Claims:1. A composition for reducing the odor of sewage; said composition comprising:
i. a nitrate salt of at least one transition metal; and
ii. a microbial mixture comprising:
• at least one first microorganism selected from the Thiobacillus strain;
• at least one second microorganism selected from the Bacillus strain; and
• at least one Yeast.
2. The composition as claimed in claim 1, wherein said at least one transition metal is selected from the group consisting of copper, silver and gold.
3. The composition as claimed in claim 1, wherein said at least one transition metal is copper.
4. The composition as claimed in claim 1, wherein said first microorganism is at least one selected from the group consisting of Thiobacillus thioparus, Thiobacillus novellus and Thiobacillus intermedius.
5. The composition as claimed in claim 1, wherein said second microorganism is at least one selected from the group consisting of Bacillus amyloliquefaciens and Bacillus subtilis.
6. The composition as claimed in claim 1, wherein said Yeast is at least one selected from the group consisting of Saccharomyces cerevisiae, Zymomonas mobilis and Schizosaccharomyces pombe.
7. The composition as claimed in claim 1, wherein the ratio of said microbial mixture to said nitrate salt is 1:1.
8. The composition as claimed in claim 1, wherein the proportion of said first microorganism, said second microorganism and said Yeast is 1:1:2.
9. A process for reducing the odor of sewage, said process comprising the following steps:
a. separating the coarser material having size greater than 12 mm, from said sewage to produce sewage free of coarser material;
b. passing said sewage free of coarser material through at least one oil and/or grease trap to produce oil and/or grease free sewage;
c. treating said oil and/or grease free sewage with a composition comprising;
i. a nitrate salt of at least one transition metal; and
ii. a microbial mixture comprising;
• at least one first microorganism selected from the Thiobacillus strain;
• at least one second microorganism selected from the Bacillus strain; and
• at least one Yeast;
to obtain a mixture; and
d. equalizing the mixture obtained in step (c), for a time period ranging from 6 hrs to 10 hrs to obtain sewage with reduced odor.
10. The process as claimed in claim 9, wherein said process further comprises a step of passing oxygen through said sewage with reduced odor. , Description:FIELD
The present disclosure relates to a composition and process for reducing the odor of sewage.
DEFINITIONS
As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicate otherwise.
Threshold odor number (T.O.N): The ratio by which the odor-bearing sample has to be diluted with odor-free water for the odor to be just detectable by the odor test.
BACKGROUND
Malodors emanating from sewage in the waste water treatment plants have been a major problem affecting the quality of air in waste water treatment plants. Odor causing compounds can be generated by reaction of various chemical compounds present in the sewage to produce odorous gases mainly, H2S, ammonia and their derivatives, that cause malodor in the surroundings. Various odor causing compounds can also be generated due to microbial reactions mainly in the equalization tank of sewage collection. An ideal means for odor control needs to treat not only hydrogen sulfide, but also organic sulfides, mercaptans and ammonia in order to reduce the odor.
Various physical approaches have been adopted for controlling odors in a sewage treatment plant. Physical means, like enclosures, that do not let odor causing gases to spread out in the surrounding environment require constructions that are not economically feasible and lack efficacy, as in the space within the enclosures, maintenance staff/personnel experience nauseating effects of the malodor. Approaches like ventilation means, to dilute the malodorous gases with air from the outside, or masking the malodor by the use of odor-masking and counter-active agents have been used but these approaches fall short of the fact that they are not focused on elimination/neutralization of the cause of odor. Chemical and biological processes have been widely resorted to for reducing odors.
US4911843 suggests a process for removing dissolved hydrogen sulfide from waste water by adding a nitrate salt which provides a source of oxygen for the naturally occurring bacteria present in the sewage waste. The naturally occurring bacteria utilize the dissolved hydrogen sulfide in their metabolism. But this patent does not mention the removal of ammonia and mercaptans present in the sewage waste water which also produce malodor.
US 5405531 suggests a method of reducing the amount of hydrogen sulfide present in an aqueous system comprising water and hydrogen sulfide and preventing the formation of hydrogen sulfide by adding nitrate and nitrite compounds, which yield nitrate ions, thereby enhancing the growth of denitrifying bacteria, wherein the denitrifying bacteria are present in the aqueous system prior to the addition of nitrate compound or added concurrently with or after the addition of the nitrate compound. The process further comprises addition of a molybdate or molybdate yielding material. This patent mentions only the removal of H2S but does not mention the removal of mercaptans and ammonia.
