Enrichment and Operation Strategies for Polychlorophenol Degrading Microbial Cultures in an Aerobic Fluidized-Bed Reactor

A 2,3,4,6-tetrachlorophenol- (TeCP-) and pentachlorophenol- (PCP-) degrading microbial culture was enriched from supernatant of municipal activated sludge using laboratory-scale continuous-flow fluidized-bed reactors (FBRs). Effluent concentrations of less than 10 μg/L were obtained within 12 days for TeCP and within 24 days for PCP at influent concentrations of 22 and 3.1 mg/L of TeCP and PCP, respectively, and at a 5-hour hydraulic retention time (HRT). Shorter HRTs at similar chlorophenol loading rates resulted in longer start-up times. Biodegradation of PCP was always more sensitive to increases in loading rate or decreases in HRT than was TeCP degradation. With TeCP and PCP loading rates of 100 and 15 mg/L·d, respectively, effluent TeCP concentrations of less than 10 μg/L were achieved even at a 3.7-minute HRT, while PCP removal efficiency started to decrease at HRTs of less than 38 minutes. During shock loading tests at a 14-minute HRT, more than 99.9% TeCP degradation was obtained at a 2 200mg/L·d loading rate, while PCP degradation remained at 73% at a loading rate of 314 mg/L·d. In batch degradation tests in the FBR, TeCP degradation followed Michaelis-Menten kinetics at initial concentrations of less than 31 mg/L, with a minimum specific substrate rate$(q_{{\rm max}})$of 0.59 mg TeCP/mg volatile solids (VS)·d and$K_{s}$(half-saturation constant) of 0.41 mg/L. Pentachlorophenol degradation was modeled using the modified Haldane equation with the following kinetic constants:$q_{{\rm max}}$= 0.066 mg PCP/mg VS·d,$K_{s}$= 1.1 mg/L,$K_{i}$(inhibition constant) = 1.7 mg/L, and n (constant) = 3. The results showed that FBR rapidly enriches chlorophenol-degrading cultures able to produce good-quality effluents. After start-up, FBRs can be operated over a wide range of loading rates for bioremediation of chlorophenol-contaminated water.