Increasing BOD5/COD ratio of non-biodegradable compound (reactive black 5) with ozone and catalase enzyme combination

Abstract

The effect of ozone and ozone plus a biological catalyst (catalase) on the degradation processes of Reactive Black 5 was investigated. The ozonation process was carried out in a laboratory-scale batch reactor with a volume of 500 ml. Chemical oxygen demand (COD), pH, color removal and the BOD5/COD ratio were measured during the process. At the first stage, only ozonation was performed, at the second stage, ozonation plus NaCl and Na2CO3, and at the third stage, ozonation plus catalase enzyme were used. As a result of the oxidation of Reactive Black 5 with only ozone and ozone plus textile auxiliaries, chemical oxygen demand (COD) removal was 34% and 19%, respectively. COD removal efficiency was 43% when 10 ml of catalase was added to the ozone reactor. Carbonate and salt have a negative effect on the oxidation of reactive Black 5 with ozone. Reactive Black 5 was degraded into sub-components, and the biodegradability of the wastewater increased. The pH value decreased from 3.3 down to 1.6, which showed that organic acids were formed as a result of degradation. The use of enzymes in combination with ozonation shows that Reactive Black5 can rapidly convert into the intermediate within the 270-min ozonation time (BOD5/COD = 0.46). COD removal was not as high as color removal efficiency. This may have resulted from the formation of colorless oxidation products. The significant increase in biodegradability after ozonation in the presence of the catalyst may also be seen as a reduction of toxic intermediates.