Wastewater from households throughout Taupo township is piped to the Taupo Wastewater Treatment Plant (TWWTP) located in Motutahae Street, Taupo. Here it is treated and pumped to Land Disposal areas where it is sprayed onto paddocks of special grass to grow haylage. This operation continues all year round.
The original Taupo Wastewater Treatment Plant was built in 1972, and although it has had minor improvements since that time, subsequent population growth has meant that volume of wastewater needing treatment nearly exceeds the amount that the Plant was designed to treat.
Parts of the treatment plant are also beginning to age. However, it is financially impractical to build a new wastewater treatment plant on another site. Such a move would cost tens of millions of dollars just to reroute all the pipelines, let alone build a new treatment plant. Therefore the Council has decided to improve the existing treatment plant.
Not only will this upgrade enable the plant to cope with anticipated population growth and replace tired components, it will also enable Council to introduce new technologies into the treatment process, improving the quality of the treated wastewater.
Part of the upgrade involved the installation of NZ’s first Monsal Digester Air Mixing system to mix wastewater and sludges together. Air is externally compressed and delivered through a series of diffusers inside the tank. The high intensity airflow through each diffuser generates a stable mixing pattern in the tank which rotates the tanks’ contents. An acoustic enclosure was installed around the compressor unit to reduce any noise to the residents living near the site in order to meet the resource consent.
Other parts of this project included 2x inlet step screens, a third Trickling Filter and pump station, 2x new compressors and multiple level controls. All of this equipment and instrumentation is controlled by a Allen Bradley Control Logix platform and Powerflex vsd’s.
After the mixing of the wastewater, sludge and air, the resultant methane gas is siphoned off and delivered to two boilers to heat water to be used in the treatment process. This reduces energy use on site and therefore the plants carbon footprint. Any excess methane is piped to a flare to be burnt off.
To do this involved the installation of multiple control cabinets, instrumentation, motor controls, hazardous area equipment and a full Scada upgrade.