An increasing amount of industrial chemicals are being released into wastewater collection systems and indigenous microbial communities in treatment plants are not always effective for their removal. In this work, extracellular polymeric substances (EPS) recovered from aerobic granular sludge (AGS) were used as a natural carrier to immobilize a specific microbial strain, Rhodococcus sp. FP1, able to degrade 2-fluorophenol (2-FP). The produced EPS granules exhibited a 2-FP degrading ability of 100% in batch assays, retaining their original activity after up to 2-months storage. Furthermore, EPS granules were added to an AGS reactor intermittently fed with saline wastewater containing 2-FP. Degradation of 2-FP and stoichiometric fluorine release occurred 8 and 35 days after bioaugmentation, respectively. Chemical oxygen demand removal was not significantly impaired by 2-FP or salinity loads. Nutrients removal was impaired by 2-FP load, but after bioaugmentation, the phosphate and ammonium removal efficiency improved from 14 to 46% and from 25 to 42%, respectively. After 2-FP feeding ceased, at low/moderate salinity (0.6–6.0 g L⁻¹ NaCl), ammonium removal was completely restored, and phosphate removal efficiency increased. After bioaugmentation, 11 bacteria isolated from AGS were able to degrade 2-FP, indicating that horizontal gene transfer could have occurred in the reactor. The improvement of bioreactor performance after bioaugmentation with EPS immobilized bacteria and the maintenance of cell viability through storage are the main advantages of the use of this natural microbial carrier for bioaugmentation, which can benefit wastewater treatment processes.

Industrial effluents often contain organic pollutants and variable salinity levels, making their treatment challenging. The high content of extracellular polymeric substances (EPS) in the aerobic granular sludge (AGS) is thought to protect the microbial communities from stressful conditions. Ammonium and phosphate removal, EPS production, and granular morphology were assessed in a lab-scale AGS reactor operated during 138 days at continuous low or moderate salinity levels (1.41–6.46 g/L of NaCl) and intermittent short-term loadings of a fluoroorganic pollutant, 2-fluorophenol (2-FP, 20 mg/L). 2-FP was not degraded throughout operation. Ammonium removal efficiency was drastically affected whenever 2-FP stressor was present, decreasing from 99 % to non-detectable conversion levels, but completely recovering after 2-FP feeding ceased. Phosphate removal, initially disturbed by exposure to stress conditions, recovered with time, even when stressors were still present. Complete phosphate removal did not occur in periods when nitrite temporarily accumulated after nitrification started to recover. EPS composition and concentration in AGS varied during operation, initially decreasing from 133 to 34 mg/g _{VSS of AGS}, during the stress phases but recovering thereafter to 176 mg/g_{VSS of AGS}. Breakage of granules into smaller ones occurred at two different operational moments due to stressors presence. The presence of 2-FP and moderate salinity levels in wastewater had more immediate detrimental effects on nutrients removal than on EPS production. The AGS system capacity to recover the nutrient removal performance and EPS production, after the withdrawal of 2-FP from the inlet stream reinforced its robustness to deal with industrial wastewaters.

Within the framework of the circular economy, there is a need for waste management alternatives that promote the reuse of materials produced in wastewater treatment plants (WWTP). An interesting option is the recovery of extracellular substances from sludge. The variability of characteristics of potential recovered bioproducts has to be assessed in full scale operational settings. In this study, aerobic granular sludge (AGS) from a full-scale WWTP treating urban wastewater was regularly collected for 4 months to assess variability in extracellular polymeric substances (EPS) composition and in granular morphology. Variations in the EPS composition occurred with time. Proteins and humic substances were the main EPS components (329-494 and 259-316 mg/g VSS of AGS, respectively), with polysaccharides and DNA representing minor components. The application of an extra purification step after extraction to obtain a purer EPS led to a decrease in the yield of each EPS component, particularly pronounced for the polysaccharides. The final product had a rather constant composition for the monthly samples. The granules showed morphological stability throughout the sampling period and the yield of EPS was correlated to the size of the granules, higher when there was a higher content of small granules (Deq<150 μm) comparing to intermediate (150 ≤ Deq<1500 μm) or large granules (Deq≥1500 μm). This is the first time that a potential valorization strategy for surplus AGS biomass is studied in a full-scale environment. Knowledge on yield and product homogeneity is important as these features are essential for downstream application of the recovered EPS.

Aerobic Granular Sludge (AGS) has been successfully applied for carbon, nitrogen and phosphorous removal from wastewaters, in a single tank, reducing the space and energy requirements. This is especially beneficial for, often space restricted, industrial facilities. Moreover, AGS holds a promise for the toxic pollutants removal, due to its layered and compact structure and the bacteria embedding in a protective extracellular polymeric matrix. These outstanding features contribute to AGS tolerance to toxicity and stability. Strategies available to deal with toxic compounds, namely granulation with effluents containing toxics and bioaugmentation, are addressed here. Different applications for the toxics/micropollutants removal through biosorption and/or biodegradation are presented, illustrating the technology versatility. The anthropogenic substances effects on system performance and bacterial populations established within AGS are also addressed. Combination of contaminants removal to allow water discharge, and simultaneous valuable products recovery are presented as final remark.