From where would you expect metals entering a digester to originate?

Metals entering a digester are most commonly expected to originate from an industrial user. Industrial processes often involve the use of metals for manufacturing, fabrication, or chemical processes, which can lead to their entry into wastewater systems. Various industries, such as metal plating, mining, and manufacturing, may discharge wastewater that contains metals, making them significant contributors to the metal load in treatment facilities.

In contrast, while a municipal sewage treatment plant does process a variety of waste sources, including residential and commercial, metals are less concentrated in these sources compared to industrial discharges. Residential waste typically has lower metal content, as it primarily consists of organic matter and household products that generally do not contain significant metal concentrations. Groundwater sources, while they can contain dissolved metals, are not a direct contributor to metals entering a digester unless there is specific contamination, which is typically not significant in relation to industrial discharges.