biodigester
From Longman Dictionary of Contemporary Englishbiodigesterbi·o·di·gest·er /ˌbaɪəʊdaɪˈdʒestə, -də- $ -oʊdaɪˈdʒestər, -də-/ noun [countable] a large container in which plant material or animal waste is changed by bacteria, producing methane and carbon dioxide