IMPROVED DECHLORINATING PERFORMANCE OF UPFLOW ANAEROBIC SLUDGE BLANKET REACTORS BY INCORPORATION OF DEHALOSPIRILLUM MULTIVORANS INTO GRANULAR SLUDGE

Dechlorination of tetrachloroethene, also known as perchloroethylene ( PCE), was investigated in an upflow anaerobic sludge blanket (UASB) re actor after incorporation of the strictly anaerobic, reductively dechl orinating bacterium Dehalospirillum multivorans into granular sludge. This reactor was compared to the reference 1 (R1) reactor, where the g ranules were autoclaved to remove all dechlorinating abilities before inoculation, and to the reference 2 (R2) reactor, containing only livi ng granular sludge. All three reactors were fed mineral medium contain ing 3 to 57 mu M PCE, 2 mM formate, and 0.5 mM acetate and were operat ed under sterile conditions. In the test reactor, an average of 93% (m ole/mole) of the effluent chloroethenes was dichloroethene (DCE), comp ared to 99% (mole/mole) in the Ri reactor. The R2 reactor, with no ino culation, produced only trichloroethene (TCE), averaging 43% (mole/mol e) of the effluent chloroethenes. No dechlorination of PCE was observe d in an abiotic control consisting of sterile granules without inoculu m, During continuous operation with stepwise-reduced hydraulic retenti on times (HRTs), both the test reactor and the R1 reactor showed conve rsion of PCE to DCE, even at HRTs much lower than the reciprocal maxim um specific growth rate of D. multivorans, indicating that this bacter ium was immobilized in the living and autoclaved granular sludge. In c ontrast, the R2 reactor, with no inoculation of D. multivorans, only c onverted PCE to TCE under the same conditions. Immobilization could be confirmed by using fluorescein-labeled antibody probes raised against D, multivorans. Tn granules obtained from the R1 reactor, D. multivor ans grew mainly in microcolonies located in the centers of the granule s, while in the test reactor, the bacterium mainly covered the surface s of granules.