Methane Production by Anaerobic Digestion of Algae

The research aims (1) at improving yields and rates of biomethanation of algae and (2) at correlating composition of algal batches with methane productivities. Previously, it had been shown with Hydrodictyon algae that a two step system (liquefaction and biomethanation) gave improved results over a one step, completely-mixed system. In the present work, the influence of environmental factors such as temperature and load on the first step were investigated. Although the results of the liquefaction varied somewhat with the running conditions, these variations were without appreciable effect on the overall methane productivities. Besides, preliminary results of a two step system, a first percolating step followed by an upflow methane digester with active biomass accumulation look promising. Application of the two step biomethanation process to the algae Tetraselmis elicited a problem of reliability with time, presumably due to enhanced concentrations in ammonia resulting from increased biodegradation of proteins. Increasing the salt (NaCl) content (presently up to 20 g × l-1) in the mixed liquor of a one step digester had no influence on the process. Biomethanation of six algal species showed good although inequal potential for methane production with yields from 0.20 to 0.33 1 CH4 × g-1 VSº. Monitoring based on volatile solids (VS) contents appears erratic in the two step process because samples contain variable amounts of compounds volatile below 100 °C. Monitoring based on COD appears more reliable. Lagoons for the production of ton amounts of freshwater Hydrodictyon algae in industrial luke-warm were constructed. Production and population analyses of the algae are in progress.