by Daniele Novara
Dairygold Co-Operative Society Ltd is an Irish dairy co-operative based in Mitchelstown, County Cork. A delegation from the Dŵr Uisce project visited the Dairygold Wastewater Treatment Works (WWTP) on 20/02/2020 to assess the potential for hydraulic energy recovery within the existing infrastructure.
In fact, Micro-hydropower schemes are an effective solution for energy recovery at the outfall of wastewater treatment plants and Pumps As Turbines (PATs) in particular are a hydropower technology particularly suitable on a small scale where a conventional turbine unit would not be economically viable.
The Dairygold WWTP is located at the foot of a hill just below the main industrial facilities, and next to the Mitchelstown municipal WWTP as shown in Figure 1. The main location investigated for energy recovery was the pipeline carrying pre-treated effluents from the industrial plant above head to the WWTP at the foot of the hill with a drop of around 12 m displayed in Figure 2. At the first step, flow and pressure data were gathered from the plant operators to provide a precise overview of the site conditions. Subsequently, the Pump As Turbine selection software developed at Trinity College Dublin as part of Dŵr Uisce research project has been applied to the selected site and helped to identify the ideal PAT and generator to be chosen.
Figure 1 the location of Dairygold Wastewater Treatment Works (WWTP)
Figure 2 the pipeline carrying pre-treated effluents
Eventually, the potential for energy recovery within the existing infrastructure of the Dairygold WWTP in Mitchelstown has been identified as 2 kW. The turbine may recover up to 7,400 kWh of electricity along a typical year, corresponding to a reduction of the electricity bill by nearly 1,200 €/year. However, given the low power output of the PAT the estimated payback time is between 11 and 14 years.