Enhancing semi-continuous carboxylic acid production from methane-arrested anaerobic digestion of cellulosic biomass by in-situ product removal with CO2-sustained anion-exchange resin adsorption

Abstract

Methane-arrested anaerobic digestion (MAAD) provides a sustainable route for cleaner production of carboxylic acids from renewable biomass. However, low acid productivity and high product recovery costs have restricted widespread industrial implementation of this technology. This study enhances carboxylic acid (C2 to C8) production from cellulosic biomass using a newly developed integrated digestion-separation system. Using a mixed culture of marine microorganisms grown under mesophilic conditions (40 °C), paper and chicken manure were co-digested to produce carboxylic acids through semi-continuous four-stage countercurrent MAAD. During digestion, multi-stage CO2-sustained anion-exchange resin (Amberlite IRA-67) adsorption was applied for in-situ recovery of inhibitory acid products from the digestion medium. Efficiency was enhanced by supplying 1-atm CO2 during the in-situ adsorption process. Compared with stand-alone digestion (control), biomass conversion and acid yield in the integrated MAAD system significantly increased by 2.28 and 2.09 times, respectively. The integrated system also increased the mass fractions of longer-chain carboxylic acids (C5 and C6) in liquid products. With various amounts of resin, the optimal normalized resin loadings for biomass conversion and acid yield were 10.9 and 14.6 g wet resin/(Lliq·d), respectively. This work demonstrates countercurrent digestion coupled with in-situ product separation via CO2-sustained anion-exchange resin is highly effective at recovering carboxylic acids from cellulosic biomass.