Nearest berlin international airport is Berlin TEGEL.
By taxi or public transport, time distance is nearly the same. Please calculate 15 minutes from the airport to main entrance of exhibition grounds.
Alternative airport is Berlin SCHÖNEFELD. From this airport you need approximately 1 hour to the exhibition grounds.
Best way to the expo-grounds is by using subway (S-Bahn)
Station for S-Bahn trains: Messe Süd
From this station, you have the direct way to the BioGasWorld entranca (approximately 1 minute walking time)
link to route map public transport