Utilize the input text as a context reference, choose the right relationship between digester and biogas from the options. Options: product/material produced, manufacturer, distributed by, industry, position held, original broadcaster, owned by, founded by, distribution format, headquarters location, stock exchange, currency, parent organization, chief executive officer, director/manager, owner of, operator, member of, employer, chairperson, platform, subsidiary, legal form, publisher, developer, brand, business division, location of formation, creator.

Let's briefly review our Aemetis biogas dairy digester and pipeline project.

Answer: product_or_material_produced