Treatment of Textile Wastewater by Combining Biological Processes and Advanced Oxidation

Treatment of textile wastewater is challenging because the water contains toxic
compounds that have low biodegradability. Dyes, detergents, surfactants, biocides and
more are used to improve the textile process and to make the clothes resistant to
physical, chemical and biological agents. New technologies have been developed in the
last decades and in particular Advanced Oxidation Processes (AOPs) have shown
considerable potential for treatment of industrial effluents. These processes however are
expensive and full scale applications are still scarce. In addition, the complex oxidation
chemistry transforms the pollutants into a very large number of degradation
intermediates which may be even more toxic than the original compounds.
This thesis presents a novel treatment approach where two AOPs, photo-Fenton
oxidation and ozonation, are used after an anaerobic biofilm process for treatment of
textile wastewater, azo dyes degradation and removal of toxicity. The biological
treatment cleaves the azo bonds of the dyes and consumes the biodegradable
compounds whereas the following advanced oxidation degrades the aromatic amines
and other by-products that are recalcitrant to biological degradation. The approach that
includes photo-Fenton oxidation resulted in higher reduction of chemical oxygen
demand (COD) than that with ozonation when treating real textile wastewater. The
latter however resulted in higher reduction of toxicity towards the bacteria Vibrio
fischeri and the shrimp Artemia salina. Mutagenic effects were detected in the untreated
and biologically treated effluent, but not after photo-Fenton oxidation and ozonation.
Environmental impact and costs of the two treatment strategies, at the operating
conditions used in this study, are high compared with the full-scale biological process
used in the Netherlands, where the wastewater is actually treated. Substitution of
artificial light with sunlight and upscaling would result in great improvements in terms
of electricity requirements and ozone consumption hence would bring down the
environmental impact to values that are comparable to the biological process,
suggesting that full scale implementation can be achieved. Further research should look
into combining this treatment approach with technologies that allow water and salt
recovery and reuse, to make the textile industry more sustainable.