TREATABILITY OF GROUNDWATER FROM A PLUME CONTAMINATED WITH PAHs AND GASOLINE HYDROCARBONS
Petroleum and derivate fuels contain noticeable concentrations of Monocyclic Aromatic Hydrocarbons (MAHs) and Polycyclic Aromatic Hydrocarbons (PAHs) in their composition. MAHs and PAHs exhibit toxic carcinogenic properties and have been classified as priority pollutants by the U.S. EPA. Among these MAHs is the group forming the mixture known as BTEX, namely Benzene, Toluene, Ethyl Benzene, and Xylene. Methyl tert-Butyl Ether (MTBE) is a fuel oxygenate used extensively to reduce gasoline emissions. These compounds are frequently found in groundwater and surface water, as a consequence of leakages from storage tanks, spills at production wells, refineries, etc. PAHs have been detected as the main constituents in coal tar found contaminating water and soil at former Manufactured Gas Plant sites. Toxic PAHs include Naphthalene, 2-Methylnapthalene, and Acenaphthene. Biodegradation of these contaminants under aerobic conditions has been proven effective for the removal of these contaminants from water in the past. The objective of this study is to demonstrate that real groundwater from Millville, NJ, that has been contaminated with PAHs emanating from a former manufactured gas plant (MGP) and leakage from an oxygenated gasoline storage tank can be treated to obtain final concentrations of 5 ƒÝg/L or lower for each contaminant. Targeted contaminants include: MTBE, tert-Butyl Alcohol (TBA), Benzene, Toluene, Ethyl Benzene, p-Xylene, Naphthalene, 2-Methylnaphthalene, Acenaphthylene, Acenaphthene, and Carbazole. Two porous pot reactors were each inoculated using two different mixed bacterial cultures and then operated for a ten-month period in a continuous mode. The influent consisted of two streams: i) the contaminated groundwater buffered with sodium carbonate and ii) an acidified nutrient solution. The total influent flow was maintained at 9.44 L/day for Reactor 1 and 4.55 L/day for Reactor 2. The hydraulic retention time (HRT) was calculated as 0.64 and 1.32 days, respectively. In all cases more than 99% removal of all the investigated contaminants was achieved. All contaminants were measured at average concentrations below 1 ƒÝg/L in the reactor effluents, except in the cases of toluene (2.67 ƒÝg/L) and MTBE (2.80 ƒÝg/L) in Reactor 1. BTEX compounds exhibited the best removal efficiencies, in both reactors (>99.99%), in spite of their higher concentrations in the influent. MTBE removal rate was measured above 99.8%. This study showed that aerobic biodegradation in an ex-situ pump and treat reactor can be successfully used to remove the targeted PAHs, BTEX, MTBE and TBA in the groundwater. The final concentrations of all contaminants were below the current regulations for drinking water. The performance of both reactors did not present significant differences, although Reactor 2 performed better.
School:University of Cincinnati
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:pahs mtbe btex bioreactors groundwater bioremediation hydrocarbons
Date of Publication:01/01/2005