Tetrachloroethene dechlorination kinetics by Dehalospirillum multivorans immobilized in upflow anaerobic sludge blanket reactors

Tetrachloroethene (C2Cl4) dechlorination kinetics in upflow anaerobic sludge blanket (UASB) reactors was determined after introducing de novo activities into the granular sludge. These activities were introduced by immobilizing Dehalospirillum multivorans in a test reactor containing unsterile granular sludge, and in a reference reactor, R1, containing sterile granular sludge.

A second reference reactor, R2, contained only unsterile granular sludge and served as a control. The kinetic experiments were performed by pulsing the reactors with C2Cl4 in a recirculating batch mode. Formate and acetate were added as electron donor and carbon source. Both reactors inoculated with D. multivorans dechlorinated C2Cl4 to an equimolar amount of C2H2Cl2 with only traces of C2HCl3 in the effluent.

In the control reactor, C2HCl3 accumulated before C2H2Cl2 was produced. A computer simulation program (AQUASIM) was used to estimate the kinetic parameters. The half-saturation constants (Ks) for C2Cl4 and C2HCl3 were almost equal in the reactors containing D.␣multivorans (17 μM and 18 μM for C2Cl4; 26 μM and 28 μM for C2HCl3), indicating no influence of sludge bacteria on the affinity of D. multivorans for C2Cl4 and C2HCl3.

The maximum dechlorination rates (kmXB) were about twice as high in the reactor containing D.␣multivorans immobilized in sterile sludge (11 mmol C2Cl4 l sludge−1 day−1 and 27 mmol C2HCl3 l sludge−1 day−1) than in the test reactor (4.4 mmol C2Cl4 l sludge−1 day−1 and 15 mmol C2HCl3 l sludge−1 day−1).

Compared to other C2Cl4-degrading systems, the dechlorination rates of the inoculated reactors and their affinities for C2Cl4 and C2HCl3 were high. Therefore, introduction of de novo activity is promising for the use of anaerobic reactors to bioremediate C2Cl4-polluted water.