EFFECTIVENESS OF THE MEMBRANE BIOREACTOR IN THE BIODEGRADATION OF HIGH-MOLECULAR-WEIGHT COMPOUNDS

This paper presents biological and physical performance data from a pi lot-scale membrane bioreactor system fed with synthetic wastewater con taining high molecular weight compounds. At steady stare, high effluen t quality was obtained and maintained for about 350 days. The membrane was effective in retaining heterotrophic microorganisms and MS-2 viru ses, eliminating the need for effluent disinfection. The flux through the membrane decreased rapidly with increasing total suspended solids (TSS) concentrations between 2 and 15 g/L. The flux increased linearly with the transmembrane pressure (TMP), before reaching a maximum. A l inear relationship between the maximum flux and the cross flow velocit y (CFV) for different TSS concentrations was observed. The ability of the bioreacter culture to degrade high molecular weight compounds in t he wastewater, and the mechanisms involved in this process were examin ed in detail by performing respirometry experiments, Casein was used a s the model compound and different initial substrate to biomass ratios (S-o/X-o) were tested. In experiments with high S-o/X-o, several obse rvations were made: (1) the oxidation of casein occurred in two distin ct steps, (2) the yield coefficient is smaller than 0.15 mg VSS/mg COD consumed, and (3) nitrification does not occur. Under low S-o/X-o con ditions, using C-14-casein, the following observations were made: (1) complete hydrolysis of casein occurs very fast (less than 100 h) and ( 2) oxygen uptake and nitrogen measurements suggest nitrification takes place. (C) 1998 Elsevier Science Ltd. All rights reserved.