Remediation of sulfur-containing pollutants with hydrocarbon-utilizing bacteria

Methods and apparatus are disclosed for remediating sulfur-containing pollutants with a hydrocarbon that is used to stimulate the growth of hydrocarbon-utilizing bacteria. The hydrocarbon is preferably an alkane such as butane. The sulfur-containing pollutant may comprise sulfate, sulfite, sulfide, disulfides, mercaptans, alkanesulfonates, dialkyl sulfides, thiosulfate, thiofurans, thiocyanates, isothiocyanates, thioureas, thiols, thiophenols, thioethers, thiophene, tetrathionate, dithionite, dialkyl disulfides, sulfones, sulfoxides, sulfolanes, sulfonic acid, dimethylsulfoniopropionate, sulfonic esters, hydrogen sulfide, sulfate esters, sulfur dioxide and any other sour gases, elemental sulfur and any other sulfur-containing material considered to be a contaminant or pollutant.

FIELD OF THE INVENTION

The present invention relates to the remediation of sulfur-containing pollutants, and more particularly relates to a method and apparatus for bioremediation of sulfur-containing pollutants with hydrocarbon-utilizing bacteria.

BACKGROUND OF THE INVENTION

The presence of sulfur-containing pollutants in effluent or wastewater solutions and gaseous emissions creates disposal problems for many industries. For example, problems with sulfate, sulfite and thiosulfate range from sewers to the eutrophication of water bodies, silting and acidification. One type of effluent in which sulfur-containing pollutants such as sulfite are present is the washwater from flue gas treatment plants. The flue gases from power stations, waste incinerators and the like create severe pollution and environmental damage due to the presence of sulfur dioxide and the associated low pH. Many industries, such as printing, mining, paper, rubber, leather and petrochemical industries produce effluent waters with high sulfur-containing pollutant concentrations.

Conventional biological treatment of sulfate, sulfite and other sulfur compounds, including effluents from gas desulfurization plants, involves reduction in an anaerobic step to produce sulfide, which in turn can be biologically oxidized to elemental sulfur. When the effluent contains little organic matter, electron donors must be added in order to provide sufficient reduction equivalents for the sulfate-reducing bacteria. Electron donors include alcohols such as methanol and ethanol, carbohydrates such as glucose and other saccharides, organic acids such as acetic, propionic, butyric and lactic acid, hydrogen and carbon monoxide.

The bioremediation of various pollutants using butane-utilizing bacteria is disclosed in U.S. Pat. Nos. 5,888,396, 6,051,130, 6,110,372, 6,156,203, 6,210,579, 6,244,346 and 6,245,235, which are incorporated herein by reference.

SUMMARY OF THE INVENTION

In accordance with the present invention, hydrocarbons are used to remediate sulfur-containing pollutants, such as solutions containing sulfur compounds. The hydrocarbons are introduced into the solution to stimulate the growth of hydrocarbon-utilizing bacteria, which remediate the sulfur-containing pollutant, e.g., by reducing sulfite and sulfate to sulfide under anaerobic conditions, then oxidizing the sulfide to elemental sulfur under aerobic conditions.

Hydrocarbons are used in accordance with the present invention to stimulate the growth of hydrocarbon-utilizing bacteria. The hydrocarbon may comprise an alkane such as butane, or may comprise other types of hydrocarbons. In one embodiment, the hydrocarbon acts as a water-soluble electron acceptor. Improved reduction of sulfur-containing pollutants can be achieved by stimulating a variety of organisms capable of reducing the compounds of interest. Rather than relying on the reducing capabilities of a single bacterial isolate, competition may be shifted toward a wide variety of organisms including bacteria, protozoa, algae, fungi and other microorganisms if a highly available or soluble hydrocarbon food substrate is available during a growth phase of the organisms. The addition or presence of a soluble hydrocarbon source such as butane affects the bacterial diversity in an ecosystem, thereby increasing the ability of an ecosystem to reduce targeted sulfur-containing pollutants.

