Valorization of non‐distilled and steam distilled lemongrass residue via anaerobic digestion

Lemongrass ( Cymbopogon citratus ) is widely cultivated for essential oil production, generating substantial lignocellulosic biomass before and after distillation. This is particularly relevant in tropical regions and small island developing states (SIDS), where local renewable energy demand is high. Lemongrass has been explored as an energy crop and anaerobic digestion (AD) substrate, but earlier studies generally considered raw biomass and postdistillation residues separately. It was hypothesized that steam distillation, by removing essential oils, would not reduce – and might slightly enhance – the biochemical methane potential (BMP) of lemongrass residues at equivalent loadings. Both materials were expected to achieve maximum methane productivity without strong inhibition at an optimal substrate‐to‐inoculum ratio. This study compared AD performance of steam‐distilled and nondistilled lemongrass under identical conditions. Biochemical methane potential assays were conducted at several substrate concentrations using the same mesophilic inoculum, reactor configuration, and incubation regime. Methane yields and production rates were quantified alongside key physicochemical substrate properties. Nondistilled lemongrass achieved 114 ± 6 mL g −1 fresh matter (FM), comparable with distilled lemongrass (120 ± 10 mL g −1 FM) at 2.5% substrate concentration. On an organic dry‐matter basis, optimum yields for both substrates fell within the lower middle range for grass and energy crops, confirming lemongrass as a moderately reactive lignocellulosic feedstock. Higher loadings reduced yields, indicating mild inhibition; distilled residues were less affected, suggesting that oil removal mitigates inhibition. These findings demonstrate that steam‐distilled lemongrass is a viable AD substrate and support an ‘oil‐first, biomethane‐second’ biorefinery concept, relevant for renewable energy and residue management in SIDS.