Short-chain carboxylate continuous production from food waste with in situ extraction: Novel design to reduce chemical input for pH control and alleviate membrane fouling

Abstract

The production of short-chain carboxylates (SCCs) from readily degradable food waste exhibits superior product value compared to biogas production, but SCCs’ high solubility poses challenges in their production and recovery. In this study, we applied two novel modules to in-situ extract SCCs from the continuously produced fermentative broth, namely direct coupling of bipolar membrane electrodialysis (BPED) and the integration of upstream membrane permeation (MP) and BPED. The remarkable extraction efficiency of BPED effectively mitigated the inhibitory effects from the accumulation of SCCs products, yielding 475.2 mg gVS−1, which was 20.26% higher than the control phase. The OH− generated by the bipolar membrane was cycled back to regulate the pH of bioreactor, thereby completely eliminating the need for external alkaline additives. The upstream MP effectively prevented ion exchange membrane fouling, and the OH− generated by BPED achieved the in-situ regeneration of MP’s alkali extract, reducing the OH− demand by 40% in MP+BPED stage. It was also observed that BPED exhibited higher selectivity towards small-molecule acetic acid, while MP tended to recover larger-molecule caproic acid. Selective extraction of specific SCC drove the product spectrum of the bioreactor to produce more SCC that was selectively extracted.