Reducing the effect of non-volatile fatty acids (non-VFAs) on polyhydroxyalkanoates (PHA) production from fermented thermal-hydrolyzed sludge

Thermal-hydrolyzed sludge (THS) can be fermented to produce volatile fatty acids (VFAs) rich liquids. These fermentative liquids are considered as a potential feedstock for polyhydroxyalkanoates (PHA) production. However, the presence of high levels of non-VFAs organics supporting the growth response instead of PHA accumulation hindered an efficient culture selection in a feast and famine regime. Lowering the non-VFAs content can compromise activities of microorganisms to take up these external carbon sources and improve the selective pressure; thus two enhanced strategies were tested to optimize the selection process: 1) increasing the proportion of VFAs in the original substrate or 2) removing most of the non-VFAs at the end of the feast phase. Results showed that the strategies resulted in PHA yields on VFAs respectively of 0.62 and 0.54 Cmol/Cmol, significantly higher than that in original SBR (0.16-0.35 Cmol/Cmol), confirming that reducing the adverse effect of non-VFAs can impose effective internal limitation and induce high PHA storage responses. In PHA accumulation tests, cultures selected with synthetic substrates accumulated a maximum PHA content of 61.4 wt%, which is the highest as ever reported among PHA production from THS. In summary, the study provided valuable references for improving PHA production from complex substrates. (C) 2019 Elsevier B.V. All rights reserved.