Drinking water and wastewater systems are generally the largest energy consumers for municipal governments. However, there is little published information available on the exact energy usage for specific systems. A recent article in Journal – American Water Works Association, looked to address this knowledge gap for drinking water utilities. The authors surveyed drinking water utilities across the United States of America. Utilities were asked for three years of annual production/delivery volumes and annual total energy usage, as well as general plant information. Data was received from 109 utilities well distributed across the USA. The average energy consumption was 2510 kW∙h/million gallons, with maximum and minimum energy consumptions of 11500 and 250 kW∙h/million gallons, respectively. The authors pointed out that differences in energy consumption is due to many factors both within and outside of operational control. Therefore, energy consumption does not indicate energy efficiency and cannot be used to compare water utilities. For example, a water system could be very efficient, but have high energy consumption due to difficult natural topography resulting in increased pumping. Conversely, a water system could have low energy consumption due to advantageous topography and high source water quality, while also having low energy efficiency due to poor operational control (ie. high leakage rates). Ultimately, the data points to the need for utilities to develop their own energy consumption baseline to facilitate continuous improvement. This will reduce the need for utilities to make generalized assumptions about their energy efficiency.
A majority of the survey respondents stated that gathering energy consumption data was the most difficult part of the survey. In fact, some respondents, after a meticulous search, were not able to provide energy consumption data. This is problematic for utilities that are looking to conduct continuous improvement or system upgrades/expansion. As the authors stated: “the lack of accessible data may well be the largest obstacle to understanding these water and energy relationships”. Collection of energy consumption information should be a part of regular monitoring, as it will allow for improved decision making when it comes to continuous improvement. Problems related to biological processes are particularly good candidates for continuous improvement as they are often fairly energy intensive. For instance, in drinking water, biological related challenges include providing sufficient primary and secondary disinfectant and overcoming increased frictional resistance due to biofilm formation. In wastewater, biological related challenges include providing sufficient aeration based on the quantity of solids in the aeration tank. Ultimately, without a benchmark for energy consumption, it’s difficult to convey to stakeholders that processes changes, capital upgrades or changes to monitoring programs will result in higher energy efficiency and a return-on-investment.