Ōtaki WWTP Aeration Lagoon Upgrade

Kāpiti Coast District Council (KCDC) engaged PDP to provide a preliminary design for a new pond base as part of the aeration lagoon upgrade at the Ōtaki Wastewater Treatment Plant (WWTP) on the Kāpiti Coast. Our Water Infrastructure team in Wellington has successfully completed this upgrade.

The upgrading works involved replacing the lagoon’s existing fine silt base layer with a new impermeable base to prevent wastewater infiltration. The WWTP consists of a pretreatment milliscreen, an aeration lagoon, a clarifier, primary sludge treatment, oxidation ponds, and a land disposal field.

Approximately 2,000 m³ in size, the aeration lagoon has mechanical surface aeration to provide dissolved oxygen into the wastewater. This oxygen facilitates organic carbon (BOD) removal and nitrification for ammoniacal-N reduction.

Microbiological growth within the lagoon leads to BOD removal through biomass growth and sludge production. Phosphorus is also removed via microbial uptake into the biomass cultivated within the lagoon.

The photo shows the completed preparation work ahead of the concrete base installation, and the time-lapse video captures the concrete pouring process in action.