Anaerobic sequencing batch reactor enhances SCFAs productivity while facilitating downstream processing

Anaerobic fermentation (AF) emerged as a promising technology to produce short-chain fatty acids (SCFAs). However, downstream processing of SCFAs is often challenging and costly due to the complexity of AF effluents that present high solids content. Sequencing batch reactors (SBRs) promote effluent separation in two phases (solids and supernatant), which can be an advantage to facilitate SCFAs downstream processing. This work evaluated the performance of SBRs operated at different hydraulic retention times (HRT) (20, 15 and 10 d) and a solids retention time (SRT) of 20 d. The maximum SCFAs concentration of 28.3 g/L was reached at HRT of 20 d, whereas the maximum bioconversion (60.7 %) and productivity (1.8 g SCFAs /Ld) were reached at  HRT of 10 d. Regardless of the HRT, the predominant SCFAs found at the steady state were butyric and acetic acids (> 70 % w/w). The SBR configuration enabled a 1.3-fold increase in the SCFAs yield (g SCFAs/g TS_effluent) when comparing the supernatant and the solids phase. The effect of different HRT was analyzed to establish the correlation between SCFAs production yield and the different microbial populations developed in the reactors. Despite the different HRT, Clostridium, Atopobium and Bulleidia were the predominant genera in all cases, demonstrating their key role in SCFAs production. These results shed light on the SBR potential to promote high SCFAs accumulation and bioconversion efficiencies even at low HRT, easing SCFAs recovery while improving waste revalorization.