Substrate and inoculum
Laminaria spp. was collected on shore in Howth (Dublin, Ireland)
in early November, 2013 in order to reproduce the case of
harvesting readily biomass available on the beach. There was no
selection of a particular Laminaria species. In the mixture harvested
from the beach, three main species were identified, namely
L. digitata, S. latissima, and L. hyperborea. The TS content was found
at 19.0 ± 2.2% Wt on wet basis, while the VS content was at
84.1 ± 0.3% Wt on dry basis. Before pretreatment, fresh seaweed
was roughly cut and immediately used without washing.
On the same day, treated and untreated seaweed were inoculated
and subject to anaerobic conditions. The used inoculum
was sewage sludge from a wastewater treatment plant (Celtic
Anglian Water Ltd., Ringsend, Dublin) operating at mesophilic
condition. The TS content of the inoculum was found equal
to 3.6 ± 0.5% Wt on wet basis, while the VS content was equal to
79.5 ± 4.0% Wt on dry basis. The pH was measured equal to
8.0 ± 0.1. Once collected from the plant, the inoculum was immediately
used and not allowed to degasify in order to reproduce the
operating conditions of a co-digestion system for further studies.
Hence, sludge only reactors in duplicate were also incubated in
order to estimate the biogas production of the inoculum which
was then subtracted from the seaweed-sludge yields.