The Porirua Wastewater Treatment Plant was commissioned in 1989 and had been operated in-house by Porirua City Council. A number of upgrade works had been made to the plant since commissioning, however by late 2013 the performance of the dewatering system had dropped to around 14% dry solids which was constraining the solids disposal to landfill.
Following the merger of Capacity Infrastructure Services and Greater Wellington Bulk Water into Wellington Water in 2014 the combined operation teams were able to work to improve dewatering performance at the site. Trials identified that an emulsion polymer was optimal and resulted in an increase to 20% dry solids being achieved. The additional chemical cost was assessed against the reduction in disposal costs and has proven to be good value for money.
These improvements have allowed the treatment plant to effectively manage the solids inventory in the treatment process, optimise landfill disposal costs and improve effluent consent compliance.