As the bio-filter (alga) was re-newed, the used media became more diluted as compared with the initial at zero time
Comparison of chemostat and batch culture
Batch culture of C. pyrenoidosa XQ-20044 was carried out in the same photobioreactor used for the continuous cultures, in order to supply basic data for comparing chemostat and batch cultures. Since the maximal lipid productivity in the chemostat was achieved with dilution rate of 0.48 d1, the same amount of nitrate that was fed into the chemostat culture at dilution rate of 0.48 d1
in 8 days was used to run an 8-day batch culture. Biomass produc- tivity, lipid content and lipid productivity were determined and compared in Table 2.
The chemostat culture with dilution rate of 0.48 d1 had twice the biomass productivity of the batch culture, while the lipid con- tent was somewhat lower than that in the batch culture. Due to the sustained algal growth and moderate lipid accumulation, the lipid productivity of the chemostat (144.93 mg L1 d1) was signifi- cantly higher than that of the batch culture (96.28 mg L1 d1). However, the lipids from both types of culture had very similar fatty acid profiles (Table 3) and the dominating fatty acid species in raw lipids were C16 and C18 (Table 2). Hence the authors re- ported here for the first time that, in comparison to batch culture, lipid productivity can be significantly enhanced by continuous cul- tivation of oleaginous microalgae with proper specific nitrate input rate (SNI). Also, to the best of our knowledge, this is the highest li- pid productivity so far recorded in chemostat study for microalgal lipid production (Table 4).
The new method proposed in this study provides an alternative way to produce lipids by using simultaneous microalgae growth and lipid accumulation, i.e., a one-step process, which was differ- ent from the classical two-step production mode using batch cul- ture. This new strategy has a great advantage over batch culture in both biomass productivity and lipid productivity. When it is ap- plied in mass culture of oleaginous microalgae, the cost of microal- gal lipid production could be reduced significantly, thus promoting the commercialization of microalgal biodiese