Simultaneous production and recovery of volatile fatty acids from fermentation process using an electrochemically assisted up-flow granular sludge bed reactor

Abstract

A continuous production and in-line recovery of volatile fatty acids (VFAs) was developed by coupling an electrochemical cell (EC) to the recycling line of an up-flow anaerobic sludge bed (UASB) reactor. The use of an easy fermentable feedstock (glucose) was proposed for a fast production of VFAs. The EC allowed the simultaneous recovery of VFAs while producing alkali equivalent and hydrogen brought to the reactor, allowing to decrease caustic addition and promoting VFA production. Duplicate systems were used with glucose at an initial concentration of 15 g/L for Phases I to III, and increased to 60 g/L in a stepwise manner during Phase IV to VI. The EC was connected using 3.5 V to the UASB reactor at Phase III (15 g/L glucose, hydraulic retention time (HRT): 24 h), decreasing by 46 % the VFA concentration in the reactor mixed liquor and the sodium hydroxide consumption by 49 %. The highest VFA concentration in the anode chamber was 4.6 times higher than in the reactor. The highest caproic acid production achieved corresponded to 6.01 g/L during Phase IV (30 g/L glucose, HRT: 24 h). At the end of the trial, the voltage was increased up to 6.0 V and the water addition in the anode chamber was stopped to build up the VFA concentration, reaching 27.80 and 28.05 g/L for EC1 and EC2, respectively. The coupled UASB-EC system showed promising results in terms of good recovery of the VFAs from the fermentation broth, decrease of the alkali demand and caproic acid production.