Addressing the Contribution of Indirect Potable Reuse to Inland Freshwater Salinization

Abstract:

Inland freshwater salinity is rising across many regions of the United States and globally, a phenomenon called the freshwater salinization syndrome (FSS). In this study we explore a potential conflict between managing the FSS and augmenting water supplies in drought prone regions of the world through the addition of reclaimed wastewater to reservoirs and groundwaters. The latter practice, called indirect potable reuse, has the potential to exacerbate the FSS because salts added to the sewage collection system, or added during the treatment process, are not removed by conventional treatment processes. We evaluate the relative contribution of three sources—two rapidly developing watersheds and a wastewater reclamation facility—to the rising sodium concentration in a regionally important drinking water reservoir in the Mid-Atlantic United States. Sodium mass loads from the reclamation facility are comparatively small when evaluated on an annual basis but dominate mass loads to the reservoir during dry weather periods. Across all timescales and sources, sodium concentrations are highest in water discharged from the reclamation facility. Sodium in reclaimed wastewater originates from chemicals used in the treatment process, industrial discharges, human excretion, down drain disposal of drinking water, and sodium-rich household products. While many of these sources are difficult to curtail, low-sodium treatment processes and education programs aimed at encouraging households to adopt low-sodium products could lead to substantial reductions in the contribution of wastewater to inland freshwater salinization and thereby improve human water security and ecosystem sustainability.