Optimization of biomass production from Stichococcous sp. biofilms coupled to wastewater treatment

[Display omitted] •Optimization of Stichococcus sp. biomass production growing immobilized in biofilms.•Seawater was used as the basis for the growth medium.•Sandblasted glass proved better for attachment compared to polyethylene and ceramic.•Two days nitrogen starvation towards the end of growth period boosted biomass yield.•Stichococcus grew optimally on winery wastewater solution after 2 days N starvation. Microalgae have been extensively used as animal feedstock and for the production of high-added value bioproducts, such as pigments and biodiesel. A promising strategy to simplify biomass recovery is by growing microalgae on flat biofilms, from where biomass may be easily harvested. Initially, the microalgae Stichococcus sp. was grown in photo-bioreactors, on seawater enriched with inorganic salts, on three different materials: ceramic tile, HD-polyethylene and sandblasted-glass, the latter of which exhibited the highest yield (up to 0.86 ± 0.02 mg cm−2 after 18 days cultivation period). Thereafter, the microalgae were grown on seawater enriched with winery-wastewater, applying nitrogen starvation during the last 2 days of cultivation, indicating biomass production of 1.00 ± 0.01 mg cm−2 (seawater plus organic carbon) to 1.30 ± 0.03 mg cm−2 (seawater plus organic carbon plus 2 days nitrogen starvation) to 1.43 ± 0.03 mg cm−2 (seawater plus inorganic carbon plus organic carbon plus 2 days nitrogen starvation). Trials on large scale photo-bioreactors confirmed the remediation potential of Stichococcus sp. for the treatment of winery-wastewater, while the organic carbon in wastewater boosted the yield of biomass production. Finally, the potential biomass yield of an industrial scale plant, treating winery-wastewater, was calculated to yield between 25−32 kg biomass (dry-basis) per 1000 m2 of shallow pond type reactor, per 18 days cultivation.