Investigation of the effect of corona discharge on biogas production from agricultural waste pistachio shell

In this study, the biogas production potential from the outer shell of the pistachio, which can be an alternative to fossil fuels and is an agricultural waste, was investigated. Pistachio shell is preferred because it is rich in minerals and vitamins. In the study, corona discharge method was used as a pretreatment technique for the first time in order to increase the efficiency of the produced gas and the effect of corona discharge on biogas production was investigated. It was observed that the corona discharge pretreatment increased both the gas production amount and the production rate. After the samples prepared for pre-treatment are laid in a thin layer between two copper plates in 2 grams each, voltage (3 Kilovolts (kV), 5 kV, 7,5 kV), time (180 seconds (sec), 300 sec. 600 sec) and frequency (50 Hertz (Hz), 250 Hz, 500 Hz) different values were applied in 3 parameters. Biomethane production potential (BMP) test was applied to each sample to determine the effect of the applied pretreatment. While 227 milliliters (ml) of biogas was obtained from the outermost shell of the pistachio without pre-treatment, the best biogas production from the pre-treated samples was found as 279 ml at 3 kV voltage, 300 sec duration and 500 Hz frequency. It was determined that the applied pretreatment increased the biogas yield by 23 %. The amount of methane (CH4) in the biogas of the corona discharge pretreatment was determined by the bioprocess control method. In this method, the produced biogas was passed through an alkaline solution (3 % Sodium Hydroxide (NaOH)) to keep the Carbon Dioxide (CO2) content and the remainder was accepted as CH4. While 165,2 CH4/g VS was obtained from untreated raw material, the best CH4 yield from pretreated samples was found as 238,9 CH4/g VS at 5 kV voltage, 300 sec time and 500 Hz frequency. It was determined that the applied pretreatment increased the CH4 yield by 45 %. In order to determine whether the applied corona discharge pretreatment is applicable or not, an energy analysis was performed by taking into account the current values recorded during the application. In the energy analysis, 2 different scenarios were used while calculating the electrical energy equivalent of the extra CH4 produced. In one scenario, the efficiency is accepted as 40 %, while in another scenario, the efficiency is accepted as 95 %. While the number of cumulative positive samples was 2 in the first scenario, the cumulative positive sample number was 7 in the second scenario. According to the energy analysis, it has been determined that 3 kV, 3 min and 500 Hz values are the optimum values for applying the corona discharge pretreatment to the pistachio shell.