A magnetic adsorbent with an approximate diameter of 1 mu m was manufactured and used for fouling control in an anaerobic membrane bioreactor, equipped with a side flow inside-out tubular ultra-filtration membrane, operated under slug flow conditions. Without the addition of the magnetic adsorbent, a short-term experiment showed that the applied slug flow conditions enabled membrane operation at a flux exceeding 20 L/m2 h with a low trans-membrane pressure (TMP) increasing rate. Then, the magnetic adsorbent (1 g/L) and subsequently more magnetic adsorbent was added that increased the concentration of the adsorbent from 1 g/L in the reactor to 5 g/L. However, the introduction of the magnetic adsorbent resulted in an increased TMP, even at the low concentration applied (1 g/L). The TMP increasing rate increased with the applied adsorbent concentration. Strikingly, addition of the adsorbent had no effect on sludge viscosity, although filterability deteriorated significantly. Removal of adsorbent from the sludge using an external magnetic field was unfortunately accompanied by significant biomass loss. Hence, under the applied conditions, the proposed methodology is not considered viable for fouling control. (C) 2012 Elsevier B.V. All rights reserved.