FIELD OF THE INVENTION :
This invention relates to a process for the enhancement of lignite biomethanation by fungal pretreatment.
BACKGROUND OF THE INVENTION:
Multiple researchers have performed methanogenic incubations with coal as a sole carbon source and without hydrogen addition (e.g., Shumkov et al 1999, Menger et al. 2000, Pfeiffer et al. 2010, Green et al. 2008, Harris et al. 2008, Jones et al. 2008, Kruger et al. 2008, Orem et al. 2010) wherein it was proposed that the biogas yield is also likely to depend on coal maturity. The conversion rates could be potentially improved by the addition of stimulating nutrients, but the ultimate yields might not be significantly improved.
Several authors proposed chemical stimulation of methanogenesis from coal (Pfeiffer et al. 2010, Green et al. 2008, Kruger et al. 2008, Toledo et al. 646 Strapoc et al. Annu. Rev. Earth Planet. Sci. 2011.39:617-65. The tested nutrients additions included ammonia, phosphate, yeast extract, tryptone, milk, agar, trace metals, and vitamins (e.g., Jin et al. 2007, Pfeiffer et al. 2010). However, it was suggested that the addition of carbon sources other than coal may cau^se overestimation of the coal-degrading capability of the consortia.
Nutrient additions typically applied in laboratory studies are similar to
the enrichment media used for the targeted cultivation of specific
microbes (for a compilation of growth media and access to numerous
archaeal and bacterial isolated, see
http: / / www.dsmz.de/microorganisms). In addition to chemical stimulation of microbial conversion of coal to methane, some authors have suggested and experimented with the addition of selected microbial consortia {e.g., Jin et al. 2007). Examples of consortia used

for methanogenic inoculation with coal in laboratory settings include a cultivated consortium indigenous to studied coal (Pfeiffer et al. 2010), a consortium obtained from termite guts (Srivastava 8s Walia 1998, Menger et al. 2008), and a consortium obtained from an abandoned coal mine used as sewage disposal [Appalachian Basin (Volkwein 1995].
Several researchers have proposed subsurface enhancement of microbial methane (Scott et al. 1994, Volkwein 1995, Scott 1999, Menger et al. 2000, Budwill 2003 Faiz et al. 2003, Scott 8B Guyer 2004, Thielemann et al. 2004, Jin et al. 2007). For example, a patent by Menger et al. (2000) suggested digestion of lignite in an underground chamber using termite microflora composed of acid formers and methanogens. Jin et al (2007) suggested fracturing the reservoir for better simultaneous nutrient delivery and enhanced surface area of coal. The only description of a multiwall field trial was presented in a patent application by Pfeiffer et al. (2010) (htt'p: / /www.lucatechnologies.com). In situ microbially enhanced CBM stimulation perfonned in the Powder River Basin showed an increase in methane production after nutrient treatment (e.g)., phosphate) compared with the expected production decline curve. The addition of microbes preconcentrated from the same formations seemed to stimulate gas production from CBM wells as well.
It may be emphasized that the prior art does not disclose any fungal mediated pretreatment as a strategy for stimulation and enhancement of biomethane generation from coal and the major focus of the prior art is on coal bed methane production.
Therefore, there is a need in the art to provide a process for lignite biomethanation to improve the fields of the biogas produced.

OBJECTS OF THE INVENTION :
It is therefore an object of this invention to propose a process for the enhancement of lignite biomethanation by fungal pretreatment.
It is a further object of this invention to propose a process for the enhancement of lignite biomethanation, which significantly increases the yields of biogas produced.
Another object of this invention is to propose a process for the enhancement of lignite biomethanation, which uses less time for the production of biogas.
Yet another object of this invention is to propose a process for the enhancement of lignite biomethanation which is more efficient and cost effective.
These and other objects and advantages of the invention will be apparent from the ensuing description.
DETAILED DESCRIPTION OF THE INVENTION:
Thus, according to this invention is provided a process for the enhancement of lignite biomethanation by fungal pretreatment.
In accordance with this invention, is disclosed a process wherein a newly isolated fungal strain is used for depolymerization of untreated Indian lignite as a pretreatment step followed by anaerobic digestion for methane production. The fungal strain belongs to Pleurotus genus. Pretreatment strategy applied here is a novel application for biogas generation. This is a two stage coal bioprocessing where a hyperactive laccase producing Pleurotus strain has been applied for pretreatment of lignite. The media used for fungal pretreatment is unique and newly

