Harvesting Chlorella vulgaris by natural increase in pH: effect of medium composition.
The freshwater microalga Chlorella vulgaris was harvested by autoflocculation resulting from the precipitation of magnesium or calcium compounds induced by a slow increase in pH in the absence of CO2 input. Autoflocculation was tested in two culture media with, respectively, ammonium (NH4+) and nitrate (NO3-) ions as nitrogen source. The culture pH increased because of photosynthesis and CO2 stripping. pH rose to 11 after 8 h in the NO3- medium, but did not exceed 9 in the NH4+ medium. No flocculation took place in any of the media. Autoflocculation tests were repeated in the NO(3-)-based culture medium by progressively increasing the concentrations of Ca2+ and Mg2+ until inorganic compounds precipitated and flocculated microalgae. The minimal concentrations for flocculation were found to be 120 mg Ca2 L(-1) and 1000 mg Mg2+ L(-1). These values were, respectively, 3.5 times and 20 times higher than those allowing flocculation by NaOH addition. Energy-dispersive X-ray spectroscopy, zeta potential measurement, and ionic chromatography suggest that the mechanisms involved are different. The rate of cell removal was close to 90% in both cases, but cells were more concentrated in the aggregates obtained by magnesium compound precipitation, with an estimated concentration close to 33 g (dry matter) L(-1), against 19 g L(-1) for calcium phosphates.
Thi Dong Phuong
TD
Nguyen
Matthieu
M
Frappart
Pascal
P
Jaouen
Jérémy
J
Pruvost
Patrick
P
Bourseau
D064751:Ammonium Compounds; D017756:Aquaculture; D002118:Calcium; D048408:Chlorella vulgaris; D003470:Culture Media / Q000737:chemistry*; D005427:Flocculation; D006863:Hydrogen-Ion Concentration; D008274:Magnesium; D009566:Nitrates
D064751:Ammonium Compounds; D003470:Culture Media; D009566:Nitrates; D008274:Magnesium; D002118:Calcium