Abstract
Wheat straw (WS) is considered a favourable substrate for biogas production. However, due to its rigid structure and high carbon to nitrogen (C/N ratio), its biodegradability during anaerobic digestion (AD) is usually low. In the present study, the effect of steam explosion pre-treatment on WS, combined with C/N adjustment with inorganic nitrogen, on biogas production was evaluated. Additionally, co-digestion of WS with protein-rich agri-industrial by-products (dried distillers’ grains with solubles (DDGS) and rapeseed meal (RM)) was assessed. Steam explosion enhanced biogas production from WS, whereas the addition of NH4Cl was beneficial (p < 0.05) for the digestion of steam-exploded wheat straw (SE). Furthermore, mono-digestion of the four different substrates seemed to be efficient in both inoculum to substrate ratios (I/S) tested (3.5 and 1.75 (w/w)). Finally, during co-digestion of WS and SE with DDGS and RM, an increase in the cumulative methane production was noted when higher amounts of DDGS and RM were co-digested. This study demonstrated that DDGS and RM can be used as an AD supplement to stimulate gas production and improve wheat straw biodegradability, while their addition at 10% on an AD system operating with WS can enhance gas yields at levels similar to those achieved by steam-exploded straw.
Highlights
The transition towards a more sustainable economy, both from an economic and an environmental point of view, can be achieved through the replacement of fossil fuels with renewable alternatives
It is likely that dried distillers’ grains with solubles (DDGS) and rapeseed meal (RM) were preferable substrates for anaerobic digestion (AD) microorganisms and their depletion coincided with micronutrient depletion
RM were present in the AD system, they offered a balanced C/N ratio, enhanced the metabolic activity and were quickly depleted, allowing for a further breakdown of Wheat straw (WS) and SE
Summary
The transition towards a more sustainable economy, both from an economic and an environmental point of view, can be achieved through the replacement of fossil fuels (e.g., coal or petroleum) with renewable alternatives. Reliance on traditional fuels could be decreased through the development of efficient strategies for biomass-derived biofuels, such as biogas, which is the main product of anaerobic digestion (AD). Biofuels are expected to play an important role in the reduction in carbon emissions, which is one of the most important causes of global warming. Biogas is a renewable gas, mainly comprising methane (CH4 ) and carbon dioxide (CO2 ), and can be used to produce heat and/or electricity. Biogas can be utilised directly as a fuel for vehicles or, following upgrade to biomethane, can be injected into the natural gas grid. Energy crops are commonly used today for the production of biofuels, such as biogas and bioethanol [1,2,3]
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