Recuperação de xantana e exopolissacarídeo semelhante ao alginato em sistemas granulares aeróbios

Abstract

Aerobic granulation systems represent a promising technology in wastewater treatment, gaining prominence for their potential in resource recovery. In addition, they are configured as a sustainable alternative in the face of the growing pressure on natural resources. Therefore, the present study sought to evaluate the recovery of xanthan and alginate-like exopolymers in this system by comparing different Aerobic Granular Sludge (AGS) systems. For this, two reactors were operated under the same conditions, differing only the presence of light energy: R1, AGS systems with photogranulation and R2, conventional bacterial AGS system. The systems operated for 91 days with 6-hour cycles and were evaluated during the granulation and maturation process. Both systems demonstrated typical results of granule growth and stability, with R1 showing faster and more stable granulation and R2 forming granules of larger diameter, better sedimentability and higher solids retention. Both systems showed high production of extracellular polymeric substances and their fractions EPS-LB (weakly bound) and EPS-TB (strongly bound), especially in the photogranulation system, which was also observed in the analysis of fluorescence spectra. The recovery of xanthan in terms of biomass was similar in R1 and R2 during the granulation period, but during maturation, R1 showed greater recovery, with approximately 139.17 ± 73.12 mg of xanthan/gVSSML, while R2 showed values around 123.23 ± 47.32 mg of xanthan/gVSSML. From the granulometric tests, it was found that most of the xanthan was recovered in granules between 200 and 600 μm in R1 and between 600 μm and 1000 μm in R2.On the other hand, when evaluating the recovery of xanthan in terms of EPS, the conventional reactor showed greater recovery in both periods (R1: 10 ± 5 in granulation and 46 ± 16 in maturation; R2: 20 ± 11 in granulation and 250± 54 in maturation, in mg Xanthan/g EPStotal). Also, in terms of biomass, most of the xanthan came from the EPSTB fraction during granulation, but in terms of EPS, the EPS-LB fraction showed a greater use for recovery. Scanning electron microscopy (SEM) showed that the xanthan structure of R2 was more cohesive and homogeneous than that of R1. The recovery of ALE was higher in R1 in both periods, with values around 748.6 mgALE/gVSSML in granulation and 280.5 mgALE/gVSSML in maturation. Therefore, all these results attest to the possibility of recovering these resources without harming the stability of the AGS system.