Marine Biomass Program: Anaerobic Digestion Systems Development and Stability Study

Marine biomass represents a significant potential worldwide energy resource that can be converted to methane by anaerobic digestion. Through efficient biomass production, harvesting, and conversion techniques, competitive methane gas costs are achievable. The objective of this research project is to develop and define an anaerobic digestion process for producing methane from giant brown kelp (Macrocystis pyrifera).

The performance of kelp in these digestion studies, in terms of loading rates, methane yields, methane production rates, and process stability is the best ever reported for particulate forms of biomass. Methane yields as high as 0.42 sCM/kg (6.8 SCF/lb) VS added yere demonstrated. Upflow solids reactors (USR1s) that passively retained solids longer than the liquid portion of the feed, demonstrated better overall performance than stirred tank reactors (STR1s) operated at similar loading rates of up to 9.6 kg vs/m3-day (0.60 Lb vs/ft3-day). The application of attached film reactors as part of two-phase systems was demonstrated.

Kelp continues to show superior performance as a feedstock for gas production when compared with other particulate biomass feedstocks. Further work on upflow solids reactors and two-phase reactor systems is expected to improve gas cost estimates over those made using other state-of-the-art reactors.