Evaluation of gasoline-denatured ethanol as a carbon source for wastewater denitrification

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Virginia Tech


Methanol (MeOH) is a common external carbon source for wastewater denitrification, because of its low cost and low sludge yield. Ethanol (EtOH), on the other hand, is more expensive, but yields higher denitrification rates. This study introduces gasoline-denatured ethanol (dEtOH), which is now being produced in large quantities for the production of E10 gasoline, as an alternative carbon source. The gasoline added, as the denaturant, is known as "straight-run" gasoline; a lower grade material that contains mostly aliphatic compounds, but lacks the components that normally boost the octane rating, such as benzene, toluene, ethylbenzene and xylenes (BTEX). Herein are presented the results of using dEtOH, EtOH (95.5% ethanol-4.5% water) and MeOH for denitrification in lab-scale, sequencing batch reactors (SBRs). We also focused on the quantification of BTEX present in dEtOH solution and the inhibition potential of these compounds on both nitrification and denitrification. BTEX content in the dEtOH solution had low and consistent concentration. Ethylbenzene and o-xylene were not detected in the reactor. The removal rates of benzene, toluene and m-xylene were 3.1°1.4, 3.4°1.9 and 0.6°0.4 ?g/L·h, respectively. BTEX were not detected in the effluent and did not inhibit nitrification and denitrification. The denaturant did not affect biomass production or the settling properties of the sludge. The yield (COD/NOx-N) and denitrification rates of dEtOH were similar to those of EtOH and higher than those of MeOH. The cost of dEtOH ($0.91//lb NO??-N removed) is slightly higher than that of methanol ($0.74/lb NO??-N removed). Using dEtOH as an external carbon source is, therefore, very promising and utilities will have to decide if it is worth paying a little extra to take advantage of dEtOH's benefits.



methanol, Denitrification, SBRs, BTEX, alternative carbon sources