BACKGROUND: Succinic acid (SA) is an intermediate in the production of commodity chemicals, but SA bioproduction has not yet been commercialized due to end product inhibition and high product separation costs. Two-phase partitioning bioreactors (TPPBs) can increase volumetric productivity through in situ product removal, although SA uptake by polymers requires a pH below the pKA2 of SA (4.2). It was proposed to reversibly reduce the pH with CO2 sparging for absorption of SA, followed by nitrogen stripping to allow continued bioproduction after returning to metabolic pH levels. RESULTS: At 1 atm CO(2) sparging lowered the pH of RO water to 3.8 but only to 4.75 in medium, requiring acid/base pH adjustment in subsequent experiments. Actinobacillus succinogenes was temporarily exposed to pH 4.2 for between 5 min and 4 h to observe the effect on subsequent growth; cells could grow after up to 4 h of low pH exposure, sufficient time for SA uptake. Because atmospheric CO(2) could not adequately lower the pH of medium, a TPPB was operated with the pH being shifted using strong acid/base; SA was recovered in situ, however, the accumulation of salts hindered further cell growth. CONCLUSION: Several key elements of this novel processing strategy were successfully demonstrated, and work is continuing with high pressure CO(2) to achieve the desired pH adjustment levels. (C) 2011 Society of Chemical Industry