Utilization of anaerobic digestion supernatant as a nutrient source in microalgal biomass production with a membrane photobioreactor

Abstract

The green microalgae Chlorella vulgaris, which is known to accumulate valuable substrates, are one of the promising bio-resources. To achieve the mass cultivation of microalgae, anaerobic digestion supernatant was applied as cultivation media in membrane photobioreactor system. In the experiment, the synthesized anaerobic digestion supernatant mimicked from activated sludge collected from an actual wastewater treatment plant in Ishikawa, Japan, was used as cultivation media. In the point of view of nutrient loading, the diluted digestion supernatant satisfied the level for growth. Especially, N/P ratio was 3.8 with high concentration of P, which was previously reported as limiting factor when treated sewage was used as media. Although the maximum biomass productivity (5.58 mg/L/day) was below the previously reported data with treated sewage, the high P concentration in anaerobic digestion supernatant could be utilized as a "supplement" in media.