Using aquatic plant biomass from de-weeding in biogas processes—an economically viable option?

Abstract

Landscape maintenance in Germany today requires regular and extensive de-weeding of waterways, mostly to ensure water runoff and provide flood protection. The costs for this maintenance are high, and the harvested biomass goes to waste. We evaluated the economic feasibility of using water plant biomass as a substrate in biogas generation. We set up a plausible supply chain, used it to calculate the costs of using aquatic water biomass as a seasonal feedstock to generate biogas, and compared it against maize silage, a standard biogas substrate. We also calculated the costs of using the aquatic biomass mixed with straw silage. Although subject to estimation errors, our results do show that it is economically feasible to use water plants as a seasonal feedstock in a biogas plant, even in markets where their disposal yields only moderate gate fees. Ensiling water plants with straw, however, incurs the added high price of straw and thus only yields a positive financial result if gate fees for water plant disposal are very high. Water plant biomass need not remain an unwelcome by-product of de-weeding waterways. The funds for its costly disposal can be redirected to the biomass supply chain and support the profitable use of aquatic biomass as a seasonal feedstock in biogas plants. However, the legal status of material from de-weeding needs to be clarified before biogas operators can act. Further development of technology for harvesting aquatic biomass is also called for.