

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Benefits:

• A lasting solution to a contentious environmental issue

• Retrofit to existing infrastructure

• Quick installation and results

• $150,000 per annum saved on the previous mechanical oxygen blanket (2009 figures)