  In the present study, different photoperiods and nutritional conditions were
applied to a mixed wastewater-borne cyanobacterial culture in order to enhance
the intracellular accumulation of polyhydroxybutyrates (PHBs) and
carbohydrates. Two different experimental set-ups were used. In the first, the
culture was permanently exposed to illumination, while in the second; it was
submitted to light/dark alternation (12h cycles). In both cases, two different
nutritional regimes were also evaluated, N-limitation and P-limitation. Results
showed that the highest PHB concentration (104 mg L-1) was achieved under P
limited conditions and permanent illumination, whereas the highest carbohydrate
concentration (838 mg L-1) was obtained under N limited condition and
light/dark alternation. With regard to bioplastics and biofuel generation, this
study demonstrates that the accumulation of PHBs (bioplastics) and
carbohydrates (potential biofuel substrate) is favored in wastewater-borne
cyanobacteria under conditions where nutrients are limited.
