Hydrogen and volatile fatty acid production from  macroalgae biomass and spent coffee grounds using  acidogenic fermentation

This PhD thesis aimed at investigating the valorisation of both Ulva biomass and spent coffee grounds (SCG) through acidogenic fermentation. To maximize the two substrates' potential for producing H2 and volatile fatty acids, a range of pretreatment procedures were applied. The first part of this research (Chapter 3) investigated the effects of process temperature (25C, 37C and 55C), ulvan extraction and lyophilisation on production of H2 and volatile fatty acids (VFAs) from Ulva biomass. Ulvan extracted biomass performed most favourably at each temperature, achieving a H2 yield of 12.8 (± 0.2) mL H2/g VS at 25 °C, 15.0 (± 1.2) mL H2/g VS at 37 °C, and 15.3 (± 1.5) mL H2/g VS at 55 °C. Additionally, the ulvan-extracted biomass gave the highest yield of total VFAs with the peak concentrations achieved at the end of the incubation (day 4), i.e. 666.6 (± 76.0) mg HAceq/L at 25 °C, 610.7 (± 66.9) mg HAceq/L at 37 °C, and 783.7 (± 31.8) mg HAceq/L at 55 °C, thus indicating that the extraction of the polysaccharide ulvan did not limit the potential valorisation of the Ulva substrate. In chapter 4, the impact of ulvan extraction and morphotype of Ulva sp. (foliose vs tubular) on acidogenic fermentation in a fed batch bioreactor system was investigated. Regarding Ulva morphology, both morphotypes exhibited comparable VFA production when ulvan was present, with peak concentrations of VFAs recorded at 2179.5 mg HAceq/L (foliose) and 2029.3 mg HAceq/L (tubular). Moreover, the ulvan extraction had no effect on the tubular morphotype, which peaked at 2165.0 mg HAceq/L. Additionally, the hydrolysis of the tubular morphotype profited from ulvan extraction peaking, at a carbohydrate release of 9.8 g glucose/L. Chapter 5 investigated the impact various pretreatments, i.e. alkali, ultrasound and static magnetic field (SMF), have on biomolecule solubilisation and anaerobic fermentation of spent coffee grounds (SCG), with a focus on H2 and VFA production. Ultrasound pretreatment resulted in the highest accumulation of VFAs (3260.0 ± 164.2 mg HAceq/L), accompanied with an increased caproic acid concentration (1114.4 mg HAceq/L). Additionally, SMF pretreatment was found to be not a viable means of pretreatment for preparing SCG for anaerobic fermentation. Chapter 6 further evaluates the valorisation of raw and ultrasound pretreated SCG in bioreactor systems. Ultrasound pretreatment resulted in an increase of 27.4% in VFA accumulation. The microbial community analysis indicated that an elevated relative abundance of Clostridia species corresponded with the peaks in H2 production. Following fermentation, the VFA-rich effluent was used as the substrate to an upflow anaerobic sludge bed reactor (UASB) to produce CH4 (9.0 mL CH4/g VS/d) at a low pH (4 - 5).

Funder

MaREI / Research Ireland

Publisher

University of Galway

Rights

CC BY-NC-ND

cbn

Collections

University of Galway Theses (PhD Theses)