Fundamental Research Of Enhanced Biological Activated Carbon Process For Removing MTBE From Potable Water Supply

MTBE (Methyl tert-butyl ether, MTBE) is a small molecule organic compound commonly employed as solvent, chemical raw material and gasoline additive (about 95%of the MTBE production) to reduce combustion knocking and harmful exhaust emissions. MTBE has a high water solubility (41000 mg/L,20℃) and is highly persistent; Its presence in groundwater often exceeds threshold concentrations of ether odor and bad taste (15-40μg/L). Indeed, MTBE has become a hazard to groundwater for producing drinking water in many parts of the world.In this research, the lab prepared highly active MTBE degrading bacteria which was acclimated by MTBE directed domestication from gas station soil, were employed to enhance the performance of an ineffective biological activated carbon (BAC) column. The MTBE concentration of the effluent was well below 20μg/L, the U.S. EPA recommended standard for the drinking water supply. Bacteria samples of the enhanced BAC systems were identified by PCR and DGGE methods to ensure that the active MTBE degraders have been properly maintained in the lab for future studies and applications of the BAC process to remove MTBE from groundwater of the contaminated sites in China.Seven GAC samples (3 bamboo based:bamboo carbon JHBG1 and JHBG2; two coconut based:GCN830 and YK-2; 2 coal based:F300 and Coal,) were tested to obtain their adsorptive capacities for MTBE; the Freundlich isotherm model was successfully employed to represent the equilibrium capacity-concentration data. The activated carbon's capacities for MTBE in pure water were much higher than the same in groundwater and tap water; they were unaffected by the MTBE initial concentration and that their rank was the same as the order of GACs'phenol number. Adsorption treatment for removing MTBE from groundwater containing natural organic matter should employ a GAC that has high values of phenol number and tannic acid number. All activated carbon samples show higher adsorptive capacities for MTBE than TBA. At an equilibrium concentration of 1 mg/L, the adsorptive capacities of GCN830 and YK-2 for MTBE vs. TBA were, respectively,5.31 and 4.33 vs. 0.785 and 0.547mg/g. YK-2 was selected for the BAC study because it had a reasonably high capacity utilization (79.9%, EBCT=5s) in the MCRB breakthrough runs for removing MTBE in groundwater.Cultures of MTBE degrading bacteria were prepared by separation and acclimation in the lab employing the soil/activated sludge samples obtained from Shanghai Coking (sludge, J), a ginkgo tree on ECUST campus (soil, Y), Shanghai Gaoqiao Petrochemical (sludge, G) and a gas station in Riverside, USA (soil, R). After 60-90 days of incubation, the MTBE degraders were confirmed in all except J by the increased turbidity of the inoculated sterile mineral solution medium containing MTBE as the sole-carbon source. For the batch degradation runs starting with MTBE concentration of 4.5 mg/L (CMTBE=4.5 mg/L), the observed batch growth rates were 10.3,6.22, and 6.04μg.MTBE.h-1 for the cultures prepared from R, G and Y, respectively; at CMTBE=28 mg/L, the corresponding rates increased to 57.8, 9.42, and 8.03μg MTBE.h-1. The batch treatment results show that R was better adapted to the increased organic loading condition than G and Y, that MTBE degradation by G or Y was inhibited by the accumulation of degradation intermediate products, and that such inhibition became less notable with increasing biomass. The R culture was about equally active relative to PM-1 pure strain, the best MTBE degraders cited in the literature, with a degradation rate of 24.2 vs.25.5mg MTBE.h-1.g dry cell-1, while it was more stable with 23.4 vs.53.2% reduction in the degradation rate after four cycles of degradation capability test runs.Intermediates such as formic acid, formaldehyde, methanol and TBA, isopropyl alcohol were detected during the degradation process of MTBE by R. TBA concentration gradually increased till the end of the run. The inorganic carbon concentration increased; its increase was much smaller than the reduction in total organic carbon concentration indicating MTBE was only partially mineralized.The poorly performing BAC column was bio-augmented by circulation of the R culture solution for 50 days; after first 95 days of treatment operation, the improved BAC column removed>90%of MTBE in the feed producing a stable effluent of<40μg/L. Bio-augmented BAC particles (seeding BAC) was employed to fill a column with new activated carbon (NYK) on the top to treat a feed of CMTBE=1 mg/L±0.3 mg/L, the new column established the BAC function and stable operation (>99%MTBE removal) in 35 days; the top NYK then became effective source of active MTBE degraders for seeding new BAC columns. The BAC column started with new activated carbon on top of the seeding BAC performed better than that started with the MTBE-saturated GAC and that a longer EBCT and/or mineral supplemented feed shortened the start up period. Mature BAC columns were resistant to changes in the feed composition and/or flow rate.The batch biodegradability study starting with CMTBE=4.5 mg/L produced data which were well correlated by the degradation rates of 1.52 mg MTBE/g biomass/h,0.0665 mg MTBE/g BAC/h and 0.110 mg of MTBE/g GAC/h for the bacteria collected from the mature BAC Col Nas, the seeding BAC and NYK, respectively. Such data have suggested that, in a BAC system, bacteria of the liquid phase were responsible for more MTBE biodegradation than the attached bacteria which degraded some of the adsorbed MTBE making the previously occupied carbon surface available for adsorptive removal of MTBE.DGGE-PCR results show that R flora had at least five kinds of bacteria; one was 98% similar to Bacterium RS58G of the GenBank, while the other four were uncultured bacteria with the source dependent physical and chemical properties.