Effects of the operational conditions on the production of 1,3-propanediol derived from glycerol in anaerobic granular sludge reactors

The aim of this study has been to produce 1,3-propanediol (1,3-PDO) from glycerol (gly) fermentation by means of a microbial mixed culture (granular sludge), as well as to establish the operational conditions of two up-flow anaerobic sludge blanket (UASB) reactors in order to achieve a maximum 1,3-PDO yield. The UASB reactors with initial pH values set at 6.8 and 5.5 were operated at 30 °C during 165 days. Thirteen variables were previously screened by a Plackett-Burman (PB) design; results showed that yeast extract, MgSO₄ and methanogenesis inhibition (by heat shock) showed a positive effect, whereas high glycerol concentration, tryptone and CaCl₂ showed a negative impact on the 1,3-PDO produced by glycerol degradation. Following four experimental periods, the highest average yield of 0.43 mol 1,3-PDO mol⁻¹ gly was achieved when sodium bicarbonate was added to the reactors. Propionate and acetate were also produced and a high microorganism diversity was detected; however, the restrictive operational conditions of the reactors led to the death of the methanogenic archaea. Nevertheless, the continuous production of 1,3-PDO from glycerol within UASB reactors inoculated with granular sludge can be considered highly feasible.