US 5984993 suggests a method to control the odor caused by volatile sulfides emanating from organic waste produced by metabolic processes, including human and animal waste, as well as industrial wastes, effluents, sewage, and the like, by contacting the waste product or their surroundings airspace with a composition which is in the aqueous form and comprises a chlorite salt of an alkali or alkaline earth metal and nitrate salt selected from sodium nitrate, calcium nitrate, and potassium nitrate. But the use of chlorite makes the process economically less efficient. Further, this patent does not mention the removal of mercaptans and ammonia.
There is, therefore, felt a need for an efficient and economically feasible process for reducing the odor emanating from sewage.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
An object of the present disclosure is to provide a composition for reducing the odor emanating from sewage.
Another object of the present disclosure is to provide a process for reducing the odor emanating from sewage.
Still another object of the present disclosure is to provide a process for reducing malodor in a sewage treatment plant.
Yet another object of the present disclosure is to provide an efficient and economically feasible process for reducing the odor from sewage.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure provides a composition to reduce odor from sewage. The composition of the present disclosure comprises:
i. a nitrate salt of at least one transition metal; and
ii. a microbial mixture comprising;
• at least one first microorganism selected from the Thiobacillus strain;
• at least one second microorganism selected from the Bacillus strain; and
• at least one Yeast.
Further, the present disclosure discloses a process for reducing the odor of sewage by contacting the sewage with said composition of the present disclosure. The process for reducing the odor of sewage comprises the following steps:
a. separating the coarser material having size greater than 12 mm from said sewage to produce sewage free of coarser material;
b. passing sewage free of coarser material through at least one oil and/or grease trap to produce oil and/or grease free sewage;
c. treating the oil and/or grease free sewage with a composition comprising;
i. a nitrate salt of at least one transition metal; and
ii. a microbial mixture comprising;
• at least one first microorganism selected from the Thiobacillus strain;
• at least one second microorganism selected from the Bacillus strain; and
• at least one Yeast.
to obtain a mixture;
d. equalizing the mixture obtained in step (c), for a time period ranging from 6 to 10 hours to obtain sewage with reduced odor.
The transition metal of the composition of the present disclosure can be at least one selected from the group consisting of copper, silver and gold, preferably copper. The first microorganism of the microbial mixture can be at least one selected from the group consisting of Thiobacillus thioparus, Thiobacillus novellus and Thiobacillus intermedius, and the second microorganism of the microbial mixture can be at least one selected from the group consisting of Bacillus amyloliquefaciens and Bacillus subtilis. The Yeast can be at least one selected from the group consisting of Saccharomyces cerevisiae, Zymomonas mobilis and Schizosaccharomyces pombe. The ratio of said first microorganism, second microorganism and Yeast in the microbial mixture can be 1:1:2. The ratio of the microbial mixture to the nitrate salt in the composition of the present disclosure can be 1:1.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
The present disclosure will now be described with the help of the accompanying drawing, in which:
Figure 1 illustrates odor response of sewage before the application of the composition of the present disclosure to the sewage: and
Figure 2 illustrates odor response of sewage after the application of the composition of the present disclosure to the sewage.
DETAILED DESCRIPTION
The disclosure will now be described with reference to the accompanying embodiments which do not limit the scope and ambit of the disclosure. The description provided is purely by way of experiment(s) and illustration(s).
There are several processes known in the art that reduce the odor emanating from sewage but none have been proven successful in removing the odor of sewage quickly, efficiently and economically for various reasons. Some of these methods have either attempted to remove the odor causing Hydrogen sulfide or to remove the BOD (biological oxygen demand) elements present in the sewage, which in many cases, resulted in a less efficient process, poor treatment, and the like. Some processes used chlorite for removing the odor of sewage. However, chlorite destroys the helpful bacteria necessary for the operation of the sewage treatment process, and also results in higher cost of the treatment process. Thus, there has been a lack of practical and satisfactory method for reducing the odor of sewage.
In one aspect of the present disclosure, there is disclosed a composition for reducing the odor of sewage.
The composition of the present disclosure comprises:
i. a nitrate salt of at least one transition metal; and
ii. a microbial mixture comprising;
• at least one first microorganism selected from the Thiobacillus strain;
• at least one second microorganism selected from the Bacillus strain; and
• at least one Yeast.
In accordance with the present disclosure, the transition metal can be at least one transition metal selected from the group consisting of copper, silver and gold.
In accordance with one exemplary embodiment of the present disclosure, the transition metal is copper.
In accordance with the present disclosure, the first microorganism can be at least one selected from the group consisting of Thiobacillus thioparus, Thiobacillus novellus and Thiobacillus intermedius.
