Ozonation of an azo dye C.I. Remazol Black 5 and toxicological assessment of its oxidation products

Abstract

The effect of ozonation (20.5 mg l À1 ) on the degradation processes of an azo dye, Remazol Black 5 (RB5; CI) was studied. Conventional parameters such as chemical oxygen demand (COD), total organic carbon (TOC), pH, conductivity, colour removal, biodegradability (BOD 5=28 ), and toxic potential of the dye and its degradation products were monitored during the process. The results obtained indicated that ozonation is a highly effective way to remove the colour of a corresponding dye solution. However, a considerable organic load still remained as indicated by high COD and TOC residues. The COD, TOC reductions were about 40% and 25% for 6 h ozonation of 2 g l À1 RB5 aqueous solution. During the ozonation process the rapid decrease of pH and the sharp increase of conductivity indicated the formation of acidic by-products and small fragments and ions which were identified by high performance ion chromatography. The BOD 28 data revealed that first by-products after partial ozonation (10-150 min) of RB5 were more biodegradable than the parent compound and ozonation can enhance the biodegradability of azo dyes. During the first 150 min of total 360 min of oxidation, the formation of first by-products with high toxic potential took place as it could be confirmed by two acute toxicity-screening tests, the bioluminescence test (Vibrio fischerii) and the neutral red cytotoxicity assay (rat hepatoma cells). The significant enhancement of microbial biodegradability after long-term ozonation could also be seen as a decrease of toxic intermediates in correlation with the ozonation time as indicated in BOD 28 biological degradation test results.

Ozonation of oxytetracycline and toxicological assessment of its oxidation by-products

“…One potential method could be the combination of traditional wastewater treatment (biological) In this study, ozonation, having a high potential for the oxidation of harmful chemicals in drinking and wastewater treatment plant effluents, has been chosen to determine the degradation rate (BOD 5 /COD) of high amounts of oxytetracycline (100 and 200 mg l À1 ) in synthetic aqueous solutions (Koch et al, 2002;Huber et al, 2003;Ternes et al, 2003;Wang et al, 2003). Additionally, the toxic potential of the reaction intermediates and products formed during ozonation have been investigated by the bioluminescence test (Vibrio fischeri).…”

Impact of ozonation on subsequent treatment of azo dye solutions

“…1 Most azo dyes contain between one and four azo bonds which are usually attached to aromatic groups 2,3 and are used most commonly in textile industries. In general, 40-90% of the dye is fixed to the fabric during the dyeing process.…”

“…Thus a large amount of unfixed dye remains in the dye bath after completion of dyeing and release of this dyehouse effluent to natural water bodies is undesirable. 3,4 Azo-dye molecules are difficult to degrade biologically under aerobic conditions. Hence colour cannot be removed efficiently from wastewaters containing azo-dyes by conventional aerobic treatment methods, such as activated sludge process.…”

Estudo sobre a utilização da lama vermelha para a remoção de corantes em efluentes têxteis

“…33 Seu peso molecular é de 991,82 g. 34 Apresenta em sua estrutura dois grupos azo (-N = N-) ligados a sistemas aromáticos, que constituem o grupo cromóforo, que absorve no comprimento de onda de 597 nm.…”