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Due to high growth rates microalgae provide an enormous potential as a source for biomass besides conventional energy crops. The algal biomass can be used for bioenergy production. Anaerobic digestion to biogas is one of the most energy-efficient and environmentally beneficial technologies for alternative energy carrier production. The resistance of the algal cell wall is generally a limiting factor for cell digestibility. In the present work different cell disruption techniques (microwave heating; heating for 8 hours at 100°C; freezing over night at -15°C; French press; ultrasonic) on algal biomass of Nannochloropis salina were carried out. The disrupted material was digested to biogas in batch experiments according to VDI 4630. The results indicate that hydrolysis of algal cells is the rate-limiting step in anaerobic digestion of algal biomass. Cell disruption by heating, microwave and French press show a considerable increase in specific biogas production and degradation rate. Compared to the untreated sample the specific biogas production was increased for the heating approach by 58 %, for the microwave by 40 % and for the French press by 33 %.

No abstract

Industrial biogas plants often do not operate in their optimum. To investigate limits of anaerobic digestion processes experiments are necessary. Economically it would be feasible to perform these tests at laboratory scale, if the tests could be transferred to industrial scale. This work presents a preliminary study, in which two different scales of laboratory digesters are compared and reproducibility of tests is investigated. Therefore, three identical glass digesters with a liquid volume of up to 22 liter and a steel-digester with a liquid volume of 390 liter were used. All digesters were started up with digestate from an industrial biogas plant, were fed with cow manure and corn cob mix, and were operated at the same process parameters like temperature, organic loading rate and retention time. Gas volumes were measured continuously. Twice a day the composition of the biogas was analyzed. Dry matter and volatile solids were quantified once a week. The presented data show a good reproducibility between biogas plants of the same scale. The transferability to a bigger scale is in an acceptable range, but depending on the organic loading rate the deviation between the different scales varies.