Performance evaluation of three mesophilic upflow anaerobic sludge blanket bioreactors treating olive mill wastewater: Flocculent and granular inocula tests, organic loading rate effect and anaerobic consortia structure

Abstract

This work evaluates the performance of two upflow anaerobic sludge blanket (UASB) bioreactors and a hybrid-UASB bioreactor treating olive mill wastewater (OMW) under mesophilic conditions. The UASB bioreactor, which was inoculated with flocculent sludge (UASB-F), achieved greater operation efficiency and higher methane production rate (1.13 L CH4/LR.d) than the other bioreactors seeded with granular sludge. The hybrid-UΑSB and the second UASB bioreactor, which were inoculated with granular sludge, exhibited low performance due to the loss of granulation. It appears that OMW phenolics have negative impact on granular sludge structure and performance efficiency. Acidogenesis was mainly carried out by Clostridiales and Sporolactobacillus spp. in all bioreactors examined. Molecular data also showed that the hydrogenotroph Methanobacterium beijingense was the main methanogen in the bioreactors inoculated with granular sludge, while the UASB-F bioreactor was exclusively dominated by a novel archaeal methanogenic linkage, distantly related to the rare methanol-reducing archaeon Methanosphaera stadtmanae.