Practical experiences with aerobic biofilters in TMP (thermomechanical pulping), sulfite and fine paper mills in Canada

Abstract

An industrial aerobic biofilter technology has been piloted extensively in Canada on several types of pulp and paper mill effluents, resulting in one full scale operational facility at one Canadian fine paper mill. In addition two industrial scale pilot plant tests were performed with the same technology, one in an integrated sulfite pulp and paper mill and one in a TMP mill. In the case of the fine paper mill, the full scale plant has two cells (8 m × 8 m × 6 m height of the media) and treats an unclarified but screened effluent with a loading of 3500 kg BOD/d. The system produces low quantities of biosludge (0.28 kg TSS/kg BOD removed), has a rapid rate of recovery after shock loadings and is very energy efficient (150 kW installed power for aeration). Pilot plant treatability studies were performed at one integrated Canadian sulfite mill using a combination of a biofilter-aerated lagoon system. The biofilter treated the most concentrated stream (sulfite pulp mill effluent) and this stream was then combined with the remaining wastewaters of the mill and polished in an aerated stabilization basin (ASB). The high quality ASB effluent (50 mg BOD/L/30 mg TSS/L) was non toxic to rainbow trout, Daphnia magna and photoluminescent bacteria. Integrated TMP mill effluents were treated in a 5 m3 aerobic biofilter filled with two types of media (10 to 20 mm and 20 to 30 mm). Under average loading conditions of 3.5 kg BOD/d.m3 media, the system produced effluents meeting regulation limits for BOD, TSS as well as for toxicity.