On-site aerobic treatment at high and varying process water temperatures.

Application: Pulp and paper mills looking to reduce their nominal water consumption can use a high-rate thermophilic aerobic biofilm process for internal treatment. Treatment reduces easily biodegradable matter.

A two-stage (2 * 1 [m.sup.3]) aerobic suspended carrier biofilm process (SCBP) was studied on mill premises for treatment of groundwood mill circulation water under high and varying process temperature. A rapid start-up was achieved with sludge from an existing mesophilic activated sludge plant treating mill wastewater. The two-stage SCBP produced 49%-77% GF50-filtered chemical oxygen demand (CO[D.sub.filt]) removals at volumetric loading rates of 3-14 kg CO[D.sub.filt][m.sup.-3][d.sup.1] and hydraulic retention times (HRTs) of 2-8 h, whereas the single reactor (first stage) produced 40%-67% CO[D.sub.filt] removals at loading rates of 7-28 kg CO[D.sub.filt][m.sup.-3][d.sup.1] and HRTs of 1-4 h. SCBP tolerated periodical temperature variations along with caustic shocks, and regained normal CO[D.sub.filt] removal within 24 hours. S!

Suvilampi and Rintala are with the Department of Biological and Environmental Science, University of Jyvaskyla, P.O. Box 35, FIN-40351 Jyvaskyla, Finland, Nuortila-Jokinen is with the Laboratory of Membrane Technology and Technical Polymer Chemistry/Cleantech 2000, Lappeenranta University of Technology, P.O. Box 20, FIN-53851 Lappeenranta, Finland. Email Suvilampi at [e-mail].