Effect of the substrate/microorganism ratio on the anaerobic production of carboxylic acids from residual glycerol

Abstract

The production of carboxylic acids and 1,3-propanediol was assessed from the anaerobic digestion of residual glycerol from biodiesel production to investigate the influence of substrate/microorganism ratio on the bioproduct profile and the kinetic of the process through the application of different mathematical models to the data. So, the experiments were performed in batch reactors for 28 days, and four substrate/microorganism ratios were tested (0.7, 1.1, 1.5, and 2.1 gCOD gVSS −1 ). About 64–77% of the initial organic matter estimated by the chemical oxygen demand of residual glycerol was converted into carboxylic acids and 1,3-propanediol (substrate/microorganism ratio 1.5 showed the highest yield). In addition, acetic acid was the bioproduct formed in the highest concentration for all experiments. Propionic acid had a higher selectivity in the substrate/microorganism ratio 1.5 and butyric acid and 1,3-propanediol in the ratio 2.1. About kinetics results, exponential models were better suited to describe process kinetics. However, sigmoidal models have also shown good fit, making it possible to correlate the substrate/microorganism ratio with velocity constant, maximum productivity rate, and lag phase time.