A comparative study on thermomechanical pulping pressate treatment using thermophilic and mesophilic sequencing batch reactors

Abstract

A comparative study on the treatment of thermomechanical pulping (TMP) pressate was conducted under thermophilic (55°C) and mesophilic (30°C) temperatures to explore in-mill biological treatment, with the intention to operate under heat-efficient conditions. The experimental study involved sequencing batch reactors (SBRs) operated over 114 days. Receiving a total influent chemical oxygen demand (COD) of 3700–4100 mg L⁻¹, the COD removal efficiencies of 80–90% and 75–85% were achieved for the mesophilic and thermophilic SBRs, respectively, at a hydraulic retention time (HRT) of 12 and 24 h. Excellent sludge settleability (sludge volume index<100 mL g⁻¹ mixed liquor suspended solids) was obtained at both thermophilic and mesophilic SBRs. A higher level of effluent suspended solids was observed under thermophilic conditions. The results support the feasibility of applying thermophilic biological treatment of TMP pressate. The treated effluent has the potential for subsequent reuse as process water after polishing, thus addressing the long-standing desire to develop water system closure for the pulp and paper mill operation.

Keywords:

• sequencing batch reactor
• thermophilic treatment
• pulp and paper effluent
• sludge settleability
• bioflocculation

Acknowledgements

The authors thank Abitibi-Bowater Inc. for providing the TMP pressate for this study. Thanks go to Dr. Steven N. Liss at Queen's University, Kingston, ON, Canada for his help in improving the quality of this manuscript.

Funding

This study was supported by Natural Sciences and Engineering Research Council of Canada (NSERC).