Maximum removal rate of propionic acid as a sole carbon source in UASB reactors and the importance of the macro- and micro-nutrients stimulation

The maximum propionic acid (HPr) removal rate (RHPr) was investigated in two lab-scale Upflow Anaerobic Sludge Bed (UASB) reactors. Two feeding strategies were applied by modifying the hydraulic retention time (HRT) in the UASBHRT and the influent HPr concentration in the UASBHPr, respectively. The experiment was divided into three main phases: phase 1, influent with only HPr; phase 2, HPr with macro-nutrients supplementation and phase 3, HPr with macro- and micro-nutrients supplementation. During phase 1, the maximum RHPr achieved was less than 3 g HPr-COD L−1 d−1 in both reactors. However, the subsequent supplementation of macro- and micro-nutrients during phases 2 and 3 allowed to increase the RHPr up to 18.1 and 32.8 g HPr-COD L−1 d−1, respectively, corresponding with an HRT of 0.5 h in the UASBHRT and an influent HPr concentration of 10.5 g HPr-COD L−1 in the UASBHPr. Therefore, the high operational capacity of these reactor systems, specifically converting HPr with high throughput and high influent HPr level, was demonstrated. Moreover, the presence of macro- and micro-nutrients is clearly essential for stable and high HPr removal in anaerobic digestion.