Specific Connection in Energy-Water Nexus

Wastewater Treatment FacilitiesThe relationship between water and energy used in wastewater treatment and water reclamation is a complex one. When water is used only once, then treated and discharged to the environment, for instance through an ocean outfall as is still the practice in most coastal cities worldwide, the result is minimal resource utility, minimal resource recovery, and maximum compounded energy use. When water is reclaimed through advanced wastewater treatment and is then reused to offset the use of potable water for non-potable purposes such as irrigation and fire protection, water’s utility is increased. Moreover, the per-unit volume energy intensity associated with water collection, potable treatment, and distribution followed by wastewater collection, treatment, and reuse is decreased. In short, water reclamation and recycling save water and energy, while single-pass water use wastes water and energy. Matching water quality with its intended use achieves the greatest water and energy utility and efficiency, thereby minimizing depletion of these scarce resources. By offsetting the demand for new water resources, water reclamation and recycling reduce water consumption and the energy used in providing potable water.

Resource Quantities

Approximately 3 percent of total U.S. electricity is used in the municipal water and wastewater sector. As much as one-quarter to one-half of the electricity used by most U.S. cities is consumed at municipal water and wastewater treatment facilities. The amount of electricity used to collect, treat, and distribute drinking water is slightly greater than the amount used to collect, treat, and dispose or reuse municipal wastewater. However, the treatment of wastewater is significantly more energy intensive than is the treatment of raw water for potable use.

Sector Challenges and WETT Solutions

WETT staff are collecting data and performing research to address some of the difficult issues in wastewater treatment and water reclamation. For example, one of the greatest challenges facing the wastewater treatment industry is the lack of unit process-specific and system-integrated data regarding energy use and energy intensity. WETT researchers are collecting such data, which facilitate comparisons between technologies. These data also will improve energy management by identifying opportunities for energy conservation. These wastewater sector energy use data and the wastewater energy conservation guide will facilitate the selection of efficient wastewater treatment technologies and the planning and design of both new and retrofit facilities.

WETT researchers also are studying a range of alternative conventional and emerging wastewater treatment processes, technologies, and systems. This work examines their reliability, life-cycle costs, ease of operation, relative energy intensity, environmental impacts, regulatory compliance, market incentives, and institutional barriers.

The handling, transport, and disposal or land application of residual wastewater biosolids require significant amounts of energy, especially as the distances from municipal wastewater treatment facilities to sanitary landfills continues to increase and as regulations governing biosolids quality and land application become more stringent. WETT researchers have proposed further study of the mass balance and energetics of residual wastewater biosolids, factors often omitted from comparative energy audits and analyses of wastewater treatment processes.