The effect of pre-ozonation on the biocompatibility of reactive dye hydrolysates

Pre-ozonation of 14 different reactive dyestuff hydrolysates at alkaline pH was investigated to assess possible relationships between ozone transfer efficiency, first order decolourization kinetics, release of initially complexed heavy metals and relative changes in the biodegradability of the partially oxidized dye waste samples. Biocompatibility of the raw (untreated) and ozonated dye hydrolysates was comparatively tracked through specific oxygen uptake rate measurements from which the respirometric inhibition of biological activated sludge imparted by raw and ozonated reactive dye wastewater with respect to synthetic domestic wastewater was determined. It could be demonstrated that preliminary ozonation of reactive azo dyes increases their biological compatibility more significantly than formazan copper complex, copper complex azo and phythalocyanine dyes as a consequence of heavy metal release associated with the cleavage of associated chromophoric groupings right at the initial stages of pre-ozonation.