Applicazione del processo a fanghi aerobici granulari per il trattamento di reflui petrolchimici
Aerobic granular sludge was successfully cultivated in two lab scale Granular sludge Sequencing Batch Reactors (GSBR, A and B) to remove organic matter and nitrogen from two different petrochemical wastewaters (PWs). The aim of this study was to define the best operating conditions (i.e., shear forces, inoculum source, Ca2+ concentration, pH) to achieve complete granulation and satisfactory long-term process performance. One PW was produced by the Integrated Gasification Combined Cycle (IGCC) and characterized by high concentrations of organic matter, ammonium and toxic substances like cyanides and phenols (IGCC wastewater); the other PW, collected from the equalization tank of the refinery wastewater treatment plant, was a poorly biodegradable mixture of all the refinery discharges which contained, among the others, sulfide, hydrocarbon and low concentrations of COD and ammonium (MS18 wastewater). In order to promote granulation and biomass acclimation during reactors’ start-up, synthetic influents were initially fed to the GSBRs and gradually replaced by real PWs, while a sufficiently high volumetric organic loading rate (vOLR, 3 kgCOD/m3d) was granted by dosing proper amounts of readily degradable organic carbon (sodium acetate, NaAc). Compact and well-settling granules developed into both reactors, which were able to treat 100% MS18 (GSBR-A) and 100% IGCC (GSBR-B) wastewater, showing good process performance in terms of organic matter (TOC) and NH4-N removal efficiencies (GSBR-A, 85% and 75%, respectively; GSBR-B, 94% and 78%, respectively). Mature granules in both GSBRs showed high density (GSBR-A, 58 gTSS/Lgran; GSBR-B, 65 gTSS/Lgran) leading to good solid-liquid separation (GSBR-A, SVI8, 39 mL/gTSS; GSBR-B, SVI8, 10 mL/gTSS) and high biomass retention (GSBR-A, 7,5 gVSS/L; GSBR-B, 4,7 gVSS/L). Although a slight inhibition occurred as the PW fraction in the synthetic influents was progressively increased, granular biomass always showed a quick recovery. As the synthetic influents were completely replaced by PWs, the supply of NaAc was progressively reduced and finally suspended in order to minimize the operating costs (the corresponding vOLR was reduced to 0,71 kgCOD/m3d and 1,15 kgCOD/m3d in GSBR-A and GSBR-B, respectively). However, both GSBRs maintained satisfactory process performance and their ability to withstand toxic substances contained in PWs. The results achieved in this study indicate that the aerobic granular sludge technology may be considered as a valid option for the treatment of petrochemical wastewaters, alone (GSBR-A) or in combination (GSBR-B) with conventional systems.
aerobic granular sludge, GSBR, petrochemical wastewater, selective pressure, superficial air velocity, inoculum, long-term operation, fanghi aerobici granulari, reflui petrolchimici, Settore ICAR/03 - Ingegneria Sanitaria-Ambientale
Networked Digital Library of Theses and Dissertations