Volatile fatty acid production from Kraft mill foul condensate in upflow anaerobic sludge blanket reactors

The utilization of foul condensate (FC) collected from a Kraft pulp mill for the anaerobic production of volatile fatty acids (VFA) was tested in upflow anaerobic sludge blanket (UASB) reactors operated at 22, 37 and 55 degrees C at a hydraulic retention time (HRT) of similar to 75 h. The FC consisted mainly of 11370, 500 and 592 mg/L methanol, ethanol and acetone, respectively. 42-46% of the organic carbon (methanol, ethanol and acetone) was utilized in the UASB reactors operated at an organic loading of similar to 8.6 gCOD/L.d and 52-70% of the utilized organic carbon was converted into VFA. Along with acetate, also propionate, isobutyrate, butyrate, isovalerate and valerate were produced from the FC. Prior to acetogenesis of FC, enrichment of the acetogenic biomass was carried out in the UASB reactors for 113 d by applying operational parameters that inhibit methanogenesis and induce acetogenesis. Activity tests after 158 d of reactor operation showed that the biomass from the 55 degrees C UASB reactor exhibited the highest activity after the FC feed compared to the biomass from the reactors at 22 and 37 degrees C. Activity tests at 37 degrees C to compare FC utilization for CH4 versus VFA production showed that an organic carbon utilization >98% for CH4 production occurred in batch bottles, whereas the VFA production batch bottles showed 51% organic carbon utilization. Furthermore, higher concentrations of C-3-C-5 VFA were produced when FC was the substrate compared to synthetic methanol rich wastewater.

Automated summary

The study showed that utilizing foul condensate for VFA production in UASB reactors resulted in high organic carbon utilization and VFA yield, with various fatty acids being produced. Pre-enrichment of acetogenic biomass improved VFA production efficiency, particularly in comparison to methanogenesis.