Textile wastewaters are rated among the most polluting of all
industrial sectors, both in terms of discharged volumes and composition,
but their most important environmental problems arise
from the high organic loads and the presence of color Azo
dyes are the most common synthetic colorants released in textile
wastewaters due to their ease of synthesis, stability and variety
of colors. Due to the electron-withdrawing nature of azo bonds,
azo dyes are easily reduced by bacteria under anaerobic conditions,
resulting in color removal with the formation of aromatic amines Key data on the health hazard associated with the majority of
these aromatic amines are limited ociated with the majority of
these aromatic amines are limited [4], but some of these azo dye
breakdown products have been considered of higher concern than
the original dye with respect to their possible (eco) toxicity and/or
mutagenicity/carcinogenicity Although these amines are generallynotfurtherdegradedanaerobically,theirpotentialfor
aerobic
biodegradation has been demonstrated for simple molecular structures Thus, staged anaerobic/aerobic sequencing batch
reactor (SBR) systems using floc-forming biomass have been
proposed for complete azo dye biodegradation, including decolorization
and further aromatic amine mineralization However, the optimization of flocculent sludge technology is
hampered by intrinsic operational features, such as poor settling
characteristics that require a large footprint and compromise
the treatment efficiency Thus, its replacement is regarded as
inevitable in the near future.
In light of the environmental problems raised by textile industry
wastewater and of the limitations of the treatment processes
currently used, there is an urgent need for effective, environmentally
friendly and economically attractive technologies for textile
wastewater treatment. In this context, the novel aerobic granular
sludge (AGS) technology is a promising bioprocess for textile
wastewater treatment. The formation and use of AGS began to
be reported in the late 1990s and has recently been applied
with success in domestic full-scale wastewater treatment plants
(WWTP) with significant reductions in footprint and energy consumption,
being pointed as the next generation of wastewater
treatment technologies In addition to the general advantages of the staged SBR
technology, AGS systems present several unique attributes [13]:
excellent settling properties, allowing shorter settling times for
good solid–liquid separation and requiring lower construction area; good biomass retention, allowing higher concentration in
the SBR and consequently lower reaction time and/or reactor volume;
ability to withstand toxicity and high organic loading rates,
making them attractive for industrial wastewater treatment applications;
aerobic and anoxic/anaerobic zones within the granules,
allowing organic matter, nitrogen and phosphorus removal in the
same system and potentially contributing to the process of azo dye
mineralization. Given the particular attributes of aerobic granules,
this compact technology has a great potential for the treatment
of the highly variable textile wastewaters, including the biodecolorization
of textile dyes that are generally resistant to aerobic
biodegradation, like azo dyes.
Despite the increasing reported applications of AGS for municipal
and industrial wastewater, textile wastewater treatment with
this technology has scarcely been reported Thus, the objective
ofthis work was to assess the applicability ofthe novelAGS technology
in SBR as an alternative to the conventional flocculent activated
sludge SBR technology for dye-laden textile wastewater treatment.
For that, the performance of two anaerobic/aerobic SBR systems,
one with activated sludge flocs and the other with aerobic granules,
was evaluatedinterms of chemical oxygendemand(COD) andcolor
removal efficiencies in the treatment of a simulated textile wastewater.
To our knowledge, this is the first time that such a comparison
is performed. In parallel to color and COD removal profiles, the
potential detoxification of the simulated textile wastewater during
SBR operation was also examined by using yeast-based assays with the eukaryotic model Saccharomyces cerevisiae. This
is a simple, animal-alternative and relatively inexpensive experimental
test system that can provide a fast preview of the potential
toxicity of chemicals/effluents meaningful for other eukaryote