COLTIVAZIONE DI FANGO AEROBICO GRANULARE PER IL TRATTAMENTO DI REFLUI INDUSTRIALI SALINI

Abstract

This study focuses on the cultivation of aerobic granular sludge subjected to step-wise increase of salinity. A bench scale Granular Sequencing Batch Airlift Reactor (GSBAR) worked for 164 days. The reactor was fed with a synthetic influent characterized by an Organic Loading Rate (OLR) of 1,6 kg COD/(m3·d) and with a step-wise increase of salinity during six experimental periods (from 0.2 to 24 gCl-∙L-1), to promote a gradual acclimation of microorganisms to the saline environment. Stable and compact granules with a diameter close to 2 mm and a sludge volume index (SVI) approximately of 20 mL∙g-1 were obtained at the end of cultivation period. The Extracellular Polymeric Substances (EPS) analysis revealed that proteins (PN) were higher than polysaccharides (PS) and their production was decreasing as mature granules were forming. When salinity was increased from 3 g Cl-∙L-1 to 24 g Cl-∙L-1, the specific EPS concentration in the feast phase was often lower than in famine one, because the transport of osmolytes from and into the cell for the acclimation to salinity required more energy and microorganisms metabolized EPS as additional carbon source in a greater extent in feast phase than in famine phase. Moreover, microorganisms continued to produce EPS also in famine phase to face the high osmotic pressure. No significant worsening in the main biological processes were observed throughout the whole experimental study. A slight accumulation of nitrites in the effluent occurred at 7 gCl-∙L-1 and at 14 gCl-∙L-1 indicating the inhibition of Nitrite-Oxidizing Bacteria (NOB) due to the salinity. The full depletion of nitrites at 24 g Cl-∙L-1 suggested that the acclimation of NOB to the saline environment successfully occurred. Finally, high salt and nitrite accumulation hampered the polyphosphate accumulating organisms (PAO), for phosphorous removal.