OZONATION OF ACTIVATED-SLUDGE TREATED CARBONIZATION WASTE-WATER

Ozonation of activated sludge treated carbonization wastewater after pH alteration (PH 4 and 12), including removal of the coagulated matter formed by pH alteration, and at an unaltered pH of 7.5, were compared. Batch ozonation at the unaltered pH resulted in a significant higher residual COD (rCOD) reduction efficiency. At the unaltered pH 0.308 g rCOD/g O-3 were removed while at altered pHs of 4 and 12 reduction efficiencies of 0.169 and 0.197 g rCOD/g O-3 were obtained during 40 min ozonation with 0.02 g O-3/1 min applied. The soluble fraction of polycyclic aromatic hydrocarbons (PAHs) was generally reduced below 0.02 mu g/1. PAHs adsorbed onto the suspended solids were reduced below 0.5 mu g/1. Continuous ozonation at the unaltered pH at residence times of 15 and 30 min resulted in average rCOD reduction efficiencies of about 0.655 g rCOD/g O-3. Also good CNS- and color reduction were obtained at both residence times tested. Yet, ozonation resulted in acute and short term inhibition of the oxygen uptake rate of unadapted sludge. Additional detoxification by a trickling filter was capable of eliminating the ozone induced toxicity. It was also shown that biological processes had a major part in this detoxification process. It is concluded that for carbonization wastewater, purification by activated sludge followed by ozonation allows a high effluent quality to be achieved but precautions for the receiving ecosystems are needed due to ozone induced toxicity.