In the start-up period (≈4.5 months) of the digester the OLR was maintained between 0.33 and 1.11 kg CODm−3 day−1 for the acclimatisation and growth of the methanogenic bacteria.
The COD removal efficiency during the start-up period varied between 62% and 91% (Fig. 2). High CODreduction in conjunction with increasing biogas production provided evidence of anaerobic microbial activity and suggests that the process was viable for the treatment of OMW (Fig. 3).