Abstract:
The present invention relates to a fast acting chemical treatment for preventing the generation of hydrogen sulfide odor by the microbial metabolic activities of sulfate reducing bacteria. Specifically, the invention relates to a method for preventing hydrogen sulfide odor generation in a sulfur species-containing aqueous medium, which includes adding to the aqueous medium an effective amount for the purpose of a sulfide scavenger treatment selected from the group consisting of glyoxal, triazine, n-chlorosuccinimide, and mixtures thereof.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a fast-acting, aqueous phase chemical treatment for preventing the generation of hydrogen sulfide odor in an aqueous medium. 
     BACKGROUND OF THE INVENTION 
     The reactivity between various aldehydes and sulfidic compounds (H 2 S, mercaptans, etc.) has been known in the art for some time. For example, Marks in U.S. Pat. No. 1,991,765 discloses a method of reacting hydrogen sulfide and an aldehyde in an aqueous solution having a pH between 2 and 12 at a temperature between substantially 20° C. and 100° C. After Marks&#39; disclosure in 1935, many patents appeared disclosing the use of aldehydes during acid cleaning of iron sulfide deposits, including U.S. Pat. Nos. 2,606,873; 3,514,410; 3,585,069; 3,669,613; 4,220,550; 4,289,639; and 4,310,435. Consumption of the hydrogen sulfide liberated by acidification of sulfide-containing deposits increased the safety of such operations. Decreased corrosivity of the aldehyde-containing acids is also disclosed in the prior art, sometimes with the addition of ancillary corrosion inhibitors. 
     Menaul in U.S. Pat. No. 2,426,318 discloses a method of inhibiting the corrosive action of natural gas and oil containing soluble sulfides on metals by utilizing an aldehyde and preferably formaldehyde. 
     Roehm in U.S. Pat. No. 3,459,852 discloses a process for deodorizing and reducing the biochemical demand of an aqueous solution which contains at least one compound of hydrogen sulfide and compounds containing the —SH group. Roehm&#39;s process comprises mixing the solution with a sulfide-active alpha, beta unsaturated aldehyde or ketone in an amount sufficient to form sulfur-containing reaction product of the sulfide active aldehyde or ketone. Two such sulfide-active compounds disclosed by Roehm are acrolein and 3-buten-2-one. 
     Formaldehyde, formaldehyde with SO 3   −2 , and acrolein are all commercially used hydrogen sulfide (H 2 S) scavengers. However, formaldehyde produces a solid reaction product and reverts readily to formaldehyde and free H 2 S. Acrolein is more expensive than formaldehyde as well as extremely toxic and dangerous to handle. The use of SO 3   −2  with formaldehyde eliminates the re-release of H 2 S but not solids formation. 
     Despite the prior art approaches to H 2 S scavenging, the provision of a product that can prevent the H 2 S formation microbiologically (rather than removal of H 2 S after it is formed) is highly desirable since it is a more effective way of controlling H 2 S odor and preventing corrosion and related problems. Existing H 2 S prevention methods that include utilizing biocides to kill microbes such as Sulfate Reducing Bacteria (SRBs) are non-selective and will kill other microorganisms, and may be detrimental to the wastewater remediation processes. These concerns are effectively negated by the utilization of the hydrogen sulfide prevention methods of the present invention, often combined with a H 2 S scavenging component chemical. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a fast acting chemical treatment for preventing the generation of hydrogen sulfide odor by the microbial metabolic activities of sulfate reducing bacteria. Specifically, the invention relates to a method for preventing hydrogen sulfide odor generation in a sulfur species-containing aqueous medium, which comprises adding to the aqueous medium an effective amount for the purpose of a sulfide scavenger treatment selected from the group consisting of glyoxal, triazine, n-chlorosuccinimide, and mixtures thereof. 
