Mixed silage of Elodea and wheat straw as a substrate for energy production in anaerobic digestion plants

Abstract

Background: Waterweeds (Elodea nuttallii and Elodea canadensis) are invasive neophytes, which have been proliferating at a phenomenal rate during the last decades in German waterways. In case of overgrowth, the strong covering of vegetation can cause problems in hydroelectric power plants and leads to limitations in ship and boat traffic as well as in use for bathing and fishing activities. After vegetation period, dead plants can accumulate and then negatively influence flood protection and water engineering works. For this reason, the aquatic biomass has been periodically removed and disposed without further use. In order to enable the energetic use of this water-containing substrate, the aim of the present study was the optimization of storage methods for an aquatic plant-based feedstock for biogas production. In climatic cold regions, substrate conservation is necessary in order to guarantee a year-round substrate availability. With waterweed (Elodea) taken as an example, the ensiling of aquatic plants was studied. The main focus was to develop practical methods for biomass conservation while producing high biogas yields. Methods: Elodea was harvested in the river Parthe in Leipzig-Schönefeld in October 2015. Silage mixtures of Elodea and wheat straw were tested after 180 days of storage for pH, volatile fermentation products, and methane potentials. The effect of different silage moisture contents and straw particle sizes on the substrate quality was studied. Results: Results show that waterweeds can be stored by ensiling and can achieve considerable biogas yields. However, with a water content of about 95%, the storability of the material is challenging. Mixed silage of waterweeds and wheat straw were suitable for storage in clamp silos. The pH values were between 4.9 and 6.5, and the volatile fatty acid content as lactic acid ranged from 0.0 to 1.9% total solid. The mixed silages achieved methane potentials between 166 and 228 mL g − 1 volatile solid (VS), which is equivalent to 52 and 72% of maize silage. Considering a methane potential of 228 mL g − 1 VS and costs for material pretreatment, the most promising silage variant was mixed silage from waterweeds and ground straw with 30% total solid content. Conclusions: Long storability of waterweeds could be possible by ensiling fermentation. Mixed silages from Elodea and wheat straw show suitable substrate characteristics for biogas production and can achieve high biogas yields.

Comparison of Clay Ceramsite and Biodegradable Polymers as Carriers in Pack-bed Biofilm Reactor for Nitrate Removal

“…As can be seen in Figure 4b, nitrite concentration in the effluent of Reactors 1 and 2 gradually increased as the HRT decreased, and the nitrite accumulation in Reactor 2 was more obvious than that of Reactor 1, suggesting that the second step of denitrification of reducing NO2−-N into N 2 was severely inhibited. The shorter HRT value resulted in a decrease in nitrate removal and an increase in nitrite accumulation in Reactor 2 mainly because of the low contact time for microbial activity [31]. Under high flow rate condition, the soluble organic carbon was quickly washed out along with the effluent before it can be utilized by the denitrifiers.…”

A potential phosphorous fertilizer for organic farming: recovery of phosphorous resources in the course of bioenergy production through anaerobic digestion of aquatic macrophytes

“…A poor availability could, depending on the main crop, be only partially improved by suitable catch crops [36]. On the contrary, substrates for biogas became mineralized by anaerobic digestion, which resulted in a higher plant availability [17,18].…”

“…The results indicate that aquatic macrophytes, such as E. nuttallii, have appropriate substrate characteristics and allow considerable biogas yields comparable to hay to be achieved [17]. During anaerobic digestion, methane (CH 4 ) and carbon dioxide (CO 2 ) are formed, but nutrients like P remain in the digestate [18,19].…”

Enhancing the co-ensiling performance of corn stover and cabbage waste via the addition of cellulase

“…Ensiling is an anaerobic wet storage method and represents a feasible and costeffective way to supply year-round biomass (Gallegos et al 2018). During the ensiling process, lactic acid bacteria (LAB) convert water-soluble carbohydrates (WSCs) into organic acids, reducing the pH to a range of 3.5 to 4.2, which inhibits the growth of undesirable microorganisms and preserves the organic matter of biomass (Janke et al 2019).…”