Potential of the cyanobacteria Anabaena sp. and Dolichospermum sp. for being produced using wastewater or pig slurry: Validation using pilot-scale raceway reactors

Abstract

Indoor trials using 0.3 L bubble columns were conducted to demonstrate the potential of two cyanobacterial strains, Anabaena sp. and Dolichospermum sp., for being produced using nutrients obtained from waste streams (wastewater or pig slurry). Filtered pig slurry diluted at a concentration of 5% (v/v) led to a biomass productivity comparable to that of the standard medium (0.72 ± 0.05 and 0.66 ± 0.09 g·L-1·day-1 for Anabaena sp. and Dolichospermum sp. respectively). When produced using wastewater, the productivity was around 0.40 g·L-1·day-1 for both strains. The process was up-scaled using a 1.04 m3 raceway reactor located outdoors and operated at a culture depth of 0.12 m. Dilution rates of 0.1-0.3 day-1 were evaluated, achieving maximum biomass productivities when operating at a dilution rate of 0.3 day-1: 20.9 and 28.0 g·m-2·day-1 for Anabaena sp. and Dolichospermum sp., respectively. The maximum total nitrogen (N-NH4+ plus N-NO3-) removal rates for Anabaena sp. and Dolichospermum sp. were 2,471 and 3,621 mg·m-2·day-1, achieved when operating at a dilution rate of 0.3 day-1. Nitrification and stripping contributed to the N-NH4+ removal. When operating at 0.3 day-1, maximum P-PO43- removal rates for cultures of Anabaena sp. and Dolichospermum sp. were 81.5 and 87.1 mg·m-2·day-1. Illumina sequencing results revealed that both strains dominated the prokaryotic community of both cultures with other notable eukaryotic and prokaryotic genus detected including human pathogens. However, annual studies are needed to assess the potential of producing biomass rich in these strains outdoors.