The Effect of KOH Addition on Nitrate Formation in Plasma-Activated Coffee Ground Solution

Plasma technology has recently been applied in various fields. In agricultural applications, plasma-activated organic fertilizer (PAOF) is a promising alternative. In this study, the spent coffee grounds (SCGs) was activated by using an atmospheric pressure plasma jet (APPJ) with argon/air as the treating gas, which was called plasma-activated coffee grounds solution (PACs). In addition, alkali was added to shift pH from acidic to neutral, enhancing nitrate concentration in PACs. Nitrate levels increased significantly, reaching 66 times that of nonplasma-treated solution. High-performance liquid chromatography mass spectrometry (HPLC/MS) analysis revealed amino acid decomposition by alkali and their participation in reactions with reactive species in PACs. The sufficient nitrate concentration and appropriate pH value exhibit advantages of PACs with the addition of alkali, showing great potential as a novel fertilizer in agriculture fields.