     The present invention further relates to a method for controlling corrosion in a hydrogen sulfide-containing aqueous medium, which method comprises adding to the aqueous medium an effective amount for the purpose of the treatments noted above. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention utilizes chemicals which can act as redox potential buffers to treat a liquid medium containing microorganisms (such as but not limited to sulfate reducing bacteria, or SRB), which can generate H 2 S odor by converting sulfur species of higher oxidation states to sulfides (S 2− ). By the addition of a small but effective amount of such agents to the liquid (e.g., wastewater, cooling water or water/hydrocarbon emulsion) medium, the sulfide is not microbiologically produced. These agents are introduced in two different ways (alone or in combination) in order to maintain the system redox potential at a level which is less favorable for the microbials to produce H 2 S. They function to: (1) quickly scavenge sulfide species generated so that the system redox potential will not further decrease as a result of S 2−  production; and (2) provide additional redox potential adjustment/maintenance by introducing mild oxidant and/or alternative nutrient sources for the microorganisms in the system. 
     Since H 2 S is a highly corrosive gas, preventing H 2 S from forming in systems such as cooling systems and storage tanks also provides an effective means of corrosion control. Further, in a preferred embodiment, the present invention relates to a method for preventing hydrogen sulfide odor generation in a hydrogen sulfide-containing aqueous medium, which comprises adding to the aqueous medium an effective amount for the purpose of a combination of (a) glyoxal and (b) a metal nitrate compound. Such materials, in a weight ratio of (a) to (b) of from about 1:3 to 1000:1, may be added to the aqueous medium in need of treatment. About 10 ppm of the treatment is preferably added to the aqueous medium, with an amount of treatment of from about 2-6 ppm being particularly preferred. 
     It has been found that the treatment of the present invention is effective and fast-acting in preventing the generation of hydrogen sulfide odor in an aqueous medium with a pH of from about 6.5 to 8. The preferred nitrate compound is magnesium nitrate, or Mg(NO 3 ) 2 . A ratio of components (a) to (b) of about 3:1 is particularly preferred. 
     The invention will be further illustrated by the following examples, which are included as being illustrations of the invention and which should not be construed as limiting the scope thereof. 
     EXAMPLES 
     The test protocol was as follows: 100 mL serum bottles were filled with synthetic nutrient medium, then stoppered, capped, and autoclaved, and allowed to cool to at least 35C. Using a 1 mL syringe with needle, the treatment was added at desired dosages to prepared serum bottles (triplicates of each dosage). No treatment was added for baseline controls. At least 6 baseline serum bottles were used. Using a 1 mL syringe with needle, 0.1 mL of prepared culture was added to each serum bottle. 
     Next, a 10 10  cells/ml concentration of the sulfate reducers was prepared (using autoclaved synthetic nutrient medium) inside an anaerobic chamber. Using a 1 ml syringe with needle, 0.1 ml of the prepared sulfate reducers culture was added to each serum bottle. The bottles were then incubated at the desired temperature. 
     The baseline dissolved sulfide levels were then measured to determine if the samples were ready for efficacy analysis. Using a 30 mL syringe with needle, 30 mL of sample was removed from each serum bottle. About 25 mL of the sample was added to a 30 mL bottle containing 0.125 mL zinc acetate solution, followed by adding 1 mL of 1N NaOH. The sulfide in the fixed sample was then measured. The remaining 5 mL of sample in the syringe was used for pH determination. Separate field studies were also conducted. 
     As shown in Table I below, the treatments of the present invention are non-biocidal in nature, i.e., antimicrobial activities are not irreversibly affected after treatment. Furthermore, the treatments of the present invention do not result in a significant alteration of medium pH at appropriate dosages. Note that at application dosages for all chemical treatments listed, approximately 100% inhibition of H 2 S production was achieved (Glyoxal at 40% actives tested throughout). 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE I 
               
