# A Coaxial Dielectric Barrier Discharge Reactor for Treatment of Winter Wheat Seeds
###### Abstract
Depending on the feeding gas and construction, DBDs can provide rather homogenous treatments. Therefore, they can be the most suitable choice for the direct treatment of seeds (seeds in direct contact with the discharge). DBDs are widely reported in scientific papers for the treatment of seeds and plants. Due to their simple and flexible construction, DBDs can be easily adapted for the treatment of different types of substrates. Table 1 summarizes a variety of volume DBD reactors and the corresponding parameters used for the treatment of seeds in the past 5 years. The majority of used DBD reactors are with planar configuration (parallel plates) operating at atmospheric pressure. Half of the listed studies (12) operate the discharge in air. To avoid high voltages because of the breakdown voltage necessary to ignite the plasma in such conditions, either the gap needs to be reduced (diminishing the amount of seeds that can fit inside) or the pressure of the gas has to be lowered. Another aspect is the application of additional rotating or vibrating mechanical parts into the system to ensure a homogeneous treatment of all seeds. [PERSON] and coauthors [47] assembled the parallel plates reactor on a horizontal vibrating table. [PERSON] and coauthors [48] mechanically moved the seeds during treatment. The planar reactor used by [PERSON] and coauthors [49] had a rotating system that provided seeds motion, and [PERSON] and coauthors [50] made use of a strong gas flow rate (15 slm) inside the reactor with coaxial configuration. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Geometry**} & \multicolumn{2}{c}{**Movement**} & \multirow{2}{*}{**Volume \(\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{ }}}}}}}}}}}}}}}}\) & \multirow{2}{*}{**Gap**} & \multirow{2}{*}{**Gas**} & \multirow{2}{*}{**Pressure**} & \multicolumn{2}{c}{**Electrical Parameters**} & \multirow{2}{*}{**Gas Temp. **} & \multirow{2}{  
In the present work, a cylindrical DBD reactor intended for the direct treatment of seeds is presented. The reactor is mounted on top of a vortex mixer device that allows the seeds to shake during the process, ensuring homogeneous treatment. The reactor, with a volume of around 88 cm\({}^{3}\), allows the easy introduction of different feed gases and can be easily scaled up, which makes it suitable as a prototype for laboratory tests and optimization. In this study, the efficiency of treating winter wheat seeds has been compared by operating the reactor with two feed gases (argon and helium) with same gas flow rate and same discharge power. The results show that even though both discharges present similar excited reactive species (N\({}_{2}\), OH, and NO), the argon plasma leads to a further reduction of the water contact angle (WCA) measured at the seed coat of wheat seeds. In contrast, the seeds exposed to the helium plasma present stable WCA values for longer treatment times. Additionally, the argon treatment leads to a much more pronounced germination acceleration compared to the helium plasma. In addition, it has been shown that varying the electrical parameters can drastically reduce the treatment time.