The effect of pre-ozonation on the H2O2/UV-C treatment of raw and biologically pre-treated textile industry wastewater

Advanced chemical oxidation of raw and biologically pretreated wastewater by ozonation, H2O2/UV-C treatment and the successive combination of ozonation and H2O2/UV-C oxidation was investigated. For the raw textile wastewater, the application of successive O3 + H2O2/UV-C oxidation enhanced the COD and TOC removal efficiency of the H2O2 (50 mM)/UV-C process by a factor of 13 and 4, respectively. In case of the biotreated textile wastewater, the preliminary ozonation step increased COD removal of the H2O2 (10 mM)/UV-C treatment system from 15% to 62%, and TOC removal from 0% to 34%, but did not appear to be more effective than applying a single ozonation process in terms of TOC abatement rates. Enhancement of the biodegradability was more pronounced for the biologically pre-treated wastewater with a two fold average increase in the BOD5/COD ratio for the studied chemical oxidation systems.

Partial oxidation of reactive dyestuffs and synthetic textile dye-bath by the O3 and O3/H2O2 processes

Ozonation and O3/H2O2 oxidation of reactive dyestuffs and simulated textile dye-bath were investigated. Effects of reaction pH, initial dye concentration, H2O2 concentration and assisting chemicals on treatment efficiency were examined. We found considerable improvement in COD and colour removal rates at pH = 11, that was almost the actual pH of the prepared textile wastewater, whereas in particular increasing the initial dyestuff concentration had an adverse effect upon oxidation rates. Removal of colour, COD and TOC were found to be fairly sensitive to the introduction of soda that is frequently applied as an auxiliary chemical during the reactive dyeing process. The addition of H2O2 had negligible effect on COD removal efficiency and decolorization rate compared to ozonation alone at different pH values. Accordingly it can be inferred that the theoretically expected effect of OH radical scavengers (e.g. carbonate, chloride) present in the synthetic dye-bath as well as introduced radical formation promoters (e.g. H2O2, OH-) were probably hidden due to the complexity of the synthetic wastewater matrix. Biodegradability of the ozonated dye-bath was accelerated by a factor of three corresponding to a 233% relative enhancement. The inhibition of the oxygen uptake rate decreased from 91% to 75% within only 5 min treatment time.