3. Limitations in algae use for biogas production processes
A reduced interest in algae biomass as an alternative source of biodegradable organic matter applied in biogas production systems is mainly due to difficulties with its use as a substrate.
Thus far conducted investigations pinpoint several factors that curb the effectiveness of methane fermentation process and may effectively
reduce or completely inhibit the mechanism of biogas production in technologies utilizing algae biomass. These factors include: cell walls that are resistant to degradation under anaerobic conditions owing to the presence of cellulose or hemicellulose compounds, strains of algae producing substances and compounds toxic to anaerobic bacteria, and the unbeneficial C:N ratio in the biomass subjected to the fermentation processes.
Such technological difficulties were proved by Dębowski. In his experiments, analyses were aimed at verifying or confirming a direct relationship between the course and technological effects of fermentation, and the taxon of microalgae applied in the process. To this end, pure cultures of microalgae from the Chlorophyta, Cyanoprokaryota and Bacillariophyceae phylum were proliferated under controlled conditions and their biomass was used in the fer mentation process. The use of algae from the pure culture Chlorophyta division during methane fermentation enabled reaching an average biogas production yield at 396.21+- 30.94 dm3/kg o.d.m. at the reaction rate of r=54.28 cm3/d. Methane content of biogas accounted for 59.73 +- 2.43%. In the series where algae of the Cyanoprokaryota divisio served as the organic substrate, the yield of biogas production oscillated around 382.45 +- 9.24 dm3/kg o.d.m., biogas was produced.