If you get too many results, try limiting with the facets on the left side of the screen.
The same tricks that help you find books in the catalog will help you find articles:
(co-digestion or codigestion)
leachate and recirculation
produc* (finds produce, produces, product, production, etc.)
Put it all together:
(co-digestion or codigestion) and produc* and biogas and "methane yield"