[Peter]

There are a few categories of digester additives that are on the market to increase biogas production.

Trace-metal nutrients can increase biogas production, but only when the digester is deficient nutrients because of the feedstock it is receiving.

Enzymes can help to breakdown recalcitrant feedstocks like cellulose and fat, because enzyme addition is expensive, we see very few digester operators that see an economic case to use them in North America.

Microbial cultures are marketed to increase biogas production by breaking down more recalcitrant feedstocks, however we have not seen wide adoption of this or clear demonstration that they can be cost effective for a full scale biogas plant.