Anaerobic immersed side-stream membrane bioreactor for single-stage cyclic recovery of volatile fatty acids from food waste

This study investigates the continuous production of volatile fatty acids (VFAs) during anaerobic fermentation and single-stage cyclic recovery of a sterile solution. Various types of de-packaged food waste (DFW) were used, both as feedstock and inoculum. The impact of substrate variability, endogenous microbiota and organic loading rates (OLR) were firstly assessed in four cyclic fed-batch cultures done at constant volume, without using the membrane module. Results showed that quantitative VFAs production (g COD L −1 ) was not affected by varying composition of the DFW. High OLRs around 30 and 15 g COD L −1 d −1 , corresponding to 4 and 8 day-HRTs respectively, allowed to produce 43 g COD L −1 of VFAs reaching a bioconversion yield around 38 % COD VFAs /COD in , at 8-day HRT. A slight effect of feedstock variability and OLR was observed on the VFA production pattern. As a main result of the study, a lab-scale anaerobic membrane side-stream immersed bioreactor (named AnisMBR) fed at 13 g COD L −1 d −1 then allowed to reach even higher values by improving the production of VFAs to 48 g COD L −1 and the biomass conversion yield to 46 % COD VFAs /COD in . In conditions of antifoam adding in the bioreactor to limit foam and subsequent crust formation, cyclic extraction of a sterile VFAs-rich solution was done without prohibitive membrane fouling upon time, opening the door to potential upscaling as part of a biorefinery approach and circular engineering.