Increased removal capacity for 1,2-dichloroethane by biological modification of the granular activated carbon process.

The removal of 5 mg l-1 1,2-dichloroethane [(CH2Cl)2] was studied in two granular activated carbon (GAC) reactors run with hydraulic retention times of below 1 h. One reactor was operated abiotically. The other one was inoculated with microorganisms able to degrade (CH2Cl)2. While the (CH2Cl)2-adsorption capacity of the non-inoculated GAC reactor was exhausted after 20 days, it apparently did not exhaust for at least 170 experimental days in the biologically activated system because (CH2Cl)2 was removed to over 95% as a result of the microbial degradation. The biodegradation was quantified: during the passage through the biologically activated GAC reactor, (CH2Cl)2 (5 +/- 1 mg l-1) disappeared, chloride ions (3.3 +/- 0.2 mg l-1) were produced, and oxygen (4 to 6 mg l-1) was consumed. Removal of 30% of GAC at the entrance of the reactor, which visibly carried most of the biomass, and its replacement by virgin GAC at the end of the column did not change the apparent (CH2Cl)2 removal capacity of the GAC column, indicating that still enough biomass was available to degrade most of the chemical fed. After the addition of the virgin carbon, the effluent concentration fell for a short period of time from about 200 micrograms l-1 to below 100 micrograms l-1, indicating partial adsorption of the non-degraded (CH2Cl)2 at the end of the reactor by the virgin carbon. Thus, the modification of the adsorption process by inoculation and maintenance of bacteria with special degradation capabilities resulted in a lower consumption of GAC and thus led to an extended service life of the GAC columns.