In accordance with the present disclosure, the second microorganism can be at least one selected from the group consisting of Bacillus amyloliquefaciens and Bacillus subtilis.
In accordance with the present disclosure, the Yeast can be at least one selected from the group consisting of Saccharomyces cerevisiae, Zymomonas mobilis and Schizosaccharomyces pombe.
In accordance with the present disclosure, the composition of the present disclosure comprises a microbial mixture and a nitrate salt of at least one transition metal, typically in a ratio of 1:1.
The microbial mixture of the present disclosure comprises at least one first microorganism selected from the Thiobacillus strain, at least one second microorganism selected from the Bacillus strain and at least one Yeast, typically in a proportion of 1:1:2.
In accordance with one embodiment of the present disclosure, the microbial mixture comprising at least one first microorganism, at least one second microorganism and at least one Yeast, is taken with the water typically in a proportion of 1:1:2:4.
The composition of the present disclosure reduces the odor of sewage and also produces an ester that gives pleasant smell.
In another aspect of the present disclosure, there is disclosed a process for reducing the odor of sewage containing at least one of inorganic sulfide, mercaptan, ammonia, BOD elements and volatile organic carbons (VOCs). The process of reducing the odor of sewage involves the following steps:
Firstly, the coarser materials having sizes greater than 12 mm, present in the sewage are removed.
After removing the coarser material, the coarser material free sewage is passed through at least one oil and/or grease trap to produce oil and/or grease free sewage.
The oil and/or grease free sewage is then treated with the composition of the present disclosure comprising a nitrate salt of at least one transition metal and a microbial mixture of first microorganism, second microorganism and at least one Yeast to obtain a mixture.
The mixture thus obtained after treating the oil and/or grease free sewage with the composition of the present disclosure, is equalized in an equalization tank, where the following reactions take place:
a) the nitrate salt of at least one transition metal reacts with the inorganic sulfide present in the sewage to form sulfides of the transition metal and nitrate radicals;
b) the sulfides of transition metal obtained in reaction (a), are oxidized in the presence of the first microorganism to produce sulfate anions and cations of transition metal;
c) the mercaptans present in the sewage react with the cations obtained in reaction (b) to produce mercaptides of transition metal;
d) the second microorganism converts a portion of the BOD elements present in the sewage to form at least one VFAs (volatile fatty acids) and also produces ammonia formation-inhibiting Barnase enzyme along with residual BOD elements;
e) Yeast ferments the residual BOD elements and produces at least one alcohol; and
f) the alcohol of reaction (e) reacts with VFAs of reaction (d) to produce at least one ester and sewage with reduced odor.
The treated sewage thus produced, has a reduced odor and the ester formed in reaction (f), gives a pleasant smell.
In accordance with the present disclosure, the VFAs produced in reaction (d) comprise acetic acid, butyric acid and propionic acid.
Reactions (d) and (e) of the process of the present disclosure, convert 10% to 20% of the BOD elements present in the sewage, the remaining 90% to 80% of the BOD elements can be reduced by a secondary treatment.
In secondary treatment, aerobic biological treatment process is used to reduce the remaining 90% to 80% of the BOD elements. The treated sewage, containing the remaining BOD elements, is passed to a secondary aerobic reactor, where, 1.2 to 1.6 kg O2/kg BOD is passed into treated sewage containing the remaining 90% to 80% of the BOD elements. In the secondary aerobic reactor, the microorganisms utilize the oxygen to convert the remaining 90% to 80% of the BOD to CO2, H2O and reduce the remaining BOD elements.
The different BOD elements present in the sewage comprises, but are not limited to, simple and complex sugars, lipids and proteins, in an amount in the range of 100 ppm to 600 ppm.
The treated sewage produced from the process of the present disclosure, typically has 97.5% reduction in inorganic sulfides, 70.6% reduction in ammonia, 99% reduction in mercaptans and 70.3% reduction in VOCs.
In an exemplary embodiment of the present disclosure, copper nitrate is used as the transition metal salt in the composition. The following reactions take place when the sewage is contacted with the composition comprising copper nitrate as transition metal salt:
a. copper nitrate salt reacts with hydrogen sulfide to form sulfide of copper metal and nitrate radicals as per the following reaction;
Cu(NO3)2 + H2S CuS + 2H++ 2NO3 -
b. the sulfide of copper metal obtained in reaction (a), uses nitrate radicals obtained in reaction (a) as an oxygen source and oxidizes in the presence of first microorganism to produce sulfate anions and cations of copper metal as per the following reaction;
CuS + 2O2 Cu2+ + SO42 -
c. the mercaptans present in the sewage, react with the cation obtained in step (b) and produce mercaptide of copper metal as per the following reaction;
Cu2+ + Mercaptan Copper mercaptide
d. 5% to 10% of BOD elements present in the sewage are converted by the second microorganism to VFAs including acetic acid, butyric acid and propionic acid and also produced ammonia formation-inhibiting Barnase enzyme along with residual BOD elements; and
e. 5% to 10% of the residual BOD elements are fermented by third microorganism and produce an alcohol;
f. the alcohol of step (e) reacts with VFAs of step (d) and produces an ester and sewage with reduced odor.
