Anaerobic mono-digestion of lucerne, grass and forbs – Influence of species and cutting frequency. (February 2018)

• Record Type: Journal Article
• Authors: Wahid, Radziah; Feng, Lu; Cong, Wen-Feng; Ward, Alastair James; Møller, Henrik Bjarne; Eriksen, Jørgen
• Is Part Of: Biomass and bioenergy. Volume 109(2018)
• Page Start: 199
• Page End: 208
• Publication Date: 2018-02
• Subjects: Mono-digestion -- Multispecies -- Cutting frequency -- Methane yield -- Nutrients; Biomass energy -- Periodicals; Biomass -- Periodicals; Energy-Generating Resources -- Periodicals; Bioénergie -- Périodiques; 333.9539
• DOI: 10.1016/j.biombioe.2017.12.029
• Languages: English
• ISSNs: 0961-9534

Abstract

Abstract: In the present study, biogas potentials of multispecies swards including grass, lucerne, caraway, ribwort plantain and chicory from two- and four-cut regimes (Mix-2 and Mix-4) for mono-digestion applying batch and continuous modes under lab-scale conditions were investigated. The gas yields in terms of volatile solids (VS) loaded from Mix-2 and Mix-4 were compared with pure stand lucerne from the four cuts regime (Lu-4). The batch test results indicate that methane yield on a VS basis was highest from Mix-4 (295 L kg −1 ), followed by Mix-2 (281 L kg −1 ) and Lu-4 (255 L kg −1 ). The results were confirmed with continuous experiments, during which the reactor digesting Mix-4 was stable throughout the experiment with low ammonia and volatile fatty acid (VFA) concentration. Meanwhile, mono-digestion of Lu-4 led to elevated VFA levels, even at a comparatively low organic loading rate of 1.76 g L −1 d −1 but it was not possible to ascertain whether this was due to organic overload alone or if high ammonia levels during Lu-4 digestion were contributing to the reduced performance. It was found that four cuts per year was suitable for a lab-scale mono-digestion system as the substrate was less fibrous and has lower dry matter content, which minimize blockage during feeding and digestate unloading. Micronutrient concentrations, including cobalt, nickel and molybdenum decreased over time during the continuous experiments and were critically lower than the optimum concentration required by methanogens, particularly in Mix-4, but the gas yields of the reactor treating this substrate showed no decrease over time. Highlights: Mono-digestion of Mix-4 demonstrates good process stability and higher methane yield. Mono-digestion of lucerne at OLR < 1.76 g L −1 may minimize risk of inhibition. Grass-lucerne-forbs at four-cut is the best substrate for lab-scale mono-digestion. Micronutrients level in DMix-4 reduces over time, yet gas yield is stable.