Abstract
The production of bioenergy from plant biomass has the potential to reduce fossil fuel use. The number of biogas facilities around the world has risen dramatically, increasing demand for feedstocks. In this study the invasive perennial grass Phragmites australis was evaluated as a biogas feedstock in comparison with Miscanthus x giganteus and Panicum virgatum. Results from three field sites for each species demonstrated that biomass yields for P. australis averaged approximately 1.82 ± 0.9 kg dry matter (DM) m−2, comparable to that of M. x giganteus. Yield of P. australis was greater than P. virgatum, which ranged from 0.49 ± 0.06 to 0.69 ± 0.07 kg DM m−2 in July and October, respectively. In mesophilic bench-top digester experiments, methane yields were greater for July-harvested material than for October, ranging from 172.4 ± 15.3 to 229.8 ± 15.2 L CH4 kg−1 volatile solids (VS) for all perennial grasses. Methane yields per hectare were highest for October-harvested M. x giganteus, followed by July-harvested M. x giganteus and P. australis, whereas methane yield from P. virgatum at both harvest times was lower than the other two species. These results suggest that P. australis is not an economically viable biogas feedstock without pre-treatment to improve methane yield.
Highlights
The number of biogas facilities in Canada and around the world is rapidly increasing, with the majority of Canadian biogas plants being commissioned in the last 10 years [1,2]
Dry matter yields for M. x giganteus and P. australis were not statistically different, whereas P. virgatum had lower yields (Table 2)
Fresh matter yields were different for each species, where M. x giganteus had the highest yield, followed by P. australis and P. virgatum (Table 3)
Summary
The number of biogas facilities in Canada and around the world is rapidly increasing, with the majority of Canadian biogas plants being commissioned in the last 10 years [1,2]. As the industry continues to grow, so does the demand for sustainable, reliable, and affordable feedstocks with high methane yields. Energy crops are currently used as biogas co-substrates, with 0.5 million hectares of biogas maize grown in Germany alone [3]. The use of energy crops in anaerobic digestion can improve biogas yields, provide a reliable and consistent feedstock supply, and overcome some of the limitations of mono-digestion by improving the C:N ratio and buffering capacity [4]. While using annual crops like maize for biogas production is viable in some regions, perennial crop species may be better suited for biogas utilization in others. Perennial grass species can be harvested for many years after planting, due to their root masses, which store nutrients from year to year
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