Parametric optimization and synergistic product characterization in microwave co-pyrolysis of pearl millet straw and anaerobic digestate for sustainable energy production

Rickwinder Singh, Christoph Lindenberger and Vivekanand Vivekanand

Energy, 2025, vol. 332, issue C

Abstract: This study investigates the microwave co-pyrolysis of digestate and pearl millet straw (PMS) by varying different factors; PMS blending ratio(wt.%), microwave power(W), and absorber dosing for sustainable conversion of organic waste into energy and valuable products. Parametric effects on product yields are analyzed by response-surface-methodology-central-composite-design (RSM-CCD) and showed significant fitting of predicted and experimental values of bio-oil and pyrogas yields. Main and interaction effects described that factors significantly impacted product yield. Maximum bio-oil yield (54 %) was obtained for 90PMS10digestate(D) at 1000W and 1:1 absorber-dosing, while ∼53 % pyrogas yield for 60PMS40D at 700W and 3:4 absorber-dosing. Co-pyrolysis of digestate and PMS meaningfully increased aromatics (12–27 %) and alkanes (15–20 %), along with reduced N-compounds (28–5.7 %) in bio-oil. Pyrogas containing (H2+CO) obtained as for 60PMS40D, 90PMS10, and 100PMS, exhibiting values of (14 % + 44 %), (15 % + 32 %), and (14 % + 28 %), respectively at 700W. Notably, 100PMS yielded maximum H2, followed by 60PMS40D. However, maximum volume of (H2+CO + CH4) obtained was 34.4 % for 60PMS40D, consequently higher than 90PMS10D and 100PMS. Furthermore, theoretical cost analysis of system showed ∼1.88 years payback period and return on investment of 52.9 %. Microwave co-pyrolysis can enhance the efficiency of existing biogas plants by converting waste into bioenergy while capturing carbon in carbon residues, supporting cleaner energy production.

Keywords: Digestate; Biomass; Microwave pyrolysis; Optimization; Clean energy; Synergy (search for similar items in EconPapers)
Date: 2025
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Persistent link: https://EconPapers.repec.org/RePEc:eee:energy:v:332:y:2025:i:c:s0360544225029020

DOI: 10.1016/j.energy.2025.137260

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