FORM 2
THE PATENT ACT1970 & THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. TITLE OF THE INVENTION TREATMENT OF BIOGAS TO REMOVE HYDROGEN SULPHIDE GAS
2. APPLICANT
(a) NAME: PRAJ INDUSTRIES LIMITED
(b) NATIONALITY: Indian Company
(c) ADDRESS: 274-275, PRAJ Tower, Bhumkar
Chowk-Hinjewadi Road, Hinjewadi Pune- 411057, INDIA
3. PREAMBLE TO THE DESCRIPTION
The following specification describes the invention and the manner in which
it is to be performed.

4. DESCRIPTION
FIELD OF THE INVENTION
The invention relates to a process for the treatment of biogas to remove hydrogen sulphide using microbes. More particularly to removal of hydrogen sulphide from biogas generated in biomethanation of organic matters in effluents of alcohol distilleries or other industrial processes, wherein in several disadvantages of the conventional process are removed making the invented process more robust and economic.
BACKGROUND
Sugar industry is one of the largest agro based industry, which contributes substantially to the economic development of several communities worldwide. The sugar factories in India produce about 15 million tons of sugar by crushing about 150 million tons of sugarcane. The annual byproduct production is about 7 million tons of press mud and about 8 million tons of molasses. Molasses is utilized in distilleries for the production of ethanol. These distilleries producing alcohol generate billion litres of spent wash annually. The spent wash formed causes disposal and pollution problems. The raw spent wash contains very high values of BOD and COD, beside solids. Therefore, to alleviate the problem of spent wash disposal it is subjected to biomethanation process where significant reduction of BOD >

and COD occurs along with production of biogas as an energy source. Further, biogas is also produced from other organic waste streams like sewage collected in municipal system or organic wastes produced in agro or industrial process industry.
The biogas so produced contains three main gaseous components, methane, carbon dioxide and hydrogen sulphide. Of these, hydrogen sulphide is toxic component as causes damage to the equipment wherein biogas is stored and used. It further leads to formation of sulphur dioxide on burning, that upon dissolution in water creates sulphuric acid. These chemicals reduce the quality and utility of biogas significantly. In the art, H2S is removed from biogas by chemical or biochemical methods. Herein, a new method of biological treatment of biogas to remove H2S from it is disclosed with its advantageous features.
BRIEF DESCRIPTION OF THE DRAWINGS
Particular examples of a method in accordance with this invention will now be described with reference to accompanying drawings: FIGURE 1 is a schematic diagram of the mass flow in the disclosed process. A raw biogas stream is subjected to the treatment by microbes in a novel system; wherein said biogas stream is passed through a column reactor [A] in which gas-liquid mass transfer occurs effectively. This leads to contact between microbes, H2S present in said biogas stream, and said microbes

oxidise H2S, trap sulphur in elemental forms; forming a clean biogas stream. Next, the spent liquid stream is carried to an activation reactor [B], wherein in the presence of oxygen, said sulphur is release in oxidised form and settles at the bottom of reactor; and microbes are regenerated for the next cycle of the process.
DETAILED DESCRIPTION OF THE INVENTION
In one of the embodiment of present invention, as illustrated in FIGURE 1, a biological process for removing hydrogen sulphide from a raw biogas stream comprises two reactors: a packed-bed column reactor [A] and an activation reactor [B] with a liquid stream containing the H2S oxidizing bacteria and said microbes supporting nutrients and growth conditions. Said reactor [A] contains a bed of supporting materials made of plastics or other suitable solid materials of small sizes on which said liquid stream is spread to increase its contact with said biogas stream to achieve maximum mass transfer between said two stream. Said reactor [B] is an activation reactor in which said microbes present in spent liquid stream coming from said reactor [A] are treated with oxygen and nutrients such that they are regenerated and further used in next cycle of the process. Further, in reactor [B] sulphur captured by said microbes settled as solid mass [residual sulphur compounds], which is removed periodically by purging said reactor. The microbes used are of Thiobaclllus spp; more particularly

