1. A single pot process for producing a biodiesel, the process comprising mixing a feedstock with an alcohol and an acidic catalyst in the presence of a water scavenger or water adsorbent for effective esterification of free fatty acid to fatty acid ester, wherein the fatty acid ester is obtained as a mixture of fatty acid ester and triglycerides, adding an alcohol and a basic catalyst into the resultant mixture to trans-esterify the triglycerides to fatty acid ester, wherein the fatty acid ester thus produced is capable of being used as biodiesel.2. The process according to claim 1, wherein the feedstock includes free fatty acid concentration of more than 1%.3. The process according to claim 1, wherein the feedstock is non-edible vegetable oil sources.4. The process according to claim 3, wherein the non-edible vegetable oil sources are plant species selected from the group comprising Jatropha, Pongamia, Madhuca indica, Neem or Rice bran oil.5. The process according to claim 1, wherein the water scavenger is selected from a group comprising 2,2-dimethoxypropane and phosphorous trichloride.6. The process according to claim 1, wherein the water adsorbent is selected from the group comprising zeolites, silica gels, acidic clays or molecular sieves.7. The process according to claim 1, wherein the alcohol is methanol or ethanol.8. The process according to claim 1, wherein the acidic catalyst is sulphuric acid.9. The process according to claim 1, wherein the basic catalyst is selected from sodium hydroxide, potassium hydroxide, sodium methoxide or potassium ethoxide.10. The process according to claim 1, wherein the acidic catalyst used in the esterification step is neutralized with the basic catalyst used in the trans-esterification step.11. The process according to claim 1, wherein said biodiesel is capable of augmenting the lubricity of petroleum diesel.12. A process for producing a biodiesel, the process comprising: a) providing a feedstock of non-edible vegetable oil source having free fatty acid in a reaction vessel attached with a column or soxhlet apparatus filled with a water adsorbent; b) adding an alcohol and an acidic catalyst in the reaction vessel; c) reacting the alcohol and the free fatty acid in the presence of an acidic catalyst to obtain a mixture of fatty acid ester and triglycerides; d) adding an alcohol and a basic catalyst into the same to trans-esterify the triglycerides to fatty acid esters, wherein the fatty acid ester thus produced is capable of being used as a biodiesel.13. The process according to claim 12, wherein the non-edible vegetable oil sources are plant species selected from the group comprising Jatropha curcas, Pongamia pinnata, Madhuca indica, Neem or Rice bran.14. The process according to claim 12, wherein the water adsorbent is selected from a group comprising zeolites, silica gels, acidic clays or molecular sieves.15. The process according to claim 12, wherein the alcohol is methanol or ethanol.16. The process according to claim 12, wherein the acidic catalyst is sulphuric acid, Hydrochloric acid or p-toluene sulphonic acid.17. The process according to claim 12, wherein the basic catalyst is selected from sodium hydroxide, potassium hydroxide, sodium methoxide or potassium ethoxide.18. The process according to claim 12, wherein the acidic catalyst used in the esterification step is neutralized with the basic catalyst used in the trans-esterification step.19. The process according to the claim 12, wherein the process is a single pot process.20. A biodiesel produced by a process comprising: a) providing a feedstock of non-edible vegetable oil source having free fatty acid in a reaction vessel, attached with a column or soxhlet apparatus filled with a water adsorbent; b) adding an alcohol and an acidic catalyst in the reaction vessel; c) reacting the alcohol and the free fatty acid in the presence of an acidic catalyst to obtain a mixture of fatty acid ester and triglycerides; d) adding an alcohol and a basic catalyst into the same to trans-esterify the triglycerides to fatty acid esters, wherein the fatty acid ester thus produced is capable of being used as a biodiesel. Hope you understand and Good luck!