Innovative wastewater treatment strategies increasingly seek to integrate pollution mitigation with resource recovery, for which microalgae present a promising solution. This study applied Response Surface Methodology (RSM) to optimise the cultivation of Nannochloropsis oceanica on sterile brewery wastewater (N:P = 1.4), quantifying the interactive effects of wastewater concentration, photoperiod, and salinity on biomass production in 250 mL flasks. Wastewater concentration emerged as the primary growth driver, with higher nutrient availability (25–100% v/v) amplifying the advantages of extended illumination (8–16 h/day), while salinity (0–35 g/L) showed an inverted-U relationship with a defined optimum (14 g/L). Structural Equation Modelling (SEM) further indicated that nutrients sourced from wastewater facilitated microalgae growth, simultaneously with an increase in cell size and polar lipid accumulation. However, daily illumination enhanced early microalgal concentration but reduced pigment content. Salinity showed a phase-dependent effect on lipid metabolism; it promoted neutral lipid accumulation as an osmotic stress response during early cultivation (Day 1–7, coinciding with nitrogen depletion), but this relationship reversed at the later stage. RSM-optimised conditions were validated in 2 L photobioreactors, yielding 0.8 g/L biomass and 199.6 mg/g fatty acids. Harvest timing proved critical; early harvesting (Day 7) favoured polyunsaturated fatty acid production for nutraceutical applications (16.5% of fatty acids), whereas later harvesting (Day 14) enhanced saturated fatty acid accumulation suitable for biodiesel (55.1% of fatty acids). N. oceanica also demonstrated robust bioremediation performance, achieving removal efficiencies of 97% ammonia, 98% nitrate, and 86% phosphate from brewery wastewater. • N. oceanica removed 85–100% of nutrients from brewery wastewater, yielding 0.8 g/L biomass. • RSM optimised wastewater, salinity, and photoperiod. • SEM revealed direct/indirect pathways linking biomass, lipids, and pigments. • 2 L photobioreactors scale-up validated model predictions. • Harvest timing enabled lipid tailoring for nutraceuticals (N-replete) or biofuels (N-deplete)
Ma et al. (Wed,) studied this question.