Pulsed electric field pretreatment enhances anaerobic digestion of cashew apple bagasse by increasing methane yield and energy recovery

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To avoid the high energy demand and inhibitory compounds associated with conventional methods, pulsed electric field (PEF) pretreatment was investigated as a low-energy strategy to enhance the anaerobic digestion (AD) of cashew apple bagasse, a lignocellulosic residue with limited biodegradability. Two stirred tank reactors (4.3 L) were operated for 42 days under mesophilic conditions (36 °C) with a hydraulic retention time (HRT) of 25.8 days: a control reactor fed with untreated bagasse and a PEF reactor initially fed with PEF-pretreated biomass. During the semi-continuous phase, both reactors were subsequently fed with untreated bagasse. PEF processing promoted complete cell disintegration (Z = 1) and induced structural modifications, as indicated by Fourier-Transform Infrared Spectroscopy (FT-IR) and Scanning Electron Microscopy (SEM), thereby enhancing substrate accessibility by disrupting the fibers' physical barriers and significantly increasing the available surface area for AD. As a result, cumulative biogas production in the PEF reactor increased by 37.67% compared to the control (75.47 L vs. 54.82 L), while methane yield increased by 22.01%, reaching 235.23 L CH 4 per kg of volatile solids. The methane concentration in the biogas remained similar (∼70%) in both reactors, suggesting that PEF primarily enhanced hydrolysis efficiency rather than altering methanogenic pathways. Dynamic volatile fatty acids (VFA) monitoring showed PEF accelerated intermediate consumption, especially of butyric acid. The system maintained low propionic/acetic acid ratios (≤0.37), ensuring stability without toxicity and enhancing methanogenic activity. Despite the additional energy input required for PEF pretreatment (22.52 kJ per kg), the overall energy balance remained positive, resulting in higher net electricity (70.55 kWh per t) and heat (634.91 MJ per t) generation. Greenhouse gas mitigation increased to 38.27 kg CO 2 -eq per t of biomass in the PEF scenario. A preliminary techno-economic assessment estimated that PEF integration could double annual cash flow and reduce the estimated payback period from 6.7 to 3.3 years under the evaluated assumptions. A univariate sensitivity analysis (±30%) shows that both configurations are sensitive to changes in heat prices, but the PEF scenario offers greater economic stability, with a payback period of 5.1 years even under a 30% drop in thermal energy prices. These results indicate that PEF is an effective pretreatment for improving methane production, energy recovery, and the sustainability of AD of cashew apple bagasse.

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