In one embodiment of the invention, a hydrocarbon such as butane is used to drive a treatment process anaerobic thereby encouraging the growth of anaerobic microorganisms capable of reducing sulfur-containing compounds. Under anaerobic conditions, sulfate and elemental sulfur may serve as electron acceptors while the hydrocarbon substrate is oxidized. The anaerobic processes may include desulfurization, sulfur respiration or dissimilatory sulfate reduction.

An aspect of the present invention is to provide a method of remediating a sulfur-containing pollutant. The method comprises introducing a hydrocarbon to the sulfur-containing pollutant to stimulate growth of hydrocarbon-utilizing bacteria.

Another aspect of the present invention is to provide a system for remediating a sulfur-containing pollutant. The system includes means for treating the sulfur-containing pollutant with hydrocarbon-utilizing bacteria in the presence of a hydrocarbon.

A further aspect of the present invention is to provide a system for remediating a sulfur-containing pollutant. The system includes a source of hydrocarbon and a hydrocarbon injection system in communication with the hydrocarbon source and the sulfur-containing pollutant. The system may further include means for collecting the treated sulfur-containing pollutants.

DETAILED DESCRIPTION

In accordance with the present invention, aerobic and/or anaerobic hydrocarbon-utilizing bacteria are used to treat sulfur-containing pollutants such as solutions containing sulfur compounds. As used herein, the term “sulfur-containing pollutant” includes sulfate, sulfite, sulfide, disulfides, mercaptans, alkanesulfonates, dialkyl sulfides, thiosulfate, thiofurans, thiocyanates, isothiocyanates, thioureas, thiols, thiophenols, thioethers, thiophene, tetrathionate, dithionite, dialkyl disulfides, sulfones, sulfoxides, sulfolanes, sulfonic acid, dimethylsulfoniopropionate, sulfonic esters, hydrogen sulfide, carbon disulfide, sulfate esters, sulfur dioxide and other sour gases, elemental sulfur and any other sulfur-containing material considered to be a contaminant or pollutant. The sulfur-containing pollutant may be present in liquids, solids or gases. For example, the pollutant may be present in an aqueous solution such as groundwater, surface water, wastewater or the like. The sulfur-containing pollutant may also be present in soil and other industrial effluents and gaseous emissions.

In one embodiment, the sulfur-containing pollutant may comprise a sulfur compound that is converted to another sulfur compound during the treatment process. Alternatively, the sulfur-containing pollutant may be converted to elemental sulfur during the treatment process. In another embodiment, the sulfur-containing pollutant may comprise elemental sulfur that is separated during the treatment process by precipitation, sedimentation, oxidation or the like.

In accordance with the present invention, at least one hydrocarbon is introduced to the sulfur-containing pollutant to stimulate the growth of hydrocarbon-utilizing bacteria. The hydrocarbon may comprise one or more alkanes, alkenes, alkynes, poly(alkene)s, poly(alkyne)s, aromatic hydrocarbons, aromatic hydrocarbon polymers or aliphatic hydrocarbons. The hydrocarbon is preferably an alkane, such as methane, ethane, propane and/or butane.

Butane is a preferred hydrocarbon due to its high solubility and relatively low molecular weight. Furthermore, butane is non-toxic and may serve as an electron donor under anaerobic conditions. In one embodiment, butane is the most prevalent compound of the hydrocarbon substrate on a weight percent basis, and may comprise at least about 10 weight percent of the hydrocarbon substrate. The other constituents of the hydrocarbon substrate may include other hydrocarbons, e.g., other alkanes. The hydrocarbon substrate may also include inert gases such as nitrogen, helium or argon. In one embodiment, the hydrocarbon substrate comprises at least about 50 weight percent butane. For example, the hydrocarbon substrate may comprise at least about 90 weight percent butane. In a particular embodiment, the hydrocarbon substrate comprises at least about 99 weight percent n-butane. The butane may contain straight (n-butane) and/or branched chained compounds such as iso-butane.

Oxygen may be introduced during some or all of the treatment time, e.g., to provide aerobic conditions. When oxygen is introduced, it may be injected continuously or intermittently to the treatment zone. The oxygen may be supplied in the form of air, substantially pure oxygen or the like.

