Lawrence Berkeley National Laboratory

Platform chemicals such as medium-chain carboxylic acids (MCCAs) can be produced from organic waste streams via chain elongation in anaerobic mixed-culture bioreactors. A product recovery system is needed to collect MCCAs from the bioreactor effluent. Membrane-based liquid-liquid extraction, the most commonly used product recovery approach, requires suspended solids removal from the bioreactor effluent to avoid membrane fouling. An anaerobic dynamic membrane bioreactor (AnDMBR) was developed to evaluate MCCA production from brewery and prefermented food waste and to produce a permeate with low suspended solids to facilitate downstream product recovery. The AnDMBR employed an inexpensive stainless-steel mesh as the support material for the development of a biofilm or dynamic membrane, which was responsible for solids-liquid separation. The AnDMBR produced a permeate quality with an average total suspended solids (TSS) concentration of 0.12 g L-1, while the average bioreactor TSS concentration was two orders of magnitude higher (21.6 g L-1). A maximum solids removal efficiency of ≥99% was achieved and good permeate quality was sustained for over 200 days without fouling control or cleaning the support material. In addition to solids-liquid separation, the dynamic membrane was responsible for a substantial fraction of the biological activity of the AnDMBR. The relative activity of Clostridiales, as determined by 16S rRNA sequencing, correlated with MCCA production and was higher in the dynamic membrane (20.0 ± 4.9%) than in the suspended biomass (5.2 ± 2.7%) in the bioreactor. This observation was consistent with MCCA production data as the permeate MCCA concentrations were significantly (p = 8.2 × 10-5) higher than that in the bioreactor, suggesting that the dynamic membrane biofilm contributed to chain elongation.