SLUDGE ACTIVITY AND CROSS-FLOW MICROFILTRATION A NON-BENEFICIAL RELATIONSHIP

For the past year a half-scale pilot plant for the anaerobic pretreatm ent of potato starch wastewater has been in operation. A reactor of 4 m(3) was equipped with a settler and a so-called membrane thickener to reduce the amount of sludge which has to pass the membrane. According to other publications on membrane supported anaerobic digesters, orga nic loadings of more than 6 kg COD/m(3)d rarely have been achieved by this reactor. A loss of 50% of activity was observed after circulating the sludge 20 times and a 90% loss within 100 cycles. It can be shown that the symbiosis between acidogenic and methanogenic bacteria is th e most sensitive part. These observations imply that a 'gentle' transp ort of sludge through the membrane module must be developed, if membra ne filtration at anaerobic reactors is to be further utilized. The res ults for an aerobic batch reactor implied that parallel to the destruc tion of sludge flocs due to the unsuitable pumps or to high transmembr ane pressure, a significant decrease of the specific activity will tak e place. Copyright (C) 1996 IAWQ. Published by Elsevier Science Ltd.