Putting the Screws on Non-Stabilized WAS: A Kiwi Experience

The Te Maunga WWTP is one of two plants servicing Tauranga (population 150,000), New Zealand. Since commissioning in 1997, waste activated sludge (WAS) has been partially stabilised in an adjacent pond. A condition in the latest permits for the WWTP required the pond to be decommissioned. An options study was undertaken to select WAS thickening and dewatering equipment to be installed. At concept design, gravity belt thickeners and screw presses were chosen as the preferred thickening and dewatering technologies respectively. As screw presses are a relatively new technology in NZ wastewater treatment plants, and WAS without any primary sludge is difficult to dewater, dewatering trials were undertaken. Based on the pilot trials, picket fence thickeners were chosen over GBTs and two screw presses were installed in a new dewatering building, along with ancillary plant. The project and results from the pilot trials and full-scale operation are presented in this paper.