LISBON, Dec 19 (Reuters) - Portugal's Galp Energia expects to begin producing biodiesel and biojet fuel from waste in an industrial-scale unit it is constructing at its Sines refinery in 2026, the business, which is mostly an oil producer and refiner, said on Thursday.

Last year Galp participated in a 75%-25% joint venture with Japan's Mitsui to invest 400 million euros ($415 million) in the Hydrogenated Grease (HVO) plant, which will have a production capacity of 270,000 metric tons annually.

It will transform waste products, such as used cooking oils, into eco-friendly biodiesel and biojet fuel, likewise known as sustainable air travel fuel (SAF), using green hydrogen produced by an electrolyser powered by wind or solar energy.

Galp said in a declaration it got on Wednesday the 3 reactors to process biofuels, which will enable the HVO system to "produce SAF and biodiesel in 2026 ... putting Galp at the forefront of establishing low-carbon options vital for the energy transition".

Galp is also investing 250 million euros in a 100 megawatt (MW) electrolyser system to produce green hydrogen to power the refinery in Sines. ($1 = 0.9637 euros) (Reporting by Sergio Goncalves;-RRB-