The existing Waimate West Water Treatment plant struggled to achieve compliance in accordance with Drinking Water Standards for New Zealand (DWSNZ) under typical operating conditions, and failed under high rainfall or flood conditions. And further, the assets were aging and in need of substantial refurbishment if they were to remain in service. Hence South Taranaki District Council decided to replace the existing treatment plant. The new treatment plant was commissioned spring 2014.
Low Total Cost of Ownership was a key objective for the upgraded plant, along with achieving consistent compliance. A number of measures were incorporated to reduce energy usage in the new plant. As part of the replacement project, it was initially assumed the existing raw water pump station would need to be upgraded however, a closer examination of the raw water hydraulics identified the opportunity to not only eliminate this pump station, but also incorporate a Pump As Turbine (PAT) installation that generates sufficient energy for the 18 ML/d treatment plant to be approximately energy neutral.
PAT installations utilise standard off the shelf centrifugal pumps coupled with a standard three phase induction motor, reducing both the capital and maintenance costs, including eliminating the need for specialist servicing. This simplicity makes the technology ideal for implementation on smaller scale installations, and makes implementation realistic for small scale applications. With increasing energy costs, desires for low carbon generation and the increasing acceptance of embedded generation within the power network there may be many opportunities for implementation of similar installations within raw and treated water networks.
This paper discusses the technical issues in the implementation of the PAT.