A CONCEPTUAL-MODEL DESCRIBING MACROMOLECULE DEGRADATION BY SUSPENDED CULTURES AND BIOFILMS

Macromolecular (> 1,000 daltons) compounds such as proteins and polysa ccharides can constitute a significant portion of dissolved organic ca rbon (DOC) in wastewater, but limited information is available on how these compounds are degraded in suspended and fixed-film biological wa stewater treatment systems. Bacteria cannot assimilate intact macromol ecules but must first hydrolyze them to monomers or small oligomers. H ere, we summarize experiments performed in our laboratory which indica te that the enzymes responsible for hydrolysis are primarily those tha t remain attached to the cell. In biofilm cultures fed macromolecular substrates, for example, no more than 8% of total hydrolytic activity was found to be located in the cell-free bulk solution. These and othe r experiments support a generalized mechanism for macromolecule degrad ation by biofilms that features cell-associated hydrolysis, followed b y the release of hydrolytic fragments back into bulk solution. The ext ent of fragment release is larger for proteins (bovine serum albumin) than for carbohydrates (dextrans). (C) 1998 IAWQ. Published by Elsevie r Science Ltd.