Long Wetlands And Pasture Irrigaton At The Blenheim Sewage Treatment Plant

The existing Blenheim Sewage Treatment Plant (BSTP) consists of two separate treatment systems. After inlet fine screening, aerated-assisted facultative and maturation ponds are used to treat domestic flows. Industrial flows are treated using a fine screen, mechanically-aerated ponds, as well as a facultative pond. Treated domestic effluent was continuously discharged to the Opawa River, and separately-treated industrial effluent was discharged to the Wairau Estuary on the ebb tide until early 2014. Marlborough District Council (MDC) has recently upgraded the pond-based system by:

• Combining the domestic and industrial effluent streams in a common maturation pond, followed by polishing treatment in a new 2km long wetland system that conveys treated effluent to close to the Wairau River mouth
• Discharging the combined effluent via a new submerged outfall into the Wairau Estuary mouth on ebb tides which carry the well-diluted effluent into Cloudy Bay
• Irrigating treated effluent onto MDC pasture land surrounding the STP when conditions allow
• Decommissioning the outfall to the Opawa River

The $15m upgrade project was completed in early 2014 and is complying with the consent conditions. This paper will describe the project from the evaluation of options, through to commissioning of the wetlands treatment and irrigation system.