Abstract
Anaerobic digestion (AD) produces bioenergy and bio-fertilizer. However, weed seeds can contaminate the substrates for biogas production. This work assesses seed viability of four weeds species origin from Germany and China under AD conditions at 37, 42 and 52 °C with different retention times. All investigated seeds were inactivated after 12 h at 52 °C, 128 h at 42 °C and 512 h at 37 °C under AD treatment. Inactivation duration varying between species and a global test showed that the countries of seeds origin have a significant effect on inactivation times. For two species, by contrast, short treatment times increased the germination rate which increases the risk of weed dispersal. An anoxic water bath treatment with identical temperatures resulted in longer deactivation times, indicating that other factors also play a role in the weed seeds elimination. The results indicate that the risk of weed seed spreading through digestate application can be minimized by an adequate retention time.
Highlights
The potential contribution of biogas to renewable energy generation from various waste and residues is substantial, both in terms of energy supply and in terms of the greenhouse gas emission reduction (Scarlat et al 2018)
It is concluded from these results that conditions within digesters can be considered homogeneous for most practical purposes
Under Anaerobic digestion (AD) treatment at 52 °C, Amaranthus retroflexus L. (AMARE)-CN was inactivated after four hours while AMARE-DE was completely inactivated after two hours (Fig. 2e,f), which is similar to the results found by Knödler (2015), showing that AMARE seeds were totally inactivated after four hours at 52 °C
Summary
The potential contribution of biogas to renewable energy generation from various waste and residues is substantial, both in terms of energy supply and in terms of the greenhouse gas emission reduction (Scarlat et al 2018). The substrates for biogas production, namely livestock manure, energy crops (i.e. maize, whole-crop cereal silage, grass silage, cereal grains, and sugar beets), and agricultural processing waste (FNR 2010), can be contaminated with pathogens and weed seeds. If these survive through the AD process, the application of such contaminated digestates entails the risk of spreading new and invasive species (Baute et al 2016; Johansen et al 2013; Westerman et al 2012b), which can lead to a reduction of crop yield, as they aggressively compete for water, nutrients and sunlight. Maize silage and grass silage are the most dominant substrates, accounting for 69 and 14% of the total mass related substrate input, respectively (Daniel-Gromke et al 2018; FNR 2019)
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