In accordance with the present disclosure, the alcohol produced in reaction (e), is at least one alcohol selected from the group consisting of ethyl alcohol, propyl alcohol, methyl alcohol and benzyl alcohol.
The present disclosure is further described in light of the following experiment which is set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. The following experiment can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial scale.
Experiment:
The sewage was taken from the Thermax Environment House, Bhosari, Pune. The sewage was at a temperature of 28°C, pressure of 1015 millibars and pH of 7.40. The sewage, taken from the Thermax Environment House, contained hydrogen sulfide, mercaptans, volatile organic carbons, ammonia and 287 ppm BOD elements.
The composition used for the treatment of sewage contained a copper nitrate salt and a microbial mixture of Thiobacillus novellus, Bacillus amyliliquefaciens and Saccharomyces cerevisiae as first microorganism, second microorganism and a Yeast. The proportion of Thiobacillus novellus, Bacillus amyliliquefaciens and Saccharomyces cerevisiae in the microbial mixture is 1:1:2. The microbial mixture was taken together with water in a proportion of 1:1:2:4 and mixed at 300 rpm to obtain a solution. Copper nitrate was added to this solution in a ratio of 1:1 followed by mixing at 800 rpm for 30 min to obtain the composition used for the treatment of sewage. The composition was used in an amount of 5 ml, for the treatment 1000 L of the sewage.
In the first step, the sewage was passed through a bar screen to remove coarser material having sizes greater than 12 mm, present in the sewage. In the next step, after passing through the bar screen, the coarser material free sewage was passed through an oil and grease trap to remove oils and greases present in the sewage and produced oil and grease free sewage. The oil and/or grease free sewage was then contacted with the composition to obtain a mixture. The mixture thus obtained was equalized in an equalization tank for 6 to 10 hours. In the equalization tank, copper nitrate salt reacted with hydrogen sulfide to produce sulfide of copper metal and nitrate radicals. The sulfide of copper metal thus produced, used nitrate radicals as an oxygen source and oxidized in the presence of Thiobacillus novellus to produce sulfate anions and cations of copper metal. The mercaptans present in the sewage reacted with the cation of copper metal and produced mercaptide of copper metal. In the equalization tank, 10% of the BOD elements present in the sewage, were converted by Bacillus amyliliquefaciens to VFA and also produced ammonia formation-inhibiting Barnase enzyme along with residual BOD elements. The amount of VFAs produced was 72.3 ppm. 10% of the residual BOD elements was fermented by Saccharomyces cerevisiae and produced an alcohol. The amount of alcohol produced was 28.3 ppm. The alcohol thus produced reacted with VFA and produced an ester and sewage with reduced odor. The amount of ester thus produced, was 12.7 ppm.
The remaining BOD elements were removed by the secondary treatment. For secondary treatment, aerobic biological treatment process was used to reduce the remaining BOD elements. The treated sewage, containing the remaining BOD elements, was passed into a secondary aerobic reactor. 750 gm/hr of oxygen was supplied to the secondary aerobic reactor containing treated sewage with remaining BOD elements. In the secondary aerobic reactor, the microorganisms utilized the oxygen to reduce remaining BOD and produce CO2.
The treated sewage thus produced had 97.5% reduction in inorganic sulfides, 70.6% reduction in ammonia, 99% reduction in mercaptans and 70.3% reduction in VOCs.
Further, the treated sewage was analyzed by 2150 B Threshold Odor Test to check Threshold Odor Number (TON) and Treatability of the treated sewage.
The total volume of sewage and odor-free water used in each test was 200 ml. Initially, 199.9 ml of odor-free water was first put into the flask and then 0.1 ml of sewage was added to the flask to make a total volume of 200 ml. A team of five observers who did not know which dilutions are odorous and which are blanks, were asked to smell each flask in sequence, beginning with the least concentrated sample and comparing with a known flask of odor-free water, until the odor was detected with utmost certainty. The threshold of a group can be expressed as the geometric mean of the individual thresholds.
