ABSTRACT: The organic matter mineralization, decolorization, biodegradability improvement, and toxicity reduction of an
industrial cotton dyeing wastewater were investigated. Di erent treatment approaches, including single and integrated processes,
were studied, namely, coagulation/ occulation per se and its combination with Fenton oxidation (approach 1), the Fenton
process alone (approach 2) and its integration with either coagulation/ occulation (approach 3) or biological oxidation in a
sequential batch reactor (approach 4). All approaches provided a wastewater that meets the Portuguese legislated discharge
limits; however, approaches 1 and 3 require smaller operating costs (1.0 €/m
3
) with global removal e ciencies for these two
strategies of 70.8% for chemical oxygen demand (COD), 66.1% for dissolved organic carbon (DOC), and 47.6% for biological
oxygen demand (BOD
5
) in approach 1 and 69.2% for COD, 60.4% for BOD
5
, and 72.4% for DOC in approach 3, along with
almost complete color removal in both strategies and toxicity reduction (0.0% inhibition of Vibrio scheri in the e uent
from approach 1). A slight increase of the e uent biodegradability was also observed (BOD
5
:COD increased from
0.26 to 0.33−0.46, and speci c oxygen uptake rate (SOUR) increased from 8.85 to 9.3−11.3 mgO
2
/(g
VSS
h)), depending on
the treatment approach. The use of a cheap process (coagulation/ occulation) as pretreatment allowed reducing the
amount of reagents needed in the Fenton process, making the latter treatment slightly cheaper and thereby reducing the
overall costs.