This work studied the effect of polyvinyl alcohol hydrogel (PVA-gel) beads, as an effective biocarrier for volatile fatty acid (VFA) production in hydrolytic reactor of a two-stage thermophilic anaerobic membrane bioreactor (TAnMBR). The two-stage TAnMBR, treating synthetic high strength particulate waste-water with influent chemical oxygen demand (COD) [16.4 +/- 0.8 g/L], was operated at 55 degrees C. Under steady state conditions, the reactor was operated at an organic loading rate of 8.2 +/- 0.4 kg COD/m(3) d. Operational performance of the system was monitored by assessing VFA composition and quantity, methane production and COD removal efficiency. Increment of VFA production was observed with PVA-gel addition. Hydrolytic effluent contained large amount of acetic acid and n-butyric acid. However, increase in VFA production adversely affected the methanogenic reactor performance due to lack of methanogenic archaea. (C) 2014 Elsevier Ltd. All rights reserved.