* Lufthansa to test new jet fuel from US-based Gevo
* Air industry trying to cut CO2 emissions
* Gevo's fuel comes from plant waste
* Partnership boosts Gevo shares (Adds background, campaigner quote)
FRANKFURT, April 23 (Reuters) - Lufthansa is testing a new type of biofuel for use in aircraft, the German carrier said on Wednesday, as the airline industry steps up efforts to cut its carbon dioxide emissions.
Lufthansa was the first airline worldwide to use biofuels in commercial flights in 2011, when it used a 50:50 mix of biofuel - gained from plant oils and animal fats - and regular kerosene to power one engine per plane on daily flights between Frankfurt and Hamburg.
However, the airline ended the trial after six months saying it was hard to find enough reliable stocks.
Lufthansa said in statement it had teamed up with U.S.-based Gevo, which produces alcohol-to-jet (ATJ) fuel, to research the blending of Gevo's ATJ with conventional kerosene for use in aircraft.
Gevo uses fermented plant waste from a range of sources to produce isobutanol, a form of alcohol which can then be converted into kerosene using standard refinery processes.
The company, which is ramping up to commercial isobutanol production, says this is cheaper than using current biofuel refining processes.
Producing lower carbon biofuels can be can be six to eight times more expensive than producing regular jet fuel but they are seen as a way of helping the aviation industry to cut down on CO2 emissions.
British Airways is also researching fuels derived from food waste and Air France-KLM has tried out fuel made from leftover cooking oil.
However, campaigners say people should be trying to cut back on food waste and that there isn't enough of such fuel for fleets of aircraft.
"It's encouraging to see airlines learning the lessons of the EU's biofuels disaster by looking for alternatives to food crops for fuel," said Robbie Blake, biofuels campaigner for Friends of the Earth Europe. "But using food waste will not be enough to power fleets of jumbo jets, and we anyway need to be cutting down on the mountains of food we throw away, as well as using it to fertilise our fields."
According to figures from global airline body IATA, air transport produced 689 million tonnes of CO2 in 2012, accounting for around 2 percent of global CO2 emissions. The body has set a target for the industry to reduce net aviation CO2 emissions by 50 percent by 2050, compared to 2005 levels.
However, biofuels have stirred debate because they often use the same crops or agricultural land that could be used for food to feed people.
The European Union for example, has wavered on a target that 10 percent of all fuels used in transportation should come from renewable sources by 2020, due to uncertainty over the environmental credentials of such fuels.
Lufthansa says it only works with biofuels that do not compete with the food chain. A spokesman on Wednesday stressed that the Gevo fuel comes only from waste products.
The research is being funded by the European Commission as part of its Blending Study project. Lufthansa will work with the German army's Bundeswehr Research Institute for Materials, Fuels and Lubricants to determine the best proportion of Gevo's fuel to regular jet fuel ahead of trying to get ATJ kerosene approved for use in commercial flights.
Shares in Gevo had jumped as much as 55 percent late on Tuesday, when it made an initial announcement about the partnership with Lufthansa.
(Editing by Keiron Henderson and David Evans)