Microalgae cultivation by uncoupled nutrient supply in sequencing batch reactor (SBR) integrated with olive mill wastewater treatment

The growth of bacteria contaminants can be controlled in heterotrophic microalgae cultures by using an uncoupled supply of glucose and nitrate. However, till now this strategy was only described for fed-batch cultivation. The cultivation in a sequencing batch reactor (SBR) could be more promising for the industrial scale. Here in this work, we tested the uncoupled supply of substrates on microalgae cultivated in SBR (feast/famine ratio = 1.33), with an optimized culture medium (based on the microalgae elemental formula), and the integration of this strategy with olive mill wastewater (OMW) treatment. SBR allowed to attain biomass productivities (P-X) proportional to the initial biomass concentration (P-X = 0.13.X-0), showing the possibility to reach the same productivities as conventional axenic cultures, by maintaining bacteria contamination at negligible values (<5%, as CFU/algae). The SBR system showed a stable biomass production (1.54 folds X-0) throughout 8 consecutive cycles (53 days), uncoupling biomass production and cell duplication. However, relevant grazer contamination reduced the growth of microalgae cells between the 4th and 7th cycle and the biomass yield on glucose (from 0.31 to 0.17 g g(-1)). The integration with OMW treatment proved the possibility to remove 52% of phenols, but the loss of fermentable substrates during OMW storage and preliminary processing (by membrane filtration) hindered the exploitation of OMW as a relevant alternative source for organic substrates.

Automated summary

The study investigates controlling bacterial contaminants growth in heterotrophic microalgae cultures by using an uncoupled supply of glucose and nitrate. The results show the promising potential of SBR system for biomass productivity. However, grazer contamination and limitations in OMW treatment hinder the exploitation of OMW as an alternative organic substrate source.