The Potential of Plasma-Activated Water as a Liquid Nitrogen Fertilizer for Microalgae Cultivation

Abstract

The influence of plasma-activated water (PAW) as a liquid nitrate–nitrogen (NO3–N) fertilizer on microalgae cultivation has been studied in this research. A helical-electrode gliding arc plasma generator (HGPG) has been proposed for practical use in a circulating PAW generation system. The arcing gap (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$A_{\text {G}}$ </tex-math></inline-formula>) between HGPG electrodes and treatment time has played a significant role in increasing electrical conductivity (EC), hydrogen peroxide, NO3–N concentration, and oxidation–reduction potential (ORP) of PAW contrasting to the pH, which has the opposite trend. At the 0.25-cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$A_{\text {G}}$ </tex-math></inline-formula> and 45-min treatment time with a 15-kV, 125-W commercial neon power supply, EC, ORP, and NO3–N concentrations of PAW are 3.40, 2.0, and 12.30 times higher than that of the control group, respectively. The pH has dropped from 7.45 ± 0.04 to 3.74 ± 0.02. Regarding the experimental result of applying PAW in microalgae farming, it could be confirmed that the PAW generated by HGPG could be used as a potential nitrogen compound fertilizer for microalgae cultivation. The highest specific growth rates (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>) of microalgae from the setup mentioned earlier conditions are 1.117 times higher than that of the control group.