Research on additives that improve the quality of silages for an enhanced and sustainable biogas production are limited in the literature. Frequently used additives such as lactic acid bacteria enhance the quality of silages but have no significant effect on biogas yield. This study investigated the effect of a new enzymatic additive on the quality of ensiling and BMP of sugar beet leaves. Sugar beet leaves were ensiled with and without the additive (Aspergillus- and Neurospora-based additive) in ratios of 50:1 (A50:1), 150:1 (B150:1), and 500:1 (C500:1) (gsubstrate/gadditive) for 370 days at ambient temperature. Results showed that silages with additive had lower yeast activity and increased biodegradability compared to silages without additive (control). The additive increased the BMP by 45.35%, 24.23%, and 21.69% in silages A50:1, B150:1, and C500:1 respectively, compared to silages without additive (control). Although the novel enzyme is in its early stage, the results indicate that it has a potential for practical application at an additive to substrate ratio (g/g) of 1:50. The use of sugar beet leaves and the novel enzyme for biogas production forms part of the circular economy since it involves the use of wastes for clean energy production.

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BACKGROUND The invasion of water hyacinth (WH) on water bodies comes with adverse consequences for humans and the environment. Using WH as a substrate for affordable and clean energy production is one way of controlling the invasiveness of the aquatic plant. In this study, ensiling was carried out with and without the addition of maize straw (MS) and eggshell powder (ES) to determine the effect of higher total solids (TS) and butyric acid contents on the biomethane potential (BMP) of WH. The silages were stored at ambient temperature for 210 days. The kinetics of biomethane production was determined using three different kinetic models. RESULTS Ensiled WH without MS and ES had a reduced BMP after 210 days. However, a combination of higher TS (40%) and butyric acid contents, resulting from the addition of MS and ES, significantly increased the BMP of WH by 64% after 210 days of ensiling. The kinetic study showed that the dual‐pool kinetic model described the BMP of ensiled and co‐ensiled WH better than the first‐order and modified Gompertz models. CONCLUSIONS Increasing TS and butyric acid contents by co‐ensiling with MS and ES is a low‐cost and sustainable method of enhancing biomethane production from WH. In this way, the invasive nature of WH can be effectively controlled (since a large quantity can be harvested and stored) and circular economy can be enhanced through the effective utilization of waste. © 2022 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).