Boosting Nitrate Production in Plasma-Activated Water by Incorporating Dolomite Minerals for Potential Application as a Nitrogen Fertilizer

The conversion of atmospheric nitrogen into nitrogen fertilizer has gained much attention owing to the increasing demand for food given the growth of the world's population. The gliding arc plasma exhibited great potential in this area and constitutes a green alternative to the conventional Haber-Bosch process of nitrogen fixation by mitigating carbon footprints. The moist air gliding arc plasma treatment has been reported to be effective for the production of nitrogen species for agricultural applications. However, the amount of nitrogen species in the treated water rapidly reached a maximum value within a short time and then no longer increased. Thus, this work proposed an innovative approach to allow nitrate production to continually increase by incorporating a natural harmless dolomite mineral. Interestingly, the results demonstrated a significant effect of dolomite on increasing the nitrate concentration from 115.76 +/- 3.15 to 263.19 +/- 4.31 mg/L. The effects of operating parameters such as the nature of the feeding gas, the flow rate, the dolomite dosage, and the temperature were investigated. The optimal conditions were established as follows: flow rate, 800 L/h; dolomite dose, 2 g/L; temperature, 45 degrees C; and moist air gas. Under these conditions, the nitrite and nitrate concentrations reached 16.09 +/- 0.50 mg/L and 294.73 +/- 5.14 mg/L, respectively, within 60 min of aging. The mechanism of nitrate production was investigated, revealing that the plasma-generated acid species catalyzed dolomite dissolution, releasing Ca2+ and Mg2+ ions. In turn, these species react simultaneously with the produced nitrate ions to form double salts of Ca(NO3)(2) and Mg(NO3)(2), which serve as reservoirs to promote their accumulation. This study demonstrated substantial nitrate production improvement in distilled water via the use of moist air gliding arc plasma and offered a promising green alternative for nitrogen-based fertilizer production.