Aerobic granular sludge bioprocesses for textile wastewater treatment

Rita Dias Guardão Moreira da Franca

Key information

Authors:

Rita Dias Guardão Moreira da Franca (Rita Dias Guardão Moreira da Franca)

Supervisors:

Nídia Dana Mariano Lourenço; Helena Maria Rodrigues Vasconcelos Pinheiro (Helena Maria Rodrigues Vasconcelos Pinheiro); Marinus Cornelis Maria (Marinus Cornelis Maria (Mark) van Loosdrecht)

Published in

11/05/2019

Abstract

Textile wastewater (TWW) represent a major source of pollution worldwide, carrying high organic loads, recalcitrant dyes (ca. 80% of textile dyes being azo dyes) and, more recently, engineered nanoparticles, namely silver nanoparticles (AgNP). The present thesis aimed to contribute for the development of an effective TWW treatment bioprocess using the novel, cost-effective aerobic granular sludge (AGS) anaerobic-aerobic sequencing batch reactor (SBR) technology. The applicability of AGS in the treatment of an azo dye-containing synthetic TWW in non-tubular, anaerobic-aerobic SBRs was demonstrated for the dye Acid Red 14 (AR14). Color and organic load removal yields of 80% were reached in 6-h cycles after 3-14 days of biomass adaptation, with more than half of the organic load being removed anaerobically. After biodecolorization through complete azo dye reduction along the 1.5-h anaerobic phase, further bioconversion of one of the resulting aromatic amines (4-amino-naphthalene-1-sulfonic acid; 4A1NS) during the 3.5-h aerobic phase was observed under high operational sludge age values. Frequent biomass wastage from the SBR negatively affected the decolorization performance. Yet, AGS SBR proved to be a robust system able to deal with organic and dye shock loads, maintaining high removal yields. Moreover, AGS resisted a 6.5-month storage period, efficiently reactivating its former treatment performance (except for 4A1NS removal) within 2 weeks and restoring good settleability. The SBR hydrodynamic regimen was optimized, with emphasis on granulation and decolorization. Aerobic granulation was successfully reached after 50 days irrespective of the applied hydrodynamic regimen, but complete color removal through azo dye bioreduction depended on the inclusion of a mixed anaerobic phase in the operational cycle. Optimal treatment performance and AGS long-term stability were obtained with a 1.5-h plugflow feed followed by 1-h anaerobic stirred phase and 3.5-h aerobic phase, including when dealing with shock loads and substrate variability in the TWW. The potential for aerobic biodegradation of aromatic amines was demonstrated in different hydrodynamic regimens, irreversible 4A1NS conversion being consistently observed in the plug-flow fed, anaerobic-aerobic SBR regimen for more than 300 days, namely after an 18-day biomass storage period. Mass spectrometry analysis revealed at least 19 molecules possibly associated with AR14 biodegradation, some of which potentially resulting from spontaneous autoxidation of the instable aromatic amine 1-naphthol-2-amino-4-sulfonic acid forming dimeric, stable products. Biotransformation of 4A1NS was proposed to follow deamination and hydroxylation of the aromatic ring.