Effect of HRT,SRT and temperature on the performance of activated sludge reactors treating bleached kraft mill effluent |
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| Affiliation: | 1. UBC Pulp and Paper Centre and Department of Chemical Engineering, University of British Columbia, 2216 Main Mall, Vancouver, B.C., Canada V6T 1Z4;2. Western Pulp Limited Partnership, P.O. Box 5000, Squamish, B.C., Canada V0N 3G0;1. Department of Environmental Engineering, Faculty of Engineering, Kasetsart University, Bangkok 10900, Thailand;2. The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan;3. Asian Institute of Technology, P.O. Box 4, Klong Luang, Pathumthani 12120, Thailand;1. Center for Microbial Ecology and Technology (CMET), Ghent University, Coupure Links 653, 9000 Gent, Belgium;2. BIOMATH, Department of Mathematical Modelling, Statistics and Bioinformatics, Ghent University, Coupure Links 653, 9000 Gent, Belgium;3. Research Group of Sustainable Energy, Air and Water Technology, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerpen, Belgium;1. Environmental Engineering, Griffith School of Engineering, Griffith University, Nathan Campus, Brisbane, Queensland 4111, Australia;2. Department of Applied Chemistry, Faculty of Chemistry, Razi University, Kermanshah, Iran;1. Eawag: Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, 8600 Dübendorf, Switzerland;2. Universidade Federal do Rio Grande do Sul, CNPq, Av. Bento Goncalves 9500, Porto Alegre, Brazil;3. Institute of Environmental Engineering, ETH Zürich, 8093 Zürich, Switzerland |
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| Abstract: | Laboratory scale research on the effects of hydraulic retention time (HRT), solids residence time (SRT), high operating temperatures and temperature shocks on activated sludge (AS) treatment of kraft pulping effluent was performed using two 51 continuously fed bioreactors. Baseline performance of the reactors was established at 35°C by operating the reactors at steady state (HRT 10–12 h; SRT 12–15 d) for a period of two months. During this period percent removal of BOD, COD, and toxicity averaged 87.9 ± 4.3, 32.4 ± 9.0, 97.7 ± 0.4, respectively. Reactor MLVSS was 1675 ± 191 mg/l, effluent VSS was 45.5 ± 11.2 mg/l and specific oxygen uptake rate was 16.5 ± 3.3 mg O2/g MLVSS·h. Varying HRT between 12 and 4 h and SRT between 5 and 15 d indicated that HRT had more of an effect on treatment performance than SRT. Longer HRTs led to improved BOD, COD, toxicity and AOX removal, while longer SRTs were not shown to significantly affect performance. Shorter HRTs and longer SRTs led to significant increases in specific oxygen uptake rates (SOURs). For reactors operated at temperatures between 41 and 50°C, removal of BOD and acute toxicity was comparable to that observed at mesophilic temperatures. COD removal was improved over that observed at mesophilic temperatures, possibly as a result of improved dissolution of organic compounds at the higher temperatures. The effect of temperature shocks (decreases of 7°, 16.5°, 32° and 40.5°C) on reactor performance was proportional to the size of the disturbance. Reactor performance returned to pre-shocking levels within 12–24 h for the two smaller temperature shocks. Approximately 72 h was needed for the system to recover from the two larger temperature shocks (32° and 40.5°C). |
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