AbstractBACKGROUNDThe role of biodegradation and physical–chemical mechanisms involved in the treatment of metal working fluids (MWFs) using a submerged anaerobic membrane bioreactor (SAMBR) was assessed in this research. Two SAMBRs were employed in series, with the second SAMBR being fed the permeate from the first bioreactor.RESULTSResults showed a low biodegradability of the MWF both in batch tests (bioconversion efficiency ≤ 3%), and operating the bioreactors continuously (bioconversion efficiency ∼0%). Among the physical–chemical removal mechanisms identified, it was found that bio‐adhesion was the most important in MWF removal (removal rate of 96.0 ± 1.64%), whereas membrane rejection was not significant (removal rate of 0.2 ± 0.18%). However, it is expected that membrane separation will play an important role in removal after bio‐adhesion has been saturated.CONCLUSIONThe inhibition of the hydrolytic/heteroacetogenic biomass was the most problematic aspect in anaerobic digestion, resulting in the need for bioaugmentation of specific microorganisms to degrade MWFs. In the case of non‐adaptation during long‐term operation, the bio‐adhesive propensity of MWFs could be used as a potential method for removing spent MWFs from wastewater streams. © 2014 Society of Chemical Industry