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).