             
             
               
                   
               
               
                 Effect of treatment on medium pH and toxicity 
               
             
          
           
               
                   
                 Scavenger 
                   
                 SRB 
                   
               
               
                   
                 Dosage 
                 Medium pH 
                 Growth 
                 PetriFilm 
               
               
                 Chemical 
                 (ppm 
                 after 
                 after 
                 Count after 
               
               
                 Treatment 
                 active) 
                 Treatment 
                 Treatment 
                 Treatment 
               
               
                   
               
             
          
           
               
                 None 
                 0 
                 6.5 
                 10 8   
                 5.2 × 10 8   
               
               
                 Glyoxal 
                 8 
                 6.5 
                 10 8   
                 8.3 × 10 8   
               
               
                 Glyoxal:Mg(NO 3 ) 2   
                 8 
                 6.5 
                 10 8   
                 6.1 × 10 8   
               
               
                 (3:1 ratio) 
               
               
                 Triazine 
                 8 
                 6.5 
                 10 8   
                 5.5 × 10 8   
               
               
                 Glutaraldehyde 
                 200 
                 7.5 
                 0 
                 0 
               
               
                 (registered biocide) 
               
               
                   
               
             
          
         
       
     
     As further shown in Table II below, the sulfide scavenger activity of the present invention is also effective in corrosion control. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE II 
               
             
             
               
                   
               
               
                 Effect of treatment on corrosion rate reduction 
               
             
          
           
               
                   
                 Treatment Dosage 
                   
                   
               
               
                   
                 Glyoxal:Mg(NO 3 ) 2    
                 Corrosion 
                   
               
               
                   
                 (3:1 ratio) 
                 Rate 
                 Corrosion Rate 
               
               
                 Corrosion Coupon 
                 (ppm) 
                 (mpy) 
                 Reduction (%) 
               
               
                   
               
             
          
           
               
                 Mild Steel 
                 0 
                 54 
                 — 
               
               
                 Pre-treated Mild 
                 0 
                 46 
                 — 
               
               
                 Steel 
               
               
                 Mild Steel 
                 10 
                 3.2 
                 94.1 
               
               
                 Pre-treated Mild 
                 10 
                 3.5 
                 92.4 
               
               
                 Steel 
               
               
                   
               
             
          
         
       
     
     As shown in Table III, the combination of sulfide scavenger (e.g., glyoxal) and nitrate provided enhanced H 2 S odor control at very low dosages. Note that nitrate compounds alone at the same application dosages resulted in no appreciable odor control effect. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE III 
               
             
             
               
                   
               
               
                 Effectiveness of different scavenger blends on H 2 S inhibition 
               
               
                 using real municipal wastewater 
               
             
          
           
               
                   
                   
                 Scavenger 
                   
               
               
                   
                   
                 Dosage 
               
               
                   
                 Chemical 
                 (ppm 
                 Head Space 
               
               
                   
                 Treatment 
                 active) 
                 H 2 S, ppm 
               
               
                   
                   
               
             
          
           
               
                   
                 Field Study 1: 
                   
                   
               
               
                   
                 Glyoxal 
                 0.3 
                 27 
               
               
                   
                   
                 3.8 
                 8 
               
               
                   
                   
                 6.0 
                 7 
               
               
                   
                   
                 8 
                 2 
               
               
                   
                   
                 10 
                 0.5 
               
               
                   
                 Glyoxal:Mg(NO 3 ) 2   
                 0.3 
                 27 
               
               
                   
                 (3:1 ratio) 
                 2.4 
                 2 
               
               
                   
                   
                 3.5 
                 1.5 
               
               
                   
                   
                 4.3 
                 1.5 
               
               
                   
                   
                 5.7 
                 2 
               
               
                   
                 Mg(NO 3 ) 2   
                 10 
                 27 
               
               
                   
                 Field Study 2: 
               
               
                   
                 Glyoxal 
                 0.5 
                 47 
               
               
                   
                   
                 4.0 
                 12 
               
               
                   
                   
                 6.0 
                 0.1 
               
               
                   
                   
                 8.0 
                 0.1 
               
               
                   
                   
                 10.0 
                 5.0* 
               
               
                   
                 Glyoxal:Mg(NO 3 ) 2   
                 0.5 
                 47 
               
               
                   
                 (3:1 ratio) 
                 2.4 
                 0.1 
               
               
                   
                   
                 3.3 
                 0.1 
               
               
                   
                   
                 4.3 
                 0.1 
               
               
                   
                   
                 5.7 
                 0.1 
               
               
                   
                 Mg(NO 3 ) 2   
                 10 
                 47 
               
               
                   
                   
               
               
                   
                 *operational variation with this data point 
               
             
          
         
       
     
     The treatment of the present invention was also found to be stable with time and temperature, ranging from about 3° C. to about 35° C., although the present invention is expected to be effective within a temperature range of from about 0° C. to about 50° C. 
     While the present invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications of the invention will be obvious to those skilled in the art. The appended claims and this invention generally should be construed to cover all such obvious forms and modifications, which are within the true spirit and scope of the present invention.