Explain the step wise procedure to obtain methane gas produced from anaerobic digestion of 1 tonne.

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Gases found in landfills include air, ammonia, carbon dioxide, carbon monoxide, hydrogen, hydrogen sulphide, methane, nitrogen and oxygen.
Carbon dioxide and methane are the principal gases produced from the anaerobic decomposition of the organic solid waste components.
The anaerobic conversion of organic compounds is thought to occur in three steps: the first involves the enzyme mediated transformation of higher weight molecular compounds into compounds suitable for use as a source of energy and cell carbon;

The second is associated with the bacterial conversion of compounds resulting from the first step into identifiable lower molecular weight intermediate compounds; And the third step involves the bacterial conversion of intermediate compounds into simpler end products such as carbon dioxide and methane.
The overall anaerobic conversion of organic industrial wastes can be presented with the following equation:

$C_aH_bO_cN_d \rightarrow nC_wH_xO_yN_z +mCH_4 +sCO_2 +rH2_O + (d-nz) NH3$

Where $s= a-nw-m$

$ \ \ \ \ \ \ \ \ \ R= c-ny-2x$

The first term in RHS and in LHS are used to represent on a molar basis such that the composition of the material is present at the start and the end of the process.
If it is assumed that the organic wastes are stabilized completely, the corresponding expression is:

$C_aH_bO_cN_d + (4a-b-2c+3d/4) H_2O \rightarrow (4a+b-2c-3d/8) CH_4 + (4a-b+2c+3d/8) CO_2 + d NH3$
The rate of decomposition in unmanaged landfills, as measured by gas production, reaches a peak within the first 2 years and then slowly tapers off continuing in many cases, for periods up to 25 years or more.
The total volume of gases released during anaerobic decomposition can be estimated in a number of ways.
If all the organic constituents in the wastes are represented with a generalized formula of the form $C_aH_bO_cN_d$ , the total volume of gas can be estimated by using 2 equations, with the assumption of complete conversion to carbon dioxide and methane.

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