Hydrolysis rates in anaerobic digesters

While researching my last post on loading anaerobic digesters with grease, I found many informational bits that can be useful for digester operators. Hydrolysis, the first step in anaerobic digestion, relies on enzymes and microbes to convert solids into organic acids used by the acetogenic bacteria. Influent makeup has a big impact on hydrolysis rates. 

From the table, you can see that primary sludge with its mix of organics has more products suited for hydrolysis than activated sludge biological solids. The waste biosolids contain a mix of extracellular polymers, slowly solubilized organics, inorganic compounds, and bacteria cells. All of this takes more time for hydrolysis than the unstabilized primary solids.

Next, you should note the hydrolysis rates drop with increasing amounts of lignin in common cellulosic materials. I found this an important factor when accepting various plant wastes for the digester.