A new method of defibring wood chips and producing chemi-thermomechanical pulp with significant capital and energy savings has been developed. The pollution load of bleached CTMP effluent varied between 40-60 kg/t for BOD5 and 120-210 kg/t for COD. The process includes a sulphite stage and the effluent contains sulphur compounds which are toxic to methanogenic bacteria. Studies have been conducted on anaerobic fixed bed reactors with upflow or downflow feed modes. It is necessary to progressively acclimate bacteria to increasing concentrations of sulphur compounds. Permanent functioning of reactors is possible with COD/S ratios near 10-12 where propionate concentrations are increasing. Upflow reactors are more efficient than downflow reactors, with a maximum loading rate of 3.5 kg COD/m3.day corresponding to 800 mg/l as S. With hybrid sludge bed/fixed bed reactors it is possible to enhance anaerobic treatment efficiency. A COD loading rate of 4.7 kg/m3.day can be maintained with a residence time of 2 days and a pollution load removal efficiency of 45% for COD (55% with complementary oxidation) and 70% for BOD5. The economics of effluent treatment give an investment cost of about 20 US$/ADt for the activated sludge process and 12.5 US$/ADt for anaerobic fixed bed treatment.

In waste paper processing mills, entirely closed process water systems cause high specific polluting problems, deteriorate the quality of the paper produced and corrode the equipment. Operating an anaerobic fluidized bed on part of the circulating water could make it possible to achieve lower dissolved organic concentration in the closed process water system. Laboratory experiments have been carried out according to the following flow-sheet : Water circuit; Acidification tank; Fluidized bed. When the anaerobic treatment is added to the water circuit, COD removal is 75% in the circuit and 65% in the acidification tank. Consequently, until reaching steady state, the organic load entering the fluidized bed decreases continuously from 28.75 to 9.86 kg COD/m3 d−l without disturbing biomass activity. From a mass balance, a mathematical model is drawn to check the COD removal in the water circuit and study the transitory period. Efficient fluidized bed performances are achieved even with high organic load (28.75 kgCOD/m3d−1) 52% to 75% COD removal are obtained in the water circuit respectively within 75 and 24 hours. The treated water represents a very small part of the circulating water. To achieve 52% COD removal the equivalent of 0.5 m3/t produced paper is treated. For a 75% COD removal efficiency, treated flow rate is 2.6 m3/t produced paper.

No abstract