Abstract

Anaerobic digestion (AD) has become an increasingly popular method of treating wastewater or sludges from animal feeding operations. Enhancement of biogas production in anaerobic digesters, through addition of commonly-available and under-utilized biomass, could benefit sustainability of farm-scale anaerobic digesters. Duckweed is a common aquatic plant that aggressively grows in farm ponds, lagoons, and other water bodies that receive agricultural runoff. As such, duckweed is a readily-available biomass that could be easily added to farm-scale anaerobic digesters. Therefore, research aimed to determine if biogas (methane) production could be improved by supplementing digesters with duckweed (e.g., Landoltia punctata). Increases in biogas production and rate of attaining peak biogas production were assessed in batch continuously-stirred reactors at 35oC. Varying concentrations of duckweed were added to dairy manure slurries and gas production was observed for 20-40 days. Additionally, subsequent research will assess changes in chemical oxygen demand (COD), pH, and fatty acids within manure/duckweed slurries in parallel with analyses of biogas production, with time. Preliminary results indicate that addition of duckweed, in the range of 0.5 to 2% (dry mass), enhanced methane and total gas production in dairy manure slurries; however, subsequent increases in methane and total gas production at >2% duckweed were not observed. In conclusion, addition of duckweed biomass, produced during treatment of agricultural wastewaters and runoff, to anaerobic digesters is a promising approach to enhancement of biogas production.

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