Semicontinuous anaerobic digestion of excessive growing aquatic weeds harvested from Lake Biwa for energy and nutrient recovery

Author(s): Masaaki Fujiwara
Email (s):
Institution or organization of origin: Soka University
Country: Japan


Over-growing aquatic weeds have caused several environmental issues all over the world. Anaerobic digestion is expected as an effective way to treat aquatic weeds because it can recover methane gas as an energy resource and nutrients dissolved in a digestate from high moisture waste. Due to the lignocellulosic components leading to low anaerobic biodegradability in aquatic weeds, pretreatment and co-digestion might help to improve energy and nutrient recovery. In this study, semi-continuous mono-digestion of alkaline thermal pretreated aquatic weeds and co-digestion with food waste were performed. The methane conversion rate showed 63.4% based on chemical oxygen demands (COD) in the mono-digestion condition. With co-digestion, the methane conversion rate was increased to 76.4%- COD. These relatively higher values than other substrates suggested that co-digestion and alkaline thermal pretreatment could increase methane production. As a result of nutrient analysis of the digestate, NH4 concentrations were 819 mg L-1 in mono-digestion and 385 mg L-1 in co-digestion, respectively, which were lower values than inhibition concentration in the anaerobic digestion process. Also, relatively higher Ca2+ and Mg2+ concentrations were observed in both conditions. The reason might be the improvement of the digestibility of the substrate. Therefore, the co-digestion process of alkaline thermal pretreated aquatic weeds and food waste is expected to be an effective way to enhance methane and nutrient recovery.

View the author’s explanation