Microbubble Plasma Processing for N‐Fertigation via Plasma Catalysis

This study reports about using a non‐thermal plasma to generate nitrate and NH3 in presence of water, in which these are immediately absorbed; creating a fertigation solution, termed in literature ‘plasma activated water (PAW)’. The N‐content has been optimised by a process‐parametric study, yielding the second‐best result reported in literature and the best when concerning scale‐up ability. Strategic catalyst studies have been conducted, in terms of plasma‐catalysis synergy, varying the type of catalyst and the location of catalyst. Silica‐supported single/binary metal catalysts and γ‐alumina powder catalysts were used. Distinct catalyst placements inside the plasma electrode zone (glow or spark) and outside in the gas‐liquid reactor were tested; with the aid of supports and without. Increasing the N‐fixation performance by about 70% as compared to non‐catalytic processing, the study used a recycling loop to further boost the N‐fertiliser concentration. A plasma‐catalyst synergy was determined by structural changes of the catalyst transiently (during plasma operation). This laboratory study achieved a result that has potential for commercial N‐fertigation at farm, when multiplied by a factor of 10 via further process intensification, a factor of 10 by increase of plasma reactor scale, and a factor of 10 by reactor parallelisation (‘numbering‐up’).