Thermophilic membrane bioreactors in the paper industry : A successful key to in-mill water treatment

Economic circumstances and environmental legislation are forcing mills to minimise their energy and water consumption and their emissions. The enabling technologies include a water treatment concept based on the five-fraction model and designed to promote Zero Liquid Effluent. One crucial component in this concept is the thermophilic membrane bioreactor (MBR) which removes colloidal and high molecular dissolved material from the wastewater. This paper describes trials of the MBR at three different paper mills in the Netherlands and Germany, and the subsequent start-up of a full scale MBR at Ugchelen, a Dutch speciality mill. The trials had shown a high success rate in different paper grades. In tissue production the reuse of effluent treated by a MBR and electrodialysis (desalting) bring : i) a positive effect on product properties ; ii) savings in water, energy and raw material ; iii) improved dewatering on the paper-machine. In liner production, the COD values of various wastewater types can be reduced to more than 90% in a membrane bioreactor at temperatures varying from 40-54°C. In specialities production, a MBR achieves a COD removal of more than 85% at treatment temperatures of 50-55°C. If the MBR effluent is used for further bleaching, not more than an additional 10% of chemicals is needed for bleaching which is as effective as it had been before water re-use. This application can lead to a reduction of fresh water intake of 40,000 m 3 per year and a reduction of water discharge of 5,000 p.e. Furthermore, because of the thermophilic conditions, another reduction of gas for heating of 700,000 m 3 per year can be obtained. These economic and environmental advantages have led to the decision to realise a full scale thermophilic membrane bioreactor, which was operational in November 2000.