Decolorization of Acid Red 1 by Fenton-like process using acid-activated clay

Colored effluents can cause irritation to skin and mucous membrane, upper respiratory tract and severe headaches to humankind. The discharge of dyes into the rivers will deplete dissolved oxygen that resulting in death of aquatic life. Therefore, the industrial dye-laden effluents need to be effectively treated before discharged into the environment in order to prevent these potential hazards.

There have been many techniques to remove dyes from wastewater. The traditional method technologies such as coagulation/flocculation, membrane separation or activated carbon adsorption, only do a phase transfer of pollutant. Biological treatment is not a suitable solution technique due to biological resistance of some dyes.

Heterogeneous Fenton technology has emerged as a successful technique to counter the rising environmental problems in the last few decades. It has been proven effective for degradation of dyes and organic pollutant to the required low limit of concentration with a wider pH value. In heterogeneous catalyst, the ion cation is "immobilized" within the structure and in the pore/interlayer space of catalyst. As a result, the catalyst can maintain its ability to generate hydroxyl radicals from hydrogen peroxide, and iron hydroxide precipitation is prevented.

In heterogeneous Fenton most of the reactions takes place either at the surface of the supports or in the pores of the support, and only a very small portion occurred in the bulk.

Clay found abundantly and combined with the functionality of iron can serve as heterogeneous catalyst in the Fenton-like reactions. Kuala Kangsar clay is special local river clay used to make water pitcher. The clay water containers are not only synonymous with Kuala Kangsar, but have become an icon for the state of Perak. Being inexpensive and widely available, Kuala Kangsar clay represents an attractive catalyst support for the removal of dyes effluent.

In the present work, decolourisation of Acid Red 1 dye solution in batch process was carried out using iron (II) immobilized on Kuala Kangsar clay as active heterogeneous catalyst. The physico-chemical behaviour of Kuala Kangsar clay was modified by acid treatment. This process could improve the catalytic activity of the catalyst by immobilizing more ions which are the active sites on the support during impregnation process. The effect of different initial iron ions loading on Kuala Kangsar clay, initial concentration of hydrogen peroxide and Acid Red 1, catalyst dosage, reaction temperature and initial pH solution on the decolourisation efficiency of the process were discussed.

The initial and final concentration of Acid Red 1 was analysed using the UV-Vis spectrophotometer (Shimadzu, model UV 1601 Japan) at maximum wavelength of 532 nm. The best reacting conditions were found to be 0.60 wt.% of iron ions loading on Kuala Kangsar clay when the dosage of catalyst is 3.0 g L-1 with the initial pH of 2.5. The optimum concentration of hydrogen peroxide is 8 mM when the concentration of Acid Red 1 is 50 mg L-1 at temperature 30°C. Under these conditions, 99% decolourisation of Acid Red 1 was achieved within 140 min reaction time. Iron (II) immobilized on Kuala Kangsar Clay represents an attractive heterogeneous catalyst in the application of textile industrial treatment plant since they are low cost, natural and environmentally friendly.

The effectiveness of heterogeneous Fenton technology has also been tested in the reduction of hydrogen peroxide concentration from semiconductor industry by using other support. The results showed that the concentration of hydrogen peroxide could be reduced up to 78% within 30 min reaction time. The next step is to develop the prototype for continuous system for the treatment of textile wastewater. This prototype would enable the researcher to study on the decolourisation of textile wastewater on the continuous system. This research is an important step towards the development of technologies that aim to combat the waste from the textile industry.