designed cost effective minimal media where minimum carbon and nitrogen source were used. The pretreatment is effected over a period of 16 to 28 days at 30±2°C. Media used for fungal pretreatment comprised of constituents as given below:
NaNOs ; - 0.5-2.5 g/L
KH2PO4 -0.5-1.5 g/L
MgS04 -0.1-1 g/L
KC1 -0.1-1 g/L
Sucrose - 0.5-5 % (w/v)
Ammonium bicarbonate - 0.25-5 % (w/v)
Triton - X - 0.001-0.05 % (w/v)
Triethanolamine - 0.01 -0.5 % (w/ v)
Copper sulphate - 0.001-0.1 mM
The pre treated lignite was further subjected for biomethane generation. The pretreated lignite sample when subjected to biomethanation at 35 to 39°C with the microbial consortia added as inoculum in a proportion of 20 to 50% % (w/v) of total solids is to 2 to 8% (w/v) of the inoculum, demonstrated an enhancement in the biogas yield (i.e., 8-9.6 L/kg) by more than one and half fold of the yield from raw lignite (i.e.5-6.3 L/kg) and initiation of biogas production occurred at a reduced incubation period (within 11-14 days) as compared to 30 days for untreated lignite.
By the developed strategy the overall methane content of the biogas produced was improved in comparison to that produced from untreated lignite. Untreated lignite biomethnation yielded 5-6.3 L/kg of lignite with methane content of 35-41%. So pretreatment of lignite with gleurotus sp followed by biomethanation was adopted to increase the process efficiency. The highlight of this process is the tremendous reduction in the initial lag period for the biomethane generation in

comparison to the untreated lignite. By pre treatment strategy the lignite undergo structural modification due to depolymerization mechanism of fungal strain. Pretreated lignite showed enhanced biogas yield of 8-9.6 L/kg with methane content of 45-47% which was one and half fold higher than the untreated lignite. The overall incubation period of untreated lignite biomethnation was about 100-120 days which has been drastically reduced to 75-90 days. Initial lag period with pretreated lignite was significantly reduced to 11-14 days from 28-30 days.
For pretreatment strategy chunks of untreated raw Indian lignite was taken with solid concentration of (20-50% TS) and moistened with the media designed for fungal depolymerization.
A prepared inoculum of Pleurotus sp was added to the lignite and was incubated at 28 to 32°C for period of 16-28 days. After pretreatment period, the lignite was subjected to anaerobic digestion with addition of media and anaerobic microbial consortia as inoculum. Optimization techniques have been employed for the most influential parameters such as substrate concentration (20-50% TS, w/v), inoculum concentration (2-8%, v/v) and C:N (30:1 to 50:1) have been chosen for the maximum lignite degradation prior to anaerobic digestion which makes the anaerobic process more efficient than the non-pretreated lignite.
The invention will now be explained in greater details with the help of the following non-limiting examples.
EXAMPLES:
Chunks of taw Indian lignite with a solid concentration of 40% TS was taken and moistened with the media consisting of the following constituents:

NaNOs -1.5 g/L
KH2PO4 - 1 g/L
MgS04 - 0.6 g/L
KC1 - 0.5 g/L
Sucrose - 4.7 g/L
Ammonium bicarbonate - 4.5 (w/v)
Triton-X- 0.025 (w/v)
Triethanolamine - 0.25 (w/v)
Copper sulphate - 0.06 mM
A prepared inoculum of Pheurotus sp at a concentration of 5% v/v of inoculumn for 35% TS w/v of lignite, was added to the lignite and incubated at 30°C for about 22 days.
The pretreated lignite was subjected to biomethanation at a temperature of 37°C for about 80 days. The biomethane generated was about 9L/kg.
The biomethane yield after pretreatment was increased significantly as compared to untreated lignite because the fungal strain which is hyperactive in nature found to depolymerize the complex structure in lignite which eventually ease the anaerobic digestion process. This not only improve the process by increased biogas yield but also shortening of the overall incubation period for biogas production.

WE CLAIM:
1. A process for the biomethanation of lignite comprising the steps of subjecting lignite in a medium to the step of pretreatment with a fungal strain belonging to Pleurotus sp. followed by-anaerobic digestion of the pretreated lignite to obtain methane.
2. The process as claim in claim 1, wherein said medium comprises
NaNOs - 0.5-2.5 g/L
KH2PO4 -0.5-1.5 g/L
MgS04 -0.1-1 g/L
KC1 -0.1-1 g/L
Sucrose - 0.5-5 % (w/v)
Ammonium bicarbonate - 0.25-5 % (w/v)
Triton - X - 0.001-0.05 % (w/v)
Triethanolamine - 0.01-0.5 % (w/v)
Copper sulphate - 0.001-0.1 mM
3. The process as claimed in claim 1, wherein the total solid in the pretreatment step is 20 to 50% w/v.
4. The process as claimed in claim 1, wherein the fungal strain is added in a proportion of 2-8% v/v.
5. The process as claimed in claim 1, wherein the fungal pretreatment is effected for 16 to 28 days.
6. The process as claimed in claim 1, wherein the step of pretreatment is carried out at a temperature in the range of 28 to 32°C.

7. The process as claimed in claim 1, whereby the incubation time for methane generation has also been reduced after pretreatment process.
8. The process as claimed in claim 1, wherein the total incubation period of the process is 75 to 95 days.
9. The process as claimed in claim 1, wherein the anerobic digestion yields 8-9.6 L/kg with a methane content of 45 to 47%.

This invention relates to a process for the biomethanation of lignite comprising the steps of subjecting lignite in a medium to the step of pretreatment with a fungal strain belonging to Pleurotus sp. followed by anaerobic digestion of the pretreated lignite to obtain methane.