Aerobic granular sludge as a source of extracellular polymeric substances and the potential of the technology combined with bioaugmentation to treat industrial wastewater

A variety of organic pollutants reach wastewater treatment plants (WWTP), often associated with high salinity levels, making their treatment challenging. Aerobic granular sludge (AGS) technology is thought to protect the microbial communities from stress due to the high content of extracellular polymeric substances (EPS). There is an increasing need to turn WWTP more efficient, with a range of opportunities for resource recovery to integrate them into the circular economy concept. The work described in this thesis aimed to explore AGS biomass as a source of EPS and to understand the variations of EPS production facing different stressors, namely 2-fluorophenol (2-FP) and salinity. Particular attention was given to the microbial communities, diversity and function, of the investigated systems. The recovery of EPS from AGS represents an opportunity for valorization of surplus biomass. AGS from a full-scale WWTP treating urban wastewater was regularly collected for 4 months to assess variability in EPS composition and in granular morphology. Variations in the EPS composition occurred with time, with proteins and humic acids as the main EPS components and polysaccharides and DNA as minor constituents. An extra purification step led to the recovery of a purer EPS form with a rather homogeneous composition however the yield of each EPS component decreased, especially for polysaccharides. Yield and product homogeneity are key features for downstream application of the recovered EPS. The effect of intermittent short-term loadings of 2-FP and low to moderate salinity wastewater on the performance and EPS production of an AGS system was studied. Ammonium removal was highly inhibited by stressors, recovering when 2-FP feeding ceased. Phosphate removal, initially disturbed by exposure to stress conditions, recovered when stressors were still present. EPS composition and concentration in the granules decreased from 133.3 to 33.7 mg/g VSS of AGS during the first phases of stress but its production recovered to 176.1 mg/g VSS of AGS even in the stressor’s presence. The nutrient removal recovery after exposure to stressors and the increased EPS production response support the robustness of AGS systems to deal with intermittent stressful conditions. EPS recovered from AGS were used as an immobilizing agent for Rhodococcus sp. FP1, a 2-FP degrading strain. The produced EPS granules exhibited 2-FP degrading ability of 100%, retaining its original activity up to 2 months storage. Moreover, the EPS granules were used to bioaugment an AGS reactor intermittently fed with low to moderate saline wastewater amended with 2-FP. After bioaugmentation, complete 2-FP removal occurred and phosphate and ammonium removal (previously impaired by 2-FP load) improved from 14 to 46% and from 25 to 42%, respectively. After bioaugmentation, strain FP1 was detected up to 3 days in the reactor effluent by qPCR and eleven bacterial isolates able to degrade 2-FP were retrieved from the AGS. Maintenance of cell viability through storage and improvement of bioreactor.