The Energy Implications of Greater Reliance on Direct Potable Reuse Water Recycling in Import-Reliant Regions: Evidence from Los Angeles County

This research explores the energy intensities to implement an advanced water treatment process, specifically for direct potable reuse (DPR) and seeks to inform decision makers on important considerations facing water managers, energy managers, and environmental actors. This study uses the County of Los Angeles as a case study to quantitatively examine the water, energy, and greenhouse gas tradeoffs of utilizing different water supply sources. This project particularly models four different treatment trains which are being tested in California, three of which rely on advanced membrane filtration to achieve pathogen removal. Across these trains, the analysis shows various energy intensities ranging from 497 kWh/AF to 1,374 kWh/AF and estimates that their use could increase energy consumption at wastewater treatment facilities by a factor of 2.3 to 3.3. DPR can refer to two distinct management approaches untreated (raw) and treated water augmentation. The former refers to introducing recycled water directly into a drinking water system distribution network, while the latter requires the water to be treated again before reintroduction to the drinking water supply. We calculate the total energy needed for raw (untreated) water and treated water augmentation strategies and compare these results to existing water supply options like imported water and desalination. The first conclusion of the analysis is that despite the high energy intensity of DPR, raw water augmentation can be relatively energy efficient when compared to imports and desalination as it avoids large uphill pumping energy costs. Treated water augmentation, however, is shown to be as energy intensive as imports to Los Angeles County. The secondary analysis of the report details likely power mixes to be utilized by different water supply sources and, thus, quantifies their expected greenhouse gas intensities. Converse to energy intensity findings, imported water has a very low greenhouse gas intensity due to its primary source being hydroelectric. Extending the analysis to the timeline on which DPR may be implemented (est. 2035), findings show that the disparities in greenhouse gas intensities are greatly diminished. This means that carbon impacts in this sector can be a lower priority during future decision-making if energy providers can achieve their promised emissions reductions.