TCE DEGRADATION IN A METHANOTROPHIC ATTACHED-FILM BIOREACTOR

Trichloroethene was degraded in expanded-bed bioreactors operated with mixed-culture methanotrophic attached films. Biomass concentrations o f 8 to 75 g volatile solids (VS) per liter static bed (L(sb)) were obs erved. Batch TCE degradation rates at 35-degrees-C followed the Michae lis-Menten model, and a maximum TCE degradation rate (q(max)) of 10.6 mg TCE/gVS . day and a half velocity coefficient (K(S) of 2.8 mg TCE/L were predicted. Continuous-flow kinetics also followed the Michaelis- Menten model, but other parameters may be limiting, such as dissolved copper and dissolved methane-q(max) and K(S) were 2.9 mg TCE/gVS . day and 1.5 mg TCE/L, respectively, at low copper concentrations (0.003 t o 0.006 mg Cu/L). The maximum rates decreased substantially with small increases in dissolved copper. Methane consumption during continuous- flow operation varied from 23 to 1200 g CH4/g TCE degraded. Increasing the influent dissolved methane concentration from 0.01 mg/L to 5.4 mg /L reduced the TCE degradation rate by nearly an order of magnitude at 21-degrees-C. Exposure of biofilms to 1.4 mg/L tetrachloroethene (PCE ) at 35-degrees-C resulted in the loss of methane utilization ability. Tests with methanotrophs grown on granular activated carbon indicated that lower effluent TCE concentrations could be obtained. The low eff iciencies of TCE removal and low degradation rates obtained at 35-degr ees-C suggest that additional improvements will be necessary to make m ethanotrophic TCE treatment attractive. (C) 1993 John Wiley & Sons, In c.