Microalgae cultivation in urban wastewater: Nutrient removal and biomass production for biodiesel and methane

• The wastewater provides nutrients for freshwater and marine microalgae cultivation.
• High microalgae growth is observed in the freshwater species when centrate is used.
• C. kessleri and C. vulgaris remove > 95% TN and > 98% TP when grown in wastewater.
• C. kessleri and C. vulgaris produce more CH4 than substrates commonly digested.
• The N-starvation derived from nutrient removal is beneficial for biofuels production.

The freshwater microalgae species Chlorella kessleri and Chlorella vulgaris, and the marine microalgae species Nannochloropsis oculata were cultivated in urban wastewater. The freshwater species demonstrated the possibility of growing in urban wastewater reaching high biomass production and nutrient removal when cultured in batch mode using a flat-panel airlift photobioreactor. Both microalgae species reached high biomass dry weights, 2.70 ± 0.08 g/L and 2.91 ± 0.02 g/L respectively, accompanied by nitrogen concentration reduction around 96% and 95%, and a phosphorous concentration reduction around 99% and 98% respectively. N. oculata was able to uptake nutrients from wastewater to grow but with less efficiency, indicating the need of microalgae acclimation or process optimisation to achieve high nutrient removals. During C. kessleri and C. vulgaris cultivation, the nitrogen consumption led to a progressive N-starvation process which increased the microalgae potential for biofuels production; both species produced 346 ± 3 mLCH4/gVS and 415 ± 2 mLCH4/gVS during anaerobic digestion, and 7.4 ± 0.2 gBiodiesel/100 gVS and 11.3 ± 0.1 gBiodiesel/100 gVS respectively.

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