The concentrations of total VFAs produced are shown in Fig. 3. The average VFAs concentrations of
effluent from R1 and R2 were 623 ± 202 and 686 ± 190 mg/L, respectively. For anaerobic digestion to
proceed normally, concentration of VFAs should be kept below 2000 mg/l. [13]. the relatively lower level
of VFAs during the start up period (Fig 3) could be attributed to lower organic loading rate. Low levels
of VFAs at all studied OLRs observed in this work indicated that the ASBR process was a system capable
of maintaining active methanogens at low levels of VFAs for the applied feedstock.