Growth and anaerobic digestion characteristics of microalgae cultivated using various types of sewage

• Chlorella was cultivated without controlling species with dewatering filtrate.
• The methane conversion ratio of the cultivated microalgae was approximately 40–65%.
• Different cultivation time did not affect the microalgal contents.
• Methane recovery mass was 0.13 NL-methane/L-cultivation liquor.
• Applicability of methane recovery from cultivated microalgae was proved.

Microalgal cultivation combined with anaerobic digestion at wastewater treatment plants is promising to recover energy. This study investigated the growth and anaerobic digestion characteristics of microalgae cultivated using nutrients in sewage. Microalgae were cultivated using primary effluent, secondary effluent, and dewatering filtrate. Microscopic observation indicated that Chlorella was cultivated using dewatering filtrate of anaerobic digestion without controlling the type of species. Batch anaerobic digestion experiments with digested sludge showed that the methane conversion ratio of the cultivated mixture was approximately 40–65%. Different cultivation time did not affect the microalgal contents. Methane recovery mass was 0.13 NL-methane/L-cultivation liquor. The C/N ratio of the cultivated mixture was approximately 3–5, but the apparent ammonia release ratio was smaller than that of sewage sludge during digestion. These results proved the applicability of methane recovery from microalgae cultivated using nutrients included in anaerobically digested sludge.