H2 is considered as the ultimate cleanest energy carrier to be generated from renewable sources. This minireview intends to point out that in addition to this function, biologically produced hydrogen is important for environmental biotechnological applications. The purple sulphur phototrophic bacterium, Thiocapsa roseopersicina BBS contains several NiFe hydrogenases. These enzymes can be used e.g., as fuel cell H2splitting catalyst or in photoheterotrophic H2production. Microorganisms that supply H2in situ facilitate the biodegradation of organic material and concomitant biogas production. Fast, efficient, and economic treatment of organic waste, sludge, manure is achieved and generation of significant amount of renewable fuel from waste is intensified. The technology has been field tested under mesophilic and thermophilic conditions with positive results.