A California Winery Wastewater Survey: Assessing the Salinity Challenge for Wastewater Reuse

Abstract

Over thirty percent of the United States is currently considered to be in a drought that is expected to have profound social, economic, and environmental impacts. Drought conditions are intensifying in the southern and western regions of the country, spurring interest in wastewater reuse in agriculture, including wine production. Presented here is the first data set of its kind to support California growers and vintners reuse of treated winery wastewater (WWW). The data provide a detailed description of California WWW, with particular emphasis on WWW salinity, required to assess benefits and risks of land application. Monthly samples were obtained over a twenty month period from eighteen participating wineries in Ukiah, Napa, Lodi, King City, and Paso Robles. Samples collected prior to (pre-) and after (post-) treatment were analyzed for pH, electrical conductivity (EC), cation and anion concentrations, specific ultraviolet absorbance (SUVA₂₅₄), dissolved organic carbon (DOC), and biological oxygen demand (BOD₅). The pH of WWW varied widely (3–12). Organic parameters (SUVA_254, DOC, and BOD₅) indicated that treatment effectively decreased organic carbon to levels that would not have negative effects on plant growth and soil. Cation concentrations (Na⁺, K⁺, Ca²⁺, Mg²⁺) observed in this study were not reduced by WWW treatment, indicating salts stayed in solution after treatment. These baseline data confirm that dissolved salts pose one of the greatest challenges to reuse of WWW. However, measurements of total salinity (electrical conductivity) of the WWW at participating wineries was found to be moderate (mean of 1.0 dS/m), and usually below thresholds for common wine grape rootstocks and soil salinity hazards. The conditions under which WWW could be recommended as a water management option in California are described.