As renewable energy sources goes, solar rays have historically hogged the limelight.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/scientists-unlock-key-turning-wastewater-and-sewage-power
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/environment-news-network
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/science-and-technology
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/energy
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/renewable-energy
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/sewage
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/waste-energy
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/wastewater-treatment