Biomethanation of Giant Brown Kelp Macrocystis Pyrifera

The results of studies conducted on the anaerobic digestion of the giant brown kelp - Macrocystis pyrifera - in laboratory-scale digesters are presented. Untreated raw kelp sustains a stable fermentation under conventional mesophilic operating conditions with a methane yield of 4.5 SCF/lb votaile solids (VS) of organic matter added and a reduction in organic matter of 50%. A materials and energy balanace presented for the kelp biomethanation process shows that 100 pounds of wet kelp as harvested and drained of physical water yields 25 SCF of methane with an energy recovery efficiency of 55.5%. The major biodegradable components of kelp are mannitol and algin, and the refractory components are cellulose and protein. The anaerobic fermentation of kelp was demonstrated as nonlimited by nitrogen or phosphorus. A stable fermentation can be developed with undiluted kelp feed or a kelp feed diluted with seawater. Thermophilic digestion of kelp exhibited unstable performance and lower yields than mesophilic digestion. Inocula derived from anaerobic marine environments did not show better performance than an inoculum derived from a mixture of effluents from domestic sewage sludge and municipal solid waste digesters. Higher methane yields may be possible through post-treatment and recycle of refractory effluent solids. Preliminary studies presented show that heat treatment alone and under acid and alkaline conditions increases the biodegradability of the digested ungasified solids.