Growth-promoting effects of phytohormones on capillary-driven attached Chlorella sp. biofilm

Using low strength wastewater for microalgae cultivation is challenged by slow growth and biomass harvesting issue in suspended systems, and growth-promoting effects of phytohormones at currently recommended dosages could neither obtain high enough biomass concentrations nor economic feasibility. This study aims to solve the issues of slow growth, biomass harvest, and phytohormone costs altogether by supplementing low dosage phytohormones in an improved capillary-driven attached cultivation device. The device displayed nutrients-condensing properties, and dosages of indole acetic acid (IAA), 6-benzylaminopurine (6-BA), and salicylic acid (SA) for highest microalgal growth were respectively 10^-6 M, 10^-6 M, and 10^-7 M, being at least one order of magnitude lower than in suspended cultures. SA was most effective in growth-promoting (up to 7.0 g/m² biomass density) and nutrients uptake (up to 98.6 % from the bulk environment), while IAA was most effective in antioxidative defenses. These results provided new insights in cost-effective and harvesting-convenient microalgae production.