Thiobacillus novellus sp. These microbes are maintained at about 30° C in about pH 7 medium with required nutrients in said reactor [B] and in said liquid stream.
In another embodiment of present invention, a raw biogas stream [1] fed to a packed-bed column reactor [A] at the bottom. Next said biogas stream is contacted with a bioactive liquid stream [5], which is supplied to said column reactor from the top part. Said bioactive liquid stream comprises hydrogen sulphide oxidizing bacteria that oxidize hydrogen sulphide and capture sulphur to form a clean gas stream [6] and a spent liquid stream [2]. Said spent liquid stream is collected in the activation reactor [B] and said clean gas stream is used for energy generation. Next, said spent liquid stream [2] is regenerated in reactor [B] by activating sulphur-oxidizing bacteria present therein by using air or pure oxygen [3] supply. The sulphur that accumulates in said activation reactor may be recovered in a pure form. These steps cause reduction of sulphur in said raw biogas stream to between 100 to 400 PPM.
In yet another embodiment of present invention, the efficiency of removal of hydrogen sulphide from said biogas stream is about 99% by volume. Herein the material used to fill said packed-bed column reactor is PVC or any effective plastic material. Said biogas stream comprises hydrogen sulphide up to 5 % by volume when passed through said column reactor at a flow rate that achieves the retention time of about 3 hours for said liquid

stream in standard conditions. The pH and temperature of liquid stream is maintained at about 7 and 30° C respectively.
The process for biologically removing hydrogen sulphide from biogas mixture provides several advantages:
1. Choking problem of packed bad reactor is removed.
2. The system comprises of only two reactors.
3. Operational parameter like cleaning of reactors is reduced substantially with increase in the efficiency of process many fold.
4. Disclosed process has efficiency of removal of hydrogen sulphide from any raw biogas stream is about 99% by volume.
Embodiments provided above give wider utility of the invention without any limitations as to the variations that may be appreciated by a person skilled in the art. A non-limiting summary of various embodiments is given in the examples and tables, which demonstrate the advantageous and novel aspects of the process disclosed herein.
EXAMPLE
In one embodiment, about 4 L of bioactive liquid stream was circulated in a packed-bed column reactor achieving a retention time of about 3 h. This stream contained sulphur oxidising bacteria that were maintained in an activation reactor supplied with nutrients and air or oxygen [aerated at

about 1 WM of air] in robust aerobic conditions at about 30° C and pH of about 7. Next, a raw biogas stream having about 55 % by volume of
[
methane about 41 % by volume of C02 and about 4 % by volume of H2S was supplied at the bottom of said column reactor. The flow rate of gas was adjusted to achieve retention time of about 3 h. The clean biogas was recovered from the top of column reactor and analysed. The spent liquid stream was collected in the activation reactor for regeneration. The concentration H2S in said clean gas stream was about 200 PPM. The sulphur that is removed from said biogas accumulated in the activation reactor that may be recovered.
While the invention has been particularly shown and described with reference to embodiments listed in example, it will be appreciated that several of the above disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen and unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims. Although the invention has been described with reference to specific preferred embodiments, it is not intended to be limited thereto, rather those having ordinary skill in the art will recognize that variations and modifications, may be made therein which are within the spirit of the invention and within the scope of the claims.

5. CLAIMS
WE CLAIM:
1. A process for biologically removing hydrogen sulphide from a raw
biogas stream comprising:'
(a) collecting said biogas stream generated in a gas production process; •
(b) contacting said biogas stream with a bioactive liquid stream comprising hydrogen sulphide oxidising bacteria in a packed-bed column reactor forming a clean gas stream and a spent liquid stream;
(c) collecting said spent stream in an activation reactor and contacting it with air or pure oxygen regenerating it to said bioactive liquid stream; and
(d) cleaning periodically said activation reactor to remove residual sulphur compounds formed in it as a result of hydrogen sulphide conversion by said bacteria in said process.

2. The process of claim 1, wherein said raw biogas stream comprises hydrogen sulphide up to 5 % by volume.
3. The process of claim 1, wherein said clean gas stream comprises hydrogen sulphide not more than 250 PPM.
4. The process of claim 1, wherein said hydrogen sulphide oxidising bacteria is Thiobacillus novellus.
5. The process of claim 1 .wherein pH of said bioactive liquid stream is maintained at about 7,
6. The process of claim 1, wherein temperature of said bioactive liquid stream is maintained at about 30o C.

7. The process of claim 1, wherein said first reactor is a packed-bed column reactor.
8. The process of claim 1, wherein efficiency of removal of hydrogen sulphide from said first gas stream is about 99 %.
9. The process of claim 1, wherein said spent liquid stream is converted to said bioactive liquid stream in aerobic conditions in said second rector.
10. An apparatus for biologically removing hydrogen sulphide from a raw biogas stream as per FIGURE 1.