Enhancing methane production from pistachio skin via optimized hydrothermal-alkaline pretreatment and Autoregressive Integrated Moving Average modeling

Lignocellulosic waste materials represent one of the renewable energy sources that is both sustainable and eco-friendly. These wastes are often improperly managed and could be energetically valorized through anaerobic digestion. However, lignocellulosic waste is known to be resistant to biodegradation due to hemicellulose and lignin and, therefore, needs a pretreatment process. In this context, this is the first study focusing on the enhancement of methane production from pistachio skin (PS), emphasizing the hydrothermal (HT) and alkaline (A) pretreatments employed separately and in combination to improve PS digestibility. HT pretreatments were performed within the temperature range of 60–100 °C, whereas A pretreatments involved sodium hydroxide concentration in the 1–10 % range. After the pretreatment phase, a 30-d anaerobic digestion was carried out under mesophilic conditions (i.e., at 37 ± 1 °C) to evaluate the cumulative methane yields (CMY). This strategy led to a significant increase (p < 0.05) of CMY (i.e., up to 415.4 mL CH4/g volatile solids) after a combined HT-A pretreatment at 5 % NaOH and 100 °C compared to control (i.e., 192.5 mL CH4/g volatile solids), followed by removal of 49 and 40 % of lignin and hemicellulose, respectively. An Auto-Regressive Integrated Moving Average, a time series model valued for enhancingthe model creation and its statistical properties, was also developed to estimate CMY. This work proved implementing pretreatment strategies can lead to a viable technique for sustainable energy production and waste handling in the pistachio industry.