Swedish start-up Volta Greentech is gearing up to build a full-scale factory to produce seaweed supplements to reduce climate-warming emissions from cattle. 

Backed by Northvolt founder Peter Carlsson, Volta Greentech is forging ahead after a successful pilot at a Swedish beef farm that showed adding seaweed to a cow’s diet cuts average methane emissions burped out by the animals by more than 80%. Based on the pilot, the supplement is planned to be grown sustainably and manufactured with renewable energy. 

The plant, dubbed Volta Factory 2, will have a capacity of 50 tons a year to feed between 3,000 to 5,000 animals. The company will raise further funds this year for the plant and research and development...