Optimization of biogas yield from organic waste using pongamia pinnata seed shell as bio-additive through integrated experimental and statistical analysis

Abstract

The rapid increase in organic waste production, coupled with the depletion of fossil fuels, has sparked interest in developing sustainable waste-to-energy methods. Anaerobic digestion (AD) of food waste (FW) is a promising technology for producing biogas, though it can be limited by substrate inhibition and process instability. This study highlights the potential of Pongamia pinnata seed shell powder as an inexpensive, plant-based bio-additive to improve AD performance. Cow dung was used as an inoculum to conduct batch experiments in borosilicate reactors with a 500 mL working volume. Additive doses of 1 g, 3 g, and 5 g were tested, and FW loading was performed at 20 g, 30 g, and 40 g. Biogas production was observed continuously for 30 days, and optimization using RSM was performed using a central composite design. Biogas yield (cumulative) rose to 1445 mL at maximum loading and additive level as compared to 1022 mL (control) at the same conditions. The highest specific yield (140.1 mL/g VS) was obtained at 30 g FW with a 5 g additive, representing a 44.6% increase. The quadratic model was found to be significant by statistical analysis (F = 30.58, p < 0.0001

R2 = 0.8793). ANOVA diagnostics confirmed the adequacy and robustness of the developed quadratic model, highlighting significant nonlinear interactions between substrate loading and additive dosage. The study establishes Pongamia pinnata seed shell powder as a promising plant-based additive for optimized biogas production and provides a statistically validated framework for process optimization in anaerobic digestion systems. © 2026 Elsevier Ltd