Treatment processes that may be used in accordance with the present invention include the use of hydrocarbon-utilizing microorganisms which may be found naturally, e.g., in water, groundwater, wastewater, effluent, soil and the like. However, in some applications it may be necessary to inoculate bacteria into the treatment zone. Suitable bacteria may include the following Groups (in addition to fungi, algae, protozoa, rotifers and other aerobic and anaerobic microbial populations found in decaying materials):

In addition, suitable bacteria may include facultative anaerobes and/or microaerophilic anaerobes, which are capable of surviving at low levels of oxygen. These bacteria do not require strict anaerobic conditions such as the obligate anaerobes. Acidophilic, alkaliphilic, anaerobe, anoxygenic, autotrophic, chemolithotrophic, chemoorganotroph, chemotroph, halophilic, methanogenic, neutrophilic, phototroph, saprophytic, thermoacidophilic, and thermophilic bacteria may be used. Hydrocarbon injection and combined hydrocarbon/oxygen injection may encourage the growth of other microorganisms such as fungi, protozoa and algae that may be beneficial to the sulfur-containing pollutant remediation process.

Hydrocarbon addition to an anaerobic system containing alternate electron acceptors such as sulfate may enhance the reduction of sulfur compounds. Anaerobically, hydrocarbons such as butane may serve as electron donors for direct metabolic, sequential metabolic, reductive metabolic or cometabolic processes.

Additionally, the activity of butane-utilizing bacteria (under aerobic conditions) through direct metabolic, sequential metabolic, reductive metabolic or cometabolic processes may enhance the oxidation of sulfide, sulfur and thiosulfate through the production of operative enzymes that function in a similar fashion to sulfide oxidase enzymes, sulfur-oxidizing enzymes, sulfite oxidase, thiosulfate-cleaving enzymes, sulfur transferase enzymes, thiosulfate-oxidizing enzymes or any other sulfur oxidizing enzymes.

FIG. 1is a partially schematic illustration of a sulfur-containing pollutant treatment system10in accordance with an embodiment of the present invention. A sulfur-containing pollutant12is pumped14to an anaerobic chamber16. The sulfur-containing pollutant may comprise, for example, effluent containing sulfur compounds such as sulphate, sulphite and thiosulphate. A hydrocarbon source18such as a butane cylinder communicates with hydrocarbon injectors or diffusers20located in the anaerobic chamber16.

After treatment in the anaerobic chamber16, the material is pumped22to an aerobic chamber24. A hydrocarbon and oxygen source26communicates with injectors or diffusers28in the aerobic chamber24. A collection tray30, or other suitable deposition material such as a membrane lining, is used to deposit treated material. For example, sulfide may be oxidized to elemental sulfur in the aerobic chamber24and deposited as elemental sulfur on the collection tray30. Treated material32, e.g., clean water, exits the aerobic chamber24. The system10may be operated in a continuous mode, or in a batch process.

As shown inFIG. 1, hydrocarbon-utilizing bacteria in the anaerobic reduction chamber16convert or remove sulfur compounds from the solution, e.g., by reducing sulfite and/or sulfate to sulfide. In the second reactor24, hydrocarbon-utilizing bacteria convert the sulfide to elemental sulfur by oxidizing the sulfide under aerobic conditions. The aerobic conditions may be achieved through the addition of air, substantially pure oxygen or any other suitable oxygen source. Alternatively, a hydrocarbon may be used without air or oxygen.

In addition to the system shown inFIG. 1, other types of ex-situ systems may be used in accordance with the present invention. For example, ex-situ bioreactors as disclosed in U.S. Pat. Nos. 5,888,396 and 6,051,130 may be used to treat sulfur-containing pollutants either anaerobically or aerobically. Furthermore, although an ex-situ treatment system is shown inFIG. 1, in-situ techniques, such as those described in U.S. Pat. No. 6,245,235, may be used in accordance with the present invention to remediate sulfur-containing pollutants in surface water, groundwater, soil and the like.