A Comparison of the Operational Energy Demand of Both Low Pressure and Vacuum Collection Systems

Climate change is regarded as the greatest threat to society in the coming years, and directly affects the water industry; with changes in temperature, rainfall intensities and sea levels resulting in increased treatment and subsequent energy costs. As one of the largest global consumers of energy, the water industry has the opportunity to significantly prevent climate change by reducing energy usage and subsequent carbon footprints. Wastewater treatment alone requires an estimated 1% - 3% of a country overall energy output while producing 1.6% of its global greenhouse gas emissions; over 75% of which can be due to the collection system. Gravity flows should therefore be incorporated where possible, reducing pumping requirements and therefore minimizing costs and subsequent carbon footprints. This study has assessed the operational energy usage of the alternative collection systems low pressure and vacuum, for use in situations in which a conventional gravity system is not practicable. This was carried out through hypothetical scenario testing using design parameters derived from literature, generating 60 hypothetical collection mains with variations in population, static head and main length. From this study, it was found that the energy demand of a low pressure system is 3.2 - 4.2 times greater than that of its equivalent vacuum system in the same scenario. Energy demand for both systems increases with population, static head and main length. However, population and therefore flow changes were found to have the greatest effect on the energy usage of both systems. Therefore, flow reduction measures should be adopted if the decarbonization of the water industry is to be achieved.