Aerobic granular sludge: formation/maintanance, system optimization and resource recovery possibilities

• Ano de defesa: 2020
• Autor(a) principal: Rollemberg, Silvio Luiz de Sousa
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Palavras-chave em Português: Saneamento; Estação de tratamento de esgoto; Lodo de esgoto; Resource recovery; Aerobic granular sludge; Wastewater treatment
• Link de acesso: http://www.repositorio.ufc.br/handle/riufc/51451

Even though the aerobic granular sludge (AGS) technology has been used for more than two decades in both new and upgraded wastewater treatment plants (WWTPs), most of them being activated sludge systems, a great number of real-scale AGS plants have operational problems. These issues are related to instability in long-term operation, especially disintegration of the aerobic granules. This work aimed to improve the knowledge about the formation, maintenance, and stability of aerobic granules, AGS reactor optimization, and recovery of by-products from the discharged biomass. The first study, conducted by respirometer tests, revealed that, while activated sludge flocs (ASF) had a yield coefficient (Y) of 0.6 g VSS/g COD, AGS had a Y average of 0.35 g VSS/g COD, which shows that AGS has lower potential to produce sludge than ASF. In the second study, the effect of different carbon sources (acetate, ethanol, and glucose) was evaluated on the formation, maintenance and microbial composition of the granule. Acetate led to high COD (> 90%), NH4 +-N (> 90%), TN (≈ 75%) and TP (≈ 40%) removals and to the formation of microbial aggregates with diameters greater than 1.5 mm. However, partial disintegration of the granules occurred. The reactor fed with ethanol remained stable through the experiment, and the removal efficiencies were similar to those obtained with acetate. In the presence of glucose, many microbial groups used it as a carbon source, especially filamentous microorganisms, which hindered the granulation process. During the third study, a conventional sequencing batch reactor (SBR) provided granules with an average diameter greater than 1 mm, excellent sedimentability (SVI30 < 43 mL/g) and high PN/PS ratio (> 1). On the other hand, simultaneous fill/draw mode SBR resulted in granules with a smaller diameter (0.8 mm) and worst sedimentability. Nevertheless, the latter operation has some advantages, such as high COD, TN and TP removals, and a large amount of volatile solids inside the reactor (> 7 g/L). In the fourth study, the effect of cycle distribution was assessed on the formation and stability of the aerobic granules. Reactors operated with A/O (anaerobic/oxic) phases with a high percentage of oxic phase, approximately 65%, formed more resistant granules and with better sedimentability, however denitrification was affected. In contrast, reactors operated with A/O/A (anaerobic, oxic and anoxic) phases, especially using long anaerobic and anoxic periods, had great nutrients removal, even though the granules were less dense and stable. The optimization in terms of system performance and granules stability was achieved in an A/O/A reactor with a small anoxic period (10% of total cycle) and 55% of oxic period, resulting in COD, TN, and TP removals above 90%, 80%, and 70%, respectively. The fifth study evaluated the applicability of the AGS technology in a pilot-scale unit treating domestic sewage. The SBR was operated in A/O/A cycle of 6 h divided in anaerobic filling (35 min), followed by anaerobic (89 min), oxic (197 min), anoxic (18 min), and settling (5 min) periods. Removals of COD, BOD, NH4 +, and PO4 3- were close to 90%. In this same study, aiming to evaluate the resource recovery possibility from the discharged sludge, it was found a concentration of phosphorus of 0.020 g P/g VSS, alginate-like exopolysaccharides (ALE) of 0.219 g ALE/g VSS and tryptophan (TRY) of 0.048 g TRY/g VSS. Finally, on a laboratory scale, the effect of operational conditions was evaluated to maximize TRY and ALE yields. The reduction of the aerobic period from 265 to 225 min and, consequently, a famine period decrease favored the formation of these by-products (251.7 ± 16.8 mg ALE/g SSV e 50.4 ± 2.8 mg TRY/g SSV), and also resulted in the formation of a very stable granule. Therefore, the operational conditions, such as sludge retention time (SRT) and cycle distribution, strongly influenced by-products formation. Lastly, this study showed that, although the recovery of TRY was possible, it had neither technical nor economic viability. Besides, ALE production was significantly higher and has a greater value-added.