The results of the Threshold Odor Test for the sewage before and after the treatment process of the present disclosure, are shown here in Table 1 and Table 2 respectively.

Table 1: Batch Study Analysis of Threshold Odor Number (TON) using 2150 B Threshold Odor Test: Before treatment of the sewage.
Total Volume(ml) Sample Volume of odor free water (ml) Sample Volume of Sewage (ml) Dilution ratio Odor Value Odor response TON (O.U.)
200 199.9 0.1 2000 0 ---- No odor
200 199.8 0.2 1000 0 --- No odor 1414.21
200 199 1 200 0 --- No odor 447.21
200 198 2 100 0 -- No odor 141.42
200 196 4 50 0 - Indifferent 70.71
200 194 6 33 1 + Indifferent 40.82
200 192 8 25 1 ++ Unpleasant 28.87
200 190 10 20 1 +++ Very unpleasant 22.36
200 188 12 17 1 ++++ Strongly Unpleasant 18.26
200 186 14 14 1 +++++ Nauseating 15.43
200 184 16 13 1 +++++ Nauseating 13.36
200 182 18 11 1 +++++ Nauseating 11.79
200 180 20 10 1 +++++ Nauseating 10.54

Table 2. Batch Study Analysis of Threshold Odor Number (TON) using 2150 B Threshold Odor Test: After treatment of the sewage.
Total Volume(ml) Treated water Volume (ml) Dilution ratio Odor Value Odor response TON (O.U.)
200 0.1 2000 0 ---- No odor
200 0.2 1000 0 ---- No odor 1414.21
200 1 200 0 ---- No odor 447.21
200 2 100 0 ---- No odor 141.42
200 4 50 0 ---- No odor 70.71
200 6 33 0 ---- No odor 40.82
200 8 25 0 ---- No odor 28.87
200 10 20 0 ---- No odor 22.36
200 12 17 0 ---- No odor 18.26
200 14 14 0 ---- No odor 15.43
200 16 13 0 ---- No odor 13.36
200 18 11 0 ---- No odor 11.79
200 20 10 0 ---- No odor 10.54
200 200 1 0 --- No odor 1.00

 odor value 1, is for positive detection (odorous sewage) of odor from sewage;
 odor value 0, is for negative detection (odor free sewage) of odor from sewage.
From table 1 it is observed that the sewage has a Threshold Odor Number (TON) of 40.82 OU before treating the sewage with the composition. The sewage, produced after treating with the composition of the present disclosure, has a Threshold Odor Number (TON) of 1.00 OU which is depicted in Table 2. The sewage, thus produced after treating with the composition of the present disclosure, has 97.55% reduction in odor based on the Threshold Odor Number.
Further, the results obtained before and after the treatment of the sewage with the composition of the present disclosure are plotted in Fig. 1 and Fig. 2 respectively. Fig. 1 shows the odor response of sewage before the application of the composition of the present disclosure to the sewage. At 0 dilution ratio, the sewage shows an odor value of 1 which means positive detection of the odor. As the dilution ratio increased to 50, the odor value of the sewage is reduced to zero and remains zero on further increasing the dilution ratio. At 0 dilution ratio, there was not any addition of odor free water to the sewage so the sewage was showing positive odor on odor detection scale. But as the dilution ratio is increased by adding odor free water to the sewage, sewage becomes diluted and shows zero odor on odor detection scale.
Fig. 2 shows the odor response of the sewage after the application of the composition of the present disclosure to the sewage. The treated sewage shows an odor value zero on odor detection scale at zero dilution ratio. This means that the treated sewage shows no odor before the addition of the odor free water to the treated sewage. The sewage, treated with the composition of the present disclosure does not require any addition of odor free water to show an odor value of zero on odor detection scale. The treated sewage continuously shows zero odor as the dilution ratio is increased from zero to 250.
TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of:
- a composition for reducing odor causing elements present in the sewage;
- a composition for reducing malodor present in the sewage treatment plant;
- an efficient and economically feasible process for reducing the odor from sewage.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired objects or results. While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Variations or modifications to the formulation of this invention, within the scope of the invention, may occur to those skilled in the art upon reviewing the disclosure herein. Such variations or modifications are well within the spirit of this invention.
The numerical values given for various physical parameters, dimensions and quantities are only approximate values and it is envisaged that the values higher than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the invention unless there is a statement in the specification to the contrary.
While considerable emphasis has been placed herein on the specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without departing from the principles of the disclosure. These and other changes in the preferred embodiment of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.