Treatment of Textile Wastewater by Combining Biological Processes and Advanced Oxidation

Abstract

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.

Abstract (Swedish)

Popular Abstract in English

Colors have always been part of human life and culture. Today natural pigments have

been substituted by synthetic dyes that usually end up threatening nature itself by

polluting the environment. To what extent can we use chemistry and biology to

minimize the environmental impact of the textile industry?

During the dyeing process a certain amount of dye, 2 to 50 percent, does not bind to

the fabric and is washed away. Companies are working on improving this process.

Meanwhile something needs to be done to avoid the dye effluents ending up untreated

in the natural environment.

Discharge of untreated textile effluents in the natural environment is a widespread

problem where the production of textiles is concentrated, for example in the south of

Asia. This is caused by lack of care and awareness, and defective regulations. Much

research has been performed to reduce the environmental impact of the dyeing process

units and appropriate technologies are now available. However, most units are very

small, sometimes just the size of a family company, and they do not have money for

treating their effluent.

Why are colors threatening the environment? Aquatic plants and algae are

indispensable for aquatic ecosystems. They use carbon dioxide and light to produce

oxygen and food, which are consumed by higher organisms like fish. The presence of

colors in water tends to stop the penetration of sunlight, hence the gradual decrease in

living organisms in rivers. Dyes can be harmful for humans, acting as irritants for eyes

and skin. Moreover, the problem does not disappear with the color! In fact, in time the

dye molecules will eventually break down and become colorless. The resulting

compounds are even more harmful than the original dyes and in some cases

carcinogenic.

Researchers all around the world are looking for an optimal treatment for textile

effluents. Common solutions for wastewater treatment include aerobic biological

processes, adsorption and coagulation. Can these be used for textile effluents as well?

Microorganisms are the main actors in aerobic biological processes because they remove

nutrients like organic carbon, nitrogen and phosphorous from water without the

addition of chemicals. The downside is that a lot of oxygen is needed for this process

and excess sludge that may contain pollutants is generated and needs to be handled in

an appropriate way. In addition, most dyes used in textile industry are not fully

degradable and the treated water could contain dangerous amines. Adsorption and coagulation remove dyes and other pollutants by transferring them from a liquid phase,

the wastewater, to a solid phase, the adsorbent or coagulant. This is however only a

temporary solution. In fact, the resulting sludge produced contains dyes and needs to

be properly disposed of, with additional costs.

Our research group is dealing with textile wastewater treatment. The project started

some 10 years ago after visiting several textile dyeing units in the south of India. The

research goal was to devise an ideal treatment which was cheap, easy to operate and

efficient in terms of producing a good-quality effluent. The strategy is simple. First, the

wastewater is treated with anaerobic microorganisms, which can reduce the total

organic content of the effluent by metabolizing the degradable compounds without the

need for oxygen. Secondly, an advanced oxidation process based on the activity of a

powerful oxidant is applied to facilitate the removal of harmful amines. We have

evaluated a few options for this last step. One is ozonation, energy intensive but “clean”.

This means that it does not produce any sludge or secondary waste. In fact, ozone, apart

from being a well-known pollutant, can oxidize aromatic compounds releasing oxygen.

A very successful process is photo-Fenton oxidation. The effluent is treated with iron

and hydrogen peroxide in the presence of light and what remains at the end is a mixture

of salts rich in iron. To verify the effectiveness of the treatment, we used a series of

toxicity tests. The costs and environmental impact assessment of the treatments

suggested in this work indicate that the technology is ready to be implemented.

Money cannot buy happiness, but it can certainly help to preserve our beautiful world.

The technology for industrial wastewater treatment is mature enough to offer solutions

to avoid pollutants from escaping into the environment. Dyestuff and other chemicals

found in textile effluents are no exception. However, industries are often not ready to

put money into waste handling, something that will not make them richer. Therefore,

the future of wastewater should be centered on the concept of water reuse, which is

profitable for industries as well as the environment.

• author: Punzi, Marisa
• supervisor: Rajni Hatti-Kaul; Bo Mattiasson; Maria Jonstrup
• opponent: Ledin, Anna, Environmental Department of the City of Gothenburg, Gothenburg, Sweden
• organization: Biotechnology
• publishing date: 2015
• type: Thesis
• publication status: published
• subject: Industrial Biotechnology
• keywords: Azo dye, textile wastewater, biological treatment, biofilm, microbial community, DGGE, green algae, photo-Fenton, ozone, toxicity, mutagenicity, LCA, cost analysis
• pages: 160 pages
• defense location: Lecture hall B, Center for Chemistry and Chemical Engineering, Getingevägen 60, Lund University, Faculty of Engineering LTH, Lund
• defense date: 2015-01-06 10:00:00
• ISBN: 978-91-7623-352-8
• language: English
• LU publication?: yes
• id: c9c2a2e0-c6a5-402d-81c1-d18c666566c8 (old id 5367868)
• date added to LUP: 2016-04-04 13:14:41
• date last changed: 2018-11-21 21:12:51