Effect of varying ratios of produced water and municipal water on soil characteristics, plant biomass, and secondary metabolites of Artemisia annua and Panicum virgatum

Abstract

Coal-bed natural gas production in the U.S. in 2012 was 1655 billion cubic feet (bcf). A by-product of this production is co-produced water, which is categorized as a waste product by the Environmental Protection Agency. The effects of varying concentrations of coal-bed methane (produced) water were studied in the greenhouse to elucidate their effects on two species as feedstock for lignocellulosic ethanol production: Panicum virgatum L. and Artemisia annua L. Two populations of A. annua were used, one from Canada and the other from Bulgaria. Plants were treated with varying ratios of produced water: control (0% produced or 100% municipal water), 25% produced, 50% produced, 75% produced, and 100% produced water. With increased concentration of produced water, the soil soluble Na increased, whereas soil soluble Mg and Ca decreased. The Na adsorption ratio (SAR) increased from 2 in the control to 21 in the 100% produced water treatment, and significant interaction was observed between the crop and water terms for electrical conductivity and phosphorus bicarbonate. SAR also increased in soils with both varieties of wormwood and with switchgrass as a result of increased concentrations of produced water. In addition, SAR was influenced by crop; SAR was higher in soil under switchgrass than in soil under the wormwood varieties. The biomass yields had significant interaction between crop and water treatments with Bulgarian wormwood consistently yielding more until the highest concentration of produced water when it decreased below that of Canadian wormwood. Bulgarian wormwood yielded the most with 131g/pot for the control followed by the 75% (118g/pot, statistically similar to control), 25% (111g/pot, statistically similar to control), and 50% (107g/pot) treatments. Biomass yields were reduced in the 100% produced water treatment. Regression analysis of the Canadian wormwood essential oil yield and constituents revealed weak correlations to increasing treatment of produced water. β-pinene, for which a quadratic yield curve was present, indicated a steep decline and leveling off of β-pinene production at high concentrations of produced water. The study shows increasing accumulation of Na and salts in the soil with increasing concentration of the produced (saline–sodic) water. High concentrations of these ions (average Na concentrations were 1156mgl−1) and salts in the 100% produced water treatment hampered growth and development of the plants. Implications of this research indicate that produced water could be utilized chemically untreated if diluted with high quality water. Produced water concentrations in dilution can be no higher than 25% in order to avoid deleterious soil and plant growth effects.