Treatment of paper coating colour effluents by membrane filtration

Dilute coating colour effluents are created during the coating of paper and board. After treating the colour effluents with ultrafiltration, the retentate can be reused as coating colour and the permeate can replace fresh water. At the same time, the load on the external treatment plant is reduced. In this investigation, pilot-plant experiments were performed at a paper mill. A high and steady flux, 120 l/m(2) h, was achieved at a colour concentration of 10-15%. The flux at 40% was lower but steady, 50 l/m(2) h. The membrane performance when treating five coating colours with varying composition was studied in laboratory experiments. The composition of the colour had a significant influence on the membrane performance. A colour containing starch exhibited the lowest flux and the lowest COD retention of the colours included in the study, while a colour in which the clay had been replaced by CaCO3 exhibited the highest final concentration of 60%.