Activity, structure, and stratification of membrane-attached methanotrophic biofilms cometabolically degrading trichloroethylene

A membrane-attached methanotrophic biofilm reactor was developed for the co metabolic degradation of trichloroethylene (TCE). In this reactor, CH4 and O-2 are supplied to the interior of the biofilm through the membrane, while TCE-contaminated water is supplied to the exterior, creating a "counter-di ffusional" effect that minimizes competitive inhibition between TCE and CH4 . In addition, this novel design provides 100% CH4 and O-2 transfer efficie ncies, promotes the development of a thick biofilm and minimizes the negati ve effects of TCE byproduct toxicity. The reactor sustained 80-90% TCE remo vals at TCE loading rates ranging from 100-320 mu mol/m(2)/d. Chloride mass balances demonstrated that 60-80% of the TCE removed was mineralized. The maximum TCE transformation yield was 1.8 mmol of TCE removed per mole of CH 4 utilized, although higher transformation yields are expected at higher TC E loading rates. The CH4 utilization rate was 0.20 mol/m(2)/d. Scanning ele ctron microscopy (SEM) revealed a dense biofilm with a thickness of at leas t 400 mu m. SEM and transmission electron microscopy (TEM) analyses indicat ed that the "holdfast" material associated with rosette formation in plankt onic Methylosinus trichosporium OB3b (M.t. OB3b) cells might also contribut e to pure-culture biofilm development. In addition, fimbriae-like structure s not commonly associated with methanotrophic bacteria were observed in pur e-culture M.t. OB3b biofilms. Finally, fluorescent in situ hybridization (F ISH) analyses showed the presence of discrete microcolonies of serine-pathw ay methanotrophs within mixed-culture biofilms. (C) 1999 IAWQ Published by Elsevier Science Ltd. All rights reserved.