3.3. PHA production and quality: a comparison approach
Results obtained in this study indicated that PHA can be produced
by fermented cheese whey, giving very good yields (Ytot,
mg CODPHA mg CODSS
1
), that were in line with those reported in
the literature for both cheese whey and other organic substrates
(Table 4).
Data obtained indicated that the second process (FCW1 as substrate)
had a lower PHA yield (Ytot of 0.24 mg CODPHA mg CODSS
1
)
than that obtained in the third process (FCW2 as substrate) (Ytot
of 0.42 mg CODPHA mg CODSS
1
). The total process yield (Ytot) was
the consequence of the soluble COD fermentation to organic acids
(Yfermentation) and of the successive acids transformation into PHA
(Ystorage), and because the storage yields for the two processes were
quite similar (Table 4), differences were due probably to the different
organic acid yield during the acidic fermentation step. Therefore,
results of this work seem to indicate that the fermentation
step played an important role in determining the subsequent
transformation of soluble COD into PHA. In particular, these results
indicated that cheese whey fermented by autochthonous bacteria
(FCW1) was less effective in producing organic acids than fermentation
performed by using heat-shocked digestate-inoculum
(FCW2), and that the fermentation process acted as limiting factor
for the successive transformation of soluble COD into PHA. Taking
into consideration data of this work in comparison with those from
the literature (considering only cheese whey substrate) (Table 4) a
very good linear correlation was found for total yield (Ytot) vs. fermentation
yield (Yfermentation) (r = 0.90; p < 0.05; n = 4).
I