Activity, structure, and stratification of membraneattached methanotrophic biofilms cometabolically degrading trichloroethylene

Abstract

A membrane-attached methanotrophic biofilm reactor was developed for the cometabolic degradation of triehloroethylene (TCE). In this reactor, CH4 and O2 are supplied to the interior of the biofilm through the membrane, while TCE-contaminated water is supplied to the exterior, creating a “counter-diffusional” effect that minimizes competitive inhibition between TCE and CH,. In addition, this novel design provides 100% CH, and O2 transfer efficiencies, promotes the development of a thick biofilm, and mmmizes the negative effects of TCE byproduct toxicity. The reactor sustained 80–90% TCE removals at TCE loading rates ranging from 100–320 µmol/m2/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, utilized, although higher transformation yields are expected at higher TCE loading rates. The CH, utilization rate was 0.20 mot/m2/d. Scanning electron microscopy (SEM) revealed a dense biofilm with a thickness of at least 400 µm, SEM and transmission electron microscopy (TEM) analyses indicated that the "holdfast" material associated with rosette formation in planktonic Methylosinus trichosporium OB33b (M.t. OB3b) cells might also contribute to pure-culture biofilm development. In addition, fimbriae-like structures not commonly associated with methanotrophic bacteria were observed in pure-culture M.t. OB3b biofilms. Finally, fluorescent in situ hybridization (FISH) analyses showed the presence of discrete mircrocolonies of serine-pathway methanctrophs within mixed-culture biofilms.