Ozonation and wet oxidation in the treatment of thermomechanical pulp (TMP) circulation waters

Ozonation and wet oxidation were studied as means of the treatment of therm omechanical pulp (TMP) processing waters. There were two objectives of the experimental research concerning circulation waters: to reduce concentratio n of lipophilic wood extractives (LWEs) and to treat the concentrated resid ues from evaporation and membrane filtration by low-pressure catalytic wet oxidation. Ozone was found to selectively react with LWEs. The selectivity of ozonation defined as the ratio of the rate coefficients of the reactions with LWEs and other organic matter was found to be from 3 to 20. The react ion was always found to be of fast or moderate rate and, therefore, no diss olved ozone could be detected in water during ozonation. However, the ozone dose necessary to remove 90% of the LWEs in TMP water was found to be rath er high, from 500 to 800 mg O-3/l. This was determined by high content of o rganic matter, COD ranged between 3 and 6 kg O-2/m(3). The implementation o f ozone for LWEs removal is therefore problematic from economical point of view. Catalytic low pressure-wet oxidation of membrane and evaporation conc entrates was found to be effective: 50% of COD were removed under 150 degre es C with subsequent increase of the wastewater biodegradability. (C) 1999 Published by Elsevier Science Ltd on behalf of the IAWQ. All rights reserve d.