Carbon speciation and flocculation in Neochloris oleoabundans cultures using anaerobically digested stillage.

The effects of bicarbonate loading rate (BLR) and pH on growth kinetics, inorganic carbon speciation, carbon fixation and lipid content in Neochloris oleoabundans cultures using anaerobically digested stillage (ADS) (2% v/v) were investigated. Four different cultures were established: culture A with BLR = 1 g l-1 day-1 and no pH adjustment, culture B with BLR = 0.5 g l-1 day-1 and no pH adjustment, culture C with BLR = 1 g l-1 day-1 and pH adjustment at 7.0, and culture D with BLR = 0.5 g l-1 day-1 and pH adjustment at 7.0. The experiments were carried out in flat plate reactors (4 l) at controlled conditions (light intensity of 134 µmol photon m-1 s-1 and photoperiod 16 light/8 darkness; temperature of 32 ± 1 °C). The effects of pH (7, 10.41, 10.65, and 12), time (15, 30, 60, and 90 min), and concentration of a cationic polyelectrolyte (CP) (10 and 20 mg l-1) on the flocculation efficiency (FE) of N. oleoabundans were also investigated. The results showed that bicarbonate was the predominant carbon species in the media and the main carbon source for microalgae growth in all cultures. The highest productivity (87.70 ± 9.70 mg l-1 day-1) and CO2(aq) fixation rate (0.15 g CO2(aq) l-1 day-1) were found in culture B. The lipid content in N. oleoabundans was affected negatively by the pH adjustment at 7.0 during its growth; higher values were found in cultures with no pH adjustment (37.10% and 38.85% dw for culture A and B, respectively) as compared to those obtained in cultures with pH adjustment (27.35% and 22.20% dw for culture C and D, respectively) (p < 0.05). Regarding flocculation, the addition of 20 mg CP l-1 was required to obtain a FE > 95% in cultures A and B, although a significant FE (40-59%) occurred without CP addition at a high pH (≥ 10.41) in all cultures.

Dual purpose system that treats anaerobic effluents from pig waste and produce Neochloris oleoabundans as lipid rich biomass.

Dual purpose systems that treat wastewater and produce lipid rich microalgae biomass have been indicated as an option with great potential for production of biodiesel at a competitive cost. The aim of the present work was to develop a dual purpose system for the treatment of the anaerobic effluents from pig waste utilizing Neochloris oleoabundans and to evaluate its growth, lipid content and lipid profile of the harvested biomass and the removal of nutrients from the media. Cultures of N. oleoabundans were established in 4 L flat plate photobioreactors using diluted effluents from two different types of anaerobic filters, one packed with ceramic material (D1) and another one packed with volcanic gravel (D2). Maximum biomass concentration in D1 was 0.63 g L(-1) which was significantly higher than the one found in D2 (0.55 g L(-1)). Cultures were very efficient at nutrient removal: 98% for NNH4(+) and 98% for PO4(3-). Regarding total lipid content, diluted eflluents from D2 promoted a biomass containing 27.4% (dry weight) and D1 a biomass containing 22.4% (dry weight). Maximum lipid productivity was also higher in D2 compared to D1 (6.27±0.62 mg L(-1) d(-1) vs. 5.12±0.12 mg L(-1) d(-1)). Concerning the FAMEs profile in diluted effluents, the most abundant one was C18:1, followed by C18:2 and C16:0. The profile in D2 contained less C18:3 (linolenic acid) than the one in D1 (4.37% vs. 5.55%). In conclusion, this is the first report demonstrating that cultures of N. oleoabundans treating anaerobic effluents from pig waste are very efficient at nutrient removal and a biomass rich in lipids can be recovered. The maximum total lipid content and the most convenient FAMEs profile were obtained using effluents from a digester packed with volcanic gravel.