Effect of thermal hydrolysis pretreatment on volatile fatty acids production in sludge acidification and subsequent polyhydroxyalkanoates production

The study compared the differences in VFAs production between raw sludge and thermal hydrolyzed sludge (TH-sludge) at different temperature (35 degrees C and 55 degrees C) in four semi-continuous acidification reactors. Optimal VFAs yield was obtained from TH-sludge at 35 degrees C (0.22 gVFA(COD)/gVS), 44.6% higher than raw sludge at 35 degrees C, since the advantage of TH-sludge in SCOD solubilization overcame its disadvantage of lower carbon biodegradability. Moreover, high temperature (55 degrees C) was proved to aid the acidification of raw sludge by 15.7% (in Y-VFAs), but inhibit that of TH-sludge by 12.2%, mainly due to the suppressed microbial activities under heat. Microbial community analysis showed that TH-sludge had a larger proportion of acidogenic microbes than raw sludge, mainly attributing to the increase of Selenomonadales (37.3% vs. 3.7%); high temperature enriched thermophilic proteolytic microbes, Anaerobaculum and Coprothermobacter. Finally, optimal acidified liquid from TH-sludge at 35 degrees C was applied for PHAs production and achieved a competitive yield of 34.6% PHAs/DCW.