Recent studies have reported improved biogas and methane yield from marine biomass when the particle size is mechanically reduced and the specific surface area available to enzymes is increased prior to anaerobic incubation. Although the advantage of reducing the particle size has been identified, an ideal particle size that would offer greater yield with a positive energy balance has not been identified for such substrate to date. As particle size reduction by mechanical means is often highly demanding in energy, this paper attempts to fill this gap for macroalgal biomass by identifying the particle size distribution allowing the highest biogas and methane yields obtained in a previous work. The study estimated that when about 80% of the particles are sized below 1.6 mm 2 , a biogas and methane yield improvement of up to 52% and 53% respectively can be achieved. The results are discussed in relation to the biogas yield, related methane content and potential inhibitory phenomena occurred during the fermentation.

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A new primary humidity generator was developed at the National Standards Authority of Ireland (NSAI). The principles of operation and overall design of the generator are discussed. The flow regime within the saturators was analysed using computational fluid dynamics (CFD) to determine if sufficient mixing takes place within the final saturator. This was later investigated by experiment and it was found that sufficient mixing takes place for flow rates up to 3 l min−1 at standard flow conditions of 101 325 Pa and 293.15 K. The uncertainty due to non-ideal saturation at 90 °C dp is discussed. This uncertainty was analysed with respect to the effect that the flow speed and latent heating in the saturators has on the saturation efficiency, separately. The uncertainty associated with saturation efficiency at 90 °C dew point was estimated from the temperature gradients along the saturation path arising due to latent heating effects. The standard uncertainty due to non-ideal saturation was found to be  ±3 mK dp.

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