3.5. Mixed acids production by semi-continuous culture
A semi-continuous culture process was established to obtain
continuous production of mixed acids. The semi-continuous culture
was maintained for 14 days after batch culture (60 day) with a
loading rate of non-pretreated red algae of 2.77 g/L/d and a hydraulic
retention time (HRT) of 30 days. During semi-continuous
culture, mixed acids levels were maintained at 42.4 g/L and productivity
was approximately 1.41 g/L/d (Fig. 2). The production
yield of mixed acids by the semi-continuous culture process was
estimated at about 84.6 g/L at 60 days, which is twice that of the
batch culture. The productivity of land biomass has been reported
to be less than 1 g/L/d [15,16], and Aiello-Mazzarri et al. [12] have
reported a maximum mixed acid production of 1.360 g/L/d from
municipal solid waste and sewage sludge, but the concentration
was very low (w26 g/L) [12]. Compared with other biomass sources,
red algae in defined mixed cultures yielded a relatively high
concentration (>42 g/L in continuous culture) and productivity of
mixed acids.