Reuse of Potassium Rich Winery Wastewater - Free Fertilizer or Potential Pitfall?.

The rapidly growing California wine industry is eagerly exploring possibilities for winery process-water reuse. Characteristic winery wastewater contains organic nutrients, high concentrations of salts, and has widely fluctuating acidity. It also contains cleaning agents, including peracetic acid (CH₃CO₃H) and citric acid (C₆H₈O₇), sodium hydroxide (NaOH), sodium percarbonate (Na₂CO₃ · 1.5H₂O₂ ), soda ash (Na₂CO₃), and potassium hydroxide (KOH). This leads to treated winery effluent rich in K and/or Na salts, which can alter soil structure and impact the soil’s hydraulic conductivity (HC). The wine industry’s shift from Na-based to K-based cleaners is producing increasingly K-rich wastewater and its effect on important soil properties is not well understood. Column experiments are ongoing to compare the effects of Na-rich and K-rich solution chemistry on soil HC. Soil mineralogy is hypothesized to exhibit a large influence on the effect of K in soils. Previous studies suggests that, depending on clay content and soil mineralogy, high K concentrations can affect the HC both positively (e.g., Ca) and negatively (e.g., Na). Certain clay minerals (e.g. vermiculite) selectively adsorb K. To examine this relationship, these experiments are being conducted with vineyard soils of diverse mineralogy (dominant in kaolinite, vermiculite, or montomorillonite), from the Napa and Lodi region, to simulate the effects of irrigation with K-rich winery wastewaters. As expected, column studies with montmorillonite soil treated with a higher SAR value (SAR 9) show much greater reductions in HC than the kaolinite soil at the same SAR value.  Responses to applications of K-rich (PAR 4) solutions are also expected to be more adverse for the montmorillonite soil than the kaolinite. The vermiculite soil is hypothesized to maintain greater HC when treated with high PAR solutions than high SAR solutions, due to K-fixation. Our evaluation of the interaction of K with various minerals will help to establish guidelines for the application of K-rich winery wastewater on vineyard soils of differing dominant mineralogy.