Nitrogen removal from sludge reject water with a membrane-assisted bioreactor

• Published in: Water research (Oxford) Vol. 33; no. 1; pp. 23 - 32
• Main Authors: Ghyoot, Wouter, Vandaele, Stefaan, Verstraete, Willy
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 1999; Elsevier Science
• Subjects: activated sludge; Applied sciences; Biological and medical sciences; biological treatment; Biological treatment of waters; Biotechnology; complete sludge retention; crossflow filtration; Environment and pollution; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Industrial applications and implications. Economical aspects; membrane separation; nitrogen removal; Other wastewaters; Pollution; sludge liquor; Wastewaters; Water treatment and pollution; biological treatment; activated sludge; complete sludge retention; membrane separation; sludge liquor; crossflow filtration; nitrogen removal; Activated sludge; Ether copolymer; Aerobe; Sulfone copolymer; Biological purification; Microfiltration; Bioreactor; Ultrafiltration; Membrane filtration; Nitrification; Denitrification; Waste water purification; Performance; Ceramic materials
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/S0043-1354(98)00190-0

The start-up of a membrane-assisted bioreactor for nitrogen removal from sludge reject water was examined. The aim was to rapidly achieve a high nitrogen loading rate while maintaining complete nitrification and to maximize denitrification with addition of methanol or acetic acid. The use of an ultrafiltration unit with a positive displacement pump for sludge recirculation resulted in complete nitrification at an aerobic sludge loading rate of 0.16 kg N (kg SS) −1 d −1 within two weeks. The use of a microfiltration unit with a centrifugal pump for sludge recirculation, resulted in complete nitrification at a maximal aerobic sludge loading rate of 0.08 kg N (kg SS) −1 d −1. With the centrifugal pump, a sudden collapse of nitrification was observed. The rapid decrease of the specific sludge activity was attributed to shear stress resulting from the high recirculation rate of biomass through the centrifugal pump. NH 3 was found to inhibit Nitrobacter at a concentration higher than 0.1 mg N l −1. Denitrification with methanol required an adaptation period of three weeks after which more than 80% denitrification was achieved. Denitrification of nitrite with methanol required a COD:N ratio of 2.3 g g −1, denitrification of nitrate required a COD:N ratio of 3.8 g g −1. With acetate no adaptation was needed and 90% denitrification was achieved. A low biomass growth of 0.092 g SS (g COD removed) −1 or 0.398 g SS (g N removed) −1 was obtained. Polymer ultrafiltration of activated sludge at a concentration of 4 g SS l −1, a transmembrane pressure (TMP) of 220 kPa and a linear flow velocity (V) of 1.5 m s −1 resulted in a long term flux of 8 l m −2 h −1. For the ceramic microfiltration membrane, a long term flux of 160 l m −2 h −1 was achieved (5.3 to 18.1 g SS l −1, TMP=200 kPa, V=3.0 m s −1).