Two Types of SILAGE Production: The most effective way of storing Arundo Donax for BIOGAS



Arundo donax is a perennial plant that acts as a perfect replacement for both traditional agricultural- and energy crops to produce biogas, thereby lessening expenses as of its high biogas yield per Ha cultivated and low agronomic and energetic inputs. In order to do this, Arundo donax biomass needs to be ensiled for preservation and utilisation purposes. Since the types of silage production methods for giant reed and the consequences of those practices on prospective biogas production is scarce, it is worth visiting two different ensiling techniques – trench and silo-bag ensiling. The basis of this article is founded on a full scale Arundo testing, in an experiment lasting over 200 days. The data attained implied that Arundo could be effectively ensiled through both methods, the bigger question being: which one was better for higher biogas yields?


Why Arundo as a feedstock for biogas silage?


Weiland argues that anaerobic digestion can use a diverse set of substrates, with energy crops becoming the most regularly exploited biomass in the agricultural sector. Giant cane for biogas production appears to not only be promising, but soon becoming a wide spread application due to its capacity to substitute for traditional energy crops. There has been many tests since Corno et al. demonstrated on a lab-scale that giant cane could substitute for corn in a mix with pig slurries, reducing total costs for electricity/biomethane production.


With literature estimating the biogas output per ton of Arundo to be between 310-320m3 and up to 413m3 per ton of Arundo, it is needless to say why Arundo is worth considering for any biogas production facility.

Combined with the cheap cultivation costs and high biomass yields per hectare, giant reed is destined for a huge role in the biogas industry.


BIOGAS to ELECTRICITY – fulfilling our energy demand with crops


The two types of silage techniques – trench and silo-bags


Energy crops – just like other agricultural crops – require to be ensiled in order to guarantee biomass disposal throughout the year. Although the behaviour of energy crops during anaerobic digestion has been studied frequently, fewer efforts have been devoted to assess the outcomes of biomass storage (ensilage) on biogas potential preservation. The biogas ensilage procedure is a practice that uses the natural fermentation carried out by bacteria, permitting crops to be stored for extended periods.


Crop silage features are manipulated by the biomass’ biological composition, in addition to the fermentation products created during ensilage. The various types of silage techniques affect silage characteristics as the different settings generated lead to the creation of unalike quantities and classes of acids and biomass degradation; the latter influencing the biomass energetic content.

The two most popular types of silage production techniques are trench and silo-bags – both favourable to ensile energy crops. Trench silos are best described as a three-wall structure with a floor in which the biomass is collected, squashed by tractor, and enclosed with plastic concealments. The silo-bag system does not necessitate steady structures, as it purely the storage of biomass in plastic bags of several sizes. It is common knowledge that silo-bag ensilage is superior over trench ensilage as it diminishes the losses of nutrients and organic matter, thus increasing the silage value. Moreover, between the two types of silage procedures, silo-bag ensilage demonstrates a lower influence to the gas emissions due to the lower total solid losses.


Nevertheless, Liu et al indicated that giant cane can be ensiled successfully without the addition of inoculum – proving that either types of silage methods are adequate.



The case study: how Arundo performed under the various types of silage storage


The harvesting was done at the end of the growing season, when the highest yield of biomass is achieved – usually between 50-80 dry tonnes per hectare for Arundo. The harvesting was done using regular agricultural equipment employed for corn; a 0.5-1 cm shredding dimension was set. In a trench silo usually used for corn silage, bale wrappers divided the biomass from the floor and walls. Neither enzymes nor inoculum were supplemented to the biomass before silage. The biomass was pressed down in order to facilitate the formation of anaerobic conditions prior to the covering of the crop with the bale wrappers. Throughout the monitoring period, the trench was kept closed.


The Arundo for the silo-bag trial was harvested by adopting the same procedure; the chopped biomass was instantly used to fill the silo-bag with the help of a bagger typically utilised for corn or sorghum ensilage. Again, neither enzymes nor inoculum was added to the biomass. The silage was tested using a sampler in altered positions within the silo-bags with the identical procedure used for the trench silo. Both types of silage were sampled after 100 and 200 days; whereby three subsamples were collected during each sampling.


Effects of Harvest Time and Frequency on Biogas Yield


Results: what types of silage techniques work best for Arundo?


The silos were unlocked and examined, and the basic characteristics were identified (Table 1). The colours of the silage were typical of an ensiled biomass and no moulds were spotted on either of the biomasses. The pHs were between 3.5 and 4 and no percolate was noticed for either types of silage. The documented temperatures proposed that the biomass has endured no aerobic degradation during storage. Although both raw biomasses had similar moisture contents prior to storage, the trench biomass was considered to have a higher moisture content. The different types of silage techniques also induced varying compositions – the trench biomass was more solid.




More important are the comparisons in Table 3. The efficiencies of different types of silage techniques on preserving biomethane were compared amongst various popular options for biogas feedstock. Amongst the corn, sorghum, rye and triticale, Arundo had the highest biomass yield (63.2-71.8 tones per hectare) and biochemical methane potential (BMP) per hectare with 21,468-26,853 Nm3 CH4 compared to corn (6,499), sorghum (6,931) and triticale (5,488). Whilst the BMP of corn and triticale were competitive, the high biomass yields of Arundo crowned the energy crop the prevailing feedstock for biogas production. What truly stands out however, is Arundo’s electric energy potential per hectare. Whilst for the silo-bag method, Arundo’s 78 MW hEE Ha-1  was higher than trench silage Arundo (75.5), corn silage (24.4), sorghum silage (21), rye (19.6) and triticale (19.3). Thus, it is clear that regardless of the types of silage methods, Arundo is potentially the strongest alternative for sustainable, low input and high yielding biogas production.




If you want to find out more about using Arundo for biogas production, visit our website and send us an email at info@arundobioenergy.com if you want to try out the energy crop.


Reference: Luca Corno et. al. () Giant cane (Arundo donax L.) for biogas production: The effect of two ensilage methods on biomass characteristics and biogas potential. Biomass and Bioenergy. Volume 93, October 2016